Fitting MK3 Swing Arm to Gearbox Cradle

thunderbolt · May 27, 2018

I have just finished installing the iso bushes in the gearbox cradle with Mick Hemmings vernier adjusters.

I am now at the stage of fitting the MK3 swing arm to the cradle. I have fitted the rubber seals to the swing arm bushes and installed the bronze bushes into the swing arm.

The rubber seals sit proud of the bush surface that rests against the cradle by a good amount. I realise this must be a fairly tight fit to prevent any oil leakage.

Does anyone have a MK3 and done this task on their bike and can give me any advice on fitting the swing arm onto the cradle. I have tried initially and the rubber seals are preventing the swing arm from sliding on to the cradle for the correct fitment.

All and any advice appreciated.

Cheers Don

Danno · May 27, 2018

If the distance between the flanges of the bronze bushings is the same as the out-to-out distance of the machined area of the cradle, you're golden and it should fit right up. Take care with the seals as they will be a bit proud of the bushes. A smear of silicone grease and a wiggle as you slip the arm on from the rear will help. The machined pivot areas of the cradle should be bare-no paint.

Esmerela · May 27, 2018

Hi Don

If you have powder coated the swinging arm you need to remove the coating on the edges of the bush housing.

thunderbolt · May 27, 2018

Thanks guys, yes the cradle had all paint and powder coat removed. It is the seal sitting proud of the bush that is causing the difficulty. Also with the seal in place I am concerned it will make it more difficult to check for any movement in the swing arm and the need to shim the bushes to remove all play.

Thanks Don

Chris ton a bike · May 28, 2018

Ideally it would have been best to check fit the bushes with a pair of old seals with the seal lip removed, then fit to the cradle and measure the clearance, and then fit the required shims with the new seals. Filing a smooth radius onto the cradle side plates edge next to the swinging arm mounting tube aids fitment.

thunderbolt · May 28, 2018

Chris ton a bike said:
Ideally it would have been best to check fit the bushes with a pair of old seals with the seal lip removed, then fit to the cradle and measure the clearance, and then fit the required shims with the new seals. Filing a smooth radius onto the cradle side plates edge next to the swinging arm mounting tube aids fitment.

Thanks Chris, Yes that all makes sense. Only problem is the replacements seals came from a local shop here in Australia and I later found out that he gets his supplies from Norvil and the thickness of these seals are different by .25mm to the Andover seals that were pulled out. It worked out ok though because the extra clearance that I was going to have to shim was taken up by the wider seals.

Cheers Don

regental · May 28, 2018

I had a similar problem on my mk3 & just shaved the rubber off so they fitted - I get a slight leak of oil when I fill the spindle full of oil but this stops after a while - Alan

thunderbolt · May 28, 2018

regental said:
I had a similar problem on my mk3 & just shaved the rubber off so they fitted - I get a slight leak of oil when I fill the spindle full of oil but this stops after a while - Alan

Alan how do you fill the spindle full of oil?

Thanks Don

regental · May 28, 2018

thunderbolt said:
Alan how do you fill the spindle full of oil?

Take out the offside welch plug and wick, lean the bike over so it resting on its footpeg & pour in EP140 oil.
You can also drill the welch plug and wick, insert a thin tube & pump in oil - a colleague leaves the tube in place and has a small reservoir attached, similar to those found on lathes - Alan

JBugaren · May 28, 2018

I just did the swing arm bushings in my mkIII. I did have some trouble initially offering up the swing arm to the cradle with the bushings installed, but then in a flash of insight, I grasped the swing arm by its rear lugs, forced them inward slightly, which conversely moved the bushings apart, and it went right on. Hope that helps, and I’m not being too obvious.

thunderbolt · May 28, 2018

Thanks guys for your respective posts. Very valuable.

Swing arm on now with cotter pins installed. I had to modify the cotter pins somewhat as I could not force them all the way home to be able to fit the nyloc nuts sufficiently to screw into the nylon inserts. I left the wicks to soak in gearbox oil with 2% moly added. Will try to fit them today.

Is current opinion to hammer the welch plugs with a flat drift to seat them or insert them in place and seal with plumbers silicone as per Fred Eaton's example on his website.

Cheers Don

regental · May 29, 2018

Some welch plugs will seal with a tap on the middle to splay the sides - others don't, so I always put apply a bit of clear sealant

Chris ton a bike · May 29, 2018

thunderbolt said:
Thanks guys for your respective posts. Very valuable.

Swing arm on now with cotter pins installed. I had to modify the cotter pins somewhat as I could not force them all the way home to be able to fit the nyloc nuts sufficiently to screw into the nylon inserts. I left the wicks to soak in gearbox oil with 2% moly added. Will try to fit them today.

Is current opinion to hammer the welch plugs with a flat drift to seat them or insert them in place and seal with plumbers silicone as per Fred Eaton's example on his website.

Cheers Don

Please, do not go anywhere near a Commando with plumbers silicone! Loctite do flange sealant 5699, gray in colour. Ideal for crankcase joints too.

thunderbolt · Jun 2, 2018

Chris ton a bike said:
Please, do not go anywhere near a Commando with plumbers silicone! Loctite do flange sealant 5699, gray in colour. Ideal for crankcase joints too.

Thanks Chris, I have ordered the Loctite sealant.

Fitting MK3 Swing Arm to Gearbox Cradle

Similar threads