yarddog53
xs rider
Hey all Ive look in my manual and can't find what the stock compression should be just got 2 more xs motors. any help thanks
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DetroitMuscle07
XS650 Enthusiast
Anything above 135 is good with no more than 5% variation between cylinders.
yarddog53
xs rider
thank you for information going to check tonight
And engines that haven't run for a long time, kicked over 100 is a reasonable start. If they will run, run em for a bit and then check. Just checked a bike that hasn't run for 8,9 years one side was 140 the other was about 90. sprayed some PB blaster in em, tried again the next day got 165 both sides by kick starter. Piece of carbon can fall on a valve seat and show zero soon as it runs and blows it out bump good compression. Then again it could have a hole in a piston.
HooliganCycles
XS650 Addict
i love PB blaster....i have decided you can spray that stuff on a rusted up bolt let it sit a minute and the bolt with pretty much unthread itself....we sprayed it in the spark plug holes on a seized up bike at work let it sit a few minutes then kicked the bike over, not only did it break free but the motor fired up...good stuff.
Ghetto
Bob it!
Yea PB Blaster is some intense stuff.
yarddog53
xs rider
Hey everybody thanks for all the help. going to parts store to get some PB Blaster. I don't think these motors ran in a long time although thay kick over. again thanks everybody.
My books call for 145 as normal. 10% between the cylinders. The PB blaster is good stuff.
As others have said, on an engine thats sat for long the compression may be low. Running the engine can bring low readings up. As they set the rings and cylinders can get a light coat of rust. This rust can keep the rings from sealing. After running the rust gets scraped of and the rings reseat to the cylinders.
The same thing can happen on the face of the valve and the valve seats.
Valves can get sticky for the same reasons. The stems get a bit of rust and can keep the valve from closing. Squirting the PB blaster around the valve stems in the intake and exhaust ports and around the valves seals can help.
Removing the valve adjuster covers and watching the valve action you might spot a valve that acts a bit sticky.
As others have said, on an engine thats sat for long the compression may be low. Running the engine can bring low readings up. As they set the rings and cylinders can get a light coat of rust. This rust can keep the rings from sealing. After running the rust gets scraped of and the rings reseat to the cylinders.
The same thing can happen on the face of the valve and the valve seats.
Valves can get sticky for the same reasons. The stems get a bit of rust and can keep the valve from closing. Squirting the PB blaster around the valve stems in the intake and exhaust ports and around the valves seals can help.
Removing the valve adjuster covers and watching the valve action you might spot a valve that acts a bit sticky.
yarddog53
xs rider
the one i ride has 125 per cylinders and run good i just got 2 more motors that i need to check. just got some of that PB blaster. Thank You for information
Renegade600
XS650 Enthusiast
On my project bike the motor had sat for how many years, but rolled over smooth....finally checked compression and had almost 150 on one side and 50 on the other....thought oh shit gonna have to pull the motor down in addition to all the other work...
Went in with the pbblaster, Kroil, and Marvels...soaked and rolled, soaked and rolled...before long the comp was coming up..by the next day I had 150 on both sides.....I figured stuck rings from sitting, or a valve hanging (pbblastered the crap out of the valves too)...
Tom
Went in with the pbblaster, Kroil, and Marvels...soaked and rolled, soaked and rolled...before long the comp was coming up..by the next day I had 150 on both sides.....I figured stuck rings from sitting, or a valve hanging (pbblastered the crap out of the valves too)...
Tom
yarddog53
xs rider
Mine is same story 160 on one side 80 on other let it soak in Marvels over night now have 140 and 125 have not yoused PB blaster yet. ( I also thought oh shit at first ) going to let soak more.
