XR650L Compression Test



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  • michaeln

Posted October 14, 2003 - 02:57 PM

#1

In order to help me get a handle on the overall health of my '98 XR650L, I bought a compression tester (fairly cheap one, $40), and after getting the motor thoroughly warmed up I pulled the spark plug (which looks good, tan/light brown) and ran the test. At first I got a reading of only 60PSI...the manual calls for 92PSI with the auto decompressor not disabled.

Hmmm.

Awfully low. Oops, I remembered I had neglected to hold the throttle wide open while cranking it. This time (and repeated three times) I got 90PSI. I figure that's good enough, given the unknown state of accuracy of the compression tester.

The reason I did the test was that the previous owner told me he'd run it out of oil once and it siezed, and the local dealer here in SF bored it next oversize and put in a new piston and rings.

It seems to run pretty good. I've installed a Big Gun Quiet can, BD smog removal kit installed, UNI air filter, snorkel removed, DynoJet kit (spring, #160 main, DJ needle with clip on #3 and BD's extra #55 pilot jet, sea level).

It uses a lot of oil though. No oil deposits on the spark plug, and it's not leaking or visibly smoking. But in 500 miles or so I top it off enough to consume about 1/3 quart of oil. The weather's been cool here in SF (not cold, but 60-ish), and I do run it on the freeway at 65-70MPH with 14/45 gearing. From what I've read, these motors do have a reputation for consuming oil, so I guess that's not really out of line.

I guess I could do the "loosen RH exhaust valve to disable auto decompressor" thing and re-run the compression check (supposed to be 199PSI that way), but based on today's tests, the motor looks pretty sound. After all, it has 14,500 miles on it and wasn't very well cared-for before I got it.

Honda specifies you do that second test if the compression is lower than 92PSI, but again I'm not all that certain of the gauge's accuracy, and that part of the test is somewhat of a hassle because I have to remove the seat and tank to get to the valve to adjust it, then run the test, then let it cool off overnight before readjusting the valve to spec. I'm lazy and don't want to go through all that if I don't have to.

Do freshly broken-in XR650Ls in excellent condition exceed that 92PSI by much? Or is my 90 a sign that the motor is in bad shape, ie: below the absolute bottom limit?

What do y'all think?

One other thought... I wonder if going from 10W40 to 20W50 might help a little with the oil consumption? 30 degrees F is about as cold as it EVER gets here, and that's cold enough that a fair weather rider like me wouldn't ride in it anyway.





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