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Compression of engine silinders

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Compression of engine silinders #1
Bit of Both Robert van den Berg Port Elizabeth, South Africa	Posted: March 31, 2012 08:56AM Registered: 1 year ago Posts: 25

Hi

As I am busy with the restoration of my 1960 Morris, I would like to know what the compression of the silinders should be?
I did a compression test, but without knowing what it should be, they mean nothing to me.

Thanks confused smiley

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Re: Compression of engine silinders #2
hammynz Rob Hammington Hamilton, New Zealand 1959 Morris Minor 1000 "GORG1S"	Posted: March 31, 2012 09:07AM Registered: 1 year ago Posts: 59

I think the compression for the 948cc cylinders should all be around 150psi. My understanding Robert is that an important factor is that they should all be approximately equal as any individual cylinder difference might indicate some problem with pistons/rings, valves etc. I am not a mechanic, so take these comments with caution!! What are the readings for your cylinders, both when hot and totally cold?

Rob Hammington
Tamahere
Hamilton RD3
New Zealand

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Re: Compression of engine silinders #3
Bit of Both Robert van den Berg Port Elizabeth, South Africa	Posted: March 31, 2012 09:23AM Registered: 1 year ago Posts: 25

I have only done a warmish test and got the following: 143,137,135 and 140.

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Re: Compression of engine silinders #4
hammynz Rob Hammington Hamilton, New Zealand 1959 Morris Minor 1000 "GORG1S"	Posted: March 31, 2012 12:31PM Registered: 1 year ago Posts: 59

When I was young, I had a Minor 100 and found it had uneven compressions. I was brave enough to attempt a valve grind and this made a big improvement. If you don't want to attempt this yourself, maybe you can find somebody who will do it for you. Before you do, take all the plugs out and put a squirt or two of oil in each cylinder. Then do the compressions again. If they improve, this indicates fairly strongly that you may have worn piston rings and/or pistons. If they don't change much, then the valves are likely to be the culprit. Your results are not markedly down from the guidelines anyway so possibly not too bad?

Rob Hammington
Tamahere
Hamilton RD3
New Zealand

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Re: Compression of engine silinders #5
Skye Skye Nott Vancouver, BC, Canada 1964 Vespa VNB 125 1966 MG MGB "The Bomber RIP" 1983 Suzuki MC GS750E "Kate" 1986 Merkur XR4Ti "The Rally Car" 1990 Volkswagen Corrado G60	Posted: April 02, 2012 12:49PM Registered: 2 years ago Posts: 168 Admin

In reply to # 803 by Bit of Both I have only done a warmish test and got the following: 143,137,135 and 140.

Looks reasonably good; as Rob said, you're looking for more than ~10% difference between cylinders to indicate a problem.

It's not as tight as a freshly rebuilt engine, but could possibly go many more years without any issues.

It really depends on what kind of restoration you're doing; if the engine is out anyway, it might be worth a "refresh" - hone the cylinders, lap the valves, replace rings and bearings, check the tolerances on everything.

Skye

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