96 Compression Test

[Jeff Gordon]

I picked up a real nice 96 over the winter, the carbs were off but was told they needed to be rebuilt. Today I pulled the plugs and and did a compression test, 95, 97, 92, 0, it was a deflating moment. I’ve emptied a can off penetrating fluid into that hole in hope that maybe it’s a stuck ring, I know it’s probably a dream but I was bummed at that moment! Am I looking at a rebuild? Anything I can check prior to that realization? Any thoughts would be appreciated.

[cranky]

NOT a wrench, but could it be a stuck valve? Its not indicating
ANY compression? I'd expect at least a bit of a blip....

[cushman eagle]

I agree with cranky,even if all the rings were stuck,you should have a little compression.
You are checking with the throttle open right? A closed throttle reduces the air a cylinder can draw in reducing compression,but not giving a 0 reading.
I think you need to see if a valve is hanging open.

[triton28]

If the oil in the cylinder doesn't raise the 0 reading to within 10 Lbs of the other 3 , then you are going to have a top end rebuild on your hands, sorry to say.
Sounds like a valve seating issue to me.
Dave

[Jeff Gordon]

Good morning....what a terrible Saturday.......thanks for the replies.....the carbs are off the bike already so airflow wasn’t a problem. When I got to the last cylinder and got the zero reading I removed the compression fitting just to be sure I had it seat properly. With the dial off the hose I put it in my mouth and cranked the engine to see if there was anything at all...you could feel a very slight compression stroke but not enough to make the gauge move......i wondered about filling the crankcase with diesel fuel or something that might give the top end a bath in something slippery. I dread the thought of taking the motor out, i’m Pretty comfortable dismantling the bike, been close to having everything off the outside of the frame, but never did a motor re & re on a voyager!,,

[triton28]

Oil of wintergreen, available at a drug store, will usually free stuck rings if left to sit in the cylinder overnight.
Whatever you use remember to drain it out of the engine before placing the engine into active service.
While you are looking for a cause of the 0 Lb reading, grab one of those small LED flashlights and look into the inlet ports and see if there is a buildup of crap around the valve guides/stems. The back visible face of the valve should be free of chunky noticeable buildup. It may be sooty and dry but still recognizable as a valve.
If wet oily carbon buildup is evident, don't even worry about compression readings as the valve stem seals or the seal between the valve and it's seat are shot and the cylinder head should be taken off, the valve seals replaced and the valves re-lapped onto the valve seats of the cylinder head.
Hopefully your problem is a stuck ring which clears itself, much less of a problem to deal with as opposed to valve issues.
Should you have to go for a top end rebuild it is pretty straight forward although time consuming with those 16 valves to deal with.
Dave

[ekap1200]

I picked up a real nice 96 over the winter, the carbs were off but was told they needed to be rebuilt. Today I pulled the plugs and and did a compression test, 95, 97, 92, 0, it was a deflating moment. I’ve emptied a can off penetrating fluid into that hole in hope that maybe it’s a stuck ring, I know it’s probably a dream but I was bummed at that moment! Am I looking at a rebuild? Anything I can check prior to that realization? Any thoughts would be appreciated.

0 psi is seems to be more than a stuck set of rings. use a tablespoon of engine oil and you should get more than 0 even with the rings stuck a bit. But 0 seems a bit odd as if the valve is bent/burnt or stuck open. Apply shop air to that cyl and listen where the air is escaping ie intake or exhaust or crankcase for a starting point Who knows how long the carbs were off and if anyone let something get into the intake and get jammed up when the valve opened. As triton mentioned , take a inspection light and look into the inlet port. Is the valve even moving ? is there anything in there holding the valve open. These engines have a rev limiter so a bent valve seems hardly the issue unless the valve was stuck completely open until you cranked it over and then it bent. I am assuming 0 was number 4 cyl ? perhaps a cam follower has become stuck in the head from sitting in the damp weather for a long time
Gene Kap.

[cranky]

"These engines have a rev limiter"

Gene, Just curious, what RPM is the limiter set at? TIA

[hank43]

Just a WAG here, but if you put plugs back into the three cyls that DO read, does the forth non-reading cyl now show some compression? Checking one cyl at a time, does any reading change?
Thinking there could be head gasket issues....or breaks between cyl walls.
Also, remove the oil filler cap, is there any compressed air from the bottom end? I have never heard of zero compression....

hank43

[ekap1200]

"These engines have a rev limiter"

Gene, Just curious, what RPM is the limiter set at? TIA

That would be a question for Carl Leo.

[Jeff Gordon]

So I put some shop air to the cylinder and discovered that the air is passing through the exhaust port. Are there any tricks I could try could try or anything I could put in thecrankcase that might free up a stuck valve or should I just resolve myself to the fact that the head needs to be removed? If I was going to get into that do I then just take the entire motor out......or just part out this beautiful bike.....seems like such a waste, but I already have a running 92!,

[triton28]

Air coming out of the exhaust port, while that cylinder is on the compression stroke, definitely warrants an inspection from within the cylinder head cover at the very least.
It is possible to remove the cover/s with the engine still in the frame as outlined in Chapter 4, section 8, of the MSM, so then you may be able to see what may be going on.
But with the cam clamps, camshaft, cam followers, spring retainer/spring, and stem oil seal in the way it may be hard to take any corrective measures. For instance, if the valve is bent the head has to come off, or if the valve is only stuck, the valve stem oil seal, if working properly, should prevent any fluid from getting down between the stem/guide interface and freeing it up.
Perhaps you may be able to give the cam followers some repetitive tapping/rapping directly over the valve stem with a brass drift and hammer to shock loosen any corrosion holding the valve open, I'm not sure. Here is a pic of what you will find under the cover.
Until you discover what is wrong it is hard to say what course of action one should take: fix or part out. As for myself, I hate parting with anything I buy so I would fix it but YMMV.
Dave

[JHD]

He never mentioned which stroke the cylinder was on. He would really need to test with shop air on different strokes. Test on exhaust stroke will let you know that intake valve is closed/not fully closed and testing on intake stroke will let you know that exhaust valve is closed/not fully closed. Testing the compression/power stroke first would make it impossible to diagnose which valve is leaking. It would seem to me that if he is getting 0 compression reading on that cylinder that it would be through a valve. Maybe rent a scope to have a look in that cylinder and intake. Might have to remove the header and have a look in the exhaust port also.

[cranky]

.. NOT a wrench.... can you put air to the engine, and spin the motor with the starter...
not knowing the motor position, it should at least pulse...

[Jimvoyager01]

Gordon said air is going thru the exhaust port....can you remove the exhaust manifold and see the exhaust valve?????