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MG MGA - Compression Readings

I've been corresponding with the owner of my "dream MGA"

I've been given the following cylinder compressions

1-185
2-180
3-180
4-185

The readings were taken at Brown and Gammon's in the UK so I think they're metric.

Does this sound right?
Tysen

Hummm

I thought 160 PSI was correct.

Could have a hot motor (ish) or shaved head.

At least they are all the same. +-5 psi is OK.

Cheers <MARK>
Mark Hester

Hi Tysen. Individual compression guages often give higher or lower readings than other similar guages. What really matters is that your compression readings are all about equal, which is what you want to see. I presume those readings are from a "dry" cmpression test? Did B&G run wet and dry compression tests? Wet and dry testing can sometimes pinpoint a problem that a dry test alone cannot. Cheers, Glenn
Glenn

Tysen
Do you understand what Glenn means by wet and dry compression tests ?
/ george
george

Thanks Glenn,

And George thanks for the opportunity to get educated.

No, I don't know the difference between wet and dry.

Tysen
Tysen

Tysen,
Here is a comment from Les Bengston from the archives-it explains it really well.
/ george
From: Les Bengtson Arizona USA ragnar@aztecfreenet.org on 28 June 2004 at 20:43:31 (UK time)
George. There are three types of compression tests--dry, wet and running. The two most commonly used are the dry and wet. I am sure you know how to do a dry compression check--warm the engine, block or hold the throttle fully open, then crank the engine over six or seven revolutions and take your reading. Repeat for each cylinder.

The wet compression check is the same except that you inject about a teaspoon of oil into the cylinder before you perform the check. (You use a pump type oil can to inject the oil. Take a teaspoon--you can use one of the wife's if you are careful and don't get caught, and see how many strokes of the pump it takes to fill the teaspoon. Then, pump that many strokes into the cylinder immediately before making the "wet" compression test.) The oil on top of the rings and piston makes a temporary seal if the rings and bores are bad. Thus, you will see a rise in compression when you do this. About 10 psi with a fresh engine and up to about 40 psi with an older, worn engine. If you do not get an increased reading when the test is performed, it demonstrates that the cause of low compression is the valves and their seats which are leaking. If this were so, you would have heard a hissing from the intake/exhaust manifolds when you pressurized the cylinders.

Now, to your exact problem. There is a test kit for the presence of exhaust gasses in the coolant. Fairly easy test and most mechanics should be able to perform it for you. If there is exhaust gas present in the coolant, it is either the head, head gasket or the block causing it. There is no way that gasses leaking past the piston rings nor valves can cause this unless there is a crack in the block or head or unless the head gasket is not making a good seal. The head gasket is the most common cause of this problem. If you are not using the Payen or Fel-Pro gasket set (for the Fel-Pro, make sure the set is marked with the head gasket "made in England"), you may wish to try it. These are a resin type gasket which have worked very well in my rebuilds and Peter Burgess also has good things to say about them. Les

george

This thread was discussed between 19/06/2006 and 20/06/2006

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This thread is from the archive. The Live MG MGA BBS is active now.