PeteH Posted October 19, 2016 Report Share Posted October 19, 2016 Hi Quick one here. What should the compression pressure be when tested with a gauge? My old Gunson Gauge is showing 1) 235psi 2)215psi 3)230psi 4)230psi. These seem somewhat high? but are within a 10% tolerance. Pete Link to comment Share on other sites More sharing options...
Clive Posted October 19, 2016 Report Share Posted October 19, 2016 compression testers are not really a calibrated instrument, so the actual readings are not that important (within reason!) If yours are all that close, I would be happy. I presume that was with wide open throttle. Have you repeated but putting a teaspoon-ish of engine oil in each cylinder? That can be informative. Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 19, 2016 Report Share Posted October 19, 2016 and done on the starter with all the spark plugs out ,, !! those figures imply you have a CR of nearly 16:1 more suited to a diesel Pete Link to comment Share on other sites More sharing options...
Steve P Posted October 19, 2016 Report Share Posted October 19, 2016 Very high i would have thought,my car runs 10:1 and that was about 180psi when new. Steve Link to comment Share on other sites More sharing options...
PeteH Posted October 19, 2016 Author Report Share Posted October 19, 2016 Hi. MY thoughts are that the Gauge (40+yrs old) needs recalibrating!. I expected about 130 to 160 psi. The engine is on the bench and the test(s) performed using a freshly charged battery, plugs out, first run "as is" second run with oil in the cylinders, I suspect the "low" reading may be due to valve leakage rather than rings. I plan now to have the head off anyway, mainly to check if the head has been converted to "unleaded" status. at which time I will have a look at the bores. I have a 12/50 manual, which shows the Compression pressure as circa 136psi. But I was looking for the 13/60 figures. which would /could be different?. Pete Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 19, 2016 Report Share Posted October 19, 2016 Unleaded work is generally just hardend exhaust seats and a tougher valve Inlets are ok as is . And compression results tend to be atmosppheric pressure x the CR eg 14.7 x 9 less any inefficiencies pete Link to comment Share on other sites More sharing options...
Colin Posted March 27 Report Share Posted March 27 Hi Chaps; My Swiss chum came over with his compression tester. Took out the plugs and turned my 1147 Saloon on each cylinder. He's now gone so I can't ask, but whereas your figures state psi (?) My cylinders were measured as follows; Cyl 4: 10 Cyl 3: 10 Cyl 2: 9.5 Cyl 1: 10 Does anyone know what units these would be?? Best, Colin Link to comment Share on other sites More sharing options...
johny Posted March 27 Report Share Posted March 27 They would be Bar where one equals 14.5psi so your readings look pretty good... Link to comment Share on other sites More sharing options...
Colin Posted March 27 Report Share Posted March 27 I think I have answered my own question . . . I think it's 'bar' . . . ? Am I correct? And, that those numbers stack up to be quite reasonable?? Link to comment Share on other sites More sharing options...
Colin Posted March 27 Report Share Posted March 27 Thanks Johny! Needed that corroboration! I am amazed - given it's the original engine on 143k miles. I've always regularly changed the oil, though! 😉 Link to comment Share on other sites More sharing options...
johny Posted March 27 Report Share Posted March 27 Yes that is good especially if the head hasnt had any valve work either... Link to comment Share on other sites More sharing options...
Colin Posted March 27 Report Share Posted March 27 Ah; well . . . When the Gov began to alert us that 4* leaded was to disappear, I took advantage of swapping to a John Kipping (ledge!) unleaded head. That was decades ago! So clearly the hardened valves and seats have done their work, too!!😉 1 Link to comment Share on other sites More sharing options...
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