Ian Vincent Posted July 3, 2018 Report Share Posted July 3, 2018 (edited) Whilst tidying some stuff the other day I 'found' my compression tester which I bought back in the early 70s and hardly ever used. Anyway, as a displacement activity from further tidying, I thought I would carry out a quick test. The engine was stone cold and I got the following results: 160psi 165psi 165psi 165psi I then repeated the test after putting a couple of squirts of oil in the bores and got 170psi 175psi 175psi 175psi All of these figures were repeatable. I then carried out a search of the forum to find out whether or not the lower reading on No: 1 is significant and it appears that as long as they are within 10% there shouldn't be an issue. However I also found during my search that I should have carried out the test at normal operating temperature and with wide open throttle. Now I can understand the reason for the normal operating temp, (I think), but haven't clue why one would need the WOT. Does anyone on here know the reason please? Rgds Ian Edited July 3, 2018 by Ian Vincent Quote Link to post Share on other sites
barkerwilliams Posted July 3, 2018 Report Share Posted July 3, 2018 If the cylinder can't draw as much air in as possible then it can't compress it to show a maximum compression figure. So readings likely to be low. On a car such as TR6 with six butterflies, possibly not all set exactly the same then each cylinder compression could show the different intake restrictions not the compression of a "standard" volume of air. WOT removes this as a variable to show how each cylinder compresses the same volume of air. Nice matched readings you have there. Alan Quote Link to post Share on other sites
Lebro Posted July 3, 2018 Report Share Posted July 3, 2018 I wish mine were that consistant Bob. Quote Link to post Share on other sites
oldtuckunder Posted July 6, 2018 Report Share Posted July 6, 2018 Don't forget on a carb'd car that just holding the throttle at WOT won't do any good as the air pistons are down, they need holding up as well as WOT, two toilet roll inners work well. Alan Quote Link to post Share on other sites
john.r.davies Posted July 8, 2018 Report Share Posted July 8, 2018 Anyone who does a compression.test for the first may not low to do it WOT. But its a compression test, not a throttle test an air filter (yes take off the air filter too. And disconnect the ignition. But the OP admits, the only reason they did it was that they had a gauge and other work needing undoing. Moral DONT do.a test just because you can, but to to.find out something that will help you diagnose a problem. And do.somebtesearch first into what thebtesults might mean. You compression is probably fine, bit the samebis true unless you know you have an.old knackered engine, or one you have built yourself after skimming the head and arent sure ( you SHOULD be sure!) about your skim calculations. Think three times, measure twice, cut once, as a great philosopher said. John Quote Link to post Share on other sites
oldtuckunder Posted July 8, 2018 Report Share Posted July 8, 2018 Think three times, measure twice, cut once,as a great philosopher said. Helen always says to double everything I ever quote, so I think that should be: Think six times, measure four times, cut twice, Unfortunately the latter has happened more than once! Quote Link to post Share on other sites
john.r.davies Posted July 8, 2018 Report Share Posted July 8, 2018 Helen is no doubt a wisevwman and the rock.of your life, but the whole point of the aphorism is to AVOID "cutting twice"! As once may be too much. John Quote Link to post Share on other sites
oldtuckunder Posted July 8, 2018 Report Share Posted July 8, 2018 As once may be too much. Why is it given a 50:50 chance of cutting something too long or too short, one always seems to err on the side of too short? Quote Link to post Share on other sites
Waldi Posted July 9, 2018 Report Share Posted July 9, 2018 Because then the 80-20 rule applies???? Waldi Quote Link to post Share on other sites
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