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 hole 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.

Magneto bearing puller

 With these old bikes every new job is a challenge. I suppose I could have sent the dynamo away to be refurbished like I do the magnetos but they're not that complicated so I do them myself. 

The E3 fitted to the Model A is a little bit different to the later E3Ls and E3HMs that I've worked on in that it uses magneto style bearings with separate races, cages and balls. Simple enough you might think - well yes, if it all goes to plan. 

What I discovered was that the reproduction armature that I bought for the E3 on the Model A, the first three-brush dynamo I have worked on, wasn't quite the same dimensionally as the old bent armature that came out and I found when I fitted the bearings for the first time that I had far more endfloat than I could cope with. To fix that you need to remove the bearing again, put a spacer in behind it to take up the end float, and fit the bearing back again - and you might end up doing this two or three times.

You need a special puller to remove the bearings and I found the details for one here:

https://www.kynoch-douglas-parts.com/html/articles/magneto%20bearing%20extractor.htm

The main tube part of the puller is made from a bit of old handlebar which I've turned internally to make the hemispherical form that will fit into the bearing race.

I turned up a plug to go in the end of that with an M8 female thread in the middle and welded it into the end of the tube. The six slots were cut with a hacksaw - you could make a much better job with a slitting saw but frankly I didn't want the work of setting it up.

There are a couple more details - the end of the threaded rod has a small disc welded to it to bear on the end of the armature shaft to reduce the likelihood of damage and the other end has a t-piece to allow you to turn it easily.

Here it is in action. Initially I used a regular worm drive jubilee clip to hold the six legs into the bearing, but they are just not strong enough and will pop out. The worm drive does not allow you to put sufficient force into the legs so I have used a much better quality hose clip - this trunnion type clip:

It works very well but you do need quite a lot of force to remove those bearings.

Charlie's shed - adjusting primary & rear chains

 The Huntmaster clicked over 400 miles on a run recently and is bedding down nicely. Checking it over in the workshop revealed a front chain that was rather loose, and of course one of the issues that you learn when dealing with these old bikes is that if the front chain is loose the rear chain will probably be tight as sometimes the gearbox will move. 

It's time to have a look at both chains, and for this we will use the on board toolkit:

First stop is under the oil tank where we find the gearbox top bolt and the chain adjuster. Loosen the nut on the right a little bit and then use the chain adjuster to draw the gearbox backwards or push it forwards.

Next you need to gain access to the primary case so that you can inspect the tension on the primary chain and later top up the oil. If this is tight use a big flat spanner to undo the inspection cover:

Now you can see the chain. This should have about 3/8" up and down movement and this should be slack movement - the chain should not be stretched tight and you should not be putting much effort into moving it. If the chain is too tight you will be putting undue pressure on the engine main and gearbox bearings, not to mention the chain itself and the clutch basket bearing. Typically the chain will get looser as it wears and you will use the gearbox adjuster to draw the gearbox backwards by a little bit to tighten the chain. When you are done, leave the gearbox adjuster where it is and tighten up the gearbox top bolt.

Turn the engine over on the kickstart and test the chain in a couple of places to ensure it's not over tight anywhere.

Once the front chain is done, we can look at the rear chain. The Huntmaster has a fully enclosed rear chain case and the inspection point is behind a grommet which itself is behind the left hand side silencer. It's easiest to remove the silencer to gain access to the chain:

This is much easier on bikes with only a simple chainguard, but on this one we can enjoy the fact that the rear chain oiler is doing it's thing in keeping the chain clean and lubricated.

Once you can access the chain, slacken off both the wheel nuts and the lock nuts on the chain adjusters shown by the spanner in this next picture. When you tighten the rear chain you must make sure that both adjusters are turned by the same amount - count the flats - to make sure that the rear wheel alignment is maintained. Be really careful with this because setting up the rear wheel alignment is a bit of a pain. Do the lock nuts up when you're done and tighten up the wheel nuts again.

When checking the rear chain it's best to turn the wheel and sit on the bike, because a swinging arm bike will always tighten the chain when the swinging arm deflects upwards. Ariel recommend 5/8" chain movement with the swinging arm deflected to normal riding position and 1 1/4" to 1 1/2" with the bike on the stand. That's quite a difference and comes from the frame geometry - the swinging arm pivot is a long way from the mainshaft centre.

SQ4 - dodgy connections

 Riding home a couple of days ago in rather poor light I became aware that the headlamp had turned itself off. A few minutes fiddling with the light switch made me realise that there was something going on with the contacts - I could wiggle the handle and the light would flash. This needed further investigation.

As far as I could tell from various blog posts, this original Lucas U39 light switch had not been apart for probably 10 years. My own skills and knowledge have improved immensely in that time and I now clean these switches with an ammonia based clock cleaning solution as shown in this post. 

The one on the bike was clearly a bit grubby. 

I stripped it out and immersed it in a 25% solution of ammonia-based clock cleaner for about 4 hours.

After a few hours, the brass parts emerge without the tarnish and looking a lot more shiny and conductive!

Here it is again, reassembled.

Charlie's Shed - tool restoration

 I've done a lot of posts on toolkits and tool rolls in the past, and here comes one more. Repacking the Huntmaster toolkit one day I noticed that a 3/8 BSW spanner was rather damaged - in typical fashion it had been sprung open by over exertion.

It's actually quite easy to fix these. I set it up in my little hearth and heated it cherry red, picking it out with a pair of tongs and giving it some adjustment with a 1 lb hammer. It's actually closed up nicely back to size.

The black finish is achieved by quenching it in oil.

Here's another one:

Charlie's Shed - a leather key wallet

 As a precursor to making the tool boxes for the Model A, I'm doing a few leather work jobs in order to learn some new skills. This first one is a key wallet for a couple of keys that I carry when working on the railway. 

Here are the two keys in a cardboard mock-up of the wallet I'll be making:

The cardboard form is laid out on a sheet of 2.5 mm vegetable tanned leather. I've learned that vegetable tanned leather is stiff and makes good boxes and holsters, and that chrome tanned leather is softer and is used for clothes and gloves.

We'll cut the leather out with a craft knife. 

When the leather is wet, it's very easy to fold and form the shapes the wallet will need. This wallet has a double fold and additionally it needs a strip stitched to the back to form the belt loop. This means that the sequence of stitching is important because effectively the belt loop stitching becomes inaccessible once the front pocket is folded over and stitched but on the other hand, the belt loop covers up some of the front pocket stitching. 

What we have to do, is stitch part of the belt loop, then the pocket, then finish the belt loop.

Here's the belt loop in place. It's stitched at the bottom, where you can see it, but it's also got two rows of stitching behind the loop one of which was stitched before the front pocket and one after.

Here's the front pocket. The leather was formed around that T-shaped key and left flat for the smaller brass key. I stitched the T-shaped key pocket first though I had already fitted the press stud.

Long after I had finished this wallet I got some Tokenole leather buffing compound which I used with a wooden buffer to finish the edges.

Charlie's Shed - chemical blacking

It's a fasteners that I've been making for the Model A are all turned from mild steel - there is no stainless on the bike at all. The plan is to use some gun blue or chemical blacking to reproduce the iron oxide finish from the original fasteners, called 'coslettising'. As an experiment I have used this product on the Huntmaster's oil filter bolt:

 Since I made it some years ago I have modified it to provide greater engagement of the thread. After turning I degreased it and suspended it in the cold blue for about 5 minutes followed by a rub over with linseed oil.

Charlie's Shed - polarising the dynamo

 The need for this post arises because I have wired the Huntmaster negative earth. The dynamo that came with the kit is probably the original dynamo which of course will be expecting a positive earth system.

What's a dynamo 

A dynamo is an electrical generator that provides a direct current using a wire wound armature moving in a magnetic field following a principle discovered by Michael Faraday in 1832. It needs a mechanical commutator to turn alternating current into direct current since the rotating armature generates a current which changes direction as it moves through the magnetic field. An important principle as far as we are concerned is that the faster the armature rotates, the more voltage and current is generated by the machine. Similarly if the magnetic field strength is increased, the voltage and current will also increase.

How does it work 

In the motorcycle dynamos that we are looking at, the armature consists of a number of coils of wire wound around a stack of sheet metal shapes. The wires are terminated in a number of copper strips at the end of the machine arranged into a cylinder. The magnetic field is provided by a coil of wire wound around a suitably shaped metal structure fastened into the inside of the machine. The engine rotates the armature and a current is generated providing a magnetic field in the field coil. 

You will note that the magnetic field is provided by an electrical coil, and consequently you can imagine that the machine will not work unless that magnetic field is present when the engine starts. This is one of the issues we have to address. 

When the dynamo starts it is disconnected from the rest of the electrical system by the cutout in the regulator box and consequently won't start to generate electricity. In practice the field coil pole piece remains magnetized at least partially, after the machine was last used and we call this residual magnetism. This residual magnetism provides sufficient field strength to induce a current in the armature as it starts to revolve. Of course as the armature starts to revolve it generates a voltage which raises the field current which in turn increases the magnetic field, which allows a higher current to regenerated - and so it goes on. The voltage will carry on rising and in practice is limited by an external voltage regulator which takes effect by limiting current to the field coils.

Why do you re-polarise it

In a world where a motorcycle dynamo is perhaps not used every day, or the dynamo is moved from one machine to another perhaps having been bought at an autojumble or perhaps having lain around for a very long time since it was last used, it's functionality maybe compromised by a residual magnetism that is in the wrong direction or is so weak that it is virtually non-existent and the machine will not work. 

Therefore we need to have a method of generating that residual magnetism or changing its direction. Changing the direction of the residual magnetism might be necessary because you wish to rewire the machine for negative earth or perhaps because the machine for which your dynamo or specified rotated the dynamo in the other direction than that for which you wish to use it.

How do you re-polarise it?

Repolarizing the dynamo is quite straightforward and is just a matter of providing a current in the appropriate direction through the field coils. If you disconnect your dynamo, and provide a temporary cable from the battery terminal (that is not earthed) to the field terminal on the dynamo, you can repolarize the field coil by touching the wire on the field terminal momentarily. That should be sufficient to change the polarity of the residual magnetism or to generate it if it has seeped away. 

The temporary cable is not really necessary. Disconnecting the wires to the regulator reveals the green field coil cable and a brown and white cable from the ammeter. This brown and white cable is actually a battery cable, passing through the ammeter from the battery. Therefore, touching this cable to the field coil cable will polarize the dynamo correctly.

FH - ignition timing

 Edging ever closer towards first start, I diverted myself from wiring activities to time the ignition.

Regular readers will know the rocker box isn't fitted yet, and I can tell you that it's much easier to set the engine in position for ignition timing without pressure from the valve springs trying to restrain you.

As I've fitted 7.25:1 pistons to this machine, I am timing it to Cyclone specification - 3/8" BTDC at maximum advance in place of the 11/32" for the home market models. Here it is on the ubiquitous Wagamama chopstick, of which I have hundreds:

The timing is set with the timing side piston at 3/8" BTDC on the compression stroke.

With the engine in the right position, I fitted my little clamp to hold the ATD at full advance. The ATD is screwed most of the way on, but is not yet on the magneto shaft taper:

With a green Rizla in the points, I can rotate the magneto until the paper just loosens in the points. It's useful to have a 4 BA spanner available to just hold the magneto shaft on that central bolt while you gingerly tighten up the ATD nut from the other side. With the petrol tank off, it's easy to reach the magneto from the timing side of the bike.

Next, fully tighten the ATD nut. You can then back the engine off and come back up to 3/8" BTDC; if the Rizla is just coming loose in the points (with the ATD still clamped to full advance), you are good to go.

Charlie's Shed - Maintenance Logs

This post records my bike maintenance activities.

This is a link to a shared Excel spreadsheet listing the maintenance tasks, the frequency with which they should be performed and the mileage at which I last performed them:

•  Square Four Maintenance Log

This post has been upgraded to a page. It's here.

Charlie’s Shed - Lucas U39 switch repairs

I’ve got a few Lucas U39 switches - in fact they are on most of the bikes. I have two on the bench at the moment, a civilian one from the FH and a military one destined for the W/NG, which has an extra position which illuminates the tail light only.

These notes are intended to record a few areas where these switches get damaged and to show ways they can be repaired. You’ll need a few simple tools and materials.

The first problem is the rotor - the part that fits in the knob is worn. It’s supposed to be a cylinder with two flats, but the flats are so worn & corroded that the knob wobbles about. What I’ve done here is make a fence around the shaft with sellotape and filled in the centre with JB Weld. It had previously been thoroughly cleaned with alcohol.

Here is a close up view of the finished rotor - I have used needle files to restore the shape of the flats fitting into the knob, being careful to ensure the pointer aligns with the text moulded into the top of the switch:

Next is a Bakelite repair, again with JB Weld. Someone has tried to prise the switch out of a panel with a screwdriver and broken the moulding in several places:

To fix these problems, the first thing to do is clean it all down with degreasers, brushes and scraping. I built a fence around the repair with some plastic card:

Removing the fence reveals hardened resin ready for shaping:

A short session with a flat file produces something we can paint:

Here we go. A little matt black U-Pol finished with a smear of silicone grease brings the Bakelite up nicely:

Next up, the contacts. Some of these switches have moving contacts operated by the rotor, which get corroded and full of muck. In this case, the spring had corroded away; to remove these contacts you have to withdraw a tiny split pin. I had to drill what remained of the split pin out with a 1 mm drill in a pin chuck. 

You can buy these torsion springs on eBay, but once you have made a few and perhaps have a few bits of piano wire lying around in various diameters it is easier to make your own.

The last job is to soak the brass parts in an ammonia based cleaner for a few hours. This removes all the tarnish:

Charlie's Shed - Lining a petrol tank

Regular readers will know that in the past few months I have made weld repairs to two petrol tanks, one of which still has a weep in a very inaccessible place.

Today I'm going to line the tank with Slosh, from Rustbuster. This is a polyurethane sealer, resistant to Ethanol, that cures in air. I've cleaned this tank already with their SP10 Tank Kleen and a selection of nuts and bolts:

Those bolts came out a lot cleaner than they went in!

The sealer comes in two bottles, for two coats. You have to pour it in, rotate it around, wait twenty minutes and repeat twice more.

You let it drain from the tap connection to avoid it pooling in the bottom of the tank.

The reason you don't want it pooling is that it gases off a little when setting, and you don't want voids in the lining:

Three hours later, or when the sealer is dry but still tacky, you do the second coat in the same way. Then you let it cure for five days. Easy peasy.

This 400 ml kit is supposed to be sufficient for a 10 gallon tank, and I'm sure it is. My plan was to seal both the MZ tank and the Huntmaster tank in one sitting, but obviously two tanks have a greater metal surface than one tank (though the two together totalled less than 10 gallons) and I wasn't confident I'd have enough for both, so I ordered some more sealer for the FH.

Now that son Tom has his MZ sparking, he's clamouring to get his tank back...