Compression Test
08-15-2003 | 09:30 AM
#1
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From: Milwaukee'ish, WI
Compression Test
I did a compression check on my 454 in a Baja Outlaw last night.
The four corners all read 110-120 but the inner siamese cylinders were only 75-80
Is this normal, due to the heat, that the inner cylinders are that far off?!?
It still runs good, I just did a check for the hell of it.
The four corners all read 110-120 but the inner siamese cylinders were only 75-80
Is this normal, due to the heat, that the inner cylinders are that far off?!?
It still runs good, I just did a check for the hell of it.
08-15-2003 | 10:15 AM
#3
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From: Milwaukee'ish, WI
No jt I didn't have the throttle open for any cylinder. What difference will that make, more or less pressure?
So that's the rule hey, 10%?
Guess I'd better keep an eye out for a long block on eBay again.
So that's the rule hey, 10%?
Guess I'd better keep an eye out for a long block on eBay again.
08-15-2003 | 11:05 AM
#5
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From: Milwaukee'ish, WI
I'm pricing new Edelbrock marinized square port loaded heads. For about the price of a quality valve job I can go to aluminum!
Yeah I ran her dry on oil, new valve covers without vents, forgot to remove oil fill cap and I spewed all my oil out of the dipstick tube
I felt like a dipstick
what a stupid mistake, any how I'm glad i run full synthetic oil, it probably saved my lower end.
I've never done a leak down test, hows it done?
Yeah I ran her dry on oil, new valve covers without vents, forgot to remove oil fill cap and I spewed all my oil out of the dipstick tube
I felt like a dipstick
what a stupid mistake, any how I'm glad i run full synthetic oil, it probably saved my lower end.I've never done a leak down test, hows it done?
08-15-2003 | 11:30 AM
#6
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From: ankeny,ia.
I've alway's opened the throttle
when testing compression, per what
various manuals say, ( not just marine)
the theory is that it lets a non restricted intake
charge into the cylinder.
In your case, I doubt it's going
to help.
Like Dennis has said, should be in
the 150 Neighborhood.
To do a leak down test, remove valve
covers, loosen up the rocker arms ,
remove spark plug, instert leak down tester
into spark plug opening, connect up air,
guage will show % of leakage.
In your case, (low compression) you then
listen for where the leakage is going,
out the exhaust ports (ex valve), back up through the
intake ( intake valve), into the crankcase,out the breathers, ( rings)
jt
when testing compression, per what
various manuals say, ( not just marine)
the theory is that it lets a non restricted intake
charge into the cylinder.
In your case, I doubt it's going
to help.
Like Dennis has said, should be in
the 150 Neighborhood.
To do a leak down test, remove valve
covers, loosen up the rocker arms ,
remove spark plug, instert leak down tester
into spark plug opening, connect up air,
guage will show % of leakage.
In your case, (low compression) you then
listen for where the leakage is going,
out the exhaust ports (ex valve), back up through the
intake ( intake valve), into the crankcase,out the breathers, ( rings)
jt
08-16-2003 | 10:14 PM
#9
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Posts: 2,558
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From: ohio
And valve overlap will change those numbers considerably. Like was said , its not the number, its the difference that counts. Ive seen many serious horsepower engines that read 90 cranking pressure. But , what do I know.
08-16-2003 | 10:23 PM
#10
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From: Chapin (Lake Murray), South Carolina
Being a Mercruiser mechanic for many years I know that all 454 engines have 155 pounds of compression if they are healthy (throttle closed, Snap-On compression tester). You probably need a valve job.
