piston ring de-tensioning
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piston ring de-tensioning
Has anyone ever heard of this?
it was mentioned to me at the weekend, whilst talking about my dad's xud 306, which has cold compression of 90psi in all 4 cylinders..
Basically, after an overheat, the rings can contract permenantly and compression is forever lost...
John
it was mentioned to me at the weekend, whilst talking about my dad's xud 306, which has cold compression of 90psi in all 4 cylinders..
Basically, after an overheat, the rings can contract permenantly and compression is forever lost...
John
Yes when the bores/rings wear there is increased blowby - and the rings get too hot - from the blast which wouldn't normally get to them if they sealed properly. To make things worse as their contact with the cylinder wall isn't good they don't cool by conduction as well as they should. There is possibly a build up of carbon in the ring grooves which will impede cooling that way as well.
The rings will loose their temper and the overheating will make them brittle as well - and eventually they break.
How was the compression measured? - measurement on a diesel isn't easy - which is why I ask.
The rings will loose their temper and the overheating will make them brittle as well - and eventually they break.
How was the compression measured? - measurement on a diesel isn't easy - which is why I ask.
jeremy
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interesting Jeremy..
unlikely to suddenly go then?
Compression tested in injector holes with a diesel comp checker, made by laser.. (about £100)
Car wont run so hot-engine test not possible.. but if 350psi is needed for combustion, 90psi will never get there..
I want to check my engine (to wild tonight out there!) I have his tester so can do mine cold and hot and make a note ,,, but will have to wait till tomorrow eve
unlikely to suddenly go then?
Compression tested in injector holes with a diesel comp checker, made by laser.. (about £100)
Car wont run so hot-engine test not possible.. but if 350psi is needed for combustion, 90psi will never get there..
I want to check my engine (to wild tonight out there!) I have his tester so can do mine cold and hot and make a note ,,, but will have to wait till tomorrow eve
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This is getting like a whodunnit
Given the gauge is OK John, those uniform reading are a little odd and now the conrods have been thrown into the equation.. I can't see it really but thinking aloud here. The car overheated and lost coolant. Towed to try to start it. Now suppose the head gasket failed and allowed water into the combustion chambers. The result would be a hydraulic lock and bent rods. Now the engine would still turn over but the pistons would not reach the top of the block resulting in a very, very much lower compression ratio, insufficient to start and consequent low cylinder pressures.
A good enough theory but it still does not adequately explain why they were all so low and uniform. There's only one thing for it John - off with its head! The last time I saw low and uniform pressures (20 psi) the problem was holes in the pistons. This was on a petrol engine and looking at the construction of a diesel piston, holing them is next to impossible.
Please do it sooner rather than later - there are hundreds of fourm members sitting here on the edges of their seats just waiting like coiled springs for the answer to this puzzler.
Given the gauge is OK John, those uniform reading are a little odd and now the conrods have been thrown into the equation.. I can't see it really but thinking aloud here. The car overheated and lost coolant. Towed to try to start it. Now suppose the head gasket failed and allowed water into the combustion chambers. The result would be a hydraulic lock and bent rods. Now the engine would still turn over but the pistons would not reach the top of the block resulting in a very, very much lower compression ratio, insufficient to start and consequent low cylinder pressures.
A good enough theory but it still does not adequately explain why they were all so low and uniform. There's only one thing for it John - off with its head! The last time I saw low and uniform pressures (20 psi) the problem was holes in the pistons. This was on a petrol engine and looking at the construction of a diesel piston, holing them is next to impossible.
Please do it sooner rather than later - there are hundreds of fourm members sitting here on the edges of their seats just waiting like coiled springs for the answer to this puzzler.
Jim
Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...