what is the acceptable compression range?
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Senior User
Joined: Nov 2004
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From: Wayland, Iowa
what is the acceptable compression range?
What is the acceptable compresion range for a 67 300 six cyl. Considering rebuilding if it is worn. It has 99,000 miles on it. And I know for sure that it is the actual miles and original motor. Rear main is leaking alot, enough to delay fixing clutch until it is leak free.
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Senior User
Joined: Nov 2004
Posts: 159
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From: Wayland, Iowa
Compression
I called a engine shop and they said 130-175 is a good range. if there is a 20-25% difference in a cylinder compared to others. Then there is something wrong going on.
Freshman User
Joined: Jul 1999
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fuzz
I have always wondered about a varience between cylinders when taking a compression test. This is because I read an article about how piston rings can rotate about as the engine runs. On a rebuild we are careful to make sure that the gaps are arranged according to spec. But what happens to this careful ring gap spacing once there are a few hours on the engine? And why bother to arrange them so perfectly to begin with? The author of this article explained that on a rebuild we need to know that the engine is the best that it can be to monitor its performance initially. After that, nature takes it's course. So then. suppose all the rings on a given piston per chance experienced ring gaps that were all lined up. Could this cause that particular cylinder to show a low compression reading? I know that on some two cycle engines the rings are pinned so they cannot rotate. Whats anybodys take on this?
Fuzz
Fuzz
Elder User
Joined: Mar 2004
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From: SOUTH CAROLINA
if the ring gaps were lined up then you would have some loss of compression and you would also have oil consumption. at the speed of the piston traveling through the bore the loss would not be huge but it would be noticable. you would also get fouled plugs with this just as you would with a broken ring. oil would not be scraped properly and would eventually foul the plug
