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Re: engine compression
Earlier, Livolsi, Stephane wrote:
>
> I bought myself a compression tester to check the compression in my
> engine, which I did, but other than finding references as a ratio (8.5:1
> or whatever) I don't know what the readings mean. I only checked 2
> cylinders so far, then the battery started getting run down (yes I do
> need a new battery!). I got 95 psi on each cylinder. Is this good?
> bad? what should it be?
>
> The patient is a Canadian 1986 (mid 85 manufacture date) 5KTQ 5cyl
> 5speed trans with no modifications at all (yet).
What you really need to use is a leak down tester, instead of
a compression guage.
Normally, I'd say 95 psi is low for compression, but what's more
important is difference between cylinders. A good value for an
engine at 8.5:1 Cr is about 110 psi. Many things affect maximum
compression ... the guage, cranking speed, hot/cold engine, what
cam timing you have, etc, etc. A leak down tester will show
problems you will never pick up with a compression test; plus with
a leak down test you can tell by listening where the leakage is.
For the compression test - get the engine well warmed up, and then
pull all the spark plugs. With a well charged battery (or keep the
charger hooked up) do the cylinders one at a time. Note two readings,
1) what the compression is after about 5 strokes, and 2) what the
compression builds up to after 10 or 15 strokes. With an engine
in good shape, you should see (almost) max readings within 5 strokes,
if it builds to considerably more after 15 strokes you either have
worn parts or a weak battery that's cranking pretty slow.
- Charlie
Charlie Smith charlie@elektro.cmhnet.org 614-271-1418
http://elektro.cmhnet.org/~charlie/ Columbus Ohio USA
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