Rotor housings are in great condition. End/center plates were lapped. All new seals clearanced correctly (triple-checked). I'll be putting in new rotors this weekend. Thinking that the seal grooves are worn.

 

I've got one now that's like that. 110psi compression on a standard gauge, nice fast cranking, and it refuses to start unless it's given a little oil. Sometimes they just feel like being bastards I guess.

 

I bet one of your pulses are down.

How does it idle? Smooth or lumpy?

 

It's remarkably smooth for a peripheral port engine.

 

Uuugh! I give up. I rebuilt the engine AGAIN. This time with a different set of rotors. Compression is up a little bit, but is still low at 60 psi for front and 75 psi for rear.



I've triple-checked everything. Replaced/redone all possible sources of compression leakage. And it's still not a good engine.



rotor housings good condition - measured and straight

end/center housings - lapped by Mazdatrix

fresh rotors with all seal grooves confirmed good

all new soft seals

all new hard seals with clearances from Mazda Comp. Tech Tips

Since I did my own street-porting, I even checked to make sure there was no port overlap.



While this is my first street-port engine, I have rebuilt stock motors before with no problems. Does anybody have any ideas/theories for what is going wrong?



Rich

 

The apex seals may have been over size in length, and should be checked before installation. A slight overlength will result in a seal held off of the housing surface.



If the compression changes little between measured dry, and measured with motor oil squirted into the housing, then it would seem a mechanical fault as above.



A porting job with way late closing line will do it as well, but more like 100 PSI than 60 PSI.



Lynn E. Hanover

 

Don't think its the seals. They were replaced once because the gaps were .008 total. New ones have been triple-checked to be .002-.004 total.

 

Are we talking side seals or apex seals? With the seals that have the joint about 1/2" from the end, a long seal holds the main part of the seal up and the end down, so a big leak that gets bigger with temperature. With the little corner piece,

the corner will be held down and the leak will be around the end of the long piece.



The side seals could be as little as zero clearance and work fine.



Lynn E. Hanover

 

Using one piece carbon apex seals.

 

Should have stated that earlier. I havent used them before, but Ive always heard that carbon seals dont seal well at low rpm.