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TR4/4A TR4 Engine compression

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MrAlex

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I looked through Bentley a few times but could not find the compression spec range for a TR4. If someone could please let me know what is considered an acceptable range it would be a help. I measured 125psi consistent across all 4 cylinders at running temp. I seem to remember a 150 number as being low/ok. I do have some smoke so I figured to do a little diag work before doing a rebuild this winter. Oil pressure is at 50-60.
Thanks....
 
Likely it's not there. Compression readings are almost never taken to be absolute numbers because there are too many variables (like how much of the plug hole the gauge fills and how fast the starter spins). If you get the same number in all cylinders, chances are that the rings & valves are sealing very well. Generally all cylinders within 5% of the average is very good, 10% is acceptable.

That said, the TR3 Bentley says 120 psi is 'normal'. A TR4 should be a little higher but not much (9.1 CR instead of 8.5 for a TR3).
 
Thanks Randall.. so maybe I should look at valve guides first (head rebuild) as a source of my oil smoke since compression and oil pressure is good. Then go to the "block". I have a spare head to go over so it might be good to just do a head job first... now now.. no comments about that comment..

"After edit": this is interesting.. found on the web: "If the gauge pumps up slowly, such as 30, 50, 70, 90, etc. to an almost normal reading, you probably have ring problems. A general rule is that a maximum reading should occur after two strokes. If oil is added to a low reading and the pressure improves, this will confirm worn rings. A persistent low reading generally indicates valve problems."

It took approx 5 strokes to get to Max pressure of 125. I will re-do with some added oil to see what results I get.
 
My father told me many years ago that if you were driving a car and let off the gas and the smoke increased it was due to a worn valve guide, (the vacuum increase would suck oil through the worn guide), if it stayed the same it was the rings.
Don’t know if he was right but it sounds good.
 
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