Passola Rebuilt - Part 2 - Fork Refurbishment

The project started.

Starting little at a time, I’m currently trying to refurb the fork. As i thought that this could be an easy fix  by just changing the seal and presto, it turns out that it will takes more than that! There’s heavy rust spot built up on the chrome coating and there’s sign of wear and tear of the component inside.  As the Haynes manual say, the least you could do is changing the fork bottom assembly.

So my quest on ebay and the internet for the long list of replacement part were not successful as there are not much things up to offer, if it does, it is just a little bit better than mine, if I bought it, I’ll end up the same issue in the near future, so it’s a NO for me.  

the fork with broken dust cover.

So I’ll be end up with following 3 options either to

1.  Get this modified to the other bike model which will not hold its originality and beside, more research, time, modification, £$$$  need to be done to find suitable fork system to suit.
2. Getting this replaced with the used one on ebay which would end up the same issue with the next replaced part
3. Modified the current one, refurbish it and there you go a so called new and refurbished fork ready to roll.

So, I’ve decided to go on the hard way on option 3. For this job, you’ll basically need to have a skill set handling the workshop equipment, GDT’s, drawing and modelling  and that’s including a know how to use a lathe machine although you could make this without it or you can just find any engineering shop to do it for you, hassle free J

As to said before we move on, do your goodself/ selves more research on this should you want to modify yours as I will held no responsible or put liable for any issue raised should you follow what I’m doing to my passola. You have been warned.

Material

1.  Acetal bar ⌀40mm dia. – for the fork dust seal cover and dust scraper- if you want to modify/ replace  it
2.  PTFE bar  ⌀30mm dia.  – if you’re changing the fork sleeve.
3. Aluminium bar ⌀30mm - for the end stopper
4. CAD software
5. Lathe machine – mini lathe should be working as well.
6. M6 x 45mm allen key socket screw
7. 22mm x 30mm x 7Rs Oil Seal - for dust scrapper/seal
8.  ⌀32mm dia Id x 3mm WT oil seal - for dust cover.
9. 
   

Here  is what we’re going to do!

In the Passola fork system, there are no replacement item as it is supposed to be change out as a set should any fork component shows sign of wear. This should not be an issue back in the 80’s where you could still find a replacement set for it.
For this, we’ll be removing the stopper end on the fork system and replace the stopper with a removable stopper for easier maintenance. With this modification, it will allows you to replace the dust cover, guides and etc.

The locking mechanism design for the end stopper, using wedge locking system where it used a wedge block to secure and hold the end stopper inplace by means of wedging the inner wall of the fork. The following depict the locking mechanism that we’re going to fabricate.

Wedge Nut  & End Stopper

Theoretical approach

So to understand this further, M6 screw will be used to tighten the wedging nut and the end stopper body together. More  force applied to tightened the screw, it will wedge out the end stopper body and hold the assembly in place. The philosophy is simple, it is using the thread rotational to create the torque and linear motion against the fork wall which will sufficiently hold the stopper in place. see below for simplified free body diagram.

So here’s how were going to do.

Step 1 - measuring
Take the measurement of the inner bore ID of your fork. In this case the passola ID is 17mm and the OD for the old end stopper is 28mm, the height of the old stopper  + the top of the fork is 16mm.

Step 2 - design

Start designing the part to your computer, and assess whether your design will work or not and minimised for material removal.

Step 3 – Machining

You can either machine the part yourself or send it to someone who can do it for you. In this case, I’m using the mini lathe that I bought off earlier to complete the job. You’ll need to plan the machining task, deciding when to cut, when to tap. This will give you an idea on how to start your work and ensure that you don’t waste the material.

The complete set, the screw is just for fitment purpose, will get an allen key for the screw.

Step 4 - Trial fit

So the moment of truth whether your idea is working as it should. At this point, you will not remove the stopper yet, just trial fit the end stopper you’ve made. The mechanism should work by holding the end stopper in place and shall not be removed once you give high enough torque on the screw. The top of the end stop should be flush to allow the spacer to be included during the assembly and the fork can fit into the fork housing.

Trial fit. noted that i've cut the end stopper before trial fit.

Step 5 cutting and removal of the end stopper on the fork.

This is when you cut the end stopper on the fork. To cut it, simply cut the weld mark on the fork or you can just cut it out from the bottom on the endstopper. You will need to do this and making sure that both left and right measurement are equal. I’d suggest using metal cutter to do this as you’l need a relatively flat surface for the new end stopper.

Grinded off end stop weld.

Step 7 Refurbish component and assembly

In this time, since you have remove the end stopper, you have access to any of the component inside the fork in which you can either re-used of refurbish.

In my case, since the fork dust is discontinued and I could not find any equivalent, I end up have to make this out of acetal and replace the seal with typical seal size 22mm x 30mm x 7 RS  that is available in the market. This seal can either be on the fork dust or the fork itself. In my case,I choose option A since  4mm after the circlip should be sufficient to hold the seal inplace and beside the fork dust cover will also help to hold it in place..  In order to secure this in place, I’m making an internal o-ring recess for32mm Diam. x 3WT

Step 8. Complete the assembly.
Assemble the part altogether and there you go, a nice refurbished fork for your passola!

Picture Shown of complete assembly of passola fork without the allen key socket screw for the wedge/ end stopper.