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post #1 of (permalink) Old 09-20-2002, 08:51 PM Thread Starter
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compression test?

Okay, I think I have asked about every possible engine conversion for a cj-7. However, I have finally accepted the fact that I'm a poor broke college student and have no means to finance an engine conversion in the near future. However, the 4.0 head conversion looks affordable and promising for me.
My question is if there is a compression test that can be done that can distinguish between leaking rings and leaking valves. Also, can it be done cheaply by a shop?
If the rings are good, then it seems like it should be fairly straight forward swap.
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post #2 of (permalink) Old 09-20-2002, 09:52 PM
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Re: compression test?

Don't waste your money haveing a shop do it. A compression tester is only about $20 and most come with instructions. To find if rings or valves are the weak link test all cylinders and record the results, then pore a little oil in the cylinder and retest. If the compression stays the same then valves are at fault. If however compression increases significently the the rings are bad.

post #3 of (permalink) Old 09-21-2002, 12:12 PM
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Re: compression test?

I know this isn't exactly what you asked, but do you get a lot of blowby? As in the crankcase spewing out exhaust gas under pressure from seals and pcv filter at the air filter, covering the air filter with oil? This is also an indication of poor sealing rings, as the pressure from above the pistons is leaking into the crankcase and escaping from the crank everywhich way it can, usually carrying oil with it.

Definately do the compression test on each cylinder. Also consider a leakdown test, which involves pressuring each cylinder one at a time with compressed air and seeing how well it seals. You will hear where the air is leaking out, intake, exhaust, etc if it's a bad valve.

It's not that time consuming to remove the head to remedy the problem if it is a valve or a head swap. You can do it in an afternoon.
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post #4 of (permalink) Old 09-21-2002, 06:54 PM Thread Starter
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Re: compression test?

Thanks for the input. This board's always helpful!
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