Join Date: Oct 2011
Location: New England
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Re: How to do compression check?
If you have done a compression check on an aircraft, you know the basics of how to do it on any IC engine. There are two differences with a diesel – you remove the glow plugs instead of the spark plugs and, because of the very high compression, you need a diesel specific compression tester.
Ever since I found a tiny crack which closed up when the engine was hot, I like to test cold, replace the plugs and warm up the engine, and then test hot. Unless the engine is completely shot, having numbers that are all close to each other is more important than the actual numbers.
Pro. testers are expensive but (this will probably upset someone) a cheap (Harbor Freight ??) tester should suffice for your purposes – remember you are looking for consistency rather than the actual number, so a little inaccuracy isn’t so important. You just need to make sure that it comes with, or you get an adaptor that fits your engine. If you can borrow or rent a professional tester, so much the better.
Having said that there are things that are as/more important that a comp. check. First, a good visual check – everything looks good ? – take a close look at the exhaust, heat exchanger, belts, hoses, etc. How well does it start, idle and run? - Make sure they don’t warm it up before you get there. Any ominous exhaust smoke? Oil is clean and not at all milky. Coolant clean and no yucky crap (that’s a tech term). No leaks before or after you run it. Any strange noises? Trans shift smoothly. Take it out and run it hard – does it overheat?
If you are confident that it passes all those tests, you are probably fine. If you are at all unsure, get a professional to look at it before you commit.
This is my opinion - it’s worth what you paid for it. Good Luck.