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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
| Posts: | 573 |
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JH specifies 110-130 psi for a cold engine. Lotus specifies 150-170 psi for an engine that has first been run long enough to bring it up to full operating temperature before doing the test. In either case, pressures for all four cylinders should be within 10 psi. 30 psi is clearly a bit low... like hole-in-the-piston low.
If the pressure re-tests low, then squirt some oil into that cylinder. It's difficult to get even distribution of the oil around a piston in a slant cylinder. So, with the piston at the bottom of it's stroke, aim for the cylinder wall above the high side of the piston. Give it a few squirts, then before the oil all runs down hill, turn the crank through a couple of revolutions, scraping oil into the piston-cylinder gap, and around the piston. Then repeat the compression test for that cylinder. 200+ rpm with the throttle held wide open.
If the new reading is dramatically improved, then the rings were not previously sealing in that cylinder and the oil helped fill the gaps, improving the result. Oil is not a fix, so it's time for a ring job.
With oil added, if the pressure result is pretty much unchanged and still low, then the rings are probably not the problem. In that case, it's most likely a burned or otherwise leaking valve... or several. It could also be a burned piston, collapsed ring lands, or a burned-through crown.
In any case, a persistent 30 psi compression reading is not going to fix itself with medicine poured in, or with anything you can fish into the hole. Having some idea what's wrong before you start is nice, but the fix will involve some degree of engine disassembly. At least removing the cylinder head, and perhaps a complete tear down.
Good Luck,
Tim Engel