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Compression Specs
- Scoot Jockey
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- 1976 KZ 900 A-4 & 1997 FLHRPI
Do these readings seem low enough to cause the engine to stop running?
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- Skyman
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I would think you would need at least 80-95 psi to run (poorly). I think with the numbers you have, that would indeed cause it not to start.
West Linn, OR
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- bountyhunter
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1979 KZ-750 Twin
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- donthekawguy
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Rathdrum Idaho
1971 Kawasaki g3ss
1972 Yamaha R5 350
1965 Suzuki Hillbilly
1964 Yamaha 125
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- Patton
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In my quest to find out why my bike quit running, I did a compression check tonight. Since the engine is ice cold, I know these readings aren't the best, but I had 40 psi in two cylinders, 50 psi in one and 70 psi in another.
Do these readings seem low enough to cause the engine to stop running?
Would add teaspoon of oil inside combustion chamber and re-test compression. Would also check valve clearances.
Good Luck!
1973 Z1
KZ900 LTD
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- Scoot Jockey
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- APE Jay
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- Scoot Jockey
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CRUD!!!
I think it's likely the head got loose during break in and that must have caused the head gasket to blow. Although tonight I am going to try the teaspoon of oil test to make sure the rings aren't at fault.
If the rings are the culprit, then the guys who did my machine worked ripped me off.
If its just the head gasket, then I'll be giving you guys at APE a call to order a 1075cc head gasket.
If it is the rings, then maybe I'll be sending you my cylinder block as well!
Just when I thought I'd be getting ready for riding season...HA!:laugh:
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- Patton
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Also a leak-down test could be very informative. If a tester tool is needed, rumor has it that AutoZone (and maybe some other auto-parts stores) has this tool and other tools available for loaning out to its customers.
The leak-down test will allow actually hearing where the compression is escaping from. If heard coming from the exhaust, it's an exhaust valve failure to seal. Or heard coming out the carb intake, an intake valve failure to seal. If heard coming from the crankcase vent, it's being lost by going down and around the piston and rings, or possibly through a damaged piston.
Good Luck!
1973 Z1
KZ900 LTD
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- Scoot Jockey
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I just finished adjusting the valve clearances, so I don't think that's the culprit. But I will recheck them.
I put a teaspoon of oil in two of the cylinders tonight and the compression jumped up to 150 psi in the cylinder that had 40 psi and 170 psi in the other.
If it is the rings causing this, I may decide to scrap this project and part this thing out. I'm not sure I want to work on this bike any more.
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- bountyhunter
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I put a teaspoon of oil in two of the cylinders tonight and the compression jumped up to 150 psi in the cylinder that had 40 psi and 170 psi in the other.
If it is the rings causing this, I may decide to scrap this project.
Odds are REALLY HIGH that it's rings with those symptoms... in fact, I can't think of a way that it's not rings.
1979 KZ-750 Twin
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- Scoot Jockey
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I am done with this project. I will be parting it out on EBay starting with the 29mm smoothbores tonight.
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