Low compression

[Cyrock]

I have a 78 XS11 that was sitting for a couple years. I just got it started I found the #3 cylinder is not working. I did a compression check of all the cylinders and found low compression on all cylinders. A couple squirts of oil in the cylinders, the readings stayed the same.

1-80 2-70 3-70 4-60

Would this be stuck rings, valves or ? Is there anything else to check or try before riping the engine apart?

[GNEPIG]

.. you did not state your milage, could need a valve adjustment.
if the rings were worn out then the oil would have helped bring the compression up some.. also could have some carbon or crap between the valves and seats, this would cause some compression leaks, just running the bike some would help clear this out- warming it up to operating temp and going for a short ride a few times

[skids]

Re: Low compression

The valve and / or seat are likely corroded. If it were mine, I would ride it for a few hundred miles in hopes the action pounds away the roughness. There is a good chance that the cylinder will fire at speed. I have seen compression come up this way.

Originally posted by Cyrock
I have a 78 XS11 that was sitting for a couple years. I just got it started I found the #3 cylinder is not working. I did a compression check of all the cylinders and found low compression on all cylinders. A couple squirts of oil in the cylinders, the readings stayed the same.

1-80 2-70 3-70 4-60

Would this be stuck rings, valves or ? Is there anything else to check or try before riping the engine apart?

[Cyrock]

I have gone on a couple short rides, it seems to run good through the full range of acceleration.

There are 29170 miles on it.

[prometheus578]

"Hey. quit pressurin' me!"

That's some low compression.
First off... is your compression tester any good? (And no, you can't use a valve from a tire's valve stem in a compression tester. They look the same, but will give readings like this.)
HHmm... low compression...? Valves usually all don't go loopy all at once, unless the cam had been out of time and whacked a few. But we won't dwell on that yet.
Is there a good air filter on the machine? I've seen bikes with low compression across the board due to the owner not running an air filter and burning grooves in the valves due to sucking in grit, etc.
I tend to agree with the others that the valves may be clogged with carbon or rust due to sitting fer a spell. (or being gummed up and sticking a little) Running it for a while will often bring them back to life.
Warped head, leaking head gasket... you may see exterior oil leakage, or you may not.
Easiest test would be to take off the valve cover and check the valve clearances. That would be the first, least intrusive test.
If they're good, then we move on.
(just reread the posts... how is the battery? If it's not up to par, the slower cranking will give you loopy compression readings)
If you don't have a leak-down tester... You can use your compression checker.
(Oh, a further note... some people forget that when doing a compression check.. all the plugs must be out and the throttle held wide open. Engine should be warm, too.)
And now... back to our story already in progress...
If you don't have a leak-down tester... You can use your compression checker. Take the little valve out of the screw in end of the compression tester's hose and screw the hose back into the cylinder. With the cylinder at TDC(all valves closed) Hook the other end of the hose to your air compressor(which I hope you have) Do not leave the wrench that you used to turn the crank with on the end of the crankshaft. When you pressurize the cylinder, the crank can spin, and the wrench can go flyin' and knock over your beer.

"Listen up, Tough Guy!"
If the air is hissing out the carb, then the intake valves are suspect. Hear air coming out the muffler... exhaust valves. Air noises out the crankcase vent, oil filler hole, etc, then it's leaking past the rings. If you're checking cylinder #1 and air is comin' out of the plughole of cylinder #2... head gasket.