Volvo's 5 cylinder engine is an open deck construction, its cylinder sleeves eventually get a taper towards the cylinder head, which forces compression rings to open wider in the upper part of the sleeve. Also the rings themselves are likely worn, not very elastic and the gap is too large, to begin with. Also the sleeves are out of round, which causes all the rings to orient in such a way that their thermal gaps are aligned in one line. That's really bad for the crankcase blow-by gases (PCV has to work harder), as well as it allows much more oil be sucked in during the intake stroke.
No cure, except replacing the piston rings with new ones. And yet this is not a long term solution, because of taper and general bore wear.
This engine is good, but not worth rebuilding without a significant construction change at high mileage, like Darton sleeves, in my opinion.
What did you do to your P2 Volvo today?
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BlackBart
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That's really interesting, what causes that? Is it temperature at the top of the cylinder? Erosion from combustion?
ex-1984 245T wagon
1994 850T5 wagon
2004 XC70 wagon BlackBetty
1994 850T5 wagon
2004 XC70 wagon BlackBetty
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vtl
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Thin cylinder walls in 2.4 and, especially, in 2.5 that don't hold well a naturally higher pressure in upper part of the combustion chamber. Add occasional detonations.
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vtl
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Yeah. This is what Volvo permits:
This is what engine from the donor car w/ 220k miles on the odo had (I was swapping out crashed chassis and took its working engine apart out of interest):
Out of round 2 is near the top of the bore, 1 is around the center.
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Willber
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Thansk, vtl, really interesting!
Do you think that my smoking is probably piston rings rather than stem seals or valve guides then, if it only occurs after long periods of high vacuum / engine braking, rather than after idling or upon start up?
Do you think that my smoking is probably piston rings rather than stem seals or valve guides then, if it only occurs after long periods of high vacuum / engine braking, rather than after idling or upon start up?
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vtl
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Likely, both. It is a good idea to replace valve stem seals, though. At this age/mileage they are long time not elastic and badly worn.
It is not an easy job to do with the engine still in the engine bay. Exhaust valves are barely accessible, you must drain oil from the camshaft valleys and degrease valve guides with acetone super-thoroughly, otherwise the new seals will fly off.
Also exhaust seals better be Volvo original. Others commonly fail in 20-30k miles. Intake could be Elring. I personally put OE/exhaust (very expensive) and Elring/intake.
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