Model A - magneto chain case

 The magneto has been sitting on its platform behind the engine for some while, ever since it came back from Tony Cooper. I'd left it off because I wanted some time to look at the seal between it and the back of the gear case, and I'd also posted some questions on the AOMCC Facebook page to try and learn about the two breathers that route out of the gear case and onto the chains. This post is about those two issues.

Let's start with some pictures. This is a page from the 1930 heavyweight parts book:

This is I think an S21/1 oil pipe union with its associated union nut and a broken nipple.

You can see it in situ here. The parts book identifies two of these unions and the other one fits into a hole right underneath the magneto chain run which is not visible in this picture but the whole is clear and the thread is good.

Club member Michael posted these three pictures on the FB page. This is a 28 bike which is not the same as 29 or 30 but gives you a flavour of what they would have used to implement these breathers.

The equivalent bike on '29 and '30 bikes appears from the back of the magneto chain case as shown here:

We will use the illustration in the parts book to invent something to head cross to the primary chain from here. It will have to have something to attach to though, to stop it wobbling about.

These pictures shows the rear chain oiler on Michaels '28. Above, we see the pipe emerging from the timing gear case and disappearing in front of the gearbox - mine will be similar, but it comes from the bottom of the magneto chain case as I said.

What we are seeing in the picture below is the other end of the same tube emerging from a gap in front of the gearbox and running along the frame rail under the gearbox sprocket, flicking up and over onto the chain. This is shown in the 1930 parts book picture above as item A6/683, but just to confuse you the parts book picture is upside down.

This is the relevant page of the 1930 parts book. We can see here that there are two S21/1 unions called up so we can be confident that if we can replicate the one we've got, will be good for the other. The next puzzle is to work out what the A6/120 component does.

This last picture shows the three elements of the magneto to chaincase seal. Left to right we have the retaining washer, the Vellumoid washer, and the felt washer that pushes up against the chain case. The Vellumoid washer is basically a thick gasket that sits across the front of the Magneto - Vellumoid are actually still trading as gasket manufacturers. It's all in reasonable shape and I put it back in as I found it.