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Ok so I recently finished rebuilding a 1978 GS400 I bought as a pile of parts for 100 bucks. If you're interested in seeing my journey and banging your head against the keyboard in rage, I'll be posting the album soon!
Everything seemed to be going well and I managed to put a couple hundred miles on it with only a few hiccups, most of which were my fault.
But I noticed as I started paying attention more that there was a definite noise coming from the engine. At first it seemed like it was coming from the top end so I did all the regular checks. Tappet shim clearances were within spec, cams looked good, no obvious problems there. Once I got the bike back running after I changed the valve cover gasket I decided to give everything a close listen with the old "screwdriver in the ear" trick and started poking around. When I put the screwdriver against the crankcase, right about where the clutch is, the noise was incredibly loud. Not quite a hollow knock, more of a tapping with some scraping or grinding. I checked all the clutch adjustments, everything was right, and the noise didn't really change regardless of the position of the clutch or whether or not it was in gear. It does seem to get quieter when revving but that might just be the sound of the engine overpowering whatever is making the noise. I have a couple videos of the sound but unfortunately they're mostly focused on the top end of the engine because this was when I was still convinced that was the location of the issue.
So because I'm incredibly paranoid and the thought of blowing up this engine scares me to death, and because I'm not afraid of a rebuild for the experience, I decided to pull it in for the season and start tearing it down until I find a problem. So far everything has come apart with very little fuss aside from some stripped JIS screws, but I'll be replacing all the case screws anyway. But I finally hit a roadblock, and it's the cylinder itself. The head came off fine, and I've removed every bolt I can find, but no matter what I do the cylinder won't budge. I've tapped it from every angle, I've heated the gasket up, I've even put a couple bolts in the holes on top and tried a slide hammer. Nothing.
There has to be something holding this cylinder on. The only thing I have found is a nut inside the camchain tunnel, but the problem is the nut is not exposed enough to get a socket on and there's no way you're getting a wrench in there. I also am not sure it needs to be removed and don't want to risk dropping it in the crankcase if it doesn't even need to come out.
Has anyone had this problem? Please tell me I'm just a moron and I'm missing something obvious. I don't mind being stupid if it means an easy solution.
Side note: Those two holes on the ends of the cylinders are threaded like bolts are supposed to go there, and the manuals mentions 6mm bolts in this location that are supposed to go through the head, but my head does not have holes through the top. There are bushings and shallow holes in the head that mate to these holes but the head does not have holes all the way through. I assume this was something added to the later models, but I thought I'd mention it in case it matters.
Videos of sound:
Picture of nut:
Picture of current status:
Everything seemed to be going well and I managed to put a couple hundred miles on it with only a few hiccups, most of which were my fault.
But I noticed as I started paying attention more that there was a definite noise coming from the engine. At first it seemed like it was coming from the top end so I did all the regular checks. Tappet shim clearances were within spec, cams looked good, no obvious problems there. Once I got the bike back running after I changed the valve cover gasket I decided to give everything a close listen with the old "screwdriver in the ear" trick and started poking around. When I put the screwdriver against the crankcase, right about where the clutch is, the noise was incredibly loud. Not quite a hollow knock, more of a tapping with some scraping or grinding. I checked all the clutch adjustments, everything was right, and the noise didn't really change regardless of the position of the clutch or whether or not it was in gear. It does seem to get quieter when revving but that might just be the sound of the engine overpowering whatever is making the noise. I have a couple videos of the sound but unfortunately they're mostly focused on the top end of the engine because this was when I was still convinced that was the location of the issue.
So because I'm incredibly paranoid and the thought of blowing up this engine scares me to death, and because I'm not afraid of a rebuild for the experience, I decided to pull it in for the season and start tearing it down until I find a problem. So far everything has come apart with very little fuss aside from some stripped JIS screws, but I'll be replacing all the case screws anyway. But I finally hit a roadblock, and it's the cylinder itself. The head came off fine, and I've removed every bolt I can find, but no matter what I do the cylinder won't budge. I've tapped it from every angle, I've heated the gasket up, I've even put a couple bolts in the holes on top and tried a slide hammer. Nothing.
There has to be something holding this cylinder on. The only thing I have found is a nut inside the camchain tunnel, but the problem is the nut is not exposed enough to get a socket on and there's no way you're getting a wrench in there. I also am not sure it needs to be removed and don't want to risk dropping it in the crankcase if it doesn't even need to come out.
Has anyone had this problem? Please tell me I'm just a moron and I'm missing something obvious. I don't mind being stupid if it means an easy solution.
Side note: Those two holes on the ends of the cylinders are threaded like bolts are supposed to go there, and the manuals mentions 6mm bolts in this location that are supposed to go through the head, but my head does not have holes through the top. There are bushings and shallow holes in the head that mate to these holes but the head does not have holes all the way through. I assume this was something added to the later models, but I thought I'd mention it in case it matters.
Videos of sound:
Picture of nut:
Picture of current status:
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