Model A - painting more bits

 A rewarding but seemingly never ending job is painting bits for the Model A. The wheels are off and the brakes are currently in pieces and here we are with two brake arms and the torque arm for the front brake.

These are the two brake plates, with the paint cleaned off with a Scotchbrite wheel and coated with primer:

These bits had their second coat of black on the 31st of July 2026.

FH - carburation

 For the record, at the 500 mile service I have changed the carburetter slide on the FH for one with a #4 cutaway.

A #3 1/2 was previously fitted, and the plugs were quite dark.

Model A - chainguard

 The latest in a long line of broken bits waiting repair before they are painted is the chain guard. 

This is a pretty simple bit of welding. Initially the mounting nut is missing so I have replaced it with a new un-plated 1/4" CEI nut welded in underneath and I've filled in the worn hole as well:

The next bit is this gap which is a piece of material worn away as the chain rubs away at the chainguard. This is a bit more complicated.

First job is to chop it out with the Wiss snips and the Dremel. Next we can make a repair patch from a scrap of 18 gauge steel sheet cut to roughly the right shape, folded in the vice and refined with the linisher.

If you're careful, you can get it close enough to weld in without any filler rod which saves clean up time and reduces the heat (and hence distortion) going into the work. This wasn't one of those occasions, as I needed a bit of filler to close the gap at one end.

It's not too bad though.

Next is the other side - a bit that had been rubbing against the rear mudguard and worn a chunk away. That's it for the welding now.

With the paint finished it looks a lot better!

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:

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.

Emerging from the crankcase, we have a breather emerging to oil the primary chain:

The equivalent pipe 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.

This is I think an S21/1 oil pipe union with its associated union nut and a broken nipple. 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 the picture above, but the hole is clear and the thread is good.

These next pictures shows the rear chain oiler on Michaels '28. Below, 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.

SQ4 - maintenance

 After a run to Norwich today, 55 miles at 27.4 mph average speed (according to my new Beeline sat-nav) the Square started making an odd noise on the way home, a bit of a squeak from the engine sounding perhaps like a leaky head gasket. I stopped for coffee at the lovely Itteringham community shop:

After going on to reserve on the way home, I thought I would have a look at the plugs and do a compression test and the picture shows the result. All four plugs are the same colour, dark chocolate, all dry, numbers two, three and four all gapped to 18 thou but number one was gapped to more like 25-28 thou, which I corrected.  

Compression figures are good and consistent at 130-140 psi.

Restarting the engine after I had put the plugs back in revealed that the squeak had gone. Now I am worrying about the oil pressure on the last part of the trip home...