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+--- Thread: compression pressures (/showthread.php?tid=5399)
compression pressures - Barry Townsend - 14-12-2020
I was wondering what the cylinder pressures should be on my 1931 RN
Currently they are all about 50psi which seems a little on the low side
I'm in the process of doing a decoke/valve job amongst other tidying up jobs.
The bores look perfect and unless I'm very mistaken the pistons look relatively new
RE: compression pressures - Chris KC - 14-12-2020
Not sure about low comp heads but I think you should aspire to at least 50% more than that.
Apologies, but have you followed the instructions with the gauge? Otherwise you may not be reading correctly.
RE: compression pressures - Bob Culver - 14-12-2020
Throttle should be open.Compression on Sevens is easily assessed on the handle. Can compare with others, although so many have raised cr it often confusing.. Should have a degree of bounce. 50 is low.
RE: compression pressures - Barry Townsend - 14-12-2020
Hi Chris
Thanks for your reply, that's about what common sense and experience suggested to me. I wouldn't expect much more from a low comp engine - BTW I've used the gauge on numerous occasions over many years including building several high performance engines, I am a retired mechanic but relatively new to Austin 7's which are still a mystery!
Kind regards
Barry T
RE: compression pressures - Reckless Rat - 14-12-2020
I would have thought that 90psi is about right for a LC engine in good fettle. You DO have to do the test with the throttle wide open (and spark plugs removed)
RE: compression pressures - Chris KC - 14-12-2020
...and engine thoroughly warmed...
RE: compression pressures - John Mason - 14-12-2020
Barry have you done the oil down the spark plug holes then done a second test to see if compression is being lost down past the rings rather than burnt or bad seating valves.
John Mason.
RE: compression pressures - dickie65 - 14-12-2020
I usually do a compression test with the engine running.
Its a bit naughty to cause a deliberate missfire and then rev the engine though, ( I have a Billet crank so less of a risk for me )
Its about time I gave it another check !!