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Compression & Valve Clearance (shim-type) -> 80 GS-85

  • Thread starter Thread starter Dave_A
  • Start date Start date
D

Dave_A

Guest
FIRST

Well, I tested the compression on this bike, being concerned that blow-by might be causing my oil leakage, and got

95 75 70 70 on 1-4, with a hot engine (method used was to run the bike at ~1200 rpm on 3 cyls with the gauge in the cyl to be tested).

Putting a small amount of oil in the 'low' cyls changes the compression very slightly (eg from 70 to 75), & the bike runs ok, so I assume it's not the rings...

Testing compression cold, by cranking the starter with the plugs disconnected gives me:

140 125 120 120

Usually, the opposite is true (due to expanding metal in the hot motor)...

Based on the sound made when hand-cranking (there is a short 'hiss' (like letting air out of a tire) from each cyl at a set point in the cycle, as if a valve was opening when it should not) I'm guessing I'm overdue for a valve adjustment, and that this is the root of the odd compression readings.. Any other ideas?

SECOND

Valve clearance (shim over bucket)...

On my 450, the 'proper' method, IIRC, for doing a VCA was to check each with the cam-lobe-tip pointing up between the cam-cap bolts like an arrow.

Is this the same on the 850, or do I have to do something with the TDC marks on the ignition pickup or the allignment marks on the cams?
 
Your readings with the engine running have NO meaning. To check the compression the throdel must be held wide open Hissing when turning by hand is normal. Valve adj is the same Have the lobe perpendicula to the cyl head and measure the clearance .03-.08 mm or .0012-.0030 in
 
SqDancerLynn1 said:
Your readings with the engine running have NO meaning. To check the compression the throdel must be held wide open Hissing when turning by hand is normal. Valve adj is the same Have the lobe perpendicula to the cyl head and measure the clearance .03-.08 mm or .0012-.0030 in
Click to expand...

Ok, valve clearance is what I thought...


WRT compression, the correct procedure for compression testing is to warm the bike up, then crank the engine with throttle open & plugs disconnected?

I'd thought it was to check with the motor running, but I guess I'm wrong...
 
WRT compression, the correct procedure for compression testing is to warm the bike up, then crank the engine with throttle open & plugs disconnected?
Click to expand...
Plugs OUT.

I'd thought it was to check with the motor running, but I guess I'm wrong...
Click to expand...
I'm wrong lots - don't give it a second thought. 8)
 
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