1963 G80CS Top End Woes
Posted: Sun Jun 11, 2017 1:33 pm
Hello folks. Motor exhibited a rattle at low revs under load, so I thought it best to have a look inside. Good job I did. A myriad of problems & questions have arisen. Starting from the top:- Valve side Rocker arm ends a bit worn, a step formed on the inlet side. Don't seem to be able to find replacements with AMOC Spares or elsewhere.
Surprised to find coil valve springs fitted. Thought it would have hairpins. Not a real issue, but the inlet valve bottom collar appears to be sitting on the valve retaining circlip & is slightly askew. I presume it should really sit over the circlip & seat on the head, as the exhaust collar seems to do?
Piston, appears a bit sloppy in the bore. No real step or wear apparent in bore though. Measurements to be taken by a professional tomorrow, but I found ring gaps are over .030 thou so they are scrap.
Now for the real problem.
Gudgeon pin appeared stiff in the little end bush but loose in the piston bosses. I removed the circlips but the pin refused to move out, even with piston heated with a blowtorch. It appears a small burr had formed on both ends of the circlip grooves, more so on one side. I tapped it gently out of the lesser burred side. Little end bush appears scored/galled. Gudgeon pin is a tight push fit in the bush. Certainly not a running fit & will require reaming. The little end bush oil hole is at five o'clock, completely out of line with the top oil hole. I am unsure as to whether the bush has seized & moved in the rod, or just been fitted incorrectly by a goon. The piston (large domed HC type) also shows signs of running on the tilt, with a polished bottom edge on the nearside skirt & at the top edge of the crown on the offside. I would say that the only movement in the little end was in the piston bosses. I can push the pin back into the piston by hand, but as soon as it passes the circlip groove it suddenly loosens & is quite free to slop from side to side between the circlip grooves. Scrap piston too I think. Hope the rod is not bent.
There was no base gasket fitted, just blue Hylomar. No bottom seals on pushrod tunnels. I assume the two thinner O-rings in my gasket set are supposed to go over the tappet bosses at the barrel base?
That's all for now. Apart from the rattle, the bike went very well before all this. All advice gratefully received. TTFN Jack
Surprised to find coil valve springs fitted. Thought it would have hairpins. Not a real issue, but the inlet valve bottom collar appears to be sitting on the valve retaining circlip & is slightly askew. I presume it should really sit over the circlip & seat on the head, as the exhaust collar seems to do?
Piston, appears a bit sloppy in the bore. No real step or wear apparent in bore though. Measurements to be taken by a professional tomorrow, but I found ring gaps are over .030 thou so they are scrap.
Now for the real problem.
Gudgeon pin appeared stiff in the little end bush but loose in the piston bosses. I removed the circlips but the pin refused to move out, even with piston heated with a blowtorch. It appears a small burr had formed on both ends of the circlip grooves, more so on one side. I tapped it gently out of the lesser burred side. Little end bush appears scored/galled. Gudgeon pin is a tight push fit in the bush. Certainly not a running fit & will require reaming. The little end bush oil hole is at five o'clock, completely out of line with the top oil hole. I am unsure as to whether the bush has seized & moved in the rod, or just been fitted incorrectly by a goon. The piston (large domed HC type) also shows signs of running on the tilt, with a polished bottom edge on the nearside skirt & at the top edge of the crown on the offside. I would say that the only movement in the little end was in the piston bosses. I can push the pin back into the piston by hand, but as soon as it passes the circlip groove it suddenly loosens & is quite free to slop from side to side between the circlip grooves. Scrap piston too I think. Hope the rod is not bent.
There was no base gasket fitted, just blue Hylomar. No bottom seals on pushrod tunnels. I assume the two thinner O-rings in my gasket set are supposed to go over the tappet bosses at the barrel base?
That's all for now. Apart from the rattle, the bike went very well before all this. All advice gratefully received. TTFN Jack