GrammaRed

iTrader: (1)

I first posted this question in the new member forum because of my low post count but it was suggested I'd have better luck getting an answer here. The original post is here:
https://www.rx7club.com/new-member-r...ssion-1044604/

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 )

RotaryEvolution

iTrader: (30)

sounds like one apex seal is sticking in the rotor slot or jammed up under the end of the apex seal. neither of those problems will ever cure themself.

GrammaRed

iTrader: (1)

Thanks for the quick reply. When I took off the exhaust manifold the seals all seamed to move without sticking. Would I be able to feel it if the small end piece of the seal was stuck?

archaphil

iTrader: (1)

Knew you would get help over here

RotaryEvolution

iTrader: (30)

the boot is in an area that you can't see or get to without disassembly. if the long apex spring is jammed under the long seal then the assist boot will have no support and bleed off compression.

if you installed the seals in one piece with the springs it is quite possible to jam the spring, i have seen it done. i install the springs after the rotor has been installed into the engine by sliding them under the long seal while assembled, this gives much less room for error as i have yet had a spring get jammed up. short spring first, followed by long spring all the way to the far end of the seal. the atkins video describes this procedure.

GrammaRed

iTrader: (1)

When I installed the seals I did it the second way you describe. The Long seal was held in the rotor with vaseline, then once the rotor was installed I put the small spring in until I heard it click into the small recess, followed by the long spring which was pushed as far down as possible. Then I stuck the little end piece of the apex seal in between the spring and long seal.
Is it possible I pushed the long spring too far, past the notch on the end of the long apex seal?

Can you clarify what the 'assist boot' is? I don't think I've seen that term before. Is that the same thing as a corner seal plug? Or the small end piece of the apex seal?

Also, if the spring is jammed in the rotor slot or under the long apex seal would I be doing damage if I keep running it? I ask because I'm still wondering if this is just a case of the seal needing more break-in but don't want to keep running it if I'm doing damage.

Thanks again for your help.

RotaryEvolution

iTrader: (30)

that way you shouldn't have had an issue with the springs. the assist boot looks like a boot, it is the small end of the apex seal.

it is possible a seal slot was damage/pinched somehow during the work and the seals still aren't moving totally freely regardless of your tests, which you never can totally tell with the engine assembled. there is also the side seals to consider which you can't check.

the other possibility is a short apex boot popped out during assembly, but it is rather rare.

GrammaRed

iTrader: (1)

Ah, the 'boot' makes perfect sense to me now.
Have you ever heard of a single seal taking much longer than the others to break-in, or is that just wishful thinking? It just drives so nicely I wouldn't even know something was wrong if it wasn't for the shaky idle and warmup.

GrammaRed

iTrader: (1)

I had the day off today and I woke up feeling like wrenching on something....4hrs in the driveway later I have my answer.

One of the boots is missing. I looked carefully incase it had stuck to the rear iron when I removed it and fallen but no dice. It's just not there.

Besides the obvious of me simply forgetting to put it in there (it was my first rotary rebuild and I was taking it very slow and carefully so I don't think that's what happened) how does this happen? I want to make sure this doesn't happen again.

RotaryEvolution

iTrader: (30)

the boot is being pressed on by the long apex spring so it is under pressure, jiggling the e-shaft during assembly usually is enough for it to pop out of the rotor if not careful. usually i will pop them out so that the friction surface is just above the rotor housing(inner edge facing down) so that when assembled it will push into the rotor.

the boot would likely have went into the coolant channels in the housings. that is usually where i find small pieces that go missing during disassembly.

VANHALEN

iTrader: (3)

Although it's pressed together, it CAN pop out during assembly ESPECIALLY when you're trying to wiggle the center iron . I had it pop out once and luckilyI found it BEFORE installing the rear iron. Helps to work on a clean floor.
Have all the parts laid out in an orderly manner so you'll know what wasn't installed.
Sometimes I see guys with parts all over the table and wonder how they missed it. Parts on one table...tools on another table.

What I use is a REALLY small dab of Krazy glue to keep it in place during assembly. Press it down and stays in place. When checking the motor during hand rotation, it pops off. Never had a problem. If the rear seal pops off , it's going all the way to the bottom (front) and everything has to be disassembled.

I use a bunch of Hylomar on the o rings so if not installed carefull it lifts up.
I've McGyvered a few clamps to hold the assembly together as you work your way back.
You never want it to come apart and take a chance of pinching the o rings especially the inner because you won't see it.

Make sure to use heavy weight oil on all internals for that first dry start.

RotaryEvolution

iTrader: (30)

one time while just replacing a rear iron the boot popped off and sandwiched between the housing and iron while poking inside the combustion chamber. result was a junk rotor housing and rotor after checking compression the rotor smashed the tip of the rotor right into the protruding boot piece.

that was a fun day....

VANHALEN

iTrader: (3)

Yikes

GrammaRed

iTrader: (1)

It always feel better hearing other people's horror stories :P

I feel lucky no damage was caused by my mistake. Another seal is on order and I'll update with the results.

Thanks for all the advice.

GrammaRed

iTrader: (1)

So I finally had the time last week to put the engine back in the car and it's running great! No more misfire when cold and I'm getting three good bounces when I do a compression check.

When reassembling I turned the eccentric shaft just to see how easy it is for one of these to pop out. It didn't take much! My experiment nearly ended in disaster when one of the small seals popped out and right down one of the tension rod holes. With a stack of small magnets duct taped to the end of some vacuum tubing I was able to retrieve it but I was worried for a minute there!

Thanks again for all the help!