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A65 Swinging Arm Silentbloc Bushes
#825967 10/08/20 12:29 pm
Joined: Sep 2020
Posts: 45
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Kevin E Offline OP
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Hi all,

I have just recently fitted some new silentbloc bushes to my newly powder coated swinging arm but I think I have not got things quite right.

I think my mistake was not to check the new silentbloc bushes in the frame before pressing them into the swinging arm. I have seen posts about some pattern bushes not being of the correct dimensions and on hindsight I should have paid more attention this, very important area, before fitting them.

Referring to the attached drawing you will see that the side plates on the frame where the swinging arm mounts on my bike measures 9.375" inside.

Am I right in assuming that when the bushes are put together, as shown at the top of the drawing they should measure the same as this dimension on their outer extremeties?

When I pressed in the new silentbloc bushes I made a jig that would allow them to be driven all the way in until the end of the outside diameter was flush with the end of the swinging arm boss. I assumed that when I did this the bushes would be butted up against each other inside the swinging arm, so that when the spindle was fitted and everything was tightened up the swinging arm would be central in the frame. This is due to the inside diameter of the bushes protruding out of the swinging arm by the same amount at each side.

I have ended up with one of the bushes moving into the swinging arm boss more than the other one. I think this is because there must have been a gap in the middle of the bushes and the one that is 'loosest' in the swinging arm has moved when I tightened the swinging arm spindle nut.

I am going to take the swinging arm out of the frame and have a second attempt at fitting new bushes.

I would appreciate the advice and thoughts of anyone who has undertaken this job and can confirm that I am thinking along the right lines and correct in how I believe the bushes should be fitted.

Thanks,

Kev E

Attached Files Swinging Arm 01.jpg
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Re: A65 Swinging Arm Silentbloc Bushes
Kevin E #826350 10/12/20 8:31 pm
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Hi, I recently fitted new silentbloc bushings into my A65 swingarm after the powder coaters pressed the old ones out - I had hoped they would survive! I used a piece of 3/4" allthread and placed thick 1" washers over the inner sleeve stubs and 3/4" washers over those (all from Home Depot). This allowed ne to press the outer sleeve flush with the end of the swingarm tube and achieve the dimensions shown in your sketch.

As the bushes were expensive I was worried about ruining them but it all went ahead with very little drama so maybe its an option. A hydraulic press would have been easier but at least my way is in keeping with the spirit of BSA maintenance and ensures that both sides are pressed in easily. I would post a picture but its too difficult!

Cheers

Dave

Re: A65 Swinging Arm Silentbloc Bushes
Kevin E #826485 10/13/20 6:21 pm
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It is important to press the bushes in on the outer sleeve only. Otherwise the inner sleeves can stop the outers from fully bottoming


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Re: A65 Swinging Arm Silentbloc Bushes
Andy Higham #826552 10/14/20 12:45 pm
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Kevin E Offline OP
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Originally Posted by Andy Higham
It is important to press the bushes in on the outer sleeve only. Otherwise the inner sleeves can stop the outers from fully bottoming

Hi Andy,

As I understand it the outer sleeves don't 'bottom out' on anything. When you press them in they should be flush with the outside of the swinging arm and this can be achieved by pressing them in with a hydraulic press, or by the method that Dave described. The important thing is that you use something that allows the outer sleeve to end up flush with the end of the swinging arm and does not allow it to travel any farther than this. The bore of the swinging arm is reduced in the middle of it, which means there is a 'step' there that stops you being able to press a bush all the way through the swinging arm. You have to take them out either left or right. This reduced section /step in the bore is not very long and if you pressed the bushes in with, for example, a jig with a slightly smaller outside diameter than the outer sleeves of the bush, you could end up with them a long way into the bore of the swinging arm before they 'bottomed out on this 'step' inside the bore of the swinging arm. Which wouldn't be good.

The other issue is the inner sleeves, which (once again as I understand) should butt up to each other in the middle of the swinging arm. This means that when you fit the swinging arm, spindle and nut and tighten it up, the inner sleeves are trapped in between the main frame side cheeks. Any up and down movement of the swinging arm will then flex the rubber in the bushes around the swinging arm spindle axis. The rotary movement of the swinging arm at this point is very small.

I have had a problem with bushes in the past where the inner sleeve dimensions have not been correct. If this dimension is more than it should be (they are too long) they are forced outwards, once the outer sleeve is all the way home and flush with the swinging arm. This will make the whole distance across them too large and they will not fit in between the main frame side cheeks, as well as stressing the rubber in the wrong 'axial' direction.

If the dimension of the inner sleeves is too short then you have the problem of them not being held tight enough between the main frame side cheeks because they are not butted up against each other. This means that you have the possibility of the swinging arm and bushes rotating on the spindle, which will wear it out eventually.

After doing a couple of silentbloc bush replacements, I have come to learn that it is a pretty straightforward job (if you have the right tools) but it is very important to check and verify the dimensions of the bushes in the frame before you attempt to press them into the swinging arm.

This is how I believe things should be, after researching the subject using documentation, advice from others, actually doing the job for real and making mistakes in doing so, which I have learnt from (the hard way).

I have made up a few tools and jigs in order to carry out the job of getting the swinging arm out of the bike (the swinging arm spindle on my bike was a nightmare to remove the first time I did it) and to press new silentbloc bushes into it. I found the easiest and cleanest way to get old silentbloc bushes out is to chain drill through the rubber and then use a big taper tap to rip the inners out. I have heard that if you use a big enough drill bit you can break through the outer sleeve with it and then the whole bush will come out using the same method. I am lucky enough to have access to a machine shop, so once I had got the inners out I put the swinging arm in a milling machine and ran an end mill down the outer sleeve until it 'sprang' loose and it literally fell out.

If anyone wants any details of the tools and jigs I have made I would be happy to pass them on.

The parts that I made for getting the swinging arm spindle out, utilising a very heavy sliding hammer, will be very useful to anyone who experiences a spindle as stubborn as mine was to remove.

Last edited by Kevin E; 10/15/20 7:58 am.

Moderated by  Allan G, Jon W. Whitley 

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