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[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]

Posted by Jack Sweet on February 22, 2000 at 12:54:20:

In Reply to: LOW COMPRESSION, PLS HELP!!! posted by Edgar on February 22, 2000 at 08:42:24:

I don't know about measuring compression with bars. However, readings that are uniformly low in each cylinder isn't so much a problem as one or two cylinders with dramatically lower compression readings than the others. As for what readings a "normal" engine will give you--well, that varies from engine to engine and type by type. And other factors come into play like camshaft wear, timing chain/belt health, etc.

Remove all your plugs. Block the throttle wide open. Screw in a compression gauge. Crank the engine over at least five times for each cylinder and write down the readings. They should all be within 5 percent of each other. So, if you have a six-cylinder car and you get readings of 160, 160, 152, 158, 168, 160, you're probably OK.

Now, put a coupple of squirts of motor oil into the cylinder before you screw in the gauge. Do the test again. If the readings come up uniformly across all the cylinders when "wet," your rings are showing some wear. This could be a good or bad thing, but since you say you're not losing oil you're probably OK.

If the readings don't change at all you may have some valve leakage.

If there are two adjacent cylinders--Nos. 1 & 2 for example--that have similar out-of-spec-low readings than all your other cylinders both wet and dry, you should start thinking about the possibility of a blown head gasket.

Have you overheated? Are you losing coolant? If not and you're not losing oil, the "low" compression readings could just be chalked up to normal ring wear and probably isn't anything to lose sleep over.

Hope this helps.

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