Isolastic Shimming Tips?

Hello!


Can anyone recommend any tips on shimming a 1970 commando. The rubber is good. Fairly new, It currently measures at about 20thousand and I'd like to get it to somewhere between 8-10k.

I've never done this before - Don't really know how to exactly, so any thoughts or tips from someone who's been down this road would be very helpful and appreciated.

Thanks!

Brian

A manual would help but here goes....
Since it's a 70 you can do this on the main stand. Support the engine with a jack - Remove the main ISO bolt - Slide out the ISO end caps, gaiters and PTFE washers - Remove the shim carriers and shims - Clean the parts - Grease all the contact points (silcone is good, some use plumbers grease) and rebuild with an extra 005" shim either side if you are sure you have 020" play. Torque the nut to 25lbs/ft.
You can do the front off the bike in a vice using spacers to replicate the frame tabs. The whole mount slides downwards after removing the end caps and all three bolts. The rear is a bit more difficult and is sometimes hard to slide out the end caps.
To check the actual play you need to lever the engine over to the one side and measure clearance on opposite side. The reading could/will vary depending how much force you use. An assistant here would help.

You mentioned that he can do this on the center stand because he has a 1970 Commando. Any different advice for somebody attempting his first Iso adjustment on a 1974 850?

Thanks So much for the breakdown.

I'm unclear on a few things....

You wrote:
"You can do the front off the bike in a vice using spacers to replicate the frame tab"- I'm not sure what you mean exactly. Are you saying to put it in a vice after you shim it and get it correct, then throw it on the frame? Wouldn't the adjustment change after I take it out of the vice?

and
"To check the actual play you need to lever the engine over to the one side and measure clearance on opposite side" - What is the best method to do this?

Thanks so much!!

To add to Keith's post, your flexible washers may not be PTFE on a '70. If not they are probably shot or completely disintegrated. I would not reuse the old-style polyethylene if there is any sign of wear, but would spring for new PTFE type.

PalmerNorton said:

"To check the actual play you need to lever the engine over to the one side and measure clearance on opposite side" - What is the best method to do this?

Thanks so much!!

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I've used a chunk of wood and you can wedge it in to move the engine over. You're only moving it a very small distance.

Anybody have a photo of this procedure (i.e., the wedging of the motor or the measurement of the gap)? I actually laughed out loud when I read in the Clymer that the first step in adjusting these Isolastics is SHOVING the motor in the frame. The mystique of the British motorcycle, indeed!

"You can do the front off the bike in a vice using spacers to replicate the frame tab"- I'm not sure what you mean exactly. Are you saying to put it in a vice after you shim it and get it correct, then throw it on the frame? Wouldn't the adjustment change after I take it out of the vice?

Click to expand...

Sorry that was confusing, I meant use the vice clamped on a side plate, then build up assy with extra shims and all parts except gaiters and torque to 25ft/lbs. Spacers are usually needed cos' the nuts can bottom out on the main bolt threads. The adjustment/reading can also change when you assemble to the frame because there are loads with the engine attached that can cock the end caps and give different readings top to bottom and front to rear and in almost any other position round the clock you can think of. The frame tabs are not always parallel to each other nor square to the ISO. Same goes for the rear which can affect the front alignment. At least you know if it's correct off the bike you have the right theoretical clearance. But if you've got consistent 020" readings in several positions do it in the frame, you have to with the rear anyway............good luck.

You mentioned that he can do this on the center stand because he has a 1970 Commando. Any different advice for somebody attempting his first Iso adjustment on a 1974 850?

Click to expand...

The major difference is that the mainstand comes off the ISO cradle, not the frame so you have to support the lower rails on blocks to take the load off the rubbers. That's what the manual tells you but then the engine/gearbox/swingarm assy/rear wheel etc is loading the rubbers. I support the rails and jack up the engine enough so the rubbers are unloaded vertically. It may not be that important, just my way really.
You could write a whole book about getting these pieces perfectly square, matched front to rear for offset etc (someone did & here is the link http://vintagenet.us/phantom/wsc.html) so I think you just have to do the best you can and find a clearance that you are happy with on the road. I went down part of that road getting offsets same front and back, squaring up the ISO tube faces and it made a difference but I didn't do all the hole repositioning that guy did.