Sunday, 23 February 2020

QR50 - Fork Dust Excluder

I'd planned to fit gaiters to my QR50 forks, but have been unable to find any to fit other than Bantam D1 gaiters, which are a ridiculous price. The alternative plan was to replicate the Honda style rubber cap used in the '70's and '80's. Since I have no rubber moulding materials or no 3D printer I thought I would machine a pair from Acetal.

This is what I came up with. They are a close fit on the stanchion for a very short length (2 mm) since I don't want the stanchions to bind in them and dislodge them. Here's one I made earlier:


The drawing shows my design. The cap features an O ring groove to provide sufficient friction to hold the cap in the slider:


Here's the bit that goes inside the slider with the O ring in place. From this stage, the caps were parted off and reversed in the lathe to machine the chamfer on the other side and to finish the stepped internal bore:


Two caps in place - looking more like a pair of fork legs now:


QR50 - Stanchions & Yokes

I might have mentioned a few times that the stanchions, which in this design have integral bottom bushes, we absolutely trashed through rust - so much so that I needed a new pair.

These are pretty hard to come by, and expensive. I decided to make a pair.

The originals are chromed steel tube, finished diameter 21.5 mm. After much deliberation I decided to use 22 mm OD 304 stainless tube, which meant the holes in the yokes needed to be eased open. I did this using 60 grit emery tape and a hone, which I made from a scrap bit of tube with a slot to carry the tape; the tube OD was reduced to allow for the thickness of the tape. I ran this slowly in the lathe:


Here's the hone. It took a couple of hours and a metre of tape to open those holes out to 22 mm.


Since I don't have a M10 x 1.25 mm tap set, I elected to rescue the old top nuts from the original yokes. I cut these out using a parting tool and a corner turning tool. I removed all traces of chrome in the process, to avoid contaminating the weld.


I used the TIG set at 50 A to put an autogenous peripheral weld down:


Two new fork legs!


The yokes come up nicely. They have been stripped and cleaned using various wire wheels; the paint is UPol Satin Matt Black over UPol etching primer:




QR50 - Rear Strut

There's nothing wrong with the single rear shock absorber on the QR50 other than that it is covered in the ubiquitous red paint. I'll strip it for cleaning, and to record how you do it.


If you have to dismantle a shock absorber, get a spring compressor. Springs, especially springs on mono-shock bikes store a lot of energy and you need to have it under control - you don't want it released unexpectedly into some tender part of your anatomy.

This little set is perfect for my needs - each compressor hooks over the spring. You'll need a different type for shrouded springs, like the ones on the FH. I'll cover those in a different post.


Here's how they are used. You will need to support them (I use a large adjustable spanner) while you operate the drive wrench, or you will risk they coming 'unhooked' at one end.


When you have them compressed enough, you can get a spanner on this nut. You might need to remove the rubber mount to get a bar in the eye, as the nut should be tight:


Here's the spring off. The bottom collar is loose and is retained by a circlip around the damper. It will slide off upwards, but in this case the damper worked fine and the whole lot just needed cleaning up on the wire wheel. The damper rod should move smoothly but exhibit resistance in both directions.


The spring is power coated and cleans up with soap and water:


I've replaced the spring the other way up. This make no difference to the way it operates but it makes it a bit easier to use the compressors, since they are operating on more coils:


And that's it, back together and refreshed:


Tuesday, 18 February 2020

Railway enthusiast?

Readers with retro-technology interests outside of old bikes might like to know that my railway blog is growing at:


Hope to see some of you there! Remember you can sign up for email notification of new posts using the dialogue at the bottom of the page.


Saturday, 15 February 2020

QR50 - brake plate stop

Last major job on the fork sliders is to weld on the stop for the front brake plate. For convenience, I have retrieved this from the old slider:


I've set up the whole assembly in the vice to ensure that it is welded to the new slider in the right place:


With it set up like this I can tack it in place. I can then remove the brake plate, and set the welder up for a fillet; the key element is to make sure I can access the weld:


With sufficient stick out and the gas pressure raised enough to keep the electrode cool, I can use some filler to complete the weld. Any excess is cleaned up with a round file. It fits beautifully:


Friday, 14 February 2020

QR50 - Fork Sliders

I've mentioned the condition of the fork legs in previous posts. The stanchions and sliders are completely ruined by water ingress, the shrouds and bump stops are missing and the springs have mostly rusted to dust. Due to the cost and scarce availability. of new legs, I decided to make some new ones on the lathe. this probably wont save much money, but it will add to my skills and will be fun - and I can adapt them if I want to.

The old parts were good enough to give me some idea of the measurements I would need, and the wheel spindle mounts were sound. I cut them off for re-use, and to enable me to get the forks apart to look at spring and bush dimensions.


Buying new springs was easy through eBay, but they came from a coil and didn't have closed ends. With a fine blow torch, it's quite easy to direct the flame to precisely enough to be able to manoeuvre the last coil without affecting the temper of the rest of the spring:



So, onto the slider and I start by fitting the bottom I cut off into the four jaw chuck. I turn off the remains of the old slider and form a 2 mm x 2 mm shoulder for the new tube



The new tube is welded in place with the TIG welder set at at 60 A, with a 2 mm electrode and a #4 shroud:


With the two sliders welded up, we can see that the tubes are parallel and the spindle is perpendicular:


This goes back in the lathe supported by the fixed steady. I've trued it up using the DTI and can now start to face off the end ready for boring.


Each slider is faced to length, bored to create a step for the top bush to sit on and then using a specially ground tool we make a square groove for a circlip to retain the top bush:


You can see the step and the circlip here:


Two identical sliders, finished - almost. One needs the brake plate stop welding in place and then we are ready for paint.


Thursday, 13 February 2020

QR50 - Petrol Tank: renovating plastics

Like most of the QR50, the petrol tank had received more than it's fair share of poster paint but it is at least intact and comes complete with its tap. The cap is unfortunately missing (like the oil tank cap) and has been replaced by a green plastic one from a Derbi:



The poster paint comes of in the sink, but the green acrylic underneath needs paint stripper:


With this gone, we can survey the damage. There are a few dings, the deepest of which pushes out with heat; other damage can be trimmed with a knife to remove it completely or make it a bit less obvious. Next, the whole tank is rubbed down with 240 grit wet and dry to start on the removal of the scratches:


When we've gone as far as we see fit, we'll move up though the grits to get it looking a bit better.

More later.