No compression! What now?

[Macmatic]

I'm trying to get my '84 GS750EF on the road, it's been in dry storage for the last two plus years...but I didn't know how dry! The previous owner drained the oil so now, among other things, the clutch is stuck.

I've also been trying to get the rings in #1 unstuck, at least I hope its just rings. Compression is #1 0(Zero), #2 130psi #3 135psi #4 145psi and blowing smoke out of the left side pipe.

At this point I'm thinking of pulling the head and cylinders, cleaning the combustion chambers, lapping the valves, checking the bores and pistons, massaging the rings back into freedom (if not busted) and putting it back together.

I THINK, if I only have stuck rings and not broken ones, I might be able to get out of this with just cam cover, head and base gaskets?

As another option I have a 2nd parts bike with good compression all the way across but ratty looking head and cyls. (Some corrosion). Since I'm on a serious budget here what about swapping the pistons and cyls from one case to the other?

Thanks!
/\/\ac

[Anonymous]

0 psi is awful low, even with stuck or broke rings, you should have some compression. Did you check to see the piston still connected to the crankshaft & is moving up & down

[Macmatic]

0 psi is awful low, even with stuck or broke rings, you should have some compression. Did you check to see the piston still connected to the crankshaft & is moving up & down

Yep. Before I did anything else I put in oil and a filter and gave it a little oil in each cyl and cranked in around by hand quite a bit to try and get some oil moving. I also looked down all the plug holes to look at the bores as best I could so I know the piston is moving.
I could see SOME compression, just not enough to stay on the gauge. I think it was bumping up to about 10-15psi but it was hard to watch it whole using all three hands to work the throttle, clutch, starter and gauge. I have to hold the gauge in the plug hole as my threaded compression tester doen't have small enough threads. I tried about three times on #1, and #'s 1 and 4 are the easiest to hold the rubber cone of the tester in.

/\/\ac



Also, I've had it running and it didn't sound like the crank was beating the snot out of anything. Didn't sound like it was even missing really.

[jtcrespo]

I may be way off base, but could you have a "holed" piston?

[duaneage]

Couple of things.

Broken valve? Is there air being forced out the carb on the dead cylinder? Is the cylinder draving air?

A broken valve spring will allow one valve to remain open. A broken intake valve or intake spring will allow induction but not compression.

Conversely a broken exhaust valve or broken exhaust spring will not allow induction because it will pull air from the exhaust pipe ( at least it will not pull very much if it does) instead of the carb.

I think you have a valve stuck open. A mere 1/16 of an inch is all it takes to drop the compression.

[gspaul]

If the comp gauge has not got the right thread you won't get the right reading,It has to leak,I think that's why you have 0 comp.
I have a comp gauge for car, so it was the wrong thread for my bike.
Got an old spark plug,bashed the guts out of it,tapped a thread to match.
One cheap adaptor.

[duaneage]

If the comp gauge has not got the right thread you won't get the right reading,It has to leak,I think that's why you have 0 comp.
I have a comp gauge for car, so it was the wrong thread for my bike.
Got an old spark plug,bashed the guts out of it,tapped a thread to match.
One cheap adaptor.

Why did he get 140 on the other three cylinders?

[Anonymous]

drain the engine oil, go buy some sea foam, remove the spark plugs and fill all the chambers up with it. let it sit over nite and turn it over without the plugs in, put a rag or something to reduce the mess.

[Anonymous]

I would bet that it is nothing more than a stuck valve. The engine probably sat with that valve open all that time and now its stuck. One should be able to loosen it by taking the valve cover off and locating the stuck valve. You already know which cylinder it is. With care, it can then be exercised back into action remembering to oil the stem as you go.

[duaneage]

I would bet that it is nothing more than a stuck valve.


Exactly.

Varnish from old gas is on the stem holding the valve open. I bet it is an intake valve. Shoot some lacquer thinner through the intake port to soften the crud up and if that fails give it a tug from up top by removing the valve cover and tugging on the retainer.

[Macmatic]

Thanks for all the ideas!

To update: Just before I left for the evening I put about 1tbsp of oil in the #1 (no compression) cyl and did another compression check. This time It quickly peaked at 40psi and dropped off as the oil got pushed out.

I know its not a holed piston as I looked in all the bores as best I could before even turning it over by hand and #'s 1 and 4 are pretty easy to see down. The piston face looks pretty good for 34k/Km.

I've got TWO compression testers, one is a screw in type with two threads and the other has a rubber cone you have to hold in the hole against compression, its a little hard on the two inner cyls but works well enough.

First order of the day tomorrow is to rig a leak down tester to try and figure out where the air is going.

Thanks again, I'll review this in the morning and get back at it!

/\/\ac Zzzzzzz

[Macmatic]

Can I swap the Cyls and pistons?

OK.... I rigged a way to pressureize the #1 cyl with compressed air and STILL can't really tell where all that air is going! I can blow into it with my lungs and it doesn't even have that much resistance. I can't really feel/hear anything at the intake or the exhaust so it must be the rings but I can't feel/hear anything at the oil filler either.

Now that I've got the cam cover off I can see that the exhaust cam looks not so great. Blueing on #1, a streak of dark that I can't feel on #2 and 3&4 look better but not really healtthy. The intake looks fine all the way across.

So I did a compression check on the bike that's supposed to be all parts...and it gives me 145/150/155/150. This is after turning it over by hand a few times and then spinning on the starter to move some oil around and then just testing everything cold, no added oil or anything.

So now my question goes back to the first post in this thread:

Can I swap everything above the case from the good engine to the other? maybe its getting pointless as the reason I want to keep the engine in the EF is cosmetic....it'll take a LOT of elbow grease to get the ES engine looking as good...on the outside.

But is I wanted to is there any reason not to swap the cyls and head over along with the pistons and use them on the rods from the engine that has bad compression now? At this point I'm ready to buy the full gasket set and crack the EF case open to see what other damage as been done....and I'm curious as hell about where all the compression in #1 is going....

Thanks for the input...if you need me I'll be out on the mower with a frosty beverage thinking this over.

/\/\ac

[Anonymous]

If you have acess to compressed air, blow it into the plug hole and then see where it is going. Also, if it is a stuck valve, one should be able to find it with a set of feeler guages. The stuck valve wont close as far and will show up as a much larger gap which now that I think of it brings up the possability of the valves on that cylinder being set wrong, that would be too tight.

[SqDancerLynn1]

Question is Have you checked the valve clearance???? If the clearances are ok I would remove the head & do a solvent test to see if the valves
are sealing You may just need to replace a valve or two & the cam

[Macmatic]

Question is Have you checked the valve clearance???? If the clearances are ok I would remove the head & do a solvent test to see if the valves
are sealing You may just need to replace a valve or two & the cam

Hey Lynn,

Forgot to mention that, I did check the valce clearence. Only on the low (zero) cylinder but it was right on at .004 to .0045 on both thte intake and exhause.

I'm pulling the engine at the moment.

/\/\ac