Show me the primary documentation supporting your anecdotal evidence. I am not doubting your personal experiences but I have yet to see any credible documentary evidence that supports your claims that, all things being equal, the 3mm seal is fundamentally more damaging to the longevity of a well built high quality rotary engine.

And by the way the Hurley site http://www.hurleyrotary.com shows exactly what I am talking about. A well machined and spec'd slot in the rotor will allow a well spec'd 3mm seal to ride up and down in that slot as smoothly as a 2mm seal in a 2mm slot. The difference will be that (under rotation) the heavier 3mm seal will be forced out into the chamber wall with higher pressure and generating surer contact that its lighter 2mm counterpart. Chattering, as I contended originally, is more likely the result of wear or an improperly machined slot or badly spec'd seal. (see their illustration of the wear areas on the rotor and seal in their Direct Tip Seal Lubrication System section).

Additionally, the rest of this site appears to confirm Hurley's fundamental agreement with many of my arguments. They provide softer metal on their 2, 3, and 3.5 mm seals than OEM standard to reduce wear on the chambers, and also talk about optional seal designs to replace the standard seal problems of sealing at low rpm. Looking at their duplex spring unit for a minute, they suggest using this to increase control of the seal at high rpm. By this it would appear that they mean the addtional spring tension adds outward force to the centrifugal force already acting on seal driving it into the chamber wall. If this is in fact a good thing, then the added 50% mass of a 3mm seal will likewise be a good thing because (at higher RPMs) it would also add outward force to the rotational forces already acting on seal driving it into the chamber wall.

PS Thanks for the tip on the Hurley site. It is quite good.


Jeff48

 

Hmmm...I dunno if this was directed towards me, but...

I didn't not say it wasn't possible - I claim it's a waste of time.&nbsp I think I've said this earlier in this thread.

If you look at the apex seal to rotor housing contact, it is very rarely a perpendicular "square" contact - the animated GIF is sorta wrong on this sense.&nbsp If you've ever messed with an open engine, you can see this easily by rotating the e-shaft and rotor within the rotor housing with all apex seals (and apex seal springs) intact.&nbsp Due to the geometry, the apex seals contact the rotor housing at very odd angles.&nbsp This means even with the wider (3mm) apex seals, you don't get full contact of the thickness (3mm) to the rotor housing.&nbsp In fact, in it's most vulnerable positions (at or around TDC) at ignition, the apex seals of the rotor face being ignited are at VERY acute angles in relation to the rotor housing surface.&nbsp Thus, the 3mm seals will exhibit very little sealing superiority over a stock 2mm apex seal; the machined angle (where the apex seal contacts the rotor housing) across the cross section of the apex seal thickess is very important!&nbsp Thus, arguing the superior sealing of a thicker apex seal is not possible - care to run the math on this?

So far I've seen only the calculated strength of a 2mm versus 3mm apex seal across it's entire width - I believe the answer was 217% stronger, but the dynamics forces are totally wrong for such a calculation.



-Ted

 

Ted

Your analysis of the angles of contact is absolutely correct and was never an issue in my analysis. In fact, I would have always been willing to cede the following point to you: a 3mm flat-topped (or machined angle) seal will have positions in each cycle where the only part of the seal contacting the housing is the leading or trailing corner tip of the of the top of the apex seal. However, this is equally true for the 2 mm variety and conceptually must be true for any thickness seal. Without a detailed analysis of the cycle and running the numbers I would be unwilling to guess whether the thickness of the 3mm over the 2mm makes the duration or location of this limited contact better or worse or equal for the 3mm vs. the 2mm. If you hold a gun to my head for a guess (no data here pure intuition only), I would say that there will be points on the housing where a 2mm has an advantage and others where the 3mm gains the upperhand.


I would, however, be willing to more than willing to guess that, given a strength test measuring only the metal in the leading or trailing tip of the flat top part of the seal when pressed against the housing, the strength of identical composition metal 2 and 3mm seals would be the same, since the same amount of tip (really just a triangular or machine shaped corner) would be in contact with the housing.

For the purpose of this discussion, I will also cede to you that in those cases where detonation occurs when only the tip of the seal is in contact with the chamber, the strength advantage of the 3mm is negated, but I will argue that its strength is not surpassed by the identically composed 2mm. However, if the detonation occurs at a point where the entire flat section of the 3mm is in contact with the rotor housing, the 3mm seal has a larger chance of surviving the effect of the explosion than does an identically composed 2mm
seal similarly placed.

Overall, however, my concern and comments have been aimed at examining the claim that a 3mm seal is, by its nature, detrimental to the longevity of the motor. My research and experience (yes, I have had more than one engine go bye-bye guys and I have a fairly good working knowledge of the insides of these beasts) leads me to believe that the 3mm seal is not the devil incarnate but actually has good credentials as an credible alternative seal in high performance settings. It is not simply a budget conscious replacement seal for rotors with worn seal slots.


Jeff48

 

Apex seals are rounded at the sealing edge, they are not flat!

 

Please re-read this post and my earlier post closely before you respond. In my earlier post I said flat or machine angled. I use the "flat" example in response to Ted's discussion of angle geometry.

In any case the apex seals I am aware of are not completely radiused (rounded). If they were truly completely radiused this entire thread would be moot because the actual contact point (physical area) of a radiused 3mm or 3.5mm seal would be identical to that of a 2mm, 1 mm or 1/3mm seal, which would eliminate the theories that a wider seal is more damaging because of the contact area. The tangent between the seal and the rotor housing would be identical in both the larger and smaller seals. That is, regardless of the radius of a circle---it still only contacts a flat surface (I know the housing isn't flat, but it is "flat" relative to the seal) at 1 point.

Assuming, for agument purposes only, that you were correct, you would not retain your argument's advantage for long. As I pointed out earlier, the apex seal is made of a material with a lower hardness than that of the housing. Within very few revolutions the radiused tip would be somewhat flattened. (In reality, because of the nature of the rotation and the shape of the housing, the flattened section would never retain a completely flat appearance but rather a series of very small flats with a slightly radiused transition between each). Once flattened, the size of each of the flattened sections of the 3mm seal would be larger than that of the flattened 2mm seal and again my discussion and Ted's analysis about acute angle contacts would be true.

Take a look at Hurley's site in its race seals section for a pictorial view of completely radiused apex seal contact points.


Jeff48

 

Excellent theory guys!
I am sure all of the above is correct and it is obvious the amount of knowledge and thought that has gone into your diagnosis is soundly grounded. Dont you think the design of the current 3 piece seal has more to do with the strength and wear resistance than you have involved in your models. The design of the seal (3 piece) lends itself to sealing within the groove aswell as against the housing far better than a 2 piece. It is obvious that the theoretical knowledge here far exceeds my levels, but I can definitely assure you that from experience and testing, the 3 mm seal will withstand more detonation than a 2mm, but will not return the same power output or wear as well as its counterpart. I do not know the scientific reasoning behind this, however discussions like this with people that do, will go a long way to atleast trying to understand them.-Thanks.
Regards-Anthony

 

Here's the way I like to sum it up when a friend askes me which is usually better...

"The only advantage to a 3mm seal is it is a big stronger and can therefore withstand more and harder detonation. If you are getting detonation, you shouldn't be relying on a seal to control it anyway. 2mm is better"

 

Wow, there is quite a lot of brain work going on in here .....I better leave lol

STEPHEN

 

At the risk of restarting an all out nuclear exchange again, I just want to say that in a perfect world (ha!) 2mm seals would be wonderful. In a world that has constantly changing ambient temps, humidity, gasoline quality and other gremlins a 3mm seal theoretically may provide that slight extra protection needed to save you $4-6K. That, my friends, is one of the best reasons for CONSIDERING the use of the 3mm (the other is worn rotor slots).

Jeff48

 

That is a good point. Even though I would recommend 2mm seals in 99% of situations, I don't disagree with anyone using 3mm just because they are good as well. Both have advantages, both disadvantages.

What about a 2.5mm seal? Is anyone on here running with them? "bEst of both worlds" type of situation maybe? (and yes, you can get them in that size)

 

Does anyone know what size apex seals Mazda uses on the RX-8??

 

Now that is an interesting question. I wonder if they are the same or if they have a new design/material/size.

STEPHEN

 

2mm apex seals I heard. Not sure how many piece or springs.

 

i'd almost put money on it that they are 2mm 3 piece seals

 

Just to throw in a monkey wrench into this whole thread...
Our experiences with 3mm seals is that detonation tend to crack them in half down the center, pointing to failure due to resonance.&nbsp This is the opinion of Paul Ko @ K2RD who has a degree in Mechanical Engineering.



-Ted

 

2mm seal well by design. Less friction im sure. I slot for 3mm though because I`ve seen too many engines with the point where the corner piece meets the apex seal cracked/missing and also when the seal wears it makes a nice gouge in the housing along the edge. If customer wants 2mm I use them, but for circuit or performance street engines I prefer the 3mm which seems to be able to cope with detonation better in real world applications that I have witnessed, not in theory or on paper. I like 2mm carbon in N/A race engines though.
I am no scientist, but I do know that from imported 12A turbo engines, and also the 12A turbo engines I have built, the life has been exceptional. I have seen applications with 20+psi boost run reliably with cracked plates being usual failure and dowelling fixes that. I know the 12A has a shorter eccentric shaft and narrower rotors (and seals) but the 3mm seals really do seem to handle punishment by rotary standards.
Tuning is critical, but I think the 3mm can offer slight leeway in terms of reliability from what I have seen. For maximum output engines, both 2 and 3mm are probably that stressed that there is no real advantage to go 3mm and the better sealing of a 2mm and reduced drag may be favourable. But keep in mind these engines are not designed to last years and do a lot of km`s between rebuilding. I and most customers are more interested in longevity and reliability. And when there is a GT30 series turbine waiting to catch bits of seal, longevity and reliability is really important. As replacing CHRA is not exactly cheap... Actually rebuilding plain bearing turbo isnt exactly cheap either...


fin.



www.drive.to/mspeed

 

Ted

I am sure that Paul's analysis is correct, but this information relates to "a possible (probable) cause for certain 3mm seal failures" rather than addressing whether 3mm seals provide any physical advantage/disadvantage to a 2mm seal in a particular application (e.g. resistence to unforseen detonation, longevity in properly tuned engines--etc). Has Paul shared any data or thoughts with you on that subject?

Jeff

 

The above was the original post of the thread.
Patrick, after reading a 10 page debate, did you ever decide?

 

He's a lazy ******, and finds this place a waste of his time...


-Ted

 

Boy, and I waste my time trying to convince HWO about dowelling a engine...


-Ted

 

why dowel when you dont need to?

that is my question.

If Peter who will probably be the one who will assemble and blue print my Semi BP motor can build a 830HP 13B PP turbo which no extra dowels and it doesn't crack plates, then a) why should i dowel my motor when i can spend the money on other things, and b) why do you seem to think every motor with over 400HP is going to crack the end plates from this Mystical TWISTING force, when there is NUMEROUS people on this forum who make over 400HP and have never cracked plates...... Your numbers simply dont compute with all the examples i have

 

From what I've been reading.. it seems very high HP 12A's should be or may need to be dowelled, but it's rare for a 13B to ever need dowling.

Am I right?

 

here is another theory from a guy who has played with a few rotary's and is an auto machinist.

the only set ups he has ever seen crack plates were later type motors, ones with mounts in the middle or rear plate that had been transplanted into early cars, like 323's, rx3's etc in which the two side mounts were not used just the a front mount, his theory being there was simply too much potential rotational length behind the front mounted motor...............

 

If that were the case, the twisting forces involved would try to twist everything the OTHER way, meaning the dowel would move upwards. That is not what happens, the dowel moves downwards, indicating that extreme chamber pressure is trying (and succeeding, to a degree) to force the rotor housing circular.

 

yes i know, it also ***** all over ted's theory too doesn't it.

am i the only one to notice a absence of his posting in this thread after your post about cracking up/down?