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Hey everyone, I had some someconsiderable power loss on a bike that Ihad running(I thought)pretty well. It had been sittin" for awhile. I did a compression test and readings were definitely less than favorable:

#1-125

#2-130

#3-0 (guage didn't jump at all)

#4-127ish

I've read that compression should be170 and 10% of each other. Whatcha think? Is sherepairable or better used as a boat anchor?
 

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Rering it! Or find a deal on a used engine. Guys find them all the time. Good luck with whatever you decide! jimsjinx
 

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#3 looks pretty sad. 170 is a target pressure. My 1100 had 90 on all four cylinders. It wouldn't run but it was an ignition problem. The advance mechanism was loose and rotated freely. It runs great now.

Was the compression taken with the engine hot and the throttle wide open? Is the throttle plate for #3 opening at all?

Zero compression does not indicate bad rings but more likely a valve problem. A remote possibility is a holed piston. This might have happened if a timing belt broke at some time and was replaced without further checking. You might want to check the condition and timing of the belts after the next step in the testing.

Put a shot of oil in #3 and see if there is a difference. This is a test for ring condition. If the compression comes up some it could be rings. If there is no or little change then it is probably a valve problem.

Pull the rocker covers on the right side and check the movement of the rockers and the valve clearance. Is one of the valve adjusters loose? Observe if both valves on #3 seem to be closing all the way. The rocker ends of the valve stems should be very close to the same height. Check that both valves are opening nearly the same distance.

An engine is an air pump or compressor if you will. A cylinder has to take air/fuel mixture in, compress it, burn it and release it through the exhaust.

Lyle, President of the Use Punctuation, Paragraphs, Capitals and Non Use of Acronyms Club.
 

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jbg777 wrote:
Hey everyone, I had some someconsiderable power loss on a bike that Ihad running (I thought)pretty well. It had been sittin" for awhile. I did a compression test and readings were definitely less than favorable:

#1-125

#2-130

#3-0 (guage didn't jump at all)

#4-127ish

I've read that compression should be170 and 10% of each other. Whatcha think? Is sherepairable or better used as a boat anchor?

If it was running fine before the "sittin", then right after the "sittin" the problem developed, My bet would be a stuck valve. Piston rings don't just disappear just from sittin.

EDIT: Zero comperssion is either aburnt valve/valve stuck open. or a hole in the piston. If it was a hole in the piston, that would create a ton of blow by into the crankcase. If it is a stuck valve, I would look at the exhaust valve. If it was the intake valve stuck open, it would be poping or blowing back up through the carb.





Put a shot of oil in #3 and see if there is a difference. This is a test for ring condition. If the compression comes up some it could be rings. If there is no or little change then it is probably a valve problem.

That's what I was tough in auto shop class way back when.
 

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I had the same problem on a kz650 motor recently. Motor had an unknown history. I pulled the head and the exhaust valve was stuck. Replaced valve and lapped rest now every thing is good. Might as well pull heads then you'll know.:?
 
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