FH - oil from the drive side cylinder

 I might have mentioned a few times that the hunt master 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 with a poked 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 bear 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 the 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 battons 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 compression test we did months ago is 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!

Model A - rear wheel

 It's over 35° C here today, and I don't feel like doing very much so I have been pottering about clearing up the workshop and listening to The Fellowship of the Ring on Audible, read by Andy Serkis.

When all the loose bits were put away I set to to remove the rear wheel rim by undoing all the spokes as I did at the front. Very therapeutic!

The rear brake drum for 1930 features this bolted in ring which is designed to retain any loose spoke heads and prevent them getting involved with the brake shoes - Ariel must have had some mishap to make them realise this would be a problem.

The ring is held in place by three square headed 2 BA bolts which come out easily.

Here is a close up:

The next step is to clean and scrape years of gunge and grease from the brake drum and hub.

The spindle is all present and correct, except that it is very slightly bent. We straighten this out with some heat in the vice.

When it's clean we can put a couple of coats of black gloss on the hub.

Model A - more painting

 This isn't very exciting post but it's important to make it to record when these items had their first coats of paint. This Tekaloid takes a long time to dry fully - about 5 weeks - and I want to know when I can assemble bits.

Today I have used the wheel to strip rust and old paint from the battery tray, the rear chain guard, the oil tank and the dynamo chain guard.

They have been degreased, had a coat of primer and their first top coat.

The second coat went on on the 9th of July.

Charlie's Shed - Concentric carburettor

 Since yesterday when I managed to accidentally drill out the pilot air screw thread on the 928, I've been thinking about how to approach carburetion on the FH. I fitted the Monobloc, which is a bit worn particularly around the mixing chamber cap screw and I realised that I would need to alter the cable lengths to use it. 

Some more thought had me realise that I could repair the damage to the 928 and have a better solution for my non-standard Huntmaster more quickly than messing about with a Monobloc. 

The first thing I did was to tap out the new pilot circuit access ports. The one in the inlet taps out to M5, but the one opposite the pilot air screw is a bit more tricky in that it's too big to tap to M6 and the wall thickness is too small to tap to M8 - but it is perfect for M7. Try buying an M7 grub screw! However, I do have M7 by 1.0 taps and dies by some streak of good fortune and I have tapped that hole M7. 

I drilled out the pilot air screw thread with I think a 4.5 mm drill. I tried tapping it M5 but I guess the whole was not clean enough for that and I had to go to M6. 

The next go/no-go job was to determine whether I could make a successful pilot air screw with a larger thread. I grabbed a bit of 10 mm brass rod:

That turned out ok. It seals most of the pilot air port (you can see the witness mark) but I suspect the thread is bottoming out somewhere. Blowing past it is quite difficult, so it will probably be ok. I replaced the tired O ring.

The next job is to seal the opposite port. I made a plug, but unfortunately the cheapo M7 die I have had for years just won't cut and is now in the bin.

A couple of days later, equipped with a new M7 die I made a new plug:

This seals the cleaning port nicely:

Now we can put it back on and road test it.

FH - Monobloc Carburetter

 I've been toying with the idea of fitting an original carburetter to the FH for a while, and finally bought on on eBay - I actually ended up with two, having bought one, it turning out to be not as described and the seller not wanting it back. That was a 389; I also have the correct 376/12.

Having messed up the 928 by not paying attention (more of that later) I fitted the 376:

It's not in too bad shape. The mixing chamber cap retaining ring is a bit loose, and of course the slide is a bit worn but otherwise it's sound. It's more or less to spec - I can easily modify the #3 slide to a #3 1/2 with a file; I have a close-enough main jet. The 928 that was fitted had a 260 and was obviously 28mm - that's about 1 1/8" which suited the 'Road Rocket' specification to which the engine is built. 

	Monobloc 1	Huntmaster	Road Rocket	Monobloc 2
Part Number	376/12	376/12	376/36	389/12
Size:	1 1/16”	1 1/16"	1 1/8"	1 3/16”
Main Jet:	260	240	290	300
Pilot Jet:	25	25	35	30
Needle Jet:	106	106	106	106
Position:	3	3	3	3
Slide:	3	3 1/2	3 1/2	3

The plan is to see how this goes before we do anything else - it should give me a better base to get the carburation right. Unfortunately I will have to make the throttle cable shorter and the choke cable longer to make this work...

'Do anything else' could mean buying a 928 Premier; it could mean buying a new Monobloc.

And the 928 that came with the bike? It wasn't the Premier, so it had the built in idle jet. I wanted to change the pilot jet size and to be able to clean the idle circuit so I drilled out both the plugs that seal off the idle drillings, re-tapped one M5 and was considering tapping the other one M7, and making a special plug - unfortunately I took my eye off the ball, and thinking if I put the plug further down I could put an M5 plug in that side as well - and drilled out the pilot air screw thread. One useless 928 body, for which you can't get a spare.

Model A - front wheel

One of my key aims is to get the machine rolling so that I can get it off the bench when I need to, to get the others on the bench for servicing etc. To that end I sorted out headstock bearings and the wear in the forks, but of course we still have no tires and the wheels are not fit to have tires fitted.

I thought I would change away from my normal method of dismantling a wheel, involving bolt cutters, and see how feasible it was to dismantle it nipple by nipple. I sprayed each nipple with plus gas months ago and I was pleased to find them all come apart easily.

Before long I had a fully stripped hub and brake drum a pile of loose spokes, nipples and a rather rusty rim - a WM1-20 which might get reused one day if I can ever buy tires for it.

Despite worrying about whether I'd made the right decision with respect to the rusty nature of the rim, the spoke heads confirmed that rebuilding the wheel was a good thing to do. Several of the spoke heads are about to pull out of the hub:

After a short period of decreasing, scraping of general muck and abrasive removal of rust, I put on a coat of primer

Followed by a couple of coats of black gloss:

The black powder coated rims have been delivered from Devon along with spokes and nipples but we will need to wait something like 5 or 6 weeks for this paint to harden before we can build the wheel. More of that later!