Xj550 engine problems

I'm slowly working my way through my xj550 engine. I got all of my valves correctly shimmed and in spec. I ran a compression test on all of the cylinders and heres what I found.

#1 85 psi
#2 75 psi
#3 75psi
#4 80 psi

A squirt of oil into each cylinder yeilded me 90 psi on all cylinders. Rings, I figure.

How hard is it to tear one of these engines apart to replace the rings, lap the valves in, check the chain tension, ect....
Am I looking at a disaster with my compression readings or do I have something to work with? (I forgot to mention the valve clearences were all negative .000 too)

I am a diesel mechanic by trade so I am no rookie when it comes to mechanics, but I am a novice when it comes to motorcycles so I just want to have an idea what i'm walking into. Any other things I should check when I have the engine apart? Thanks

 

I think you should redo your compression test. Since they are all pretty uniform and the il didn't bring up the compression much, it sounds like you didn't have the butterflies open or carb slides up or out of the way when you did the test. I think the easiest way is to just remove the carbs from the intake boots when doing the compression test.

 

It could just be that the rings are stuck. How long has it sat?

 

I'll fully disagree. Removing the carbs is a whole lot more work than twisting the throttle.

 

Welcome aboard. You'll learn fast.

Gary H.

 

A little ATF in each cylinder and let sit for several days should loosen the crud in the rings if there is some there.

 

Worst case, removing the head, cams, and block is not a big deal on these engines. Being air cooled makes them a lot simpler to work on. Assuming you put some sort of rust buster on the exhaust nuts ahead of time, you can probably have the head off in less than two hours... maybe even as little as an hour if you have all the right tools and nothing is frozen or stripped. Once the head is off, removing the block takes just a few minutes.

Since oil didn't much help compression, though, it could be bent or burned valves rather than rings.... I would expect a good 120PSI at sea level for these bikes.

 

i wouldn't take it apart just yet. make something up to put some air in the cylinders and listen to the valves for leaks. if it sounds good, run it and see if the rings seat.
something to think about, when doing a compression test with the throttle open, what opens the carb slides all the way. just a thought

 

good to hear you got your valves in spec.
the rings are very expensive if you can find them.
try the 1part atf and 1 part acetone, or equal amount of kerosene instead of atf. (thanks K-moe)
and your sure the tester is good?
also remove the air filter when testing
while your at it read
The Information Overload Hour

 

Nothing. There isn't enough vacuum at idle to open the slides, let alone when just turning the engine over. If that were a factor then Yamaha would have specified a special tool for holding the slides open when performing a compression test.

 

valve specss
intake

exhaust

compression test by fsm 14 psi differance between cylinders max


do you have a factory service manual?