Quote Originally Posted by exftrplt View Post
I'm not making myself clear. For years we had compression testers without calibration orifices. With this tester any cylinder that had leakage to below 60 psi "failed". Then someone ( I think Continental ) decided that the number was not that important, cylinder condition was. At about this time a new compression tester appeared. This tester had included a calibrated orifice and slightly different testing protocol. So my questions are who decided to put the orifice in the tester? Who decided the orifice should be .040"? Who decided on the testing protocol?
There was never an automatic failure at <60 psi compression differential. Many mechanics would call it a failure, and often times cylinders were failing at that pressure, but not necessarily so. I have had engines that were less than 60 psi on a compression diff chk, but were still acceptable and flown for a number of hours yet before overhaul. The "master orifice" added to the gauge sets gives a comparison leakdown for large bore Continentals and was a recommendation from Continental. I never knew or cared what size the reference port was.