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...

FH - oil from the drive side cylinder

 I might have mentioned a few times that the Huntmaster has been burning oil from the drive side cylinder, manifested as an oily exhaust pipe, and oily spark plug, and smoke when pulling away. It's always done this ever since rebuild. I had been hoping that this was just really bedding in but after 550 odd miles I think I have to admit there's something wrong. Since it's back in the workshop for its 500 mile service the rocker box has to come off anyway to retorque the head and we can do some investigation.

I had hoped that the rocker box drain might be blocked and excess oil being sucked down the exhaust valve guide but a poke down the drilling with a bicycle spoke reveals the hole is completely open - as I had expected since I cleared the hole out during rebuild.

Removing the head revealed this - a bit of an oily mess on the drive side (that's on the right of the picture) and a fairly normal looking though dark combustion chamber on the timing side.

And then this! That bare piston crown is the drive side, the one that is smoking. There is barely any carbon deposit there at all compared to the other side which looks quite normal to me. It should be noted that the mixture is quite rich at the moment as the mileage is not really high enough to do any proper plug chops.

This is the timing side exhaust valve.

And the drive side exhaust valve, looking a lot hotter.

Here is the upper side of the head gasket - that is the side that touches the head itself. The area within the red ring shows I think a leak from the cylinder into the head bolt drilling and possibly into the drive side exhaust valve drain. Perhaps this explains both the smoke and the oil coming from the cylinder head joint and dripping onto the primary drive case.

It pays to be careful when removing the cylinder. I released all the nuts and made sure that I collected them all with their washers and put them aside. Next we used the leather mallet to loosen the cylinder joint which was quite straightforward - not forgetting that the forward magneto pickup has to come out to remove the cylinder. 

It's wise to lift the cylinder with the pistons in their uppermost position so that you can lift the skirts above the crankcase mouth to get a couple of pieces of wood into the joint to support the weight of the cylinder. You can then introduce a suitable cloth into the gap to prevent any broken bits of ring or circlip falling into the crankcase. 

Once you have lifted off the cylinder the wooden battens can support the pistons.

Removing the cylinder very carefully reveals two pistons in very good shape - to be expected since they have only done 550 miles. The purpose of this exercise of course is to check that the rings are sound and indeed they are so we can take some comfort in the knowledge that the results of the compression test we did months ago are supported by rings which appear to be in very good condition.

Investigating the head gasket sealing area and the bolt holes reveals a couple of interesting points. Well, one main point really and that is that most of the cylinder head bolts open into a gap between the fins, a few fins below the head joint and secondly that one of the front middle two bolts doesn't pull down properly as the thread appears to be very tight. This is in the area where we suspect the leak to have been.

We will leave this for now as I have a day on the railway tomorrow and some other bits to do. I've made a post on the FH Facebook group to make sure that I've selected the right tap to clean these threads out!