need help again. compression test on a 1981 hilux

[jcs1987]

as about its down big time 1 is 80psi 2 is 80 3 is 150 4 is 140.. what could it b? motor is a 18r

[Dazza]

Could be a blown head gasket that is leaking between the two cylinders that are low. Best way to check what is leaking is to screw a compession gauge fitting into the plug hole of the cylinder that is low. Make sure that cylinder is at top dead centre and connect compressor up to the compression gauge fitting. If you hear air leaking into the carby it is an inlet valve leaking. If you can hear air leaking through the exhaust it is an exhaust valve leaking. If you hear air leaking when you remove the oil filler cap, it is rings or cracked piston. If you hear air leaking out another spark plug hole it is the head gasket leaking between cylinders. You can make a fitting to connect a compressor hose to the sparkplug hole by smashing the end off an old sparkplug and welding an air fitting onto it.

[td42gq]

Also try a wet test, add some oil to the cylinder through a plug hole and see if the compression comes up. If you have a considerable increase in compression it's probably in the rings. The oil helps to seal the compression rings. Just remember to not add to much oil as it can hydraulic lock the cylinder