Compression

So I finally got everything wired back together on my 81 xj650 maxim after replacing the fuse box and cleaning some of the electrical connections. I bought a new battery and was finally able to do a compression test. This was done with the intake manifold open, no boots, no carbs, no nada. Cylinders 2, 3 and 4 all read around 120, while cylinder #1 was around 85. Is this something I should be greatly concerned with or can I let it slide a bit?

 

85 seems low to me, all 4 cyls on my 81 750 pressed over 150. I didn't do much research though, so I'm sure someone will pop up that knows what the limits are off hand.

 

Put a little(tbsp) of oil in that low cylinder and see if it comes up. If not, check valve clearances. If it does, you might have a ring problem on that cylinder.

 

I still have to check my valve clearances and adjust the shims as needed. I'll go add a tbsp of oil and see if that helps, thanks Richard.

 

Hells yeah. I put a little oil in the cylinder and rechecked the pressure. It was at 175. That means I'm good....right?

 

Actually that usually indicates a rings issue. No change could be valves. Sorry

 

Is that going to be a "put the bike on stands and pull the motor" kind of issue?

 

probably

 

I would hold up for a bit and put a few miles on this engine. Recheck after about 50 - 100 miles or so. See if it come around. If the bike has been sitting for awhile it might be dry and just need to get the juices flowing. Now if your carbs were running rich lets say that alone could dry out that cylinder. I say run it and recheck. Good Luck

 

I believe on the 650 you can pull the head in frame. I have not done it but I think others have.

 

He can certianly take it apart in the frame. I had the 750 cylinders off.
I would advise to make sure you need to do that. Parts=$$

Oil up the other cylinders and see if they are all the same or close. I'm still thinking dry cylinder and bad compression test on #1.

 

You can pull the head but to change the rings you have to pull the jugs, right? Bet that can't be done in frame!

 

It can be done in the frame.
But, like MN-Maxims said, If it's been sitting for a while, rings may be gummed up or washed out from a overflowing carb/stuck float. Might try and run it for a bit, then re-check compression.

 

once the head is off you have more room

if you can get he timing chain off and the guides out you should be able to i would think

measure your jugs add 2 inches(cylinder sleeve) and see if you have enough room to slide them up by measuring from the top of the jugs to the frame

 

Before I start pulling the head off or trying to pull the motor out of the frame I'll let the juices flow and see how that helps. The biggest problem is I don't have a motorcycle license and I'm sure as hell not going to ride around illegally so the most I can do is up and down the private parking lot of where I live. How much do you think I should let her run before I try to recheck the compression? I got her fired up today. First button press after cleaning the carbs and some other basic maintenance.

edit: I do know how to read, just sometimes I don't. 50-100 miles then recheck, thank you very much MN-Maxim, and also thank you to everyone for responding so far.

 

Jon, after I get mine put back to gether again, (painting the tank, knee dent removal), we need to hook up and road trip a bit.

 

I'm all for it Alka. I take my MSF course the weekend of April 24th and I know I'll be DYING to ride by that date. So long as I have my bike running reliably.