My brother's low mileage (48K) 1988 Micra has started bellowing thick bluish smoke from the exhaust over the last couple of weeks but otherwise runs ok.
I did a compression test yesterday and No.1 cylinder was 10 psi down on the others. Suspecting either bore damage or valve stem oil seal problems I removed the cylinder head. No.1 piston was totally clean and carbon free whilst the other 3 pistons showed the expected build up.
What could explain this and the smoking? I can see no bore scoring or unusual wear and the valves all look ok (although I haven't yet removed them). Could valve stem seals fail in such a short space of time - but that wouldn't explain the clean piston.
Any ideas would be welcome.
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Here's a possibility from the car by car breakdown on this site: "Fuel pump diaphragms fail, leaking neat petrol into the oil sump leading to severe engine wear and possibly even an explosion. Failed engines not worth replacing now, even at API's low prices."
HJH
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Doug,
Most common cause of a remarkably clean piston crown is water ingress into the cylinder, most usually due to a head gasket problem, but sometimes via failed inlet manifold gasket where manifold is water-heated.
10psi difference is not enough to indicate a serious ring/bore problem, but could be the result of dry rings due to their having been "steam cleaned"!
Only slight contradiction is "thick bluish smoke", where water ingress would give a white smoke/steam emission.
I would take a good look at the head for distortion / cracks, and put it all back together and see how it goes. Do fit a new inlet manifold gasket as well as the head gasket, and while the head is off is the ideal time to do the cambelt as well.
Regards, Adam
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Adam
My immediate thoughts regarding a clean piston were that there was a coolant leak into that cylinder. Can't think of anything else that would give the effect. It's ben going on for a while though if it's really clean.
Regards
John
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On some Nissan engines of this era this was a common problem and was caused by a crack in the cyl. head. It started in the oil passageway in the cylinder head and the oil ended up in a combustion chamber. The symptons were always the same, sudden plumes of blue smoke, eventual plug fouling, good compressions. The head and valves look OK as the problem is internal.
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But a clean piston ??
Adam
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The oil could act as Redex was supposed to. To add to my earlier reply, I've taken valves out to check for cracks in the inlet tracts and so on. Never any sign of oil ingress. Must say that the engines I've come across with this problem had the oil feed between 2 and 3 cyls. And it was always No.3 that oiled up.
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Adam's right - the engine is knackered.
Just hook the old engine out and fit an API replacement
Not worth mucking around with the old unit when the API ones are so well priced
Rgds
David
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Whoa there David !!
I never said the engine was knackered, just that there is a strong possibility of a head gasket problem, which should be no big deal.
If Steve's useful information/experience is correct I suppose it could mean a replacement head, but still not SO bad !!
Regards, Adam
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