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  1. #1

    One cylinder compression higher than the other???

    1997 787 GSX.

    Last check I believe the psi was like 160 in mag and 145 in pto (have to check those #s again), almost seems like one piston comes up just a hair higher than the other but this was no scientific test, just a pen. I will have to measure this to be sure.

    What could cause this in the engine? Crank install, piston rod length issue? Crank was a hot rods unit with the rods and bearings already installed. New pistons, rings, gaskets etc..

    Any ideas?


  2. #2
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    Quote Originally Posted by andytk5 View Post
    1997 787 GSX.

    Last check I believe the psi was like 160 in mag and 145 in pto (have to check those #s again), almost seems like one piston comes up just a hair higher than the other but this was no scientific test, just a pen. I will have to measure this to be sure.

    What could cause this in the engine? Crank install, piston rod length issue? Crank was a hot rods unit with the rods and bearings already installed. New pistons, rings, gaskets etc..

    Any ideas?
    yamaha use to do this on there twins because of crankshaft tortioning on the pto side on there 760 motors also check your cylinders to see if they have been removed some people change 1 cylinder and cut the base gasket in half they may have used a thicker 1 on the rear that would explain this.

  3. #3
    Thing is I rebuilt this entire engine with new Counter Balnace bearings, new crank (hot rods), new gaskets, blasted all the paint and repainted engine, the gaskets were installed with a coating of threebond on both sides of gthe gaskets. Engine was torqued to specs on all bolts, new rings,pistons, etc.. Break in was done by the book. I cant figure it out. Not sure how much of a long term prob this will be anyhow I just want to know since I totally redid this thing, and it hauls ass just has an extreme top end cut out issue and sometimes have to choke it or wot it to start after running, maybe jetting?

    All new black fuel and new oil lines, filters etc.

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