Exhaust Valve or Rings?

[PHeller]

Can't get my bike to run on the right cylinder. Runs great on the left, but I suspected either a bad plug. After testing the plugs and coils, I did a compression test.


Tested compression. Warm engine:

120: LEFT
60: RIGHT

Wet:

155: LEFT
150: RIGHT

Tested after both sides had dried a bit:

150: LEFT
115: RIGHT

So as the right side cylinder dries out, it's losing compression. I can't determine if this is a valve or a piston ring. Any ideas?

 

[jay760]

I fitted an ignition system the other day, which said you couldn't check for a spark on a single plug as the spark basically went down one lead across the head and back up the other lead, if you had something similar to this it would look like the spark is jumping from the side of the plug where it would be jumping to the side of the plug.

 

[smokeeater495]

Maybe the plug is fouled and causing it to arc from the electrode direct to the plug body. Look up inside the plug for little black boogers.

 

[PHeller]

Changed title and post to reflect new information.

 

[Classic]

You've already spec'd out your valve train?

 

[grizld1]

PHeller, wetting down the cylinder has no effect on the seal between valve and valve seat. Your problem is in the seal between rings and cylinder.

 

[PHeller]

Rings? Bummer. This engine has sat for 3 months, so maybe I can loosen it up?

Otherwise I've got a spare engine whos time has come.

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[5twins]

If one sat for years maybe but 3 months shouldn't do that. We'd all be in trouble after winter storage if it did.

 

[PHeller]

So how can I be absolutely sure its the rings?

I plan to clean the exhaust valve, recheck clearances (loosen them up a bit) and do the compression test with the carbs completely open to see if anything changes.

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