Lama
XS650 Member
Hi all, I would really appreciate any of your thoughts on why my XS650 has twice broken the double row ball bearing that is on the gearbox input shaft, behind the clutch basket.
First some history: I bought this bike in 1993 with about 20 000 miles on the clock, (it was registered in 1981 and had 6 former owners).
In 1995 I discovered some broken clutch shock absorber springs. I had Halco Tuning fit their conversion (3 new springs and 3 plastic spacers)
In 1997, now with 34 000 miles the engine was vibrating so badly that I had the engine overhauled and this including the crank being overhauled and was re-bored to 2nd oversize. A year later I found that one of pillars of the clutch boss was cracked and replaced just this part of the clutch.
In 1998 I fitted a Boyer Branson electronic ignition system, the type that also does away with the auto advance mechanism.
In 2003 (48 500 miles) while crossing France the engine nipped up. Once the bike was recovered back to England, my local XS650 specialist (LPS in Wiltshire) stripped the engine and found that the gearbox input shaft bearing’s outer race had broken up and some fragments has circulated around the engine and damaged the bores. At this time they were unable to obtain a new replacement for this double ball bearing and so they used a carefully examined second hand one when they rebuilt the engine again.
This time it was over bored to accept modified J.E pistons to take it to about 710cc, 10:1 CR and kawasaki GPZ500S carburettors (EX500 in USA) were fitted. I had the carb jetting set up on a rolling road dyno and showed 53bHp at the rear wheel but would only run on one cylinder at tick over, it was very tricky to start and would kick back. (The electric start and its gears had been removed during this last rebuild). I spent a lot of time trying to sort these second hand carbs out and looking for air leaks and dealing with some electrical issues.
Eventually I bought another second hand set of GPZ500S carbs and swapped the jets and needle shims. Now it started easily and ticked over well but only made 23 bHp.
I was riding the bike, trying to sort out the carb issues until, with about 55 000 miles the clutch behaviour felt wrong (I can’t remember the detail now) so I took the clutch off and found the bearing behind it had cracks in its outer race. Fortunately all the bits were still held in place but I was very concerned that this had happened again!
Other things probably not connected to this problem but I will mention it it case it:
Sometime after the second engine rebuild I noticed that with the engine running and in gear and the clutch pulled in, I could only paddle the bike backwards a few inches before something locked up and stopped it going back further. If I then turned the ignition off it rolled back easily.
Also, I was revving the engine to the red line while riding, and later was told by the operator of the rolling road dyno that the bike’s tacho was very slow to rise above 6 000 rpm. I wonder if I was actually going way past the red line and this could have caused harm.
At this time I put the bike to one side, wondering what to do until I was told about someone who modified XS650 engines for sidecar motor-cross and I took the engine to him for examination. He told me that none of his many 880cc (I think) conversion race engines had ever had a problem with this bearing. He spent some hours looking for an underlying problem but didn’t find one, so fitted all new bearings to both gearbox shafts (the double race bearing had now become available again) and bolted the crank cases back together.
I have recently put the engine back in the frame but haven’t fitted carbs yet. I would have liked an explanation for this repeated failure. On one hand I feel that if it fails a third time I will be kicking myself and asking ‘What did I realistically expect!’, but I would also like to have the bike back on the road this summer.
On line searches have not found this to be a common problem, has anyone else experienced it?
Does anyone have any suggestions?
Thanks
First some history: I bought this bike in 1993 with about 20 000 miles on the clock, (it was registered in 1981 and had 6 former owners).
In 1995 I discovered some broken clutch shock absorber springs. I had Halco Tuning fit their conversion (3 new springs and 3 plastic spacers)
In 1997, now with 34 000 miles the engine was vibrating so badly that I had the engine overhauled and this including the crank being overhauled and was re-bored to 2nd oversize. A year later I found that one of pillars of the clutch boss was cracked and replaced just this part of the clutch.
In 1998 I fitted a Boyer Branson electronic ignition system, the type that also does away with the auto advance mechanism.
In 2003 (48 500 miles) while crossing France the engine nipped up. Once the bike was recovered back to England, my local XS650 specialist (LPS in Wiltshire) stripped the engine and found that the gearbox input shaft bearing’s outer race had broken up and some fragments has circulated around the engine and damaged the bores. At this time they were unable to obtain a new replacement for this double ball bearing and so they used a carefully examined second hand one when they rebuilt the engine again.
This time it was over bored to accept modified J.E pistons to take it to about 710cc, 10:1 CR and kawasaki GPZ500S carburettors (EX500 in USA) were fitted. I had the carb jetting set up on a rolling road dyno and showed 53bHp at the rear wheel but would only run on one cylinder at tick over, it was very tricky to start and would kick back. (The electric start and its gears had been removed during this last rebuild). I spent a lot of time trying to sort these second hand carbs out and looking for air leaks and dealing with some electrical issues.
Eventually I bought another second hand set of GPZ500S carbs and swapped the jets and needle shims. Now it started easily and ticked over well but only made 23 bHp.
I was riding the bike, trying to sort out the carb issues until, with about 55 000 miles the clutch behaviour felt wrong (I can’t remember the detail now) so I took the clutch off and found the bearing behind it had cracks in its outer race. Fortunately all the bits were still held in place but I was very concerned that this had happened again!
Other things probably not connected to this problem but I will mention it it case it:
Sometime after the second engine rebuild I noticed that with the engine running and in gear and the clutch pulled in, I could only paddle the bike backwards a few inches before something locked up and stopped it going back further. If I then turned the ignition off it rolled back easily.
Also, I was revving the engine to the red line while riding, and later was told by the operator of the rolling road dyno that the bike’s tacho was very slow to rise above 6 000 rpm. I wonder if I was actually going way past the red line and this could have caused harm.
At this time I put the bike to one side, wondering what to do until I was told about someone who modified XS650 engines for sidecar motor-cross and I took the engine to him for examination. He told me that none of his many 880cc (I think) conversion race engines had ever had a problem with this bearing. He spent some hours looking for an underlying problem but didn’t find one, so fitted all new bearings to both gearbox shafts (the double race bearing had now become available again) and bolted the crank cases back together.
I have recently put the engine back in the frame but haven’t fitted carbs yet. I would have liked an explanation for this repeated failure. On one hand I feel that if it fails a third time I will be kicking myself and asking ‘What did I realistically expect!’, but I would also like to have the bike back on the road this summer.
On line searches have not found this to be a common problem, has anyone else experienced it?
Does anyone have any suggestions?
Thanks