Lowest compression before engine rebuild?


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Hi guys,

My 2.3 1995 XL 5 speed manual is showing average compression on the 100 range, no oil burning yet though. What's the lowest you have seen running "ok" before it starts burning oil?. I'm using 20W50, it lives in the tropics, that's what most "old" cars use around here.
 


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Dirtman

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Relative compression (all cylinders being close to equal) is alot more important than the overall compression. 100psi across all cylinders and no burning oil, keep driving for another 100k miles.
 

adsm08

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90 PSI is the lowest that will still be enough to run on.
 

tomw

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You might not need a rebuild. You may be able to determine the cause of compression drop using a bit of oil fed into the cylinders before taking a reading. The oil would seal the rings for a short while, engine not running, and if they were the leaky area, they'd show significantly improved compression. If compression improves slightly, it may indicate that the valves are no sealing well, allowing leakage. If that's the case, removing the cylinder head and cleaning up the valve seats may cause a significant improvement in compression without a rebuild. Historically, having a valve job done was not uncommon. Gaskets were sold in 'valve grind sets' to include just those needed to work on the cylinder head. Haven't looked lately.
If you have the time, removing the valves, lapping the valve and seat together, replacing the valve stem seals, and installing with a new head gasket may show marked improvement. You also have an opportunity to replace the timing belt, all hoses, coolant, and replace the thermostat if it is aged. Even where you live, it is a good thing to get the engine up to proper temp as quickly as possible.
tom
 

adsm08

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Gaskets were sold in 'valve grind sets' to include just those needed to work on the cylinder head. Haven't looked lately.
Still are, they call them "head sets" now. They usually come with head gaskets valve seals, intake, valve cover, throttle body, EGR if equipped, and thermostat.
 


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