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I have just split the crank cases on my ’27 J. The cases are in good shape overall.
When I came to inspect the flywheels however I could see the damage shown in the attached photos. Looks as though the con rod may have broken at some time by the marks / crack. Having used a small mirror I can see the crack does not extend the full width of the rim but its pretty bad
My first question is whether this flywheel is usable or repairable or whether I need to find a replacement? If I need a replacement do I need to just one or would it be better to find a pair ?
I have no experience of how durable the flywheels might be. All I can say it that the motor was running when I got the bike albeit not doing many road miles.
The sprocket shaft measures at 0.997.5 / 0.998. My book says replace if its worn more than 0.001. Pinion shaft is 0.935. So it looks as though both shafts are worn about 0.002
The sprocket shaft was quite tight on the bearings though. The rollers measure at .250 but I’m not sure my mic is accurate enough to detect if they are oversize. Could well be .0001 oversize which might account for the tight fit.
The connecting rods are in good shape and there is only slight discernible lateral movement in the female rod , less still in the male and no movement in either up and down. My guess is that the crank shaft bearings/bushes and con rods were replaced after the damage was done to the flywheel.
My second question is about replacing the sprocket and pinion shafts. Can I safely use what I have or are they actually worn out? I want the engine to run as well as possible.
I cannot imagine I will find an OEM set that are in better shape that what I have. I see repro sets available – I would welcome hearing from anybody who has rebuilt the bottom end using repro parts. What are the pitfalls, things to look out for.
Thanks for your help
Martin
in the uk
I have just split the crank cases on my ’27 J. The cases are in good shape overall.
When I came to inspect the flywheels however I could see the damage shown in the attached photos. Looks as though the con rod may have broken at some time by the marks / crack. Having used a small mirror I can see the crack does not extend the full width of the rim but its pretty bad
My first question is whether this flywheel is usable or repairable or whether I need to find a replacement? If I need a replacement do I need to just one or would it be better to find a pair ?
I have no experience of how durable the flywheels might be. All I can say it that the motor was running when I got the bike albeit not doing many road miles.
The sprocket shaft measures at 0.997.5 / 0.998. My book says replace if its worn more than 0.001. Pinion shaft is 0.935. So it looks as though both shafts are worn about 0.002
The sprocket shaft was quite tight on the bearings though. The rollers measure at .250 but I’m not sure my mic is accurate enough to detect if they are oversize. Could well be .0001 oversize which might account for the tight fit.
The connecting rods are in good shape and there is only slight discernible lateral movement in the female rod , less still in the male and no movement in either up and down. My guess is that the crank shaft bearings/bushes and con rods were replaced after the damage was done to the flywheel.
My second question is about replacing the sprocket and pinion shafts. Can I safely use what I have or are they actually worn out? I want the engine to run as well as possible.
I cannot imagine I will find an OEM set that are in better shape that what I have. I see repro sets available – I would welcome hearing from anybody who has rebuilt the bottom end using repro parts. What are the pitfalls, things to look out for.
Thanks for your help
Martin
in the uk
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