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960 - sudden loss of compression S90-V90

posted by  someone claiming to be Ross on  Mon Oct 10 06:32 CST 2005 [RELATED]

The car - 1995 960 290,000 km

The circumstances - when starting in the morning (about 5C overnight), start-up was normal, but after 1 to 2 seconds, the engine died and there was a fair amount of blue smoke from the exhaust. When trying to restart, it was obvious from the sound of the starter that there was something wrong with the compression. Checked the timing belt - in good condition and timing correct. Checked compression and got 0,67,30,20,0,60. Compressed air blown into the sparkplug holes appeared to be coming out the exhaust.

At this point, I bit the bullet and removed the head which is now at the machine shop for inpection (results due tomorrow).

Any ideas on what happened here? The engine had been running beautifully up until this point.

The only theory I have been able to come up with is that very gentle driving (never over 100 km/hr) over the past 1500 km (trying to save gas, money and extend dwindling oil reserves) allowed deposits to build up in the combustion chambers and/or on the valve stems. On start-up either the exhaust valves stuck partly open, or flaking deposits in the comb chamber broke loose and lodged betweeen the exh valve faces and seats. On head removal, there were a lot of soft carbon flakes lying on the piston tops. The area was much dirtier than it was when I removed the head about 25,000 km ago to replace a leaking head gasket (head was planed then and gasket has been fine ever since).

Any and all ideas/suggestions welcome.

Ross






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