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MG TD TF 1500 - compression in pounds

1954 mgtf 1250 engine
Just rebuilt engine and installed it.
Ran Compression check from front of car going to rear and got the following results: 120-111-111-120. Is there an acceptable range and am I in it?
Ed Eastman

The 120 readings are roughly appropriate, but the two 111 readings are low. Who did the final assembly and how much running time is on the engine? Could be a ring gap issue.

Reed Yates
'54 TF
Reed Yates

the 120 readings are OK but the 111 readings are in my opinion on the low side at 93% of the other two.

Ideally they should all be within about 3% on newly rebuilt engine but personally unless you really want to pull the thing apart again and can live with a difference of 7% I would leave as it is.

My opinion and your engine so obviously your call.

Cheers , Pete.
Peter Thomas

I was under the impression that 10% was the accepted variation in compression? Ed. That is just about what I am getting in my newly rebuilt TD engine, I just did the breakin and need to retorque the head and reset the valves. Then I will check the compression again.
BEC Cunha

I would not accept any variation in compression greater than 3% on any engine I have personally built but I should point out these engines are at the "blueprint" end of the market.

Peter Thomas

I would rerun the compression test. Run it with the engine warm and the throttles locked open and the carb pistons held up.

T. L. Manion Thomas

You need at least 500 preferably 1000 miles on a new engine to allow it bed in properly before taking any compression readings. If after running this distance your readings are still the same then this is perfectly acceptable.
Iain MacKintosh

You could try a "wet" compression test. Put some engine oil in each cylinder, through the spark plug hole, leave it for a short time, then test again. the oil will act as a temporary seal around the rings. If you still have these figures then it is not the rings it could be either the valves or the head gasket.

John Scragg

This thread was discussed between 09/06/2007 and 11/06/2007

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