Joined: Jul 2019 Posts: 187 Threads: 42
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Location: North Wales UK
Car type: Austin 7 RN 1931
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
Buy an Austin 7 they said, It's easy to work on they said !
Joined: Aug 2017 Posts: 3,425 Threads: 107
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Location: Darkest Bedfordshire
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.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
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.
Joined: Jul 2019 Posts: 187 Threads: 42
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Location: North Wales UK
Car type: Austin 7 RN 1931
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
Buy an Austin 7 they said, It's easy to work on they said !
Joined: Aug 2017 Posts: 2,427 Threads: 33
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Location: Deepest Frogland 30960
Car type: 1933 RP Standard Saloon
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)
Joined: Aug 2017 Posts: 3,425 Threads: 107
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Location: Darkest Bedfordshire
...and engine thoroughly warmed...
Joined: Dec 2017 Posts: 1,160 Threads: 68
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Location: Nottinghamshire. Robin Hood County
Car type: Austin Ruby Mk1 1935
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.
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.
Joined: Aug 2017 Posts: 747 Threads: 13
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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 !!
