(11-10-2017, 03:55 PM)Derek Simmons Wrote: Hi, it's helpful to hear what has been said about cylinder compressions as my 1937 Ruby has pressures of between 85 & 95psi and I was wondering if it was a bit on the low side because I recall testing an old 1960's Mini and getting 140psi plus!! If you squirt engine oil into the cylinder before taking the pressure and you get a higher reading it could indicate bore wear. Would that be a fair assumption?
(1) Get the engine thoroughly warm - at least 10 mins running (shroud the radiator)
(2) Remove all four spark plugs
(3) Disconnect coil from battery
(4) Prop accelerator pedal down with a broom handle (open throttle valve)
(5) Screw gauge into each cylinder in turn and measure highest pressure reached on starter (may take 5 - 10 turns)
(6) n.b. a steady cranking speed is needed, if battery is low results will tail off
(7) If weak rings suspected introduce a teaspoon of engine oil into cylinder and measure again (a marked change confirms an issue)
(8) If adding oil doesn't make a difference suspect a burned valve
Best level for a 'sports' A7 in peak condition: 115 PSI
Typical level for a road-going car & perfectly OK: 80-90 PSI (variation is not only wear but head type, skimming, valve overlap etc.)
( ref. ~100 psi minimum for a modern OHV engine)
A "fault" is indicated by 1 bar / 15 psi variation between two cylinders
n.b. It's well worth checking your tappet clearances from time to time!