A RESTART - Front Suspension

1st June 2011






When I took the front wheel out I noticed that the wheel mounting arms were of different stiffness and there was slack in their operation.  I had previously discussed this with Patrick who had recommended stiffer springs as these will greatly improve the performance of the suspension.  He sold me a pair of front springs that he had taken from one of his scooters and the necessary bushes, bump stops washers and gaskets ready for the refurbishment.

The first thing to do was to remove the outside front cover.  Not knowing the construction I was cautious.  Having removed the three bolts retaining the cover I found that using a punch on the cover at the end with the single bolt hole the cover would rotate about the grease nipple.  I eventually managed to remove the cover without too much damage to the paint work.  (Before starting I had agreed with myself that I was prepared to repaint the scooter once I had got it running and any rework completed).  With the cover removed I was able to see workings covered in grease.  I don't understand the lubrication system, there is grease everywhere except where it's needed, on the bearing surfaces.

Having cleaned the parts I found that the bearings were in fact worn.  I decided tackled the bearing in the outer cover first as I could work on the bench.  The bush is fitted into a blind hole in the cover and there is no way of getting to the back of it to push it out.  There appeared to be a little space between the end of the bush and the bottom of the hole in the cover but I had no extractor that would fit.  Patrick had indicated that he used a small grinder to cut through the bush but didn't show it to me so I was going to have to come up with a method of my own.  I don't have a grinder small enough and I was concerned about damaging the cover casting.   I resigned myself to cutting through the wall of the bush in the hope that it would relieve the pressure so that I could pull the bush out.  




Using a broken hacksaw blade and a 10mm stroke I set about cutting into the bush.  It took forever but it had the advantage of allowing me to control how close I came to the cover casting.  Having made the first cut there was no obvious signs of the pressure being relieved.  My solution was to make another cut alongside the first and then remove the bit between the cuts.  More aching muscles later and the second cut was complete.  Because of my caution about not cutting into the cover the bit didn't fall out.  


I could see that I was close and so I used a punch to push the thin sliver towards the centre of the bush.  This tore the final  attachment to the bush and I could remove the sliver.  A quick tap to the edge of the split bush and I saw it move.  Using a nail head in the small gap at the bottom of the hole I was able to pull the bush out of the cover.  Success and no damage to the casting.


 


 With the bush removed I could see the shoulder in the bottom of the hole on which the end of the bush sits.  With the bush in place there would be no space to use an extractor so grinding or cutting is the only solution.

Removal of the bush in the fork casting required a different approach.  I wanted to use controlled force so that ruled out just driving the bush out from the inside using a hammer and drift.  I made up an extractor which enabled me to use a bolt to apply a steady force to push the bush from the inside.  This worked fine and I quickly had the bush out.  The bush looked fine but when the leaver arm was fitted there was a lot of slack so I hoped the replacement would be an improvement.


To replace the bushes I first put them into the freezer for a couple of hours.  I hoped that this would reduce their outer diameter.  When I came to fit them I carried them to the garage in a wine bottle cooler sleeve in order to slow the warming process.  (nice idea but they have so little thermal mass I expect they quickly took up the temperature of the casting into which I was fitting them and so lost any gain I had achieved).  
The outer cover was simple, line up the bush and squeeze it in using the vice until it hits the flange in the bottom of the hole.  All went well despite my concern that the bush might not go in square.  Had this been the case I would have had to destroy my new bush to remove it.

Recessed end of the bush is under the washer

For the fork casting bush I could reverse my extractor and squeeze it in.  It's important to fit the bush round the correct way - the recessed end is fitted facing the outside of the casting.  There is a shoulder in the casting which defines the final position of the bush so I hope that the distance between the bushes corresponds to that required by the leaver arm.  It's all a bit academic because the gasket thickness has a impact on this dimension.  The original gasket was very thin and the replacement is thick (and badly made, it needed adjusting to fit) so we shall see.  Again I'm not sure if the chilling of the bush made any difference but the bush went in with no problem.

 




I did a trial fit of the leaver arm in the bushes and found that the cover bush was too tight and so I had to scrape it to make it fit.  I hadn't done this for ages and using Engineer's Blue and a scraper was really rather satisfying.  I guess the leaver arm shaft was worn because I had to accept fitting the arm relative to the cover and accept it was tight in other positions.  I didn't consider this a problem as the angular movement is very restricted.

Lower spring - original

Now for the suspension springs.  The original springs were 197mm long and the replacement ones 219mm long, 22mm longer.  This presented a problem in that with spring and the ball cup in position there was insufficient room to get the leaver arm ball end into position.  Patrick had indicated that it was a simple matter of compressing the spring and then holding it in this position through the grease nipple hole in the fork below the mud guard. 



 
I had made a tool which enabled me to compress the spring and used an 8mm bolt tightened down onto the spring inside the fork tube.  Unfortunately this doesn't work as there is too much spring below the clamp point and as I removed the compression from the end of the spring it returned almost to its initial position and didn't leave enough space to insert the ball end of the leaver arm.

I finally had to lift the spring to the required height and retain it there with a spacer.  Spacer 27.0mm long x 4.0mm diameter.  My compression tool reacted directly on the surface of the ball socket in the end of the spring.  I didn't like this but couldn't think of any other way at the time, at least the socket was hardened and the end of the bolt was softer.

With the end of the spring and ball socket held in position I could now insert the leaver arm.  I now only remained to remove the retainer, in a controlled manner.  It was tempting to use something to just force it out but I was concerned that with the forces involved this could prove disastrous.

The only solution was to use my compression tool directly on the underside of the ball.  I accepted this crude approach on the grounds that the ball was hardened and this surface only contacts the bump stop.  A couple of turns and the spacer was removed and I still had my fingers and eyesight.

















 Once the spring compressing nut is removed the leaver arm is forced down to rest on the fork casting.  Fitting the fork plug bolt  complete with the new bump stop requires a certain amount of force.  Since I was not keen to try to leaver the arm up I just had to insert the plug and screw it up into position.  Best not to look at the distortion of the bump stop during this operation.  Once in position everything looks fine.


Having put grease where it was needed I didn't think it was necessary to cover everything in grease.  Over time grease would fill the box from overspill when greasing the bearings of the leaver arm.

With the cover back in place I was ready to refit the wheel mounting arms.  There is a small fiber washer that fits into a recess in the bush and is covered by a thin steel washer.  The wheel mounting arm is fitted tight up against this steel washer.  There is only one position that the arm can be fitted restricted by a cutout in the splined shaft of the leaver arm  Once in position the clamp nut is tightened.

TOOLS  

Spanner to remove the  plug bolt at the bottom of the front fork.  A bolt simply welded into a length of steel bar.  Reduces the risk of damaging the socket in the aluminium bolt.

Fork bush removal and insertion tool

Spring compressor.  Used during the fitting of the replacement spring.  A modified  fork end plug bolt.  A thread is tapped into the centre of the bolt.  Screwed into the end of the fork to compress the spring by adjusting the centre bolt.