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Original Message
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| RE: Difficult to diagnose on internet but.......... |
| By Craig M - 12/19/2000 4:05:37 AM; IP 64.12.104.49 |
S7MS, covered the oil pretty good, only guestion I have about the oil system is how much pressure does the engine produce at idle when cold and when hot, and at 1800 RPM and above? Usually if the oil pressure drops off considerable after warm up this usually means the mains are worn enough to bleed off the oil pressure some, but not always.
Compression varies. But the reading you get should be within 10 PSI or so within each other. Also, Alitude, Barometric Pressure, and compression ratio effect compression readings. So if you like 4000 foot above sea level the reading would be alittle lower and 500 foot above seal level, sea level also has an effect on Vacuum pressure as well, which is another reading that tells you how healthy your engine is ( vacuum usually runs 17" to 20" HG depending on the altitude, the higher the lower the reading. .
Usually if no valves are leaking compression on a strong 9.0 to 1 ratio engine should be somewhere around 150 to 165 PSI. with the engine warm when testing and close to sea level. The more miles sometimes the less compression you will have I'd Say anything below 110 is pretty weak. But, most say the cylinder will still fire find with pressure as low as 80 PSI.
If you have a really weak cylinder you can isolate the problem by removing the valve stem from you compression test gauge and with that cylinder at TDC you can screw in the compression test guage apply shop air pressue to say 80 psi. ( engine must be at TDC or that cylinder valves will be open causing a false reading) Now remove the air cleaner and listen at the carb. if you hear a hissing sound your intake valve is leaking. Listen at the tail pipe, if you hear a hissing sound the exhaust valve is leaking. now remove you oil filler cap and listen at the hole if you hear a large amount of air the compession rings are leaking. ( the rings will bleed some air by a small amount may be normal) ( a rubber hose or doctor stenscope will magify the sound better) ( also, if you hear a leak rotate the crank alittle each way to ensure the valve was closed, you will hear a large amount of air when the either valve opens up.) This is kind of long and maybe more information than you wanted, sorry . RC |
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