rear isolastic mounting bolt is smaller than the bush

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tommy666bikes

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Hi all hope you can help or advise a new member to this forum , I have a 72 commando which i have owned for 11 years , any way recently i started getting more and more vibes through the left side footrest so i thought i would replace the isos with the vernier type supplied by norvil (les emery) however when i came to fit the rear iso it was found that the rear mounting bolt was a fair bit (around 25 thou ) smaller than the hole through the centre of the new iso rubber , surely this cant be right as this would allow the whole plot to move around on the rear engine mount bolt , has anyone else ever come across this problem ? do the 850 models have a larger rear engine bolt? any help or advise would be greatly recieved
regards Tom
 
Can you measure your iso bolt with a caliper? I have the rod out of an 850 sitting in my shop right now and another out of a 750 fairly close at hand. I think they are the same but I will check it out.

Russ
 
tommy666bikes said:
i thought i would replace the isos with the vernier type supplied by norvil (les emery) however when i came to fit the rear iso it was found that the rear mounting bolt was a fair bit (around 25 thou ) smaller than the hole through the centre of the new iso rubber , surely this cant be right as this would allow the whole plot to move around on the rear engine mount bolt , has anyone else ever come across this problem ?
Click to expand...

It has been mentioned a few times.

post108831.html
 
rvich said:
Can you measure your iso bolt with a caliper? I have the rod out of an 850 sitting in my shop right now and another out of a 750 fairly close at hand. I think they are the same but I will check it out.

Russ
Click to expand...
Hi Russ Thank you for you for your reply , the bolt is 1/2 inch diameter
regards Tom
 
I recently fitted Norvil vernier isolastic kits to my 1970 750 and I found exactly the same problem. I saw no point in referring it back to Norvil as my previous technical questions to Les were met with, shall we say, static.
I measured the ID of the tube at 15mm, while the thru bolt is 1/2".
The problem is somewhat alleviated at the "fixed" end, as the collar at that end closes down onto the shaft. However, it only has a bearing width of 3mm, which could lead to rapid wear.
Luckily, I have a lathe and I made bronze bushes, about 16mm long, to press into each end of the tubes on both the front and rear isolastics.
 
MFB said:
I recently fitted Norvil vernier isolastic kits to my 1970 750 and I found exactly the same problem. I saw no point in referring it back to Norvil as my previous technical questions to Les were met with, shall we say, static.
I measured the ID of the tube at 15mm, while the thru bolt is 1/2".
The problem is somewhat alleviated at the "fixed" end, as the collar at that end closes down onto the shaft. However, it only has a bearing width of 3mm, which could lead to rapid wear.
Luckily, I have a lathe and I made bronze bushes, about 16mm long, to press into each end of the tubes on both the front and rear isolastics.
Click to expand...
Hi Thank you for your reply , i myself have had the same problem with norvil it seems that when they have sold the part they dont give a damn whether it it suitable for the the intended purpose or not and seem unwilling to offer any help or advise , i certainly wont use them again , i guess im gonna have to make up some bushes as you did
regards Tom
 
rvich said:
Can you measure your iso bolt with a caliper? I have the rod out of an 850 sitting in my shop right now and another out of a 750 fairly close at hand. I think they are the same but I will check it out.

Russ
Click to expand...
Hi Russ the bolt is 1/2 inch diameter
regards Tom
 
I also had the same problem. the hole down the middle of the is just over 13mm dia. Still havn't found a suitable solution. would be a very thin bush?
 
Why not some fairly tight bushings in each end to hold the stud from moving around? Not that I have this problem. I would think once you tightened things up it may not move anyhow? Is it one long tube or is it multiple like the early bikes?

Dave
69S
 
It would be easier to push in a rod and then drill it out to half inch than to make a bushing to fit. Of course you will wish you had a lathe handy.

Russ
 
Adding my two pennie's worth here, The rear iso bolt should locate , thats why the original 1/2 inch hole was a good push fit... as many have found out!.but i have read the cradle /frame holes are not in true alignment...so the iso tube clearance allows the cradle to find a centre. :shock: If this is fact i can see the advantage,but again it's poor engineering to grip the ends .if the bolt become's loose the cradle's may be twisted out of true , and there is a lot of force trying to do just that! so providing a slack hole in iso tube's is a poor idea.

It's hard to get 1/2 bore tube 3/4 dia, so seamed cheaper metric tube is often used. ....by some, fact!!
 
rvich said:
It would be easier to push in a rod and then drill it out to half inch than to make a bushing to fit. Of course you will wish you had a lathe handy.

Russ
Click to expand...
I think im gonna go for the making a bush option but i know it will be a very thin walled bush but i cant see any other way , it cant be right having the bolt lose in the bush like it is , i just cant see how the isos can do there job properly if this bolt is slack , must be a few commandos out ther with very dodgy handling and heavy vibration, regards Tom
 
If it's seamed tube you need to ream,bore or drill the tube first, the wall thickness is 1/8 so a 2 mm increase will be about right, Lathe required . Make the bush 25mm long in brass. alloy bronze is purfect if you can get it.
 
I have been wondering if you could use epoxy to fill the space. There are epoxies out there that are used to bed boat motors that would handle the cyclic loading. You coulf fill the cavity and then drill it out. It would be a fairly easy procedure that could even be done on a drill press if you were careful about setting up the tube for drilling. Of course the cost of buying the epoxy might be more than finding isos made with the proper size tube.

Russ
 
rvich said:
I have been wondering if you could use epoxy to fill the space. There are epoxies out there that are used to bed boat motors that would handle the cyclic loading. You coulf fill the cavity and then drill it out. It would be a fairly easy procedure that could even be done on a drill press if you were careful about setting up the tube for drilling. Of course the cost of buying the epoxy might be more than finding isos made with the proper size tube.

Russ
Click to expand...
Hi Russ ive got a pal with a lathe who seems to think he can make up a bush to fit in either end of the iso so fingers crossed we should be ok , ill let you know the outcome , many thanks for your help and advice ,, ps ive emailed les emery at norvil motorcycles who i bought the rear iso from,, as yet i have no reply from him but when i do i will let you know his thoughts and what he suggests as to what to do to solve this problem
regards Tom
 
Hi Tom
Regarding the question of cyclic loading on the bushes you are thinking of making, I really wouldn't worry about that because, as Jim Comstock pointed out in the link provided by L.A.B., there should be no loading at all between the tube and the thru-bolt. This is because the tube is locked to the frame plates by the tension of the bolt and should not be able to move. My intention in fitting bushes was merely to ensure that the whole lot was positively located during the assembly process, in the way that the original isolastics were.
Regards
Martin
 
MFB said:
P.S.
Norvil's web site says that Les doesn't do email. Good luck.
Click to expand...
Hi By the look of it Les doesnt like to help much at all unless hes getting paid , guess ill be getting my parts elsewhere in the future
 
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