buying a atomic-4 please help

rbtmoon · #1 (**permalink**) 06-07-2006

I want to buy a boat that has an atomic-4. the engine runs great, no smoke,plugs are clean, exhaust pipe clean, starts well, runs smooth. looks clean and well cared for. Just to be safe I did a compression test on a warm engine. The results surprised me. #1. 110 #2. 100 #3. 90 #4. 120. Accourding to all I have read the range 90 to 125 is acceptable but shouldn't the compression be only 5 or 10 pounds difference on each cylinder????? Can anyone help me out? I really want this boat but I cannot afford to have major engine problems. Is there a valve about to go on #3? Please help!
Thanks

Robert Moon rbtmoon@shaw.ca

jared · #2 (**permalink**) 06-08-2006

The way that the cylinder pressure tapers off across three cylinders (110-100-90) but is still good on the 4th (120) would make me think that the cylinder head may have warped a little and the head gasket is suspect. If they were all within ten pounds of each other, and the variation was at random, I'd suspect it was just old age and other things but that taper...sounds like time to have a mechanic take a look, or do some more testing.
You might want to ask Don Moyers or someone with extensive A4 experience directly to confirm that, or how to check it out better.

tenders · #3 (**permalink**) 06-09-2006

You should make a great big deal about this to the seller, but I frankly wouldn't worry about this a bit.

Maybe there is a little warping or a weak gasket between #2 and #3. Or a rough valve in #3. But 90 pounds is enough to keep running indefinitely, there may be nothing wrong at all. Put some Marvel in the gas as recommended, measure again after a few dozen hours of running, and see what happens. If the rest of the engine is in pretty good shape, taking the head off, milling it, and replacing the gasket should take you a day and cost $100. And that's only IF it gets worse.