Tuesday, 12 January 2021

Model A - First Impressions of a Clutch

Isn’t it a bit early to be looking at the clutch on that bike, when you have so many others in the pipeline I hear you ask? Well, yes it is, but a while back I lost one of the tank bolts on the W/NG - you might remember I made a new one; I am diverting myself with lathe jobs as a distraction from all the welding on the QR50, and part of the lathe work is to collect the bits for the gear control on the Model A, and to do that I need to mount the tank - which is another lathe job, as one or two of the bolts are missing - so I need the tank mounting rubbers for that too, and I also want to trial fit the tank on the FH and I have no rubbers...

So what I need to do is to get an order for Jeff Hunter Engineering, who will supply all the rubber bits and what I am going to do is order as much of the rubber as I can, for all three Ariels. And this is where the clutch comes in - the Sturmey Archer clutch in the Model A has a rubber shock absorber in the clutch and this is bound to need some attention:


So let’s have a look. It’s very easy to get to as in 1930 Ariel were not using the fully enclosed and sealed primary drive, and my primary cover is off awaiting time on the welding bench:


Clearly, two of the retaining bolts, springs and spring cups are missing. Those bolts actually have screwdriver slots under that muck.

Under the pressure plate, the basket and centre are very good indeed:


The plates are reasonable too, but I wasn’t expecting Ferodo linings:


The parts list clearly shows a cork lined clutch:


Yet if we look in the Sturmey Archer book from the period, there is a Ferodo option for the three plate clutch. Interesting.


We’ll have to replicate these parts, though I wonder if they have been intentionally omitted. Ferodo clutches of the period can be quite heavy - the one on my W/NG is much less pleasant than the cork clutch on the SQ4, for example.


Still, it will be a long time before we have to deal with that problem.





QR50 - Oiling System

The little QR50, as a two stroke, has an oil injection system consisting of an engine driven pump supplying metered oil direct to the carburetter float chamber from a reservoir in the frame spine. Keen readers might recall the stopper I made for the oil filler behind the headstock.

As we near the end of the project we need to think about hooking up the system; the pump has been ready for a while and is a replacement for the original which had a smashed casing. I’ve got a twist grip with the two into one cable which operates both the throttle and the oil pump, so we just have to pull it all together.

The first step is the banjo which takes the oil from the frame tube to the pump, and to a tube leading back to the headstock as a visual indicator of oil level:


Typical of Honda, this couldn’t be anything easy could it - like a standard banjo that I could buy. No! The fitting in the frame is M9 x 1.0, so I have to make the banjo bolt from scratch. For me that is the tricky bit as I don’t have much experience cutting threads on the lathe and I am certainly not going to buy an M9 die that I will never use again.

Next, we need a banjo to go with it. Tricky again, because the banjo needs an internal annular groove for the oil to run around. We need a tiny boring bar, like this one:


This is ground from a blunt 5 mm twist drill and mounted in a bit of 1/2” bar, retained with an M4 grub screw.

Using the new tool, the interior is bored to give an annular space:



When the internal features are ready, I put the banjo in the tail stock v-block to drill the holes for the oil line connections:


With the banjo parted off I can do a trial fit on the bike to think about where the lines will route:


I’d planned to use 3/16” hydraulic tubing, which I had knocking about:


Whilst this was functionally a sound idea, it transpired that the feed to pump and the connection to the filler neck were going to need 5 mm bore line, so these 3/16” stubs were too small. I went home for tea, as it was below zero outside and I couldn’t feel my fingers.

Next day, I made some 6 mm stubs from some brass round bar and sweated them into the banjo:


That looks much better.

Regular readers might wonder why this takes so long. Look closely - with the oil pump in place, the dummy swinging arm doesn’t fit properly:


Inching closer, I made this brass fitting to hold the cable adjuster. I'll slim that nut down for appearances sake.