- Joined
- Feb 14, 2015
- Messages
- 28
I am rebuilding my 1971 commando from the ground up. Right now, I have the forks and front wheel assembled to the frame. I bought new adjustable isolastic assemblies. I wanted the front one to be the assembly which requires no modification to the motor mount (part number 067337 I believe). I got the later version (067116). I installed the rear isolastic assembly. The assembly was a tight fit even when set at zero clearance. I spread the frame lugs slightly with a threaded rod to get it in. After setting the clearance to .010”, I noted that the clearance was not uniform around the entire collar. Minor issues. I may be able to improve both problems with a little precision filing. After mocking up the front iso unit using the crankcases, some issues became apparent.
1) The “stack” height of the new fixed collar and end cap is .140” greater than that of the original pieces. This does not include the lip of the end cap which fits over the tube. It is clear that if installed as is, the front of the engine would be moved over. The solution would be to remove material from the fixed collar end of the tube. How much must be determined by measuring the space available.
2) The adjustable collar on is a loose fit on the bolt through the frame lugs. The bolt is .500” and the inside diameter of the iso tube is .530”. The fixed collar has a sliding fit on the bolt. This means that the only thing stopping the adjustable collar from moving on the frame lug is friction created by the clamping force of the bolt. If this friction is overcome by the force required to compress the rubber, then the collar will move around on the lug. The only way to know is to completely assemble the bike and run it. Seems like a bad idea. This was discussed here: isolastic-conversion-kit-t5378.html
I don’t know if the isolastic unit designed for the earlier front tube will resolve these problems. It seems like the best solution is to mock up the entire assembly with the crankcases and cut the front tube to allow the space between the tube and the frame lugs to equal the stack height of the end caps and collars. In other words, make the front iso tube to fit my particular frame.
1) The “stack” height of the new fixed collar and end cap is .140” greater than that of the original pieces. This does not include the lip of the end cap which fits over the tube. It is clear that if installed as is, the front of the engine would be moved over. The solution would be to remove material from the fixed collar end of the tube. How much must be determined by measuring the space available.
2) The adjustable collar on is a loose fit on the bolt through the frame lugs. The bolt is .500” and the inside diameter of the iso tube is .530”. The fixed collar has a sliding fit on the bolt. This means that the only thing stopping the adjustable collar from moving on the frame lug is friction created by the clamping force of the bolt. If this friction is overcome by the force required to compress the rubber, then the collar will move around on the lug. The only way to know is to completely assemble the bike and run it. Seems like a bad idea. This was discussed here: isolastic-conversion-kit-t5378.html
I don’t know if the isolastic unit designed for the earlier front tube will resolve these problems. It seems like the best solution is to mock up the entire assembly with the crankcases and cut the front tube to allow the space between the tube and the frame lugs to equal the stack height of the end caps and collars. In other words, make the front iso tube to fit my particular frame.
