While working on a oil pump priming issue on a '56 Mk 1, I figured it would be a good idea to check the compression. Will oil pressure/oil delivery affect compression test results? I used two different testers on two different days and the results were 80-90 psi in each cylinder (I anticipated 155 psi.)
The battery I used started at 13.5 volts and was at 12.4 when I finished testing. Battery was recharged back to 13.5 for the 2nd test. The JL archives did not reveal a relationship between oil delivery and compression test results.
I’ve read about chemicals that might free up stuck rings and what to look for after removing the cam covers. I still have to drop some oil into the cylinders and do a leak down test. But, I don’t know if the low compression could be caused by oil pressure or, oil delivery. Thanks
No
that’s too low and there is something gravely wrong requiring teardown.
You can only try and isolate the area to get better understanding of the problem by pouring a bit of oil in effected cylinder and see if compression rises. If so, Rings/bore wear.
Otherwise run compressed air down plug hole while valves are supposed to be closed. Air coming out intake or exhaust will reflect valve issues of that cylinder.
Verify valve timing is correct too.
Losing coolant? oil mixed with water? head gasket.
This stuff is well documented. A search will help you…but don’t fool yourself, it is not normal and head (at least ) must be removed for inspection.
No magic liquid will remedy with that low a compression.
I had 130 and it went of to 160 eventually after patient, patient coaxing, lubrication, water spraying into cylinder, soaking valves in Seafoam (perhaps kerosene would have done just as well, but kerosene destroys rubber. Use diesel instead)
Neverthless, I got other issues so I must rebuild.
Compression test results with throttle open (do I have to prop the piston up?) Battery charged.
1 110
2 110
3 90
4 80
5 30
6 80
With oil added to cylinder:
1 110
2 110
3 90
4 90
5 40
6 100
Background on this car/engine: I was told by the seller it had been 95% rebuilt by a reputable shop when I purchased it as a “basket case” about 15 years ago. I assumed everything was done correctly. But, starting to have doubts. The sump did not have oil in it, radiator was not installed.
"does the motor crank over & hand-turn freely?"
"what is compression spec for 2.4 motor?"
The motor does not turn by hand - it needs a socket wrench and, it takes about 24 ft lbs of torque to move it - plugs out.
From what you’ve said about the engine, sounds like partial seizure of piston rings?
An engine that has been left to stand for this length of time could easily have this problem. If bores are not scored/ worn and pistons the same,you MIGHT get away with just ring replacement?
Looks to me like 1-3 have valve-sealing problems, while 4-6 have valve-sealing AND ring-sealing problems. Actually, I would also prop the carb pistons up…opening up the carb throats to eliminate restrictions…and repeat the same 2 tests.