Thread: Yamaha XT500
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Old 04-27-2008, 05:40 AM   #74
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Joined: Mar 2006
Oddometer: 1,902
Originally Posted by haydenslides
unfortunately, i'm thinking piston/rings might be on the agenda for my xt...
Time to pull out the compression tester. No sense tearing the poor thing down before you check it.

Help me out here guys, I haven't done this in a while. The old drill was:
1) remove plug
2) insert compression tester
3) be certain gas and ignition are off
4) hold throttle wide open
5) kick engine over until compression reading on guage stops rising
6) record results
7) remove tester
8) insert a few tablespoons of engine oil in the cylinder
9) repeat test
10) compare results

Every compression tester seemed to be a little different in the old days, so we tried to keep a record for comparison. For bikes of unknown background we tried to find a sound example to use as a baseline.

If the reading goes up after you add the oil, the rings aren't sealing very well. If the reading stays very low even after you add the oil, the valves aren't sealing very well.

A cylinder leak down test, where you pump air into the engine and measure how long it takes for it to escape, is a more sophisticated measurement. I've never done it.
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