RX7 13B 4 UR AZZ

Have all the engines you built with these experience the same problem?

BDC

Most, yes, to varying degrees. Some will show very slight overheating-like symptoms while others are mosquito killers. When I tore my motor apart earlier this year, I had two o-rings that were on the cusp of splitting on the sides and I'd had that motor together for 3 years. The only symptom I ever saw that was problematic was during initial start-up. On the flip-side, I built a motor for a customer that was from the first couple hundred miles showing gross symptoms that were getting progressively worse; enough to the point where the car wasn't drivable after awhile.



B

AnthonyNYC

What exactly are you referring to? Apex Seals? If you are start a new thread so we don't confuse this one and elaborate on what you have seen, I'll throw my 2 cents in since I think we are on the same page.



Anthony

dac

You guys are freaking me out... I just bought RA's kit 2 weeks ago. I see exactly what you are talking about. I haven't yet put my motor together.



So do I ditch these seals and buy a set from Mazdatrix (another $100)

trydis7

People have reported having no problems. If you are concerned, go with the stock Mazda seals.

Can you measure the RA kit inner and outer oring diameter in a few places?



Thanks

dac

Sure can... What are you looking for? The outter seal is a square one.

trydis7

The outer square seal must be a stock seal. I have not heard of any outer seal failures.



Failures seem to be occuring with the inner teflon oring in the areas facing the hot side of the engine.



I'm looking for the outer diameter/thickness of the oring in a few different places as measured with digital calipers.



One theory is that an oring diameter .098"+ does not leave enough room for thermal expansion of the oring in the groove. The expansion opens enough of gap in the plates to expose them to combustion gases, resulting in early failure.

RX7 13B 4 UR AZZ

makes sense but with no acknowledgment from the mfg. hard to get things revised.

mazdaspeed7

As for your theory, I disagree. With a properly cleaned out o-ring groove on housings that have never been lapped, there is adequate room. Now if you dont scrape all the deposits out of the groove, or if you use lapped housings, the volume of the seal groove is reduced, which may not leave room for expansion. Ive built at least a dozen engines with these seals with not a single failure, including a couple of high stress turbo motors.



The RA kit uses an OEM mazda outer seal, or at least they used to. They are also not subjected to the higher surface temperatures of the housings near the combustion chamber, nor the small amount of pressure that makes it past the housings to the seal. The outer seals rarely fail on any rotary.



The set of RA o-rings I have at the moment all measure out between .098 and .099.

trydis7

Thanks for the measurements and confirmation on the outer OEM seals.



Heck if I know what the root cause of the orings failures are? I would just like to try to narrow it down.



I believe Lynn has commented here/elsewhere? on the surgical cleanliness for the grooves to be able to seal properly. Although, I would expect that coolant leaking past a seal into the engine would not show the split orings BDC and others have seen only on the combustion side. If anything, I would expect leaking coolant to protect the seals.

I also find it hard to believe that BDC slapped together dirty housings repeatedly. The inner coolant grooves are dead easy to clean.



IIRC, From the Creavey.com guides, oring seals had a "nominal crush". 0.098 was too big. 0.093 might also have been too big - I'd have to go back and check.

Several people have commented that the pressures these orings are dealing with are at the really low end of capability anyway.



You bring up another possible variable.

If lapping a few thou off a housing might make the difference between failure and not, then a 5-10 thou too big oring would also be important based on the volume of oring groove.

One other comment was that there should be something like a 20-30% expansion (volume) allowance for oring expansion.



BDC, were any of engines with failed orings lapped? how much?



Mazdaspeed7, what (if anything) do you use to help install these orings? hylomar? petro jelly? how much?



Also, what sealant do use between the housings?



Thanks

dis~7