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simonshearer · #3 12-04-2010, 09:07 AM

You're using psi versus kPa, right? How did you perform the compression test? I assume the engine cranks over. Did you get four "puffs" on each cylinder (four compression strokes on each cylinder)? What was the reading on the first of the four puffs in that lowest one? It should be at least 50% of the final reading - if not, there's an indication that the rings are worn.

There are really only three ways for the compression to escape - valve leakage, piston ring leakage (or a hole in the piston), and cylinder head gasket.
Did you follow up with a wet compression test? Simply add three squirts (no more than three) into the cylinder and retest; if the first-puff reading is much higher and the final reading is much higher than without the oil, the cause of the low compression is worn or defective piston rings. If the compression reading is only slightly improved, then I'd work on valve testing.

Do a cylinder leak test next.

You'll need compressed air because you want to have a constant air pressure applied to the cylinder. Make sure that the cylinder is at TDC (because then the valves will both be in the closed (seated) position). It is likely that air will be heard or detected leaking out somewhere.

If the air is heard leaking out of the oil filler cap, the rings are the culprit; if you can hear or detect air escaping out the tailpipe, it's probably a defective exhaust valve; if you can hear air coming out of the throttle body or air inlet, it's probably a defective intake valve. If that's all good, undo the radiator cap, and if there's air bubbling out of it, then it's possibly a blown head gasket (or a cracked cylinder head).

You can do all this easily and inexpensively before going to the expense of pulling the head off.

Let us know the results.

My brother in law lives in Mt. Eliza but he won't be any help to you, unless you want someone to serve beers after you've identified the problem!