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phil400
Crazy Horse

Canada
504 Posts

Posted - 30 Dec 2017 :  4:07:02 PM  Show Profile  Reply with Quote
I did the test today on my friends car, all were in the 120-130 range except for #?s 5&6 which were 80, squirt some oil in, first crank jumped to 90 and then it dropped back down to 80.

Popped the valve covers and all the rockers move same amount, all pushrods spinning.

Original 40 year old shortblock, safe to assume the rings are shot?

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive.
77 T/A sold
85 Monte Carlo SS sold
83 Mustang GT sold
"Let me tell you what Melba toast is packing"

GtoGuy32
Crazy Horse

USA
851 Posts

Posted - 30 Dec 2017 :  4:25:14 PM  Show Profile  Reply with Quote
I would imagine the rings are on their way out or OUT all together, like you said.

What compression ratio is the engine?

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phil400
Crazy Horse

Canada
504 Posts

Posted - 30 Dec 2017 :  5:42:47 PM  Show Profile  Reply with Quote
8-1 compression.

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive.
77 T/A sold
85 Monte Carlo SS sold
83 Mustang GT sold
"Let me tell you what Melba toast is packing"
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Blued and Painted
Chief PONTIAC

USA
3505 Posts

Posted - 31 Dec 2017 :  2:18:16 PM  Show Profile  Reply with Quote
If it were rings the pressure would come up closer to normal.
I'm thinking more likely valves not sealing.
If the push rod is not tight when off the lobe and spins while running, a valve and seat problem is indicated.
U might try pumping some regulated air in the suspect cylinders and listen for air exiting exhaust, carb, or crankcase.
I say regulated because the engine needs to be at TDC on tested cylinder. It hard to hold the crankshaft with full line pressures applied.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 31 Dec 2017 2:20:31 PM
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phil400
Crazy Horse

Canada
504 Posts

Posted - 31 Dec 2017 :  5:12:32 PM  Show Profile  Reply with Quote
I?ve read many times and was told that the pushrods should be spinning and that it means the cam is fine and not going flat, is this wrong?

I?ll put some air in the cylinder thanks, a valve not sealing would be a easier fix.

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive.
77 T/A sold
85 Monte Carlo SS sold
83 Mustang GT sold
"Let me tell you what Melba toast is packing"
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phil400
Crazy Horse

Canada
504 Posts

Posted - 03 Feb 2018 :  9:36:55 PM  Show Profile  Reply with Quote
Update: put some air into suspect cylinders and sure enough, #6 had air coming out of the carb and #5 out the exhaust. Looks like we?ll be R&R the heads, thanks for the tip it worked great.

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive.
77 T/A sold
85 Monte Carlo SS sold
83 Mustang GT sold
"Let me tell you what Melba toast is packing"
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