Clearance between ISO adjusters and frame lugs

Today I did a trial fit of the front engine mount to the frame together with cradle and encountered some problems.

My 72/73 Combat is using vernier type adjusters front and rear together with nylon washers. I don't the make of the kit although I suspect its RGM.

First problem is that the mounts are very tight in the frame lugs, even with the adjusters screwed in fully. I have sanded off the powder coat from the lugs but the ISM adjusters are still tight especially the front.

I do have a mini lathe so could skim a small amount from the ISO adjusters, but which side should I machine, both sides or just one? How much clearance should there be between frame lugs and ISO adjusters with the half inch turn adjustment?

My other problem on the front mount is that central shaft with the rubbers mounted is offset on one side by about 2mm . On this mount I'm reusing the rubbers as they appear to be in good condition and have "RGM" marked on them. Is this OK or should I fit new rubbers?



All info welcome

gunnag said:

I do have a mini lathe so could skim a small amount from the ISO adjusters, but which side should I machine, both sides or just one?

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I doubt it matters too much as the frame/rolling chassis probably wasn't made to that level of accuracy in the first place, and if it was, it probably won't be now.

gunnag said:

How much clearance should there be between frame lugs and ISO adjusters with the half inch turn adjustment?

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None. When the Iso. assembly is tightened, the internal tube, adjuster and fixed abutment should be 'locked solid' between the frame lugs.

I suggest you go by feeler gauge clearance rather than turning the adjuster a set distance as the clearance tends to reduce as the assembly (front through bolt and rear stud) is tightened, so check the clearance in stages as you tighten (to 25 lbs ft). The RGM instructions to "back off the adjuster by 1.5 holes" or "half a turn" - Norvil instructions) is not guaranteed to give "the required 0.006" clearance" in my opinion.

gunnag said:

My other problem on the front mount is that central shaft with the rubbers mounted is offset on one side by about 2mm. On this mount I'm reusing the rubbers as they appear to be in good condition and have "RGM" marked on them. Is this OK or should I fit new rubbers?

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Can't you move the shaft/tube over 2mm?
I notice you have the front adjuster on the 'wrong' side, not that it matters too much with the pre-Mk3 conversion kit it doesn't matter as far as alignment is concerned (although some may think it does).

http://www.rgmnorton.co.uk/csi/1245184/ ... ctions.pdf

http://www.norvilmotorcycle.co.uk/techtalk04.htm

Thanks LAB,

I think I will go in steps on my lathe taking a small amount from the adjusters on each side until I get a loose sliding fit.

I see what you mean about using feeler gauges to check the adjustment in stages whilst tightening the studs, so will do it this way.

Regarding the offset front rubber, I can push the mounting tube back so that its central in the bore, however the rubber seems to have a memory and springs back. I expect the rubber has become mishapen from its previous use but was hoping it would re adjust itself when I fit the mounts to the engine & frame and tighten the bolts.

And well spotted about fitting the adjusters on the wrong side, I will swap them over.

gunnag said:

Regarding the offset front rubber, I can push the mounting tube back so that its central in the bore, however the rubber seems to have a memory and springs back. I expect the rubber has become mishapen from its previous use but was hoping it would re adjust itself when I fit the mounts to the engine & frame and tighten the bolts.

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It sounds like you need to move the rubbers not just push on the tube.

Actually, what might be best would be to pull the complete set of rubbers from the mounting and see what condition they are in. The look newish from the outside and maybe just need reassembling.

I guess the best way to pull them out would be to use theold method of a threaded rod and a large socket over one end of the mounting tube.

gunnag said:

Actually, what might be best would be to pull the complete set of rubbers from the mounting and see what condition they are in. The look newish from the outside and maybe just need reassembling.

I guess the best way to pull them out would be to use theold method of a threaded rod and a large socket over one end of the mounting tube.

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The outer rubbers should be reasonably tight inside the tube (if they are still any good). A suitable lubricant should help with removal (and replacement).

Don't remove material from the adjusters!

Just take a length of allthread rod a few inches longer than the rear mount, set up a nut a few inches apart in the middle, then some 1" o.d. washers, than slip it into the front mount and screw the nuts apart 'till you spread the mounts about 1/4" wider than they need to be. When you release the tension, they will spring back to near the proper width. Repeat, as it probably will be just short of enough. Get it to where there is JUST available clearance.

Repeat in the rear.

What is the length of the mounts and adjusters ( minus shims) when the collars are fully tightened. It is certainly possible the adjusters are made wrong, but it is just as likely that the frame loops are bent in a little.

Greg

I have now managed to get the front ISO mount to fit by shaving about 0.5mm from each adjuster, I also removed, inspected and refitted the ISO rubbers with red grease, they seemed in good condition and are now centralised in the mounting bore.



I wish I had read your post earlier GrandPaul and was thinking about prising the lugs apart, however as the frame was recently aligned, I figured the mounts should have the correct width so it would be better to shave the adjusters.

grandpaul said:

Don't remove material from the adjusters!

Just take a length of allthread rod a few inches longer than the rear mount, set up a nut a few inches apart in the middle, then some 1" o.d. washers, than slip it into the front mount and screw the nuts apart 'till you spread the mounts about 1/4" wider than they need to be. When you release the tension, they will spring back to near the proper width. Repeat, as it probably will be just short of enough. Get it to where there is JUST available clearance.

Repeat in the rear.

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+1 :mrgreen: