What's your compression?

Since I was working on the bike the other day I figured I might as well do a compression check. My bike with 27,000 miles came up with the following....

#1 - 130 psi
#2 - 130 psi
#3 - 125 psi
#4 - 125 psi

Looks like I will have a rebuild in the near future. What numbers are you seeing?

 

I just checked an 82 650 with 45K miles on it today. 150 across the board.

 

No one else does compression tests?

 

125- - 130- - 125- - 30

My dead 750 maxim, #4 comes up to 60 with PB Blaster sprayed in.
I already bought another motor. Anyone seen a 30 PSI reading "heal" itself, like un-stick a ring? by running it and using penetrant?

Is there hope?

 

TIMEtoRIDE, If you only came up to 60 on #4 with the PB, I'd take a look at your valve clearances on #4 and the rest while I was in there...

82 XJ650Lj Turbo, 19k mi, 125, 126, 128, 125 when checked before I bought it, not running for several years. Gonna have to do a re-check just to see where they are now since I've got it running.

 

isn't it true that turbo engines have lower compression? what is a XJ650 (non-turbo) supposed to be? at what point do you get worried? mine are at all around 140 so i think they're pretty good but i don't really know other than the fact that it screams!

 

07spacker That's correct, an 82 turbo 650 runs an 8.5:1 compression while an 82 650 maxim runs a 9.2:1.

Everything I've seen, if there is more than 14psi difference between cylinders, you may be starting to have problems(rings or valves).

 

hmmm.... good to know for future reference i suppose!

 

Thank you. You got me to check... 145 on #1. 150 on #2 through #4

 

rpgoerlich- - good tip, someone coulda just kept driving, so I pulled the cover and checked with--a strip of aluminum from a "soda" can, instead of a real feeler gauge. Got clearance on all 8. So it's rings. Bummer.

Also, I turned the motor in 5 th gear, rolling the tire by hand, and the cams rolled forward. I thought the motor rolled "backwards". then I pulled the Alternator cover, and it rolled forwards too! Which shaft rolls backwards?

And my XJCD's arrived after 3 weeks. I'm happy!

 

I guess you wont know until you open it up. I bought an 80 xj650 a while back and checked it. It showed just under 14psi diff on #4 and was making some strange noises. I had checked it with 30wt oil and it went up a little from 90 to 110 but was still low. I opened it up and had cylinder damage on #4 from water sittin in it. Found a used stock cylinder and gaskets and it run like a top. I regret selling it for sure !

It sounds to me like you have a valve not seating properly.

 

ignorance is bliss

 

Yeh, but I've re-cond and sold 6 bikes since then, 5 yamaha's and 1 zuk. Working on the Turbo now. Who knows I may keep this one...