how to check compression
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how to check compression
i've been reading posts of people checking their cylinder compression, and giving the PSI ratings for each cylinder.
my truck has a 302, and i was wondering how i can check the compression myself? what kinds of procedures are involved? is there a kit i can buy? or is this something a mechanic has to do? also, for a 302, what should the compression be in each cylinder? thanks, nissanjon
my truck has a 302, and i was wondering how i can check the compression myself? what kinds of procedures are involved? is there a kit i can buy? or is this something a mechanic has to do? also, for a 302, what should the compression be in each cylinder? thanks, nissanjon
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how to check compression
I dont know what the specific pressure should be for the 302, but to test pressure, you need a compression testing gauge (duh) 
It looks kinda like a tire pressure gauge with a 8-10" hose attached to it, and (usually) a brass threaded end with two size threads (one for each size of plug opening). All you do is unscrew a plug, screw in the gauge and crank the engine, and the gauge will retain the highest pressure achieved. There is a release button to reset the gauge. I think summit racing has a gauge like this for about 20-25$
Hope this helps...
Chuck
It looks kinda like a tire pressure gauge with a 8-10" hose attached to it, and (usually) a brass threaded end with two size threads (one for each size of plug opening). All you do is unscrew a plug, screw in the gauge and crank the engine, and the gauge will retain the highest pressure achieved. There is a release button to reset the gauge. I think summit racing has a gauge like this for about 20-25$Hope this helps...
Chuck
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how to check compression
thanks chuck. exactly what to you mean by "crank the engine". you you mean crank it manually somehow, or just turn the key and fire it up?
also, anyone else know the proper cylinder compression for an 1987 302?
thanks guys
also, anyone else know the proper cylinder compression for an 1987 302?
thanks guys
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how to check compression
>thanks chuck. exactly what to you
>mean by "crank the engine".
>you you mean crank it manually
>somehow, or just turn the key
>and fire it up?
just turn the key for a few seconds, whether or not it catches... if it does, it'll run horribly, of course. Then turn it off after maybe 2-3 seconds. You have to do this to each cylinder, which can be TONS of fun! Might as well change the plugs if you haven't for a while
Chuck
>mean by "crank the engine".
>you you mean crank it manually
>somehow, or just turn the key
>and fire it up?
just turn the key for a few seconds, whether or not it catches... if it does, it'll run horribly, of course. Then turn it off after maybe 2-3 seconds. You have to do this to each cylinder, which can be TONS of fun! Might as well change the plugs if you haven't for a while
Chuck
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how to check compression
thanks guys. maybe i'll pick up a compression tester and do it this weekend if i get a chance.
anyone else out there know the proper cylinder compression for a 302? i have the haynes manual, would it be in there? if so, i can just look it up.....
anyone else out there know the proper cylinder compression for a 302? i have the haynes manual, would it be in there? if so, i can just look it up.....
Post Fiend
Joined: Jan 2000
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From: Dryden, ON, Canada
how to check compression
In order to do a correct compression test, the engine must be brought up to O/T, then all the plugs pulled, and the throttle wide open. I read this in Popular Mechanics a few years back, and forget the reasoning, but thats what it says to do.
Evan MacDonald
Evan MacDonald
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how to check compression
thanks for the info
when you say "throttle wide open", how is that accomplished? is that simply a matter of holding down the gas pedal?
when you say "throttle wide open", how is that accomplished? is that simply a matter of holding down the gas pedal?
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how to check compression
Nissanjon,
Evan was right ..First thing to do to prevent the engine from starting is pull the coil wire off and make sure its touching some metal otherwise you ll have sparks flying all over the place . Removing all the plugs lets the engine spin freely . The wide open throttle lets the maximum amount of air in the cylinders . Finally , record all the numbers you get and I belive the rule isnt so much the the highest pressure , but that all the cylinders are within 20% of each other . If the engine is healthy , you should see 100 to 150 psi per cylinder . I may be a little off with the numbers , going from memory here . Also let the engine make 3 or 4 revolution per cylinder , and you crank the engine with the key . Good luck .
Paul
Evan was right ..First thing to do to prevent the engine from starting is pull the coil wire off and make sure its touching some metal otherwise you ll have sparks flying all over the place . Removing all the plugs lets the engine spin freely . The wide open throttle lets the maximum amount of air in the cylinders . Finally , record all the numbers you get and I belive the rule isnt so much the the highest pressure , but that all the cylinders are within 20% of each other . If the engine is healthy , you should see 100 to 150 psi per cylinder . I may be a little off with the numbers , going from memory here . Also let the engine make 3 or 4 revolution per cylinder , and you crank the engine with the key . Good luck .
Paul
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