Yesterday a friend came by with an "80" 240D which was running BAD. Compression test showed +-60 lbs on #3 so we decided to try a "leak down test" to try and determine if it was a valve problem or the 'bottom end". I removed the shrader (sp?) valve and gauge from the compression tester, added a valve to control the air flow. We hooked up the air to #3, adjusted the cam so both valves on that cylinder were closed and opened the air valve, hopping to hear air escaping from the air cleaner or exhaust pipe. But alas, we could hear it coming up through the timing case. When I got the head off the cylinder wall of # 3 was badly scored. Never having done a leak down test before I was wondering about a couple things...The engine rotated a little when we put the air to it and when I got the head off the piston was most of the way down, So my question is ....isnt the test spoz to be done with the piston at TDC to avoid "rotation"? How is TDC found, (Ah, unless you are doing #1 )

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"