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Tappet clearance & compression

  • Thread starter Thread starter BigVic54
  • Start date Start date
B

BigVic54

Guest
Please help. I just adjusted my tappets for the first time and I think I made a mess of it. My piston's compression have either dropped or gone away. Will poor tappet clearance cause this?

Thank you for your help.
 
Its a 1982 GS1100LG. I used a feeler gauge, measured the existing tappets, did the math and put new ones in. However, I think I screwed the pooch as one piston that was at 140LBS now has none and another has dropped significantly.
 
I think you're going to have to take us through the maths to start with. It could be your method but it's easier to start with the maths.
 
The "maths" part is easily taken care of by taking advantage of the offer in my sig.

The "method" part might need to be explained, as the process can be easily misunderstood by a first-timer.

Most don't understand that you set the cam lobes in the position shown in the manual and measure TWO clearances without moving anything. Not measuring with that method can easily give you wrong readings.

.
 
My #3 cylinder wasn't firing. I cleaned & adjusted the carbs, adjusted the tappets and put everything back together. Before I did this the compression in #3 was 140lbs, now its almost 0. It would seem it was the tappets. Could the carbs affect the compression?
 
Go back and check clearances, again....according to the exact method in the manual. Chances are you have a couple too tight.
 
I opened it up and checked the clearances again. This time I paid more attention to the location of the lobes on the cams. The gaps were anywhere between 1.0 and 2.0. I've moved some around and will order some new ones. Does anyone think this would be enough to lower the compression?
 
Did you mean .01? .1 mm would not cause your issue, but I am questioning what you are actually reading. If you mean .01 mm, most feeler gauges don't go down that small. It would be a special set.

If they are reading as large as .2 mm, you may have a bent valve
 
8ball said:
Did you mean .01? .1 mm would not cause your issue, but I am questioning what you are actually reading. If you mean .01 mm, most feeler gauges don't go down that small. It would be a special set.

If they are reading as large as .2 mm, you may have a bent valve
Click to expand...

Prior to changing the shims the compression was good. After changing them it dropped. Nothing else was done. I don't see how it could be a bent valve. The gaps are anywhere from .07 to .15
 
0.15mm is fairly large, but not wildly crazy. Going up 2 sizes on a shim will fix that gap.
0.07mm is within spec.
Do a leakdown or makeshift leakdown with a compression tester.
Put the cylinder to TDC where the valves are all closed.
screw in your compression tester hose into the spark plug hole, attach an air hose with low air pressure(~45psi?)
Listen for air leaking/hissing.
If you hear a significant amount of air leaking, chances are, your valves are bent.
 
I made the Rookie mistake last week of using an Imperial feeler gauge to measure metric gaps. All my tappets ended up being around .23 mm when I used the 10 thou feeler gauge. Instead of their proper measurement between .08 mm and .13 mm. This was on a GS1150ES with adjustable screw tappets (16 of them!) but it wasn't too much of a pain to do it all again - except for having to take all the fairing off.
 
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