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Old 02-07-2012, 08:53 PM   #1
1972Stingray4Speed
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Member Since: Feb 2011
Location: Beloit WI
Default 327 SB Chevy compression test results..help?

1972 Corvette engine issue
I just did a compression test on my 327 and came up with
F 1: 151 2: 0
R 3: 151 4: 164
O 5: 140 6: 160
N 7: 150 8: 145
T
The 327 is a 1968 and has around 60,000 since last rebuild, heads were rebuilt at the same time. This was back in 1975 though.
I did the compression test with the engine at running temp, then when I got the zero reading I did a wet test with oil in that cylinder. The wet test did not improve the compression so I know it's not rings. I found out I have a collapsed lifter on that cylinder, the other one for the same cylinder was feeling "soft" when I pushed on the rocker arm.
Any tips or advice you guys have would be appreciated...
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Old 02-07-2012, 09:11 PM   #2
63mako
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Quote:
Originally Posted by 1972Stingray4Speed View Post
1972 Corvette engine issue
I just did a compression test on my 327 and came up with
F 1: 151 2: 0
R 3: 151 4: 164
O 5: 140 6: 160
N 7: 150 8: 145
T
The 327 is a 1968 and has around 60,000 since last rebuild, heads were rebuilt at the same time. This was back in 1975 though.
I did the compression test with the engine at running temp, then when I got the zero reading I did a wet test with oil in that cylinder. The wet test did not improve the compression so I know it's not rings. I found out I have a collapsed lifter on that cylinder, the other one for the same cylinder was feeling "soft" when I pushed on the rocker arm.
Any tips or advice you guys have would be appreciated...
Valve stuck open.
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Old 02-07-2012, 09:27 PM   #3
Ben Lurkin
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Too much of a difference bet 8 and 5 as well. Try the oil trick in the others and see if you get different readings. If so, it's time for a leak down test. That will help you isolate the leak(s) better.

Without the benefit of that info, I would guess your exhaust seats are pounded out. That old of an engine doesn't have hardened exh seats. They don't like unleaded gas. It may be time for a new set of heads and valvetrain.
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Old 02-07-2012, 10:42 PM   #4
1972Stingray4Speed
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Originally Posted by Ben Lurkin View Post
Too much of a difference bet 8 and 5 as well. Try the oil trick in the others and see if you get different readings. If so, it's time for a leak down test. That will help you isolate the leak(s) better.

Without the benefit of that info, I would guess your exhaust seats are pounded out. That old of an engine doesn't have hardened exh seats. They don't like unleaded gas. It may be time for a new set of heads and valvetrain.
I have a new lunati cam part # 07102. I plan on getting my heads rebuilt as well as new lifters. The one lifter on the right side on front side #2 came apart when I took the rocker arm and pushrod pressure from it. That and the spring on that same lifter is broken in two places... I think I found the problem. Question I keep asking myself is why did both of those parts break on the same valve..
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Old 02-07-2012, 11:29 PM   #5
63mako
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Originally Posted by 1972Stingray4Speed View Post
I have a new lunati cam part # 07102. I plan on getting my heads rebuilt as well as new lifters. The one lifter on the right side on front side #2 came apart when I took the rocker arm and pushrod pressure from it. That and the spring on that same lifter is broken in two places... I think I found the problem. Question I keep asking myself is why did both of those parts break on the same valve..
Stuck valve. Remove the rocker arm and tap the top of the valve with a mallet. It will probably be stiff and not want to open and/or close. Spring might have broken and it bounced off the top of the piston slightly bending it or the valve stem is seizing in the guide. Even bad seats or worn valve will still get some compression.

Last edited by 63mako; 02-07-2012 at 11:35 PM.
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Old 02-08-2012, 12:37 AM   #6
Ben Lurkin
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Quote:
Originally Posted by 1972Stingray4Speed View Post
I have a new lunati cam part # 07102. I plan on getting my heads rebuilt as well as new lifters. The one lifter on the right side on front side #2 came apart when I took the rocker arm and pushrod pressure from it. That and the spring on that same lifter is broken in two places... I think I found the problem. Question I keep asking myself is why did both of those parts break on the same valve..
Broken spring? What 63 Mako said. . . It really doesn't take much to bend a valve.

With regards to your heads, consider a set of vortec heads instead of rebuilding yours. For about the same money, the vortecs will give you a lot better performance.
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Old 02-09-2012, 10:00 PM   #7
1972Stingray4Speed
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Broken spring? What 63 Mako said. . . It really doesn't take much to bend a valve.

With regards to your heads, consider a set of vortec heads instead of rebuilding yours. For about the same money, the vortecs will give you a lot better performance.
I am planning to replace the heads now, after pulling one off I realized that they were the smaller valve camel hump heads. The whole time I have had the car the previos owner had said they were the 2:02 &1:60 heads. So time for new heads and more performance for my small block. Will go well with the cam I have to put in it as well as the headees I had put on last fall..
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Old 02-09-2012, 10:00 PM
 
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