Apex Seals

Last updated: March 17, 2002

Date: Sat, 21 Apr 2001 05:17:13 -0400
From: Gordon Monsen (gmonsen@fast.net)

There are two Hurley seals that are commonly used by rebuilders. the "standard" Hurley longlife seal and the double spring racing seals. i'd recommend the double spring racing seal. their benefits are:




Date: Sat, 21 Apr 2001 23:04:37 -0400
From: Gordon Monsen (gmonsen@fast.net)

with the standard hurley "longlife" springs, my car had 17 inches of vacuum. after several very high boost runs (to 20 psi), they failed. however, the motor didn't really detonate with a bang, as it does with standrard seals and springs. there was no damage to the rotors or housings. we are putting in the double spring racing seals now, which we believe will withstand high boost without failing. these runs were only made up to about 7000 rpm, but in daily driving at 16 psi on a street-ported motor, i ran it to 8500 regularly under boost with no problems.

as far as quantifiable data, i think there probably isn't any. ari at rotary performance has been using hurley seals the longest, i think, and he has never volunteered anything but what you would call, subjective, anecdotal commentary on them. dave barninger at kd rotary has been installing either the standard or more recently the double spring versions for some time and he doesn't have any hard data either, just his observations and qualified opinions. i know that dave went to england to meet with hme before becoming a distributor and discussed them at length with hme staff last year.


Date: Mon, 23 Apr 2001 10:13:56 -0400
From: Tom Walsh (TWalsh@achieversusa.com)

As one of the first people on the list to get the Hurley seals I think I have the longest time on a set.

I currently have a Hurley set of seals in my motor with over 25K miles on it. The motor was installed in April of 1999. (See what happens when you take care of your motor?)

The motor has pulled 12" of vacuum since the day I turned it over... This is actually due in part to the aggressive street porting.

I have yet to break down the motor... But I am afraid that it is coming soon enough... The car is requiring fill ups of coolant weekly... So I fear that the Hayes coolant seals might be in trouble. (D@mn Dex-a-Cool)

Upon break down I will let everyone know the benefits or negatives of these seals.

I don't know when the motor is going to be pulled... As I am trying to purchase a house right now and that is taking up most of my time and energy.

The reason I went with the Hurley seals is enlarged corner section which spreads out the force of the spring into a much greater contact area of the rotor housing. This is why the seals are better for the life of the rotor housing. These seals can be used with regular 3mm springs as the corner section of the seal is shaped much the same way a stock 3mm seal is shaped, at least on the bottom side of the seal which is where the spring is perched.

Another thing to check out... and one that I plan on getting done to my next set of rotors is the Hurley Direct Tip Seal Lubrication System. Often times over the life of a rotary engine the seal, or seal groove, will wear to the point that it is out of tolerance causing the seal to bind and break at high RPMs. I am hoping that this system will provide much needed longevity in this region.


Date: Mon, 25 Sep 2000 08:47:49 -0700
From: Michael Gurgainers (gurgainers@blomand.net)

I have been using Atkin's Rotary's apex seal in the engine I build for some time now. I really like them, as they seat so much faster and cause less damage to rotor housings than Mazda factory seals. However, I detonated my engine the other day and one let go (totally my fault, I can not/will not fault the seals).

I am considering using John Almeida's (sp?) ceramic seals from Powerhouse Engineering. I was wondering if anyone has used these before, what their opinion is vs the Iannetti seals that are approved by MazdaComp, what is the wear characteristics of the seal, and how much boost was run. I spiked my boost (accidently, one missed keystroke on the PFC will cause a rotor and housing to turn to slag) to 18psi (ooops) with no other fuel enrichment other than what was programmed for 12psi.

I am hoping to prevent this as I have been told by some that these ceramics seals will take much more abuse (having to tune an engine without realtime, high res A/F ratio monitoring on a chassis dyno constitutes abuse IMHO). Please do not respond if you have not used ceramics seals in your own motors in the past or have spoken directly with those who have (IE. no hear-say please!). If you have information on these I would like to speak directly to you via Phone as I have quite a few technical questions if you have the time.


Date: Wed, 8 Mar 2000 16:09:25 -0500
From: "Eddie Versace" (eddieversace@starlinx.com)

Ianetti(sp?) stopped making his 3mm seals b/c of too many problems with them, or rather the rotor housings. If either are machined even slightly less than perfect, it almost always results in another rebuild rather quickly. Stick with 2mm seals.


Date: Fri, 27 Feb 1998 23:42:01 -0800 (PST)
From: NetBlazer (netb@world.bc.ca)

> Ok does this mean that the ceramics are more durable and all around the best?

Most will advocate using the ceramic seals for only high boost turbo applications. I did notice that the 3 and 4 rotor Kudzu chasis Can Am cars racing at Daytona (normally aspirated) were using them. I think the motivation for the above advocation is due to the cost alone.

The advantages in any engine are that the ceramic material used has a lower coeficient of friction than the more conventional ductille iron seals, and the material is a lot harder. The lower friction, means less wear to the surrounding parts (apex seal grooves, rotor housings, and side housings), and less wear to the seals due to both the lower friction, and harder material. The wear characteristics have been described to me as negligable, but initially enough for them to break in correctly.

Other advantages, are that the ceramic material has less physical mass, so requires less spring pressure to keep them in contact with the rotor housing surface at a given rpm, plus due to the lower coeficient of friction you can use more spring pressure without causing an appreciable increase in wear. Either one of the above means the engine can run at higher rpms without the seal floating, which can cause hot exhaust gasses to travel back into the intake cycle of the other rotor chamber and cause pre-detonation which is one of the major concerns in any non diesel engine.

Stock apex seals can overheat, and warp which is not a concern with the ceramic seals. The ceramic seals although not indestructable, can take a lot more detonation than stock seals. They can also stand up to a lot more boost/power output.

Now for why people stray away from them: ceramic 2 piece 2mm or 3mm seal set costs $1770, plus in the case of the 3mm seals you have to buy double the number of apex seal springs. You could go for the single piece 2mm or 3mm seals for $1200, but will have less compression under 4000 rpm over the 2 piece seals.

After getting past the 'you don't want those!...why not?...because they cost a lot'....banter, I have heard from several rebuild places, and Franchesco Ianetti himself that when it is time to rebuild the engine, you can re-use the ceramic seals over and over again (the gift that keeps on giving?).

I have seen and heard about far too many rotary engines where either the seals break from detonation, or wear out the rotor grooves making the seals not fit properly, and eventually breaking the corner seals (non solid corner type seals where Mazda thought a piece of rubber might prevent this), and doing major damage to both the rotor, housing, and turbine wheel. The cost of doing a premature rebuild alone is enough to make the cost of the ceramics seem like a bargain, plus the cost of the damaged housing/rotor..then add in the amount of pain and suffering you will go through when the mustang you were racing when the stock seals went beats you :)


Date: Thu, 11 Sep 1997 21:43:52 -0700 (PDT)
From: NetBlazer

Well, I have spent several hours talking to Francesco (sp?) Iannetti on the phone (3 seperate occasions mostly on his quarter :)

He is the designer/owner of the company that makes the expensive, low mass, high strength ceramic apex seals that are only sold through Mazda Comp. Aparently many racing teams run them, including the Downing team (Rolex 24 hours, etc), Mostly Mazda, Pettit, etc...

Anyway a set used to cost around $1500. Due to recent material improvments he was able to increase their strength and lower their cost. A set is now around $50 an apex seal cheaper, so somewhere around $1100 a set. This is very good news as I have been saving up to build my engine (core with 15000 easy miles on it sitting in my garage waiting for 3mm one piece ceramics)

The advantages are they can withstand higher rpms without floating, they can use a higher spring force than stock, without adding any additional wear, which gives better sealing. The wear they do cause is insignifigant, and they won't wear out anywear near as soon as stock seals, or cause the same dammage to the rotor grooves, or rotor housings that stock seals do after high mileage. They can take more detonation, higher boost pressure, leaner conditions, etc.

The only downside I have heard of is cost. I think their cost is insignifigant when compared to the cost of new parts when one of the stock seals decides to break, and tear into the rotors, housings, and turbine blades. Plus the cost of a complete rebuild at that time..OUCH.

They are available in 2mm one piece and 3mm one piece, and a more expensive 2mm 2 piece and 3mm two piece. The 2 piece will seal a little better at the rpms you street drivers like, and not any better at the higher rpms. The 2 piece seals are also more expensive. Many street cars are running the one piece seals with no complaints, and thats what I plan to go for. Also it was mentioned that a customer with an airplane powered rotary did some tests and found that the 1 piece ceramic seal had higher vacuum than the stock 3 piece seal due to the increased spring pressure. Iannetti's tests have shown that the 2 piece seal is better than the 1 piece, but the torque difference he quoted me was in inch pounds, and was from a 3 rotor, so I consider it approx 50% higher difference than our 2 rotor engines.

Finially he asked me to post his new website address. The deal is he is currently wanting to take orders for a rotor clock that he designed and has hand crafted, for christmas. (they are made to order and takes many weeks as they are mostly hand crafted and polished). The clock is pricey, but beautiful. The rest of the site is not finished, but the rotor clock section is complete. I am trying to get him to put up some info on the ceramic seals, but he said that would take some time to do as he is very busy. Web Site

From talking with him I got the impression he loves the rotary due to many of the reasons we love it, and he is in for the long haul, and not ready to give up on it, even though sales of the apex seals only trickle in.

Date: Thu, 18 Dec 1997 07:09:21 -0600

According to Mazda Comp (I asked them if the Lanettis were streetable), the Lanetti seals are much stronger, lighter, able to operate under higher spring pressures, and even enjoy some self-lubricating properties. They have greater beam strength in a 2mm size than a comparable stock seal in 3mm width. As far as wear characteristics, they are supposedly easier on the chrome lining of the rotor housings than a stock seal. Although few people use them in street motors because of cost, they are streetable.

In short, they (Mazda Comp) didn't see any drawbacks, except the high price.

Date: Wed, 4 Feb 1998 15:23:20 -0800 (PST)
From: NetBlazer

A problem has been discovered by one of his customers relating to apex seals sticking: For more power, it is a good idea to keep clearances tight, between the apex seals and the grooves. The problem relates to shops who machine out the grooves to 3mm. The procedure is to cut one side, based on the corner seal, then the other side. The problem arrises when the corner seal is not seated perfectly, which can be caused by casting inperfections in the rotor (yes the rotors are cast iron), or corner seal. In many cases one side of the groove can be off from the other side, which under load can cause the seal to bind, and cause it to stick, creating a lost of combustion containment and detonation.

How they figured out what was causing it: An engine with the ceramic 1 piece 3mm seals was exhibiting the symptoms. The seals were replaced with softer carbon seals, and the symptoms went away. Then the seals were replaced with the hardened seals Mazda Comp sells and the symptons came back (same motor). The reason the carbon seals didn't exhibit the symptoms was because they are softer and will quickly wear in the spot that is causing it to stick, eliminating the problem. Replacing the seals with the 2 piece ceramic seals also eliminated the symptoms.

I have been told by several people that the 2 piece are going to yield more low end, and are a better setup. I have still shied away because they are not as stong as the single piece seals. Franchesco said they have done testing on them, and they will take the abuse from a 2 rotor engine putting out 600hp at the rear wheels (24psi boost) all day... Thats enough assurance for me, combined with the less chance of them sticking.

To prevent the single piece seals from sticking either make sure the grooves are straight (no-one seems to be able to guarantee that) oand/or machine the grooves to have .0015" clearance on each side of the apex seal, or .0030" total clearance.

For the 2 piece ceramic seal, use between .0005" and .0015" clearance per side.

If you are running Mazda Comps hardened apex seal instead of the ceramics, use the same specs as the ceramics.

The motor that is making 600hp at the rear wheels has extra dowel pins added to the housings to prevent the sandwich from twisting around. Aparently Pettit can do this, as well as a couple other places which I don't know yet if they do for other people or not, but will find out before sharing their info.

He also mentioned that he got a call from a list member who had heard of the ceramic apex seals off the the lsit, but didn't hear where to get them. Mazda Comp is the designated direct reseller 1-800-435-2508

Also note you can get 2mm ceramic apex seals which are also very good, and don't require the machining. The Mostly Mazda race cars are running the 2mm ones at 20PSI boost with no problems.

The cost is about 4 times that of stock apex seals, but is what I consider cheap insurance considering they will save you 3-4 times their cost (maybe more depending on the cost of the mods to your engine) the first time they don't break in a situation the stock ones will. Plus your rates don't go up after you make a claim on that insurance either :)

Date: Sun, 1 Mar 1998 10:06:06 -0800 (PST)
From: NetBlazer

In most cases the dealers themselves do not rebuild rotary engines, and just swap in MTC (Mazda Technical Center) rebuilt crap engines..oops did I say that out loud...so they couldn't do it anyway.

I am biased towards Hayes Rotary, so I will just list a few of the places I know have done them. This list is harly complete. Pettit, PFS, Hayes, XS Engineering, Mostly Mazda, Redline Performance, Carlos Lopez Racing.

The last two I do not know if they do work for people off the street, or just their own stuff, and referrals.

If you are doing the 2mm one or two piece seals, any rebuilder can handle it. If you are doing the 3mm two piece seals, any rebuilder on that list can for sure, plus any rebuilder who has a machine shop who does their 3mm rotor machining (rotors that came stock with 2mm seals need this) can do it.

The problem comes from 3mm 1-piece. If they do not get the groove perfectly cut to be in line with the corner seals (often times a casting imperfection in the rotor could cause a problem) then the seal may bind, and you have worse problems. The same is true for using the 3mm Hardened carbon seals on a NA engine. The 3mm 2 piece seal which is a very good idea for street/race use anyway doesn't have the same problems with binding.

Also note, when rebuilding an engine and going with 3mm seals, it is a good idea to go with the 85 13B solid corner seals. Mazda changed design, and now have a large hole in the corner seal, which they fill with a rubber insert. The corner seal is lighter, but prone to breakage because one side of it is very thin.

Date: Thu, 5 Mar 1998 00:59:40 -0800 (PST)
From: NetBlazer

Okay, I now know why they are so expensive...we are paying for the case they come in :) The case is a block of wood, that has Ianettit USA and the logo burned into the back, on top it is felt lined, and the whole thing is in a plastic sleeve. It's so nice, it sorta seems a shame to put the seals in. I guess I will have to get a second set to put on my desk :)

There is also a x-ray of the seals, and I can't see any impurities in it. I would hope no end user ever would. I know Franchesco said every once in a while there are which is why every one gets x-rayed (obviously pre-screened).

The seals are soooo smooth...its sorta like touching soap stone, but different...definately have a finish on them that you couldn't get on a ferrous alloy.

Iannetti 2 Piece 3mm Ceramic Apex Seals:





Date: Wed, 17 Mar 1999 11:46:59 -0800
From: "Jim LaBreck (Solutions IQ)"

I made the mistake of spending nearly $1,900 on 3mm Ianetti 2-piece ceramic seals. While I concede that they will stand more abuse than the factory seals, detonation will still break both. Sandy reported that the ceramic seals in his engine withstood several good detonation pops before breaking while Mandeville was trying to tune his Motec, but that the replacement engines with factory 2mm seals only withstood one or two good pops. Proof that both will break, but that the ceramics will withstand more abuse. The point? Don't detonate.

3mm factory seals chatter, increase the problems of poor lubrication at the seal edges (away from the MOP injection port) and will eventually chip and wear both seals and housing. Brooks has first hand knowledge of this problem, which can only be combated by running pre-mix oil in the gas tank, as far as I know. Short of increasing the number of MOP ports in the housing, there is no way to ensure that enough lubricating oil reaches the edges of the seals to reduce wear besides running pre-mix. Someone correct me if I'm wrong, thanks.

The additional mass of the 3mm seals also makes them float at a lower rpm according to what I've heard from several sources. Floating is when the apex seals are no longer in contact or in limited contact with the rotor housing's surface. At this point, they are no longer able to transfer heat to the housing, and as a result, they may warp, bind, or break. Also, they are no longer doing an effective job of sealing the combustion process, and pre-ignition and/or detonation are the resulting side effects. While the ceramic seals with their much lighter mass will resist floating to a greater extent, the real solution is not to turn a turbocharged motor to rpms that a N/A motor would be comfortable with. The factory 2mm seals float at approximately 8,000 rpm, and I've been told that the factory 3mm seals will float under boost at a somewhat lower rpm, making them somewhat less effective in the operational range of the 13B-REW. The factory 2mm seals are sufficient providing that enough fuel is being administered, and with the possible addition of a solid corner seal.

While there are some people who are enthralled by technology to the exclusion of objective reason (and I don't omit myself from this category in certain situations), those people (and I'm not naming any names, but one of them was the key reason why I wasted $1,890 on the ceramic seals which are now in an engine which his father owns, with my loss on the engine almost equivalent to the cost of the seals...) should examine the problem from a different viewpoint. It is not building a bigger or better seal that is the solution. The solution is providing an adequate amount of fuel to eliminate or drastically reduce the possibility of detonation.

If when I started modifying my car someone had had the knowledge and foresight to advise that I spend as much or more on my fuel system as on other mods, I probably would have had a much better engine history. Of course there's no guarantee that something else won't happen, and with my first engine, that happened to be the stock clutch letting go at increased power levels. The result was a thrown corner seal on the rear rotor at about 14,000 rpm. No one had the knowledge or foresight to advise me to upgrade my clutch at the same time I was doing all of my initial mods, either, but that's the way it goes. Stressing the importance of proper fuel delivery is very important, in my opinion.

My advice? Save the money you would normally spend on those Blitz rims, the VeilSide body kit, a huge intercooler, 3mm ceramic seals, or whatever else you really could live without, and sink it into a comprehensive fuel system upgrade.

One solution is to scrap the factory ECU, since it really can't cope with delivering fuel in a satisfactory method for 2-rotor engines producing more than 400 horsepower anyway, and spend the money on a stand-alone aftermarket fuel computer from Haltech, Electromotive, or if you have the funds, a Motec.

Another solution is to use a piggyback fuel computer to adjust delivery to larger injectors, like Carlos and others have managed with greater or lesser success with the PFS purple box. Then get some bigger injectors. Get a bigger fuel pump. Get larger fuel line. Once you have these mods, you can (as Tri-Point has proven) run any combination of intake, downpipe, midpipe, and exhaust you want with almost no need to control boost (the Tri-Point downpipe actually causes spiking by design, I've heard) and be assured that you have enough fuel for any situation to prevent the detonation that no magic apex seal will live through.

Just my opinion after two motors, untold thousands of dollars invested, and a full working knowledge of how almost each and every part on my car is removed, is reinstalled, and how it operates... your mileage may vary.


Jim responds on why he didn't use his 3mm ceramic seals...

Date: Sun, 5 Dec 1999 15:28:39 -0800
From: "Jim LaBreck" (jimlab@earthlink.net)

Never fired up the engine they were put into, that's why. That was the now infamous Hayes Rotary engine where I got taken for a bundle AND a mint 6,000 mile '95 core (with one bad rotor and one bad housing), which they kept and substituted heavily used (and wrong year) parts for.

That engine was dropped into the car, and of course I realized that I'd probably just blow it up, and since it was too pretty to do that to, I decided to let someone else have that honor. And they have. :) Actually, I think it's only been overheated, probably due to more shoddy Hayes Rotary assembly, with less than 2,000 miles of use, but the apex seals should be fine. Not my problem any more. :)

Without starting another huge debate over which is better, simply realize that moving up to 3mm OEM seals increases the weight and width of the seals by 50%. The metering oil system cannot provide an adequate amount of lubrication, especially since it injects at the center of the housing, so the outside edges of the seal are going to be subjected to 50% more wear and tear than if they were 2mm seals. As people have found out, this can lead to chipping of the surface of the rotor housing and cracking and chipping of the outer edges of the apex seals, resulting in reduced efficiency in sealing the combustion process and hence less power.

50% more mass in the seal also means that the point at which they float (pull away from the housing) will occur at a lower rpm (or so I've been told). At that point, they are no longer transferring heat or sealing effectively, so they will tend to warp or crack, and pre-ignition can occur because of poor sealing. This is at high rpm, obviously, near redline.This does not occur, I'm also told, in engines which are not under pressure, so 3mm steel seals in a naturally aspirated engine work just fine. I got this information indirectly from Francesco Ianetti, the maker of the ceramic seals, so it may be a load of "sales pitch", but I've never had anyone argue that this wasn't the case.

The cure to the lubrication problem is to run pre-mix (oil) in the fuel. It's a pain, of course, but can prevent several problems. The facts are, though, that there are many high performance engines using the stock 2mm seals. The benefits of this, beside the fact that they're cheap, are that the rotors can then be machined for 3mm seals if anything bad happens, more often than not. Where do you go when you're already at 3mm? 4mm? Maybe, but more likely, it's time for a new rotor. Also, they wear less, seal fairly effectively, and are cheap to replace if no damage is done to the rotor or housing in the process. Where the 3mm seals do have an advantage over the 2mm seals is that a solid corner seal can be used, which keeps the seal aligned in the rotor groove and prevents the corner seal from breaking. Or at least from breaking as readily. When the corner seal lets go, scoring of the side plates is almost inevitable. It also allows the apex seal to move much too readily in its groove, which often cause the apex seal to fail as well. This usually results in at least one side plate being replaced as well as the rotor housing and rotor, and more than likely the turbine blades of the rear turbo.

A ceramic seal's main benefits are reduced weight and reduced wear. They are almost impervious to wear, and with a significant reduction in weight, they are far less likely to float under pressure. They are, however, extremely expensive, and they will break just like a standard apex seal. They will withstand a bit more abuse, and will withstand more detonation than a factory apex seal, but they will break eventually, just the same. Sandy Linthicum said that when he was having Mandeville Racing tune his engine and Motec system, that because of a bad harness, the engine(s) were detonating badly. He mentioned that the ceramic seals he was using held up to several loud pops before breaking. Past that point, they used engines with 2mm standard seals, I believe, and he said that they broke after only one or two pops (detonation). The bad harness was eventually diagnosed as the cause of their problems, and I believe he then had the final engine built with ceramic seals. Since he's one of only a few that I know of using them, or having used them, you might contact him for more information on his experiences.

Personally, I don't see that they're worth the extra money. You could replace your rear rotor, housing, and seals at least twice for the price of the ceramic seals. With proper and careful tuning, you shouldn't have to replace anything. I never expected to get 100,000 miles out of any of my engines. In fact, I've never put more than 30-35,000 miles on any car I've ever owned, so longevity wasn't a concern. I was looking for a snake oil cure-all which would keep me from blowing any more engines, and these aren't it. I'd recommend investing the extra money in your fuel system and engine management system, to be perfectly honest. Spend the money there and you won't be needing to replace seals, ceramic or otherwise.

As for damage to the engine when they disintegrate, I can't verify one way or another. I've never blown up a ceramic seal engine and been able to inspect the damage. I would suspect that you may save your rear turbo because the Inconel blades will probably survive slicing and dicing the ceramic material whereas they will not survive intact if a standard apex seal goes through them. I speak from experience here. :) I also don't know if they'd be crushed to powder internally and save the rotor housing from being destroyed, but I tend to doubt it. They may minimize damage, but I don't think they'll simply come apart and leave everything else intact.


Date: Wed, 17 Mar 1999 20:19:06 -0500
From: Sandy Linthicum (sandy_linthicum@mindspring.com)

I have a set of the one piece 3mm Ianatti seals in it. They are good to about 45psi of boost (assuming the engine is properly tuned for it). We broke a set of the 2 piece 2mm Ianatti seals on the dyno after 15-20 severe instances of detonation (ie. sounding like someone threw about a trashcan full of cans down concrete stairs). Even then, only one seal broke on the tip.

The 2 piece Ianatti seals, provide superior sealing at lower rpm and give better compression, hp & torque at these rpms. At higher rpm ther is minimal difference. Being a single piece, the one piece design is clearly superior in strength and gives you much more margin when things go out of spec. The Ianatti design concept is not directed towards making the seals impervious to detonation but towards improved performance.

Iannati/ceramic seals are approx 50% lighter than steel, do not expand or contract on temp change (practically), do not absorb water and have less than 1/2 the friction of steel seals. In my application this allows using competition apex seal springs to give greater spring pressure while still keeping friction below that of a 2mm stock seal. This low friction and the characteristics of the ceramic also make rotor housing wear virtually zero. Of course the seal do not wear at all either and can be used rebuild after rebuild.

Now, whether they are worth the additional $900 (ie. $1200 for a set compared to $300 for stock seals) is another matter - they were worth it for me.

The use of them however is not a simple swap for the steel seals, characteristics are different and matching dimensions, clearances and parts is much more critial.


Date: Fri, 6 Oct 2000 05:21:44 EDT
From: TristarX@aol.com

    >that while the ceramic apex seals are "easier" on the hard chrome surface
    >of the rotor housing, they are fragile if say...spring float (not sure if
    >this occures in high reving rotaries) occures and induces a slight tilt to
    >the seal. While a steel unit might bend and scratch the rotor housing, 
    >it will likely hold up and allow engine use...again this is a preconception 
    >and I welcome anyone that can correct me here. 

Yeah I have heard on the forum that with Lanetti ceramics, it's lighter so less chance for spring float, and in terms of strongness, people have claimed to witness 8-10 detonation before the seals gave away while the stock seals gave away in 1-2 pop of detonation. But the conclusion for the story was that all apex seals will break under detonation, so it's not to cure the symptom but solve the problem. Botton line don't get any detonation I guess any seals would be fine.

As for high revving, I think the ceramics are better candidate than steel factory simply because they are lighter.

    >Concerning 3mm apex seals: I believe (again a poor choice of words, but
    >it's a true sign that I don't have faith in what I am about to state) that
    >most that run 3mm apex seals do so out of...(here it comes)...cheapness!>>

Heh, you got me. Well sort of. My motor was bought with 3mm already so I had no choice but to replace with new sets of 3mm for this time motor rebuild. But say if my motor was stock to begin with, I probably will still choose 3mm cuz it's cheaper than changing both rotors to new. Machining is very critical, and I don't know where my shop did their machining but car seems to still run fine so far. Either way I am not a true believer of 3mm apex seals since 2mm or 3mm, they will still pop under 1-2 sec of detonation.

It all comes down to., how much money you have type of thing?? Since we are at it about changing new rotors, it's the same thing as why not change new rotor housings, side housings just incase they might be slightly warped or has a small microscopic crack.


Date: Fri, 6 Oct 2000 09:05:59 -0400
From: "Nicholas Riefner" (racin@worldnet.att.net)

You use two apex seal springs with ceramic seals, so it is a stiffer setup. I have been using 3mm ceramic seals for quite a while now. I got them when I started experimenting with stand alone computers, and tuning, etc.. I tortured one engine terribly(long story...), and it broke a seal. Only one. The damage that was done to the engine itself from the detonation was terrible, but only one seal wound up letting go. Without ceramics, the engine would have popped LONG before it did. Now, when it did let go, it broke a triangular wedge out of the seal, which then destroyed a housing. But again, the housing was already ruined from chatter, so the seal had been doing its job very well.

I have inspected the current engine in Project N-tech, and I can tell you that there has been precious little wear to the rotor housings using the seals, which confirms their anti-wear quality to me. As for the side seals, you do them just as you would with any other apex seal, really. Just check clearances, and get them within spec.

Ianetti seals are quite expensive, but they did hold up to COUNTLESS episodes of detonation before finally letting go. If you are not pushing the envelope, then you have no need for them, other than as a very expensive safeguard against the possibility of some stray detonation for unknown reasons. They are also re-useable, which is nice, if you plan on rebuilding engines often.


Date: Fri, 6 Oct 2000 09:16:49 -0400
From: Gene Felber (gfelber@talussolutions.com)

A few Atlanta club members posed this exact question a couple of months ago to Jim Downing who races the 600+ HP 4-rotor Mazda Kudzu in the Grand American Series (as you all know he used to race in IMSA, ALMS, has raced for Mazda at Le Mans, etc.). His response was that the ceramic seals were so easy on the housings that they typically go ALL SEASON without rebuilding the engine (including the Daytona 24 hour race) and that that scratches or imperfections in the housing were more detrimental to seals than potential shearing. His current car is NA and I assume shear force is lower than on a turbocharged rotary, but he used the Ianetti seals on the turbos as well. Unfortunately, he didn't mention if he went all season without rebuilds on those motors...

Perhaps if shearing occurs it can be greatly excacerbated by housing imperfections? That is, a seal subject to detonation or other shearing forces fares a lot worse when it is bending AND simultaneously moving over an imperfect/scratched surface.

With regard to the 3mm seals, I agree completely.


Date: Fri, 6 Oct 2000 09:41:01 -0400
From: Tom Walsh (TWalsh@achieversusa.com)

Here is what I have heard (and know) about ceramic seals.

Ceramic is a great material because of its natural properties.

Ceramic handles heat VERY well. (There was some use of all ceramic air cooled motors in the 80's but I don't think anything ever became of them.)

Ceramic is a light weight material (so less rotational mass inside the motor... Higher revs...).

Ceramic has a self lubricating property which makes it much more friendly to the chrome on the rotor housings. This can be very beneficial if you are running a larger contact area on the rotor housing (3mm with stiffer spring rates).

Ceramic doesn't wear down as quickly as steel. Now this can be a good thing... Or a bad thing depending on where the wear is occurring. There was some discussion over problems that were occurring with high boost applications with 3mm apex seals. But before I do that let me give a little back ground:

Wael you are correct about your assumption in regards to the 3mm seals being used in lieu of new rotors. What happens is as the rotor rotates around inside the engine the load points on the side of the apex seals shift from one side to the other depending on its location in the motor. This "rocking" of the seals cause not only wear on the sides of the apex seal but also on the sides of the apex seal channel. As with any motor, wear occurs to both components over time. The bottom and sides of the apex seals become worn (I have a set of 3mm seals with 11,000 miles on them if you would like to see what I am talking about) as well as to the top and bottom areas of the apex seal channel on the rotor. So during a rebuild (if done professionally) the tolerances of these apex channels are "mic'ed" (measured with a micrometer) and are normally out of spec. So instead of throwing the rotors out and buying new ones (I don't even know how much they cost new... I guess around a $500 each?) the rebuilder will take the old rotors and send them off to a machine shop and have the apex channels machined out to just under 3mm. They then (if they are professionals) use gapping slivers and files to get the clearances as near to perfect as possible. Often times they will leave it a little on the thin side which will pinch the seals slightly, but due to the wear of the metal on metal contact, the pieces should wear into "spec". For this reason a break in period is crucial (change your oil OFTEN).

So now if we change the mix up a little bit and use ceramic seals with their self lubricating and low wear properties, we develop a problem. The apex seal channels will pinch the ceramic seals because the above "break in" method, but because ceramic will self lubricate the contact area, the channel will never "open up" due to wear. This will cause the apex seals to bind in the channel.

One other area of concern is the corner seal (in 2 piece seals), and this is more of an issue of the apex seal design in general rather than of size or composition. The corner seal (which is a pain in the @ss during assembly) is designed to spread the force of the spring laterally through the larger section of the apex seal through the angled section of contact. What happens is part of the spring force is also focused directly on the very narrow area of contact that the corner section actually makes with the rotor housing. This will often produce a corner seal "groove" on the rotor housing. (Just a tip... If you are buying used rotor housings makes sure that you do not have a corner seal "groove" on both sides of the rotor housing. It is often common place for the rebuilders to take a rotor housing that was used once and install the corner seal on the opposite side of the existing "groove" to get more life out of the rotor housing. This is often a bad idea as the rest of the apex seal can not make a proper seal on the other "grooved" side. This will give you a raised section of your apex seal that will not seal properly either. I have a picture of this too...)

So the corner section groove can be a problem with rotor housing wear... So Hurley Engineering makes an enlarged corner section seal design. (I am currently running a set in my car). This design is supposed to help spread out the spring force over a larger area and help with rotor housing wear. My car has 24K miles on the motor with these seals and I have not had a problem. I am interested in seeing how the rotor housings fair but I will wait until the motor tells me it is time. :-)

And if you have read down this far... I a little tid bit for you... When a ceramic seal shatters and imbeds itself into the rotor, no matter how cool it looks or how tempted you might be to run your hand over it... DON'T... You will bring back a bloody mess. :-)

And yes... 3mm seals will also imbed themselves into the face of a rotor too (I have one of those too)...


Date: Fri, 6 Oct 2000 10:51:57 -0400
From: "Karagiannis, Demetrios, CTR, OSD/C3I" (Demetrios.Karagiannis@osd.mil)

Wael I partially agree with you for most of the people on the list sticking with a high quality 2mm apex seal is a great option. But we can not forget that they have physical limitations even if the air/fuel is correct when you start running over 25psi and then throw a little n20 on top of it things :) start to happen. I was a advocate for 2mm seals for a long time till I started getting crazy with my car. As far machining the rotors to accept the new seals have a reputable shop machine them for

you and don't replace them with stock 3mm seals its a waste of money to machine them to put in stock quality 3mm seals. I had RP do mine and have zero complaints I'm also using the same type of seals they use and all I can say is this it is one of the best investments I have made probably second to the RP fuel system :) I know most people omn the list don't run these boost levels but remember this it is better to be safe the sorry.


Date: Fri, 6 Oct 2000 09:10:57 -0600
From: dbeale (dbeale@harddata.com)

OK. Here is my take on this (mostly guess'), numbered for those who wish to argue/disagree/inform:

  1. The Ianetti apex seals are carbon/ceramic (from adds and price list descriptions - I haven't seen them). This would provide some extra lubrication to the rotor housing and the seal slot in the rotor, and therefore the seals may "track" better in the slot and maintain a better seal with the housing.
  2. Ceramic is usually lighter than steel, so they would be "gentler" on the rotor housing when they "flutter" (lower mass = lower momentum).
  3. Any apex seal will "flutter", usually after passing over the exhaust port (in the current production engine design - it remains to be seen if side exhaust ports will reduce this substantially). This "flutter" causes the second most severe damage to the rotor housing chrome (the most severe is caused by the fires of combustion induced extreme temperature fluctuation), and puts the apex seal in danger of cracking (you can see the marks it leaves if you disassemble an engine). It also reduces horsepower, because it allows the compression pressure to leak (and makes it very difficult to predict how much extra fuel to add to control detonation - another reason the RENISIS engine is so powerful).
  4. Mazda went to 2mm seals to reduce the momentum of the seals and therefore the forces they and the rotor housing experience during this "flutter", thereby also reducing the "flutter".
  5. Apex seals and piston rings wear with use. They get thinner as you accumulate miles on the engine, eventually getting thin enough to crack under normal loads (if the assembly survives that long ;-). This is probably why the 3rd gen engine life is so short - normal loads are much higher than even the 2nd gen and this failure mode is reached much sooner. I'd bet many apex seal failures are a result of this rather than detonation in an engine not exposed to changed conditions (more boost). The ceramic seals would last much longer under "normal" loads, as they would wear much more slowly.
  6. The apex seal springs are not effective at RPMs over, say 2000 (no figures, just a guess). The seal springs are there for starting/low RPM seal control. At high RPM the seals are firmly pressed against the housing by centrifugal force reaction. The springs may provide some control during "flutter", but I doubt it's substantial. They are not strong springs, especially when hot (300 to 400 deg. F).
  7. Most importantly, the Ianetti seals were designed for racing. They are really for better survival at engine RPMs between 6000 and 10,000, and below that any benefits are gravy. They may seal less well ;-) than stock seals at lower RPMs (higher mass is beneficial at low RPMs).

Sorry it's so long. I tried to include as many of the variables I knew of as I could.


Date: Fri, 6 Oct 2000 09:04:15 -0700 (PDT)
From: brent settle (leafsblue@yahoo.com)

On a interesting note:

At MADS last spring I think Peter Farrell was speaking with a group of us(did that include you Gordon?) about 3mm apex seals high boost and such.

He was quick to mention he felt that the 2mm seals were the way to go in any application, and he was talking STOCK apex seals. He said through extensive reasearch and development he felt the 2mm's combusted, lubricated and gave a more steady powerband. The biggest thing he thought, which is still commonly overlooked(not in all cases) is the weak link in the fuel system. Peter pretty much implied it should be your first upgrade before anything.

With all of these thoughts in mind Peter was quick to mention that different tuners will: "tell you different things."

Mazda's been making rotary engines for about 40 years, and have had more reaserch and development than Peter, and they have never(to my knowledge) used 3mm or ceramic apex seals for stock motors.

So if you choose to believe Peter or not that is up to you. I think the main benefit with 3mm apex seals is they are more resistant to detonation than the stock 2mm's. But for 1000's of dollars less, I don't really think they are worth it.


Date: Fri, 06 Oct 2000 09:43:45 -0700
From: Blake Qualley (vrm@aracnet.com)

    > Mazda's been making rotary engines for about 40 years,
    > and have had more reaserch and development than Peter,
    > and they have never(to my knowledge) used 3mm or
    > ceramic apex seals for stock motors.

Not true. Mazda used 3mm seals in early 13Bs, like the GSL-SE. Obviously, they moved to thinner seals, so your point is still made: Mazda, with more resources than most of us -- apart from Wael and Gordon, of course :-) -- moved to 2mm seals, so that says _something_. OTOH, Mazda's priorities are not necessarily the same as "tuners" or performance enthusiasts. Mfrs are always making compromises for engine life, reliability, fuel economy, etc. and are usually only concerned with engineering for stock-level performance. What the mfrs do in competition environments is also suspect, since they are bound by rules which we are not, and otherwise make *no compromises* (like the engine lasting for more than a few hours). Ultimately, the best guides are the "tuners", as even with limited resources, they spend more time making the *right* compromises for their customers.

That said, I have no comment on the 2mm vs. 3mm vs. ceramic anything debate. Interesting subject, however....


Date: Fri, 6 Oct 2000 16:02:17 -0400
From: "Karagiannis, Demetrios, CTR, OSD/C3I" (Demetrios.Karagiannis@osd.mil)

I still feel strongly that you will reach physical limitations of the seal a good example is what we call blow by. Think of it like this I hate to bring up a piston engine but it is just a example so don't kill me. Let's say you wanted to run beef up a piston powered car would you upgrade the crank pistons rods and run stock rings just because GM always runs stock rings? no of course not because even with the engine tuned perfect you will reach a point where there is failure do to nothing else besides physical limitations. Granted it is probably around the 25psi 28psi 520rwhp) but it does exist. I realize this does not pertain to most people but I have done some R&D myself (at my own expense :( if any one with a haltech would like to see the logs I will share) and I figure I could pass it on to the rest of the list.


Date: Fri, 06 Oct 2000 16:58:42 EDT
From: "Chris Weiland" (guyute182@hotmail.com)

    >3. Any apex seal will "flutter", usually after passing over the
    >   exhaust port (in the current production engine design - it remains
    >   to be seen if side exhaust ports will reduce this substantially).
    >   This "flutter" causes the second most severe damage to the rotor
    >   housing chrome (the most severe is caused by the fires of
    >   combustion induced extreme temperature fluctuation), and puts the
    >   apex seal in danger of cracking (you can see the marks it leaves if
    >   you disassemble an engine).  It also reduces horsepower, because it
    >   allows the compression pressure to leak (and makes it very
    >   difficult to predict how much extra fuel to add to control
    >   detonation - another reason the RENISIS engine is so powerful).

this is ABSOLUTELY correct..chipping will hopefully be a thing of the past with the new RENESIS (btw, anybody know if mazduh released their technical on the new engine??? need it for senior project :)....it should also be noted that another reason they used 2mm seals is to reduce seal "lift-off"...which occurs when the sum of the forces in on the seal create a 0g type situation as the seal is accelerated downwards(basically)...this creates "blow-by" over the seal, which causes uneven heating to the seal and cracking, premature failure, etc...

the other major consideration when picking apex seals is the material...i.e. material matching for apex seal to the rotor housing coating (adhesive wear between the two will change with temp rises and falls, which is pretty bad in RE)...btw, anyone know what they're coated with to begin with??

i read a paper from 93 where this guy created a "custom" rotor housing coating/apex seal material combination which totally kicked butt...compared to the stock materials combination in mazduh's engines the new material combination's volume seal loss was neglible.... :) oh and also: the new material combination was actually STRONGER than it was when it went in the test engine...suggestioning some kinda strange coating/apex seal matrix interaction!


Date: Tue, 30 Mar 1999 15:58:22 -0500
From: Tom Walsh (TWalsh@achieversusa.com)

Time for an update to the on going "Life and Trials of Tom Walsh" story. As some may know, my previous motor let go on February 1st. It has taken me 2 months and more money that I care to calculate, but I am now the proud owner of a brand new 13B-REW rebuild courtesy of Pettit Racing.


3mm Apex Seals, but not your everyday "run of the mill" 3mm apex seals. These are the Hurley Engineering 2 piece seals with the enlarged corner seal section, and straight 45 degree cut between the pieces. Of course I am the first motor that Cam has put these in, so who knows how good they really are... I am the "guinea pig".


This is a direct link to the frames page to get a better idea of what I am talking about. (I tried to get the link all on one line, so it will be easier to click on.)


Date: Thu, 13 May 1999 06:42:19 -0400
From: John.Duarte@clariant.com

I have been running 3mm seals made by "RX7 Speacialits" of Canada which are similar in design as the "Hurley" seals with the bigger corner piece. They took longer to break in but have been holding up to quite bit of detonation. Seals are made of the same material used for racing piston rings and that's all I know...


Date: Fri, 6 Oct 2000 17:20:44 -0400
From: Tom Walsh (TWalsh@achieversusa.com)

    > What great info...so....your suggestion for a good compromise
    > seals are??
    > Ceramic? Hurlye's? 3mm, 2mm, 1piece, 2piece, single spring,
    > double spring??

Good question. I actually believe that you said it best when you stated "compromise" which couldn't be a more accurate description. You, and you alone, must decide what your are going to compromise for.

Do you want reduced wear on your rotor housings? If so you can go with cermaics or you could go with regular seals with a premix.

Are you going to be running sick amounts of boost? Then perhaps ceramics aren't in your best interest in the 3mm form due to the bind that is common in the high boost applications.

Perhaps your car isn't dialed in, or you will be adding a huge turbo to the mix... While the ceramics can handle the detonation the thought of forking over more money for another set gives me the willies...

Do you want a good fit on your seals? Purchase a new set of rotors and use stock 2mm or ceramic 2mm seals.

Do you want better sealing, but reduced wear? Get 3mm ceramic seals with dual springs and new rotor housings.

I believe that nobody has a better understanding of your needs other than yourself. Only you know if you are going to be running 20lbs of boost. At which point 3mm ceramics would probably bind in the seal channel.

For typical applications you could go out and buy a new set of rotors, rotor housings and ceramic 2mm apex seals and motor off into the sunset. If your money is a little tight... A new set of rotor housings, and reuse your old rotors and mill them out to 3mm and put a set of Hurley's in there. If money is really tight... reuse your old rotor housings and your rotors and put a set of stock 3mm in there.

Every application has a trade off. Sometimes it is price... Other times it is wear... Other times it is longevity.

I run the Hurleys because I couldn't afford a set of ceramics at the time (I can now). I also do not run crazy levels of boost. My car sees 10lbs of boost 95% of the time. I do kick it up to 12lbs of boost when the need arrises...

I also have a set of Hayes coolant seals in my car. There was never a question in my mind that I was going to have them in my car as it is a necesity to have them. But that was another trade off... That was extra money I spent to make sure I had one less thing to worry about...

In general one piece seals are great for race applications... they suffer poor sealing at lower RPMs making them a bad choice for street driven vehicles. Two piece are the standard for street driven applications... To the extreme Hurley makes a 3 piece seal (you have to see this thing to believe it) that offers enhanced sealing at lower RPM ranges... But it the most bizarre contraption I have ever seen... Not to mention it is only available in a 3.5mm or 4mm size...

BTW: In case you are wondering... no I am not affiliated with Hurley in any way. I am simply speaking about items which I have experienced first hand.

So in conclusion: The best seal? Which ever one you think is right for your application.

If I had the money... I would have gotten the 3mm ceramics. Why? Because they offer the best sealing (with the dual springs) and least amount of wear for my application. What I chose was in my opinion the next best thing. Hurleys. Reduced wear (compared with other 3mm designs, from what I had seen and heard) and the price was what I could afford.

Hope that helps clear it up a little more.


From: Fastrotor@aol.com
Date: September 5, 2000

My name is juan barajas. I have been running 2 different engines one running high boost and the other bridgeport holley. I have tried seals from hurley in europe and the atkins seals and had nothing but problems.

The problem with the Atkins seals is the radius on top of the apex seal is completely flat causing low compression.

The Hurley seals did not last long they detonated after a few dyno runs and ended up broken.The problem with the Hurley seal I was told is the corner chip is too large causing blow by ending up in pre-detonation.

This is why mazda made there corner chips small to avoid blow by. After all my engine blowing adventures I was referred to a racing shop in California that makes custom parts for Mazda rotary engines. He suggested to me to purchase his 2mm metal apex seals and 2mm solid corner seals. He said this is the right remody for my problem. Ever since I have had no problems with engines and have one person to thank: POWERHOUSE ENGINEERING. Their web site is www.mazdacomp.com. Tell them juan barajas sent ya!!

(Editor's note: this is NOT Mazda Comp, which is how everyone refers to Mazda Competition Parts, Mazda's parts group. Just wanted to clear up any confusion. --Steve)

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