I have had 2 of my Cosmo engines go in a large way.

First engine: Massive lean out due to overboost and maxed out injectors. 100% was around 15psi and 7800rpm in third gear. Overboost was 20psi+ and 8000rpm in every gear, including 4th. I couldn't hear the detonation because I had the wastegate open to the atmosphere. Here are the results:




Second engine: Engine was run and tuned on Elf Turbo Max race fuel. Engine didn't really like it and soon spat out the side seals. Here are the results:





Not pictured is the mangled exhaust sleeve. The side seals in the front rotor on this engine were all gone, hence the burns on the side of the rotor from the combustion process.

I have used 3mm HME 2 piece seals in all my Cosmo engines. In both above melt downs, the Apex seals were not broken. On the second meltdown, the seals were scratched as can be seen on the rotor pic and they were replaced. Both above engines had the twin spring setup, my current engine has single spring.

Why do I run 3mm? I prefer that margin of error the 3mm give me. Is it because my tuner doesn't know what he is doing? HA! No. Its because there are a million variables that could occur at any moment to cause one ping and boom a 2mm engine goes. Sure it costs a little extra to setup, but I would prefer a little extra for piece of mind than having to rebuild an engine sooner than expected!

 

This maring of error of 3mm seals is total bullshit ! (not an attack on you steve)

I have had 2mm seal engines detonate like a machine gun going off near your head 3 to 4 times each time for a period of like 2 seconds and in every case the seals have not failed ! In fact I have examined them under a microscope and reused many of them with no problems.

I think that people are confusing an engine that is basically a run down POS with an engine that has fresh parts in it?

A new 2mm sealed engine will crack the engine (dowled or not) or colapse the rotor before the seal will break in my experience, and I have a bit of experience...lol

I am a very experienced 3mm apeax seal user, and I for one will never go back to using them, ONLY if the rotors are beyond using 2mm will I use the 3mm seal. There is no engineering benifit to using 3mm seals. They are heavier, they cause more friction and they cause more stress to corner seals (in 2 piece and 1 piece design) & they do not seal as well ! ALL OF THIS MEANS LESS POWER COMPARED TO A 2MM ENGINE

 

I also cannot spell

 

3mm seals should be better - just like you cant beat cubic inches............ erm yeah, and we all know that isn't the case. its from the same school of thinking though

 

that still doesn't answer my question. i am more interested in the difference between the double spring and single spring apex seals. does anyone have insight on sticking/fluttering seals at high hp and rpm. would a double spring setup be better for a high hp configuration or is the stock 3 pc. good enough.

 

When you look at the forces in action in the combustion chamber, or any sector of the engine you will quickly realize that gas pressure is what holds the seals against the housing and what stops the seal from lifting of the housing as it approaches the minor axis's on either side of the rotor housing, as the magnitude of the centrifugal force throwing the seal inwards (bottoming in the groove) is far higher than what ANY spring or springs can hold, proper apex seal to groove clearance is what is important to keeping the seals on the rotor housings.

Springs are only there for low gas pressure situations, I.E. like starting the engine.

What is important, is to use the lightest strongest seal, and that my friend is the std 2mm 3 piece Mazda seal.......the ONLY Exception to this is the Iannetti seals which in 3mm form are lighter than the 2mm Mazda seal (I have used these) Also they make 2mm seals as well, but I have not used these, these would be lighter again, The problem with these seals are that they are expensive but more so that they do not seal as well due to design (not 3 piece).

There are no issues with 2mm stock mazda seals, the only issue some people have is that they cannot believe why there engine builder suggested other (inferior items) when technicaly and from a cost standpoint nothing realy matches the stock seals.

How much power are you planning to make? You know they are proven to over 800bhp?

 

The std 2mm is a double spring set up....

 

Ok, I went with 3mm Seals because I thought they were better. Maybe that wasn't the best idea but my car should be ready any day now so its a moot for point me since I have the engine already back together.

Since everyone seems to say 2mm are better, let me pose this : What type of actual performance downgrade am I going to get by USING 3 mm seals, if any?

Everyone keeps talking about the 2mm seals being better but I'm not seeing any quantifying numbers that give any details like 1% loss of HP, compression, longevity etc. Okay, so 2 mm seals are the way to go. BY HOW MUCH?

 

DavidDeco, this is only my findings...so by all means it is not gosple, but I have seen differences in power of around 4% between the two different apex seal options.

When I ran 3mm I could not run as much ignition timming (around 2 to 3 deg less @wot) I also saw that my a/f ratio was slightly richer with all other variables settings being the same (turbo,porting, exhaust etc etc) Also peak torque happened at a sligthly lower range around 100 to 200 rpm I believe due to increased friction wich lowered the peak power for the same boost level, In terms of reliabilty the 3mm seals cause more wear on the rotor housings due to the increased wear associated with the extra weight and surface area, there design also causes corner seals to crack with extended use at high power, by extended I mean in the region of 30000km use street engine which is raced around 10% of its life.

Rotor housing life is reduced by around 25% to 40% compared to running a 2mm Mazda seal v's a 3mm Mazda seal.......The Only 3mm seal I have used that I have found better is the Iannetti in terms of less wear on the rotor housing (but they have other issues), I have not used Hurley seals. After my experiences I have returned to the stock 2mm seal, as it is good enough for me.

 

I've also heard you really should run premix with 3mm seals.....is that right??? I've seen a rotor housing from a 3mm motor that had what I assume were "chatter" marks all in it.....feels like rough indentions (kinda like a bunch of waves) going accross. Anyway, can that be caused by running 3mm without premix? If not what causes it? The car was running fairly low boost (14psi) with no premix and there really wernt that many miles on it. The car ran lean on the dyno and cracked the end plate. Did the detonation cause it???

STEPHEN

 

If you're using 3mm seals with an OMP designed for 2mm seals, then you really should be adding additional oil. Mazda reduced the amount of injected oil when they went from 3mm seals to 2mm seals in '86.

I would PREFER that you should throw the OMP away and premix exclusively, no matter what... But that's neither here nor there.

 

what material are the stock 3 pc. seals made from. are they cast, forged, or billet?

 

While premix makes a degree of logical sense in terms of lubrication, I have one question---what effect does a premix have on the injectors in terms of dispersal pattern and fouling?

 

Conceptually, 3mm have more surface area than the 2mm seals. It'll have more friction on the surface and stress. The average of 50% wear makes sense since there is 50% more area that contacts the housing.

Dave, have fun with your 3mm seal engine. You shouldn't worry about 2mm vs. 3mm seals. My 3mm engine lasted a very long time (50k miles) before I overheated the water jacket o-rings during one hot texas day.
Just tune the car correctly or take it to a good tuner.

I've always been curious about the effects of pre-mix on injectors. However, pre-mix was made to be mixed with fuel. I'm not sure if it was intended for carbs or injectors, but I know some marine vehicles use pre-mix in their fuel.

J

 

Premix gas, which is really nothing more than adding two stroke oil in a small ratio (usually between 30:1 and 70:1), has historically been used in two stroke carbuerated engines, from chainsaws, lawnmowers, outboards to motorcycles. The OMP, as I understand it, dumps the oil into the mix post-injector. Before I dump the OEM injection system or augment it with additional oil, I would like some definitive data on the effect of a higher viscosity than spec'd fluid being put through a metering jet. I am combining this post and my earlier post to a new thread in this forum (To premix or not to Premix) so we don't take up so much 2mm/3mm bandwidth. Thanks

Jeff48

 

If the 3mm seals and the 2 mm seals are of equal hardness (currently a somewhat hardened mild steel), and the chrome plating on the housings are of the harder type (beginning with the 1989's), does it not make sense that the 3mm seal would have no more impact on the chrome than would a 2mm seal of the same hardness and that the 3mm seal would last 50% longer than a 2mm.

To me, saying that a 3mm seal will wear the chrome plating on the chamber surface faster than a 2mm seal is like saying that the edge of a 3 inch thick piece of glass constantly rubbing against a diamond will wear the diamond away faster than a 2 inch piece of glass. Harder substances abrade softer without degradation.

If I am missing something here, please advise.


Jeff48

 

Here is what I've experienced...

The 3mm seal is heavier - they are more susceptible to chattering/bouncing at high RPM. They're more likely to damage the chrome on the rotor housings. They require more lubricant than the 2mm seals, which alone should tell you that they're harder on housings.

 

While I am sure your observations of the condition of the housings are correct, and I understand your contention, I wonder if this is an equally possible alternative, the damage is the result of some cause other than chatter due to seal size (weight). Since the 3mm seal is heavier, isn't it just as likely that, at all RPMs, the heavier seal will be LESS prone to chatter and bounce because it is subject to a higher amount of centrifugal force throwing the seal more tightly into the housing.

While I would agree that the heavier/thicker SEAL may be prone to more wear (hence the need for more lubricant) I am still not sure how a material of substantially lower hardness can be abraded by the higher hardness chrome. The only regular scenario where I can see the 3mm doing more damage to the chrome than a 2mm is where equal amounts of impurities exist in both size seal metals and that those impurities are of a higher hardness rating than the surrounding seal metal and that the impurities are also of a higher hardness than the chrome plating in the rotor housings.

The only other way I can see more damage done to a rotor housing by a 3mm than a 2mm is when the chamber contains cracked, blistered, otherwise damaged or low quality chrome. In such a housing, the chrome and the underlying non-plated metal would be much more damaged by a 3mm contact point, but not in a high quality, undamaged rotor housing.

Just some food for thought!

Jeff48

 

I'd imagine the imperfections in the metal (chrome) would cause the bouncing or chatter, as you have mentioned above.

These bounces would be further exacerbated by the higher rpm when the centrifugal force is stronger.

As for the abrasion, I believe it'll wear the chrome faster with the thicker apex seal. Given that the material and imperfections are the same, the 3mm seal has more mass and surface area. Thus, the 3mm seal has more hardness than the 2mm seal (hardness is measured by mass per area or knoop hardness). When you apply the same centrifugal force to the seals (2mm and 3mm), the mass will directly affect the force applied to the chrome surface. Now consider the heat from combustion (and chrome's nice heat conductive property) and I believe it'll reduce the hardness of a material as temperatures rise (Correct me if I'm wrong and it may be insignificant unless at very high temperatures).

The malleability and toughness for the chrome alloy are probably significantly higher than the apex seal material. However, you're still scrapping thin layers, bumping and scratching tiny areas many times over.

J

 

Because the 2mm seals are markedly lighter, they're less likely to bounce. (Think of a suspension.. the apex seal would be "unsprung weight")

I'm sure the 3-piece construction helps in this regard, too.

 

Actually, Knoop hardness is an indentation scale and is figured by a load being applied to a diamond indenting tool and the dimensions of the resulting indentation are measured. The Knoop hardness number (like Rockwell, Brinell etc.) is the ratio of the applied load to the area of the indentation. The size of this impression is quite a bit larger than any of the individual grains or hard particles. Hardness numbers measure only the average hardness of many particles. On the other hand abrasion resistence can be up to five times different in two materials with exactly the same test hardness. This occurs because of the homogenaity of the metal. When measuring the hardness of two metals you may arrive at equal hardness numbers even though the structure of those metals will cause a different abrasion rate. For example chromium carbide iron is primarily very hard particles suspended in a very soft matrix and yields a given hardness scale rating. On the other hand, tool steel, with a hardness exactly equal to that of chromium carbide iron, is essentially a homogeneous structure with a uniform hardness. When tested for abrasive quality though, the chromium carbide iron is hugely more abrasive than the equal hardness tool steel because of the very hard particles found therein.

Now, in the application at hand (rotor housings and seals), chrome plating is a homogeneous material with a Brinell scale rating of 1000. The seals on the other hand seals are basically a homogeneous hardened steel (excepting impurities) with a Brinell rating of beteen 650-700. Since both materials are homogeneous in nature, the abrasive effect will be acting on the lower hardness steel, and only abrasive effect on the higher hardness chrome rotor housing should be the result of the occasional stray higher hardness inclusion, which will quickly be expelled from the surface of the seal. So given the fact that both seals are made from equally inclusion free material, the 3 mm seal will outlast the 2mm seal by a 50% margin and do no more significant damage to the chrome.

I still don't get why a lighter weight seal will seal better as the result of high RPMs. Maybe (and I empahsize, maybe) at no and low RPMs the apex seal spring pressure can more easily force a lighter seal in contact with the rotor housing surface and perhaps the 3 pc seal would make low rpm contact even easier, hence better compression figures at low rpm, but I don't see why, when pressured by equal rotational speeds, a higher mass is not thrown outward with more force (and therefore less likely to kick back toward center) than its lighter weight counterpart. Again, the only way I can see any counter-centrifugal force being applied at all would be if the housing surface were significantly wavy or chattered during the casting or plating process. In that case the housing should have been rejected before the unit was built.

Again--just something to think about.

Jeff48

 

The problem with 3mm sealing is due to bounce.

Take a look at what's left of my old 12A... 3mm iron seals can't be revved beyond 8500 or the seals chatter. Any significant use beyond 8500 makes the seals crac kfrom this chattering. In my case, one of the seals chattered itself cracked, and it failed roughly 60 miles later as the revs went up past 6200 (which is the point at which the 12A 3mm seals begin chattering).

The rotor housings have marked chatter marks on them, and a small amount of flaking. The rotor housings looked PERFECT 23,000 miles before when I assembled the engine.

 

Man, you sure make me feel not so bad now about having asked for the 3mm seals.

 

Peejay
I totally understand and believe your account of what happened to you. But a few things bother me about the generalization to all applications.

First, the 12a housings had considerably lower quality chrome plating than do the current 13b housings and the apex seals for those years are still spec'd out to be considerably harder. This would account for the increased likelihood of damage by 3mm seals over equally spec'd 2mm.

Second, it would actually appear that chattering is a function of lateral movement not bounce. If you, in fact have chatter it is more likely caused by an improperly spec'd seal slot (too wide or shouldered top). This lateral slop allows the top part of the seal to trail behind the slot until the rpms go down, at which time the seal tries to catch up to the slot and chattering (dragging) against the chrome on its way.

Finally, I am unfamiliar with any rev limit for 3mm seals or warning that they will "chatter" beyond that limit. Please direct me to a primary source for that information.

Thanks
Jeff48

 

I think you need to re-examine the motion of the apex seal and the apex seal spring relative to the rotor housing.&nbsp I think Hurley Engineering in the UK has a animated GIF that shows the apex seal and spring in oscillation while going over the rotor housing.&nbsp I think it's obvious where weight comes into play once you figure in the oscillations.

This is a good example of theoretical versus real-world experience.&nbsp All the experienced folks know the heavier seals do no work better.&nbsp You're trying to contradict their experience with a false assumption.&nbsp Sounds like the proverbial egg in the face?


-Ted