Nick Jackson (2) Posted October 11, 2008 Share Posted October 11, 2008 Thought I'd try out my new toy bought by someone last Christmas. Couldn't check No.1 properly because the alternator was in the way but Nos. 2 to 6 were 157, 150, 158, 161 and 170 (avg) in PSI. Are these acceptable in variation? The difference between No.3 and No.6 looks massive at 20PSI. What would be the effect on the engine of having this situation and, more to the point, what is causing it? I did No. 6 and got 171 the 1st time and rechecked to get 169 the 2nd time. Thanks Nick J. Link to comment Share on other sites More sharing options...
Alex Posted October 11, 2008 Share Posted October 11, 2008 Nick, I think the accepted norm is uoto 10% difference yours sounds good and healthy there.Alex Link to comment Share on other sites More sharing options...
willcolumbine Posted October 11, 2008 Share Posted October 11, 2008 Doesn't sound like there's too much to worry about there. The difference between cylinders can be caused all manner of things. Slight differences in piston height, con rod length, bore diameter, piston ring gaps etc etc will all add up to a slight difference. Then theres the calibration of the tester etc etc. Link to comment Share on other sites More sharing options...
Nick Jones Posted October 11, 2008 Share Posted October 11, 2008 Were these done with throttle open? If not, small difference on throttle balance = quite marked difference in compression reading. Those figures look good enough though.Nick Link to comment Share on other sites More sharing options...
Nick Jackson (2) Posted October 11, 2008 Author Share Posted October 11, 2008 "Then theres the calibration of the tester"I'll have you know I put my pint down to take those readings you know! (Oh you mean the gauge itself do you?)It was a Gunsons tester. Instructions said disconnect ignitiona and crank over for 5-10 seconds. Didn't touch the accelerator. General viewpoint is that there's nothing amiss here. Good - another thing off the list then.Thanks Link to comment Share on other sites More sharing options...
JohnD Posted October 12, 2008 Share Posted October 12, 2008 This is a Pi, right?So throttle bodies in pairs.You'll note the back pair have higher compression than middle, or No.2. If you didn't have the throttle open, may mean that back throttle body has poorly closing butterflies, so more air aspirated than the middle one, so can achieve greater compression.Open the throttle wide as poss to take compression readings.Also suggest disconnect fuel pump while you do it.John Link to comment Share on other sites More sharing options...
Tim Bancroft Posted October 12, 2008 Share Posted October 12, 2008 And check your valve clearances. Link to comment Share on other sites More sharing options...
Nick Jackson (2) Posted October 12, 2008 Author Share Posted October 12, 2008 Yes PI, and throttle bodies in pairs. No 5 was basically the same as 3 & 4, with only 6 very high though. Will check that pair anyway though.Did the valve clearance once and they were all circa 0.017" which I belive is right for a Std 150 TR5 Piper cam. Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 13, 2008 Share Posted October 13, 2008 always have the throttles open you need to get the air in easy, ( cant run with mouth shut),, and crank till max reading is observed with a good battery and starter and ALL plugs Out.it must spin over at a good rate +- 10% is quite normal Peter Link to comment Share on other sites More sharing options...
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