Compression tests

I did a bunch of compression tests on the Bandit this weekend, as the sparks were looking pretty weak and the bike doesn’t seem to be feeling that well in general (shockeroo).

The dry compression test went fairly well; all four cylinders were in the ~140psi range. I don’t remember the exact numbers offhand, but they were all right at the low limit of acceptable. The manual says compression should be between 140-206psi. Have I already talked about this? It seems familair. Ah well. Losing my mind already.

Anyway, since the readings were low, I figured I’d do a wet compression test. I’d never done one before, but here’s how I understand it: you put a small amount of oil (a tablespoon or so) into the sparkplug hole and then redo the compression test. The oil will seal up any gaps/holes in the piston rings, so if the new readings are a lot higher than those from the dry test, it’s probable that you have piston ring problems. If the readings are the same, then the oil didn’t make a difference and your problem is somewhere more in the top end (valves, etc).

I think I did something wrong with the wet compression test, though, because suddenly, I was getting really super high readings: mid- to high- 200 psi. That just doesn’t seem kosher. I’ve been thinking all day about what could cause the compression readings to go sky-high after adding oil.

It was suggested on ST.n that I added too much oil (entirely possible as I just eyeballed it), thus changing the compression ratio to 14:1. I haven’t wrapped my head around that explanation yet, though.

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