| Re: [GMCnet] compression check procedure [message #320648] |
Tue, 18 July 2017 10:59  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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First have the engine warmed up. Remove all spark plugs. Unplug the primary
connector on the hei distributor. Remove air cleaner. Open the throttles
wide open. Crank the engine, starting with # 1, through 5 compression
strokes. Record reading. Proceed through the remaining 7 cylinders.
On a thoroughly warmed up engine, you should see at least 140 psi or higher
on your gage. If adjacent cylinders read low (under 100 psi) you more than
likely have a head gasket issue.
After you complete the test, then repeat except squirt a teaspoon of
30 wt. oil into the plug hole before cranking the engine. If the
compression jumps 20 % or more, you might have poor ring sealing. No change
or slight change is o.k.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Jul 18, 2017 8:46 AM, "Joe williams" wrote:
Hello again,
I built a set of the 2 x 4 jack stands ( thanks Steve )and they work great,
got the cv boot changed , front end greased, oil changed , and now going
to change plugs and thought I'd do a compression check to get a baseline
for the motor. I've never done one before so what's the best procedure, hot,
warm, cold,manual says to disconnect the HEI,do I just remove wire clips on
side of dist? I don't want to do something stupid and screw up the HEI
what should I expect for results on a 403 with 69,000 mi
thanks again for all your help
--
Joe Williams
1978 Royale rear twin
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