ZW 944

After the car started hesitating big time under acceleration, and misfiring at idle, I first changed the plugs, wires, and distributor, when the problems persisted, compression test showed:

Cyl 1: 142 psi
Cyl 2: 140 psi
Cyl 3: 140 psi
Cyl 4: 0 psi <----hmm.

Tore it all apart, and found the smoking gun. When this happens, what happens to the chunk of metal?? At this point, should I pull the turbo to see if it got sucked through? Also, how are the valve guides supposed to be replaced? I've found lots of info about replacing the valve stem seals, but not the guides

Not gonna lie though, for only running on 3 cylinders, it idled pretty dang well!

ZW 944

I'm kinda surprised nobody's had experience with this before given how many others in the past have burned valves. I guess at this point I should probably just pull the turbo just to be sure.

User 52121

Probably a good idea. You're part of the way there already.

Sixline

Someone correct me if I am wrong but this was caused by burning oil, correct? That carbon looks pretty caked on.

Ben951S

I'm a member of this club. We slapped a rebuilt head on over the weekend and all was well. Happened at the track 200mi from home and I drove it back on 3cyl.

Dave W.

Usually the missing metal from the valve is melted away, then it gradually cools and deposits itself along the crossover pipe.

Laust Pedersen

The likely mechanism for a burnt valve is as follows:
Carbon in the combustion chamber flakes off in small pieces, each of which has a small probability of getting caught between the seat and the exhaust valve when it closes. If the stuck carbon piece is large and solid enough to cause leaking exhaust gasses, then those gasses at high combustion pressure act as a welding flame, which for each combustion event may cut a small piece off the valve.

Since it is not a big piece breaking off at once, there is little chance that a burnt valve does damage downstream. I am not sure of the effect, if it is burnt all the way to the sodium, which in that case would be released almost immediately.

Moral of the story: Keep the combustion chambers as clean (oil-free) as possible.

Laust

Tom M'Guinn

Looks like you got your money's worth out of the valves anyway. If it's all stock, you can swap it for one at Lindsey that's ready to go, or most local machine shops for do it. Laust didn't take the chance to point out the importance of EGT's either -- if your tune is off, you can overheat and burn valves too. Laust has an EGT temp sensor to monitor that.

Oh, and your garage is begging for a work bench

Paulyy

Answers are there for you,

But you need some shelves!! and a work bench

ZW 944

I agree! A workbench would be wonderful, but as the place is actually just a townhouse I have while I finish up school, I'll be moving down to Florida in the fall.

I did happen to see about the EGT probes, but I think the issue could have been with an oil leak at the valve seal or vacuum leak related rather than the fault of the tune, as I just have the rogue A-tune, and I don't think any of the many others with A-tune have experienced this. The pistons all had a lot of deposited material on them, heres a pic of that, maybe there's a reason for the buildup?



I sure hope I didn't kill the turbo as its a relatively new cheater from evergreen, cost a decent bit, it would be a shame to upgrade this early haha. I'll know for sure in about a week, waiting on a couple special 15mm wrenches to take the x-over off...

Dougs951S

Is that a beer cup I spy under the hood?

ZW 944

An *empty* beer cup yes - I'd never set a full one there - hahaha.

jerome951

I'm a member, too. Happened @ Daytona coming thru Nascar 4 a couple years ago.

Put on a rebuilt head and the car has run fine ever since.

Chris White

Its a club membership that you have to earn!
BTW - the missing part of the valve went out the pipes at a vapor. Once you take the head apart you will see that the back side of the valve looks like it was channeled with an torch.
Laust is correct on the idea of a small chunk of carbon holding the valve open - the heat and pressure of the gasses escaping is really powerful. 1600 degrees+ at 1,000 psi can do damage quite quickly!
While its apart make sure you cure the oil issue - either bad guides or a lot of blowby from the AOS. If you intercooler is full of oil then its the AOS, if that's dry then its the guides.

ZW 944

Update: Everything is apart! Its amazing how much I can get done on the car when I don't have school at the same time. Valves are out and turbo is off. I ended up pulling the turbo both for peace of mind (it looks perfect still) and to replace the AOS seals which had accumulated a lot of grime in the surrounding areas. I post pics up probably tomorrow.

Next step: Clean everything up, order parts, and replace the valve guides. Any suggestions for doing the guides? All I've been able to find is that a special "punch" tool helps and that its best to freeze the new guides first.

I'm planning on using the teflon valve seals from Paragon with an adhesive.... haven't figured out what would be best yet. Probably like permatex ultra black.