Reasons for this carbon buildup?

[dikidera]

So while working on my cylinder head, I noticed that while it was normal to have carbon buildup on the exhaust ports, all my valves are covered in a flaky layer of carbon, while the exhaust valves are covered in a white layer.

While I did have a bad headgasket, antifreeze shouldn't have entered the other combustion chambers which had 200 psi compression, so pretty much perfect condition.
This means the bi-fuel e.g CNG must have been dirty and caused all this crap, but the carbon buildup also says something else.

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20230423_143633.jpg (449.02 KiB) Viewed 694 times

[scot850]

It could just be oil leaking past the valve stem seals. The inlet valves don't tend to get as hot so it may mean it carbonizes rather than burns off. Exhaust valves are hotter so it may burn off more. Spark plug I can see looks normal.

We don't have CNG over here in regular cars so I don't know what is normal.

Neil.

[vtl]

This is leaky valve stem seals.

[erikv11]

Volvo branded only on the valve stem seals. Buy them in the bulk pack, not individually.

[vtl]

Degrease the valve steams thoroughly. They should be super dry, or the new seals will pop off. Don't glue them, like some folks do - most of glues become soft once heated and act like a grease.

[dikidera]

Could this also be why I had 200+ psi on the cylinders and even 210 on cyl 5 where I shouldn't have had the headgasket affect them? Which would mean I may find lower compression in those after replacing the valve stem seals, as the oil does help seal the combustion chamber better?

It's a NA engine, so I actually expected at the time to have this high of a compression if the cylinders were not worn and there were no other issues. Even in the cylinders with the bad head gasket, I got at least 160 to 180 psi.

[vtl]

No. I think your measurements are wrong. My compression was spot on with a good brand gauge, even with more severe carbon and calcium buildup than yours.

[dikidera]

So what is the actual compression in a normal Volvo 5 cylinder NA? Like I said, I believed 200+ psi to be correct as well as the tool itself.

For a turbo engine it should be of course lower. In any case, I didn't see anything about PSI numbers in VIDA. And what I did find is that if for a T5 with a static CR of 8.5:1, 160-180 psi is good, then for a 10.3:1 static CR, 200 psi seems pretty in the ballpark of what is normal.

I always do a compression test with WOT(if it's even possible with the ETM).

[vtl]

Actually, I converted it wrong. 1.3-1.5 MPa is a good range for N/A engine, which translates to ~190-215 PSI.