Hey all

I wanted to know what compression should a resonable 1275 GT/coopers motor have??

Pulled all the plugs out, and compression tested my motor and got the following

Cylinder 4=160
3=160
2=90
1=105

Now there is a problem with cylinders 1 and 2, i thought the most likely explanation was a blown head gasket. Does this seem like the most logicaal explanation.

This motor has run for about 5seconds in last 20yrs so cant comment in how it used to run.

Thanks Brenton

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It is looking like head gasket but I take it this was a dry hot test? Have you also done a wet hot test?

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The motor was cold when i tested, I think i read your supposed to do a check when the motor is hot, but does it make a difference?

A wet test?
Do you mean when you chuck a bit of oil down the plug hole and turn it over, then it tells you if its a valve stem seal or compression ring or somethiing like that?

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It is more meaningful / accurate if the test can be done at or near operating temperature. Yeah, for the wet test, squirt a bit, not too much, oil in the plug hole to make a temporary seal if the rings are cactus.

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Ok so i should do a wet test, and if compression picks up i know its rings and if nothing happens i know its head gasket ?

What is a reasonable 1275 compression range?

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Yeap.



Not straight forward to answer. Depends on cranking speed but more so Camshaft timing.

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Ok cool, so how much is a little bit??

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Without knowing the specs of your engine i would say your results for 3 & 4 are good, the kind of numbers you hope to see. 1 & 2 are saying something is wrong.

200psi means very high compression, 150+ is basically the norm

Like a little bit of oil down the hole how much is a little bit

Thanks mini mad matt.

Thanks GTwowog for your help

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basically just enough to sit on top of the top ring all the way around - a few squirts from an oil can...

A wise old mechanic once told me that the 'actual' compression readings were less important than consistent readings - esp when using an al cheapo compression gauge. All in the same ball park is good, big variance is bad!

Gavin

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1971 Clubman GT - Jet Red
1980 Mini 1000 - Bold As Brass
1967 Riley Elf - Red/White
2002 MINI Cooper - BRG/White
2005 MINI Cooper - BRG/White
2022 MINI Cooper SE - BRG/White