Date: Wed, 29 Jul 1998 11:48:40 +0000
From: Eric Goforth
The last time that I removed my front Isolastic mount to shim it, I also noticed that the clearances were very uneven. I decided to have the ends of the tube machined parallel at a local machine shop. The machinist checked the tube in several places and found that the maximum variation in the length of the tube was like one or two thousands. This was puzzling since the variation in clearance was something like eight thousands. After looking at the mount I realised that this was due to the outer, main bushes not being perfectly square in the tube. Since these bushes locate the throughbolt, they locate the outer collars. So the problem in uneven clearances was that the collars were not square, the endcaps were square.
After working with the bushes I was able to get the clearance variation reduced, but figured that the factory tool might the ticket for getting these perfectly square in the tube. I call Phil Radford at Fair Spares and told him what I had discovered and asked him what he thought about the factory tool. While he didn't really knock the factory tool, he said that what he did to get these square and also to get the clearances equal on each side was to fully assemble the mount and torque it down as though you were going to check the clearances off the bike. Then clamp the mount in a vice and turn the through bolt.
When the through bolt is torqued down the a shoulder on the collar presses against the pressed in sleeve on the bush which presses against the spacer tube. So what you have is metal-to-metal contact all the way through the mount. So if you've lubed the bushes with silicone grease they will turn when you turn the throughbolt. I had the mount back on the bike when I was told this but I plan on trying it the next time that I take it off. I'd imagine that the clearances should be uniform after two or three revolutions of the bush.