I recently rebuilt an S5 NA engine that is idling rough but stable, and misfires when cold below about 3000rpm. I have checked compression a few times and I'm getting one good pulse and two weak on the rear rotor with the compression tester valve held open.

At first I was hoping that after a few hundred km of break-in compression would improve but I've put about 1000km on it so far and it's still the same.

I pulled the exhaust manifold off and ran my finger along the apex seals, as far into the housing as possible and pushed the seal in to check the spring pressure. Everything that i could see or feel seems ok, though I know there's a good deal of seal I couldn't check.

Because it runs great above 3000rpm, feels like it makes good power and cruises nicely once warm my best guess is that one of the apex springs didn't seat, though that is just a guess.
Compression with the valve closed on the tester is 100psi and isn't dropping like I would expect it to if a piece of seal broke off and was wrecking the housing.

So my questions to the experts are:
1) Is it possible the seal just needs more break-in time?
2) If I didn't seat the spring properly is there any chance it will seat itself?
or 3) Is it definitely in need of being torn apart again?

Rebuild details:
This was my first rotary rebuild
I used atkins apex seals, springs and gaskets/ soft seals
Reused side seals and corner seals ( I had 2 engines to pick out the good ones and clearances were in spec)
This is an S5 NA engine with mild porting done in an 87 GXL with S5 turbo/manifolds/intercooler, MS1 ecu

Any advice would be appreciated (though I think it's obvious I'm hoping the answer to Q 1 or 2 is a yes :P )

 

I recently learned the hard way that these engines must have a certain amount of oil supplied to the apex seal during operation to get good compression. Perhaps that rotor isn't oiling properly and therefore not getting good compression.

 

If you are talking about the OMP and injectors that's not an isue for me since I premix. I probably should have mentioned that in my first post.
If you mean something else let me know, and thanks for the reply.

 

One good pulse and 2 low is a side seal issue

 

89fc3sgtu:
Everything I've read says that one good pulse and two bad means apex seal issues. A bad side seal would have two good pulses and one bad.
Here's one of the places I read that:

Is My Engine Blown?

Not sure what a bad corner seal sounds like though.

 

your right im sorry i got that backwards. i dont know what a bad corner seal would do either. you could run it and see what happens but if it is an apex seal or spring and it gives could tear up a rotor and housing

 

you would be better off posting a question like this in the second gen forum, as this is the newbie side and many of the people that would know the answer to your question simply do not come here. You seem to know what you are talking about and I suspect a few well known re builders will respond to you there. I will watch for a thread to pop up as I have a similar issue on a S5 Tii that was "supposedly rebuilt"

 

archapil, I thought it might be the case that the people I need to reach would ignore the new member section but I didn't have enough posts to put it in the second gen forum. Now that I do I will take your advice and start a thread over there.

 

89Fc3sgtu: I did some searching and it looks like a bad corner seal would show similar compression to a bad apex seal so that's a possibility.
The fact that the engine runs smooth at higher revs is what makes me think it's an apex seal spring. I imagine the seal being pushed outward from its momentum would help it seal even with a bad spring. That's still just a guess though.

I've started a thread with the same title over in the second gen section now hoping to reach a wider audience

 

To update this in case anyone doesn't find the thread in the Second Gen section, after talking with RotaryEvolution I pulled the engine back out. Tearing the engine apart I've found that one of the small ends of an apex seal was missing. I don't know what happened to it but at least I know how to fix it.

Thank you for all the help