SPECS: s5 NA, ~30k miles on R&R rebuild, Streetported, No 5/6th ports, typical exhaust mods, stock intake box, and that's basically it.


Alright here it goes :/


I was on my way to work this morning, and about 20 minutes into the 25mph drive(traffic, fully warmed up, had oil pressure etc) the car just started misfiring, and sounding like a subaru. I tried revving the motor with some real quick gas petal taps(I do this when my motor does quirky **** like idle hunt, and it usually goes away really fast) real quick, but nothing happened. I drove it all the way to work, which was about a 15 minute drive. I quickly check the spark plugs, coils, wires etc. everything looked good... and then I put the plugs back in, excluding the rear trailing plug, pulled the EGI fuse, and gave it a crank. this is what I heard

PSHHH!, tss, tss. PSHHH! tss, tss. :'( which is indicative of either a stuck, or cracked apex seal correct?

Where do I go from here? Obviously rebuilding is an option, but I want to know how to confirm that the seal is either stuck, or cracked.

Most of the time I read about a blown apex seal, it is when someone is BEATING on the car. not putting around in 2nd gear

 

Well first thing is to check your compression . there are a few new threads on the subject of checking compression or maybe you know how . take the exhaust manifold off and turn your engine over to expose the apex seals and just feel with your finger and see if one is stuck . If you push on the seal you should feel a bit of movement . you should be able to see them move also . if no movie he is stuck . Do you city drive it lots ? maybe he just stuck on some carbon build up .you might want to decarbon it before you take the exhaust off . That's a start . let us know what you find .

 

not sure how to decarbon it though. ATF? Seafoam?? I have no clue

 

Steam clean it or use the zoom zoom cleaner from Mazda... if it really is a stuck apex seal. The only real way to tell if you have a stuck/chipped/broken/missing apex seal without pulling the engine is to pull the exhaust manifold, which is luckily pretty easy on an NA engine. Do that after doing a steam cleaning of the engine internals. That consists of warming the engine up fully, then sucking in about a gallon of water through a vacuum hose with the engine rpm about 2-3k.

Good luck.

 

Never use ATF on the little engine . it creates lots of ash and takes a lot of ignition to make it burn . if you have a stuck apex do what Agreen suggests . One thing if you are going to steam it make sure you are putting the water in the proper rotor .the manifold has separate runners so if you suck the water into the rear part of the intake and the engine is missing on the front rotor it probably won't help much so maybe do both front and rear sections . hope that makes sense

 

An apex seal isn't going to "stick" while you're driving and carbon isn't going to cause problems while running either (especially on a low mile rebuild that shouldn't have much carbon buildup to begin with). It would stick after sitting for a while, like weeks. Sounds like a break to me. I'd suspect either some sort of foreign material or an apex seal slot that was too wide/damaged when built.

 

yep, apex seals only really stick after you shut the engine off. if you lost compression while driving then you are unfortunately SOL and probably have a fractured seal.

you should also try to determine the cause of failure such as lean AFR that burnt the seal, preignition due to timing issues or just a faulty engine rebuild. i did have one that sounded similar to this, the short apex seal spring broke on 2 apex seals and got wedged under one end of the seal and warped the seals. according to the owner it happened with just one quick acceleration trip, but it was a twin turbo so the additional ICTs were probably a huge contributor.

 

Well the apex seals are perfectly fine, and are all springy. I already pulled the motor, and the apex seals checked out :scra tch:

I'm guessing it's a side/corner seal??? Idk, either way I'm ****** confused. I'm hoping it wasn't something completely stupid, because I already swapped in another rebuilt motor last night >




Well it wasn't the apex seals, but something made it lose compression on two faces. I'm really confused about this.. could it possibly be an invisible hairline fracture?

 

You pulled the motor but didn't tear into it yet I assume?

If it's not an apex seal it'll be a corner seal. The PHHH.. tss.. tss.. indicates two dead chambers which a side seal would not cause.

If there were used components put into the motor when it was built it's possible a groove was not cleaned out completely and a piece of carbon dislodged causing a seal to stick. Or if too much metering oil (or premix) is used it can cause a seal to jam which generally will break a side seal but I guess could take out a corner seal. If you had a bridgeport I would think maybe you caught a seal edge but again, would not expect this after so many miles. It would generally happen right away.

 

EDIT: forgot to answer you're question. But no I haven't had time to crack it open yet

Must be a corner seal.

Any ideas on why this happened? It definitely wasn't running lean, actually ran quite rich(fireballs, grumbling & popping on decel, etc.) And there did seem to be quite a bit of dark carbonish material stuck on the rotor face from what I could see through the exhaust ports

 

i assume you just looked into the exhaust port or spark plug holes which won't tell you if all the seals are intact. Atkins seals for example usually just chip off a piece of the sharp edge of the long seal and you cannot see the break until you tear the engine apart. the result can be as low as 30psi on 2 chambers for a single chipped seal.

 

Correct...what you need to be looking for can't be fully seen with a flashlight through the exhaust ports, you can only see about half the seal that way, meanwhile the area that's most likely to chip or break off is in the hidden 50% area that you won't be able to see until you tear it apart.

 

I'd be paying very close attention to the apex seal groove tolerances when you crack it open. But like everyone said before. No way to tell til you get in there.