928drvr86.5

My 86.5 was running rough yesterday and making a strange noise which I guess would be blowby past the valves. The noise goes away ~2000RPM and power picks up, things smooth out.

No loss of coolant or mixing, so I am not thinking head gasket, rather burnt valves. I promptly went home and did a compression test, the car was driven 30 miles, so it should have been up to temp. Cylinder 3 and 6 are 60PSI, no change with a shot of oil into the spark plug hole. All other cylinders are 150-155 PSI. 160K miles on the car, I bought it with 76k 10 years ago, and as far as I know the engine has never been apart.

Once the engine is pulled, who should i seek to perform the valve job on the heads? Should the heads be milled even though the gaskets seem to not be the issue? What's typically included in a valve job? Are valves re-used if possible or am i looking at some major coin to replace all rather than the burnt culprits?

surfridermason

Maybe some carbon is on the valve seat. Before you pull a motor to do all this work, suck some water into the motor through a vac line at a very slow controlled rate, at above 2000 rpm (don't let the rpm drop or the motor stall while you do it). This would steam clean the combustion chamber and valves..... it doesn't hurt to add injector cleaner to the mix..... If you pull the heads and clean them, when you lap the valves in just replace the damaged ones.... all would be overkill... but if ya got the dough ya got the dough

Plenty of testimony out there that will reveal the effective result of steaming...

928drvr86.5

I hear ya on the dough thing. Yeah I guess I forgot to mention the Seafoam I put in through the vacuum line, I did that last night after finding the bunk compression numbers. I was thinking perhaps there was carbon in the valve seats. I do that once a year with noticable improvement, this time it did not help.

davek9

Can you get your hands on a bore scope and take a look see?
Also the hardest part about pulling the eng is making up your mind to do it.

I have been advised if the heads look good with no pitting and are true, don't cut them, check the guides, clean up the valve seats (that are good), replace all the valve seals and the many gaskets/hoses and reassemble.

surfridermason

Damn. Well at least you tried it and ruled it out.
I'm no wizard (or merlin for that matter, merlin was a wizard right?)
I just took apart 10 85/86 cylinder heads (for the valves). Your motor have HIGH MILES, been BURNT UP, or something caused a super lean condition recently (or a longer drawn out mildly lean condition over many miles) to roast a valve? Interested to hear what it was....GOOD LUCK

There were some burnt valves.... but none so bad that looked like un-serviceable

SQLGuy

Any chance the you had an overrev that might have led to some valve/piston contact? It's harder to do on an automatic, but if you had the tranny in 2nd you could do it.

928drvr86.5

I do drive it hard, but it shifts below 6K, I don't think it was over-revved. I'll need to invest in a wide-band O2 sensor and AF meter to investigate the lean condition, maybe the Ebay chips had something to do with it.

surfridermason

What do the plugs look like on the weak cylinders? any white at all?

928drvr86.5

The plugs were changed last year, on the weak cylinders the plugs were cleaner than I thought they should be, very little residue. The other cylinders were light-brownish which i think is about right.

Dave928S

It does sound like you have to perform surgery .. but it'd be handy to know what you're up against, and know your options, before you get started.

If you can get hold of a good endoscope with a wide angle lens you can see the valves and that might give you a bit more information. I have a heine 8mm shaft optical scope and can clearly see the head gaskets and valves in a motor.

Also if you lock (or it'll rotate) each one at TDC compression stroke, and feed compressed air in through a spark plug adaptor, that'll give you a really clear idea of where your compression is going ... you can hear it through exhaust or intake (open everything up on the intake so you don't do damage and can hear), pressurising coolant system or giving massive blowby into the crankcase (although you seem to have ruled the last two out). Normal can be judged by doing the same on a good cylinder (you do get some normal ring blowby).

Strange that the motor picks up over 2000rpm ... you'd think power would be down over the whole range.

SQLGuy

Any popping (backfiring) at idle? That's the main symptom I had on my motorcycle engine with non-sealing valves. Also had pretty nasty carbonization in the worst of the cylinders.

Damage in that case was caused by an overrev, and bent all intake valves, but bent #3 more than the others.

928drvr86.5

That is the next step, I would like to know what is going in there before tearing it down. I won't be able to do much about it, but it will be nice to know going into the job.

I'm guessing the leakdown isn't quick enough to keep up with RPM at that point, it did have 60PSI on both weak cylinders, not zero. I will add that it does run strong above 2000 RPM, almost as strong as it usually does but I CAN still feel something is not right. It's almost like a vibration I can pick up that shouldn't be there. I've been driving this car for 10 years, so I notice when things change.

Looking forward to the "pull" , not the expense. Still wondering who the cylinder head expert would be for having the head work done? Carl at 928 motorsports seems the logical choice and Horicon is only 2 1/2 - 3 hours away.

928 Is My Favorite Time of Day

Just a layman thinking here, but have you considered it might be weak/failing lifters or weak valve springs? Won't change the fact that the engine has to come out but still better than burnt valves. Also Merlin was actually a Magician. Don't know how that's different than a wizard though. Best of luck with the repair.

Joe

Dave928S

Sounds logical. Taking a guess from what you've said I'm thinking exhaust valves, as I'd think there might be more interference with other intake charges (and more power loss) with dud intake valves. I'm intrigued as to what the problem actually is ... keep us posted with what you find.

surfridermason

Me too. Could worn compression rings caused by the crank defect in the oil passage cause this? Does that passage supply oil to the cylinder at all?

Head gasket is a good choice for an easy culprit..... but there would be evidence you would think.

Maybe it's just a very classic case of cutting valve seats and lapping the valves in... Other valve damage such as burning would be surprising, at least to me- but I'm a newbie .