GS500 Repair

Old 06-17-2011, 12:20 AM
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Join Date: Jun 2011
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Default GS500 Repair

I recently bought a GS500 (2002). First thing I did was a compression test. Full throttle, spark plugs out and grounded, at least 5 cranks per cylinder.
The results were only 90 PSI on the left cylinder, and 120 on the right.
Next, I did the tablespoon of oil test on the left cylinder to determine whether the loss of compression was on the top or at the bottom. After pouring the oil, and re-testing for compression, I got the needle on the tester to go rapidly up and down, hitting a max of about 150 psi.
If I read on the Internet this procedure correctly, this should mean that the compression loss is happening below the top of the piston, either rings, piston, cylinder, or a combination of those.
I went ahead and opened up the cylinders. I measured everything, and to my dismay and surprise, everything is within spec! The pistons, after cleaning them, look almost new. The cylinders look even shiny! The rings actually seem to be over spec!! I'm thinking that there could be a possibility that whomever assembled it last didn't stagger the rings on the left cylinder.
The cams on the camshaft (intake) are under spec. Now, I'm going by the Clymer manual, but I'm a bit suspicios of it because the diagram it has of the carb is different from the carbs the bike has.
I'm also unsure of this camshaft's cams being undersize because the measurement I took was almost identical on both cams. Besides, if the cams could cause loss of compression, it would've affected both cylinders, as both cams have the same dimension.

Anyway, I'm asking for suggestions. I'm thinking of simply assembling it as is, and re-test, but I'd like to make sure I'm not failing to do something.

Some comments, please?

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