4 cylinders, 0 compression, help!!

[Guest]

I am stumped on this one. Bought a non-working but clean looking 1980 gs550e with 17K miles on it (had been sitting for at least two years). Two different compression testers showed practically no compression across all cylinders. Two cylinders showed maybe 30 pounds and sea foam treatment or oil made little to no difference.

The strange thing is I can't find anything to explain no compression. The valves look decent besides a little carbon build up. Though I could not test them under pressure, I put pools of solvent in them and they all held their seals. The head gasket was in tact. And the cylinders themselves seem in great shape, they still have visible factory cross hatches. I spot-checked bore size, ring size, and everything is within speck. Valve clearences weren't great, but two of the cyclinders were within range and so shouldn't explain the problem. The timing chain and sprockets were also in the correct position, though I failed to check for tdc when I examined the timing. The only hint of anything is that the piston heads look like the might have been coming in close contact with the valves because in the carbon build-up on the valves and pistons, I could see a slightly polished area in the shape of the valve on piston, and a matching area on the valve. After removing the carbon build-up on the rest of the area though, this disappeared. In other words, if they were making contact, it wasn't hard enough to scuff or damage the valves or pistons.

I am quickly reaching the end of my trouble-shooting. Sorry for the long post but I wanted to be somewhat thorough on own before asking for help. Now, could someone PLEASE HELP ME?

[Billy Ricks]

Are you lifting the slides of the carbs up out of the way when you run the test? With CV carbs the slides don't lift much when cranking. Twisting the throttle won't bring them up.

[Billy Ricks]

Not only do the slides need to be manually raised, the throttle should be opened to get the throttle plates out of the way so the cylinders get a good fill.

[smagnusen]

Thanks for the reply. I did not lift the slides, could it be that simple? sidenote: I thought it was strange that I was getting air blowing out of the carbs when I went to turn it over.

I want to say that I did a test with the carbs off as well but I can't honestly remember.

[smagnusen]

If the slides need to be up to get any compression, it makes me wonder how the bike would ever manage to start normally.

[Billy Ricks]

If the slides need to be up to get any compression, it makes me wonder how the bike would ever manage to start normally.

Properly balanced carbs will let enough air in to fire. Getting the slides up and throttle plates open should help your numbers some, how much is anybody's guess. If for some reason the throttle plates are close fully it's going to hurt your numbers.

[nabrams]

Somthing is very wrong if you're getting numbers below 30 psi, no matter where your slides and throttle are at.
You say the head gasket is intact - how are you so sure? I know that when I had a head gasket leak on my Honda CB750, it was not at all obvious to me till it got really bad. Maybe the nuts that hold the head down are torqued very loose. Did you put your hand all around the head gasket while cranking to see if you feel any air puffing out anywhere?

[nabrams]

Also, does the bike start? If the numbers were really that low it would be nearly impossible to start. maybe you're not doing the readings right?

[smagnusen]

Agreed, I'm not dealing with low compression, I'm dealing with no compression, something is really out of sort. I did feel around the head gasket, checked bolt torques before I took them off, and examined the head gasket after I removed it for any signs of blow out. Everything was in order.

Of course, the bike doesn't begin to start. 0-30 psi is a long way off from the minimum compression needed.

[fgh]

Thanks for the reply. I did not lift the slides, could it be that simple? sidenote: I thought it was strange that I was getting air blowing out of the carbs when I went to turn it over.

I want to say that I did a test with the carbs off as well but I can't honestly remember.

That would indicate that the cams are not timed properly. Check your cam timing again.

[nabrams]

OK, now in order to get compression there has to be some point at which BOTH exhaust and intake valves are fully closed. Maybe the cam chain is on the cam shafts in such a way that this is never happening?
You can eyeball it by rotating the engine with a wrench slowly while the cam cover is off. When the cylinder is on the compression stroke you should NOT feel any air getting past any of the valves for that cylinder. You need to use "feel" rather than "hear" because you may hear air from the other cylinder.
The fact that you were getting contact between cylinder and valves also points to an improperly positioned cam chain (relative to the cam shafts).

[robertbarr]

Has to be cam timing. The question is, how did it get to the condition you found it in? 17k = fairly young.

Since you've pulled the head, the timing evidence is lost. The only thing to do is reassemble, making sure you go through the tensioner as well, and PUT the cam timing where it belongs.

[Nessism]

That would indicate that the cams are not timed properly. Check your cam timing again.

My guess is that you have your cams timed 180 degrees out.

[smagnusen]

I'll certainly be checking the timing when I reassemble. Though the sprockets and chain up top were correct, I failed to check the pistion positions. If that is the problem, I would be really curious to know how it got that way. Those chains are tight and skipping a link or more would be tough. Still scratching my head to think of anything else to check before reassembly...

Thanks again for everyone's help so far. This sight is such a fantastic resource. p.s. would it be unacceptable to temporarily reuse the gaskets? The idea being to replace the gaskets if and when I actually get the bike started. I figure I could spray some soapy water around the head gasket to check for leaks.

[Dave8338]

Thanks for the reply. I did not lift the slides, could it be that simple? sidenote: I thought it was strange that I was getting air blowing out of the carbs when I went to turn it over.

I want to say that I did a test with the carbs off as well but I can't honestly remember.

Sounds like you cams are 180 degrees out of time...trying to compress on an intake stroke will blow air out the carbs for sure. :shock: