I just finished rebuilding my engine a few days ago compression tested it and it failed. It has RA super seals. My question is how tightly should the apex seals fit in the groove. I believe I have mine in there so tightly that the springs cannot push them out enough to get compression. When I look through the exhaust ports some of the seals are easier to push in then others, and some are hanging out more then others.

 

they should slide freely with very little clearance from my understanding.

 

What did you clearance them to? There is a big difference between 'building' and 'assembling/slapping together' an engine.

 

^ +1

what was the clearance?

 

It is extremely unlikely that the apex groove clearance was too tight. I like to shoot for .002 and I rarely am able to get that, it's usually .0025 or so because of rotor wear.

I've never used RA seals though.

Now what is more likely is that a corner seal is hanging up or there is debris in a groove that is preventing the seal from moving.

Also it is somewhat pointless to compression test an engine that has never been run. I assume this is what happened.

 

Well I can see from the exhaust ports that not all of the seals apex seals are out as far as others, and some are harder to push in then others. Would startup of this engine pull those seals out to where they need to be from the centrifugal force? In correspondance with those seals being not as far as others some of the puffs on the compression are weaker then others. I had a starter hooked up to it spinning it pretty fast and got better results as i worked the seals out with some wd40 and pushing on them. I need to know quickly wether i should start over or fire it and see what happens. I dont have time i am already signed up for a drift event in a week. Also some of the seals are sitting higher on one side then the other looking through the exhaust port.

 

Take the engine back apart and measure the clearances. What was the side seal to corner seal gap? How much end play? Why are you doing a compression test on an engine that has never run? That makes no sense. The apex seals should move freely. All the seals should move freely. If anything is binding and you start the engine it's either going to run poorly or its going to break and then run really poorly, if at all. Check the FSM, Haynes, pineapple vids... Google...to find "how to set the clearances". Do you have feeler gauges?

 

Did you thoroughly clean the carbon out of the apex seal grooves? I can't see any other reason why they would be that tight, unless the stock 3-piece seals let go and fucked up the groove.

Mazda has FSM with all the specs and clearances for a reason, if you choose to ignore them you're kind of on your own. If the apex seal does not move freely in the slot it will not have the ability to seal throughout the engine cycle, and you have wasted your time.

If that was me, I'd see if I can get a running used engine in there for your event while you take this one out and check everything over again, THOROUGHLY clean it, and make sure all seals move freely and are within tolerance.

 

thanks everyone, i took it back appart, and my problem was excess glue that i used to glue the corner pieces to the apex seal. It made the apex seals wider then they should be and made it hard for them to slide in.

 

In that case you should have just installed the engine and run it. You just created a lot of work for yourself for nothing.

 

other than time, you've lost nothing. chalk it up to a lesson learned and move on. i hope all else was in order.

 

Good to hear bud, good job. For future reference after you glue them, scrape any residue off either side of it, although I'm sure you figured that out.

 

a fast, light wipe with some acetone on a rag melts the excess glue off

 

Anytime you install a seal you need to get the clearance specs recomended for the type of seal and check them for each seal. The clearance for each seal will vary. Carbon seals for example need more clearance than stock or ceramic seals because they expand with temperature. Also get in a good habit of checking all your clearances for all the seals, bearings, housings, rotors, and irons. This will ensure good compression and a long lasting motor. Good luck.

 

yea dude haha, i got it i scraped them and they fell in perfectly now. GOt alot to do in a short amount of time !

 

^^Best of luck getting it all ready in time

didn't mean to be negative with my last reply, was having a rough day

 

...and that is a lot of why it's pointless to test compression on an engine that's never been run

Whenever I manage to glue seals in such a way that they actually stick together, they always seem to glue cockeyed and if they even go into the slots without popping apart, they bind a fair bit. They've only failed to crack loose once, and that time they popped apart a very short time after I (finally) got the engine started.

Helpful hint: When gluing seals, make them deliberately overlong, so tightening the tension bolts forces the glue to break free.

 

yeah, i try to keep them long. however, i'm happy with them just staying together and straight enough to fit the slot. single spring engines aren't so bad, but the double spring engines can be hell. it took a while for me to learn that i could just glue the small spring to the seal, then glue the long spring to the corner piece and it makes life so much easier.