Square Four - another clutch

 Well, I recorded in my last post that the Square Four clutch was slipping badly, so badly that as I rode it up the hill back to the workshop the engine speed was soaring and it was clear that the clutch was on its last legs.

I've said many times before that these bikes are very easy to work on. One thing I've always done when accessing the clutch is removed the footrest - but actually you don't need to do that. All you have to do is remove the nut and rotate the footrest on its mounting out of the way - you don't have to break the taper at all.

Even before I dismantled the clutch it was clear what happened - you could smell the burnt cork and there were bits of it everywhere. Stripping the clutch down revealed carbonized cork inserts - I could put my finger through these and they would just disintegrate.

Fortunately I had a spare set of 90 corks - that's enough for three plates - sitting in the workshop. Once I'd spent a couple of hours cleaning the mess off the plates I put these in boiling water for a few minutes.

You can push them in with your fingers - or a bit of wood is sometimes useful. It does make your fingers hurt after doing all of them, but it doesn't take long really.

I thought there was one missing - so I rescued a wine cork from the bin.

It's easy to slice these up into the right shape.

As it happened, as soon as I started clearing up the plastic bowl I've used to soak the corks I found the missing one so I didn't end up using my homemade one.

A couple of hours work had all the plates re-lined.

When you put new corks in, I always fit them to the bike wet. When you initially fit the plates they will only just be retained by the basket slots but the next day you will find they have settled a lot. You can see in this picture that the first friction plate is now well into the slots - this is about 24 hours after reassembling the clutch and all the corks are now dry.

I tested out a couple of days later, and readjusted the cable. The bike started straight away though as normal the clutch was stuck - I have always had to free the clutch before starting this one.

SQ4 Clutch Investigation

 After the Blakeney run, Tom reported that the SQ4 clutch was slipping when he got home - he couldn't get it to go over 50 mph without the clutch slipping. 

We rebuilt it using the new plates from the W/NG, which got it's old Ferodo plates back; middle grandson Felix helped with the job:

We made a little pointer to show the pressure plate was lifting squarely:

Oddly, it wouldn't function with the old pushrod - We had to add 1/8" to the pushrod length, having found the original 12 3/4" wasn't long enough but 13" was too long. We settled on 12 7/8".

A month later, we had the opposite problem where it wouldn't disengage - Tom took it apart again and adjusted it, and all was well. Sticky new plates, or some intermittent fault?

Charlie's Shed - Re-corking Cutch Plates

 For no good reason, other than the fact that the Square Four cork clutch is excellent, I decided to replace the part-worn Ferodo lined clutch plates. The W/NG clutch had always felt more severe by comparison and while the Ferodo clutch is correct for the W/NG, sometimes I do stuff because I feel like it!

The plates and corks come from AOMCC Gearbox Spares, and very good they are too.

The first step is to warm the corks in boiling water to make them soft and pliable. They were in the soup for about 15 minutes.

I fished the corks out in small batches with a draining spoon.

These are the plates - they look like they have been laser cut. The edges are very crisp and clean - the holes are perfectly shaped and there are no burrs. Oh - and they are perfectly flat!

You push the corks in from the wide end of the slot, trying to keep an equal amount of cork protruding from the plate on each side.

Push the cork down, and manoeuvre the wide end in until it is sitting evenly all around the slot.

Repeat the process until you have done all the corks in all the plates!

As it turned out, after drying overnight the stack of plates was too thick for the basket.

What you do now is to work each side of each plate against a large flat board covered with sandpaper. This is 120 grit - I rubbed each plate over a couple of times to make sure the corks were level and to take a fraction off each one. Very soon, the stack fitted in the basket.

At the same time, I renewed the clutch springs - also from AOMCC Gearbox Spares. On the left is the old spring; on the right, the new spring. Whilst the old spring is clearly collapsed, the odd thing is that it is the same wire diameter as the new one - springs for a Ferodo clutch should be heavier.

Model A - First Impressions of a Clutch

Isn’t it a bit early to be looking at the clutch on that bike, when you have so many others in the pipeline I hear you ask? Well, yes it is, but a while back I lost one of the tank bolts on the W/NG - you might remember I made a new one; I am diverting myself with lathe jobs as a distraction from all the welding on the QR50, and part of the lathe work is to collect the bits for the gear control on the Model A, and to do that I need to mount the tank - which is another lathe job, as one or two of the bolts are missing - so I need the tank mounting rubbers for that too, and I also want to trial fit the tank on the FH and I have no rubbers...

So what I need to do is to get an order for Jeff Hunter Engineering, who will supply all the rubber bits and what I am going to do is order as much of the rubber as I can, for all three Ariels. And this is where the clutch comes in - the Sturmey Archer clutch in the Model A has a rubber shock absorber in the clutch and this is bound to need some attention:

So let’s have a look. It’s very easy to get to as in 1930 Ariel were not using the fully enclosed and sealed primary drive, and my primary cover is off awaiting time on the welding bench:

Clearly, two of the retaining bolts, springs and spring cups are missing. Those bolts actually have screwdriver slots under that muck.

Under the pressure plate, the basket and centre are very good indeed:

The plates are reasonable too, but I wasn’t expecting Ferodo linings:

The parts list clearly shows a cork lined clutch:

Yet if we look in the Sturmey Archer book from the period, there is a Ferodo option for the three plate clutch. Interesting.

We’ll have to replicate these parts, though I wonder if they have been intentionally omitted. Ferodo clutches of the period can be quite heavy - the one on my W/NG is much less pleasant than the cork clutch on the SQ4, for example.

Still, it will be a long time before we have to deal with that problem.

Charlie's Shed - Fuel Tap Plungers

If you find yourself short of plungers, or the shaft of your adjustable plunger is damaged, they are quite easily made if you have access to a lathe.

The brass centre of the adjustable plungers, which is often short from having the slotted end broken, can be made from a bit of 3/8" round bar. Chuck this in the lathe and turn a suitable length to 5/32" - the best way to do this is to turn an 1/8" or so to exactly the right diameter, then use this short length as a guide to turn the rest in one pass. With a sharp tool this shouldn't be too much of a problem and it avoids the tiny bar bending away from the tool, which will result in the outside diameter being over size.

Chamfer the end and cut the thread - it's 5/32" BSW. Make sure you use a tailstock die holder or back the die holder up with the tailstock to keep it square - you don't want that thread wandering off.

Give it a polish and part it off:

Assemble it into the plunger and you are done:

The shaft I have made here is a bit over-length compared to the old one - maybe I will adjust it a tad. Notice the diamond knurl. I don't have the cutters for that - straight and diagonal knurls yes, but not the 'inverted' diamond knurl. Rather nice, and easier on the hands...

Post war plungers, as I mentioned in my other post on the subject, are non-adjustable unlike their prewar forefathers, and because of this I think it makes sense to update them with an O-ring seal.

The hexagon reserve plungers are made from 0.600" 303 stainless steel hexagon bar. You'll need a decent length for chucking and for the milling operation. Chuck the bar with a couple of diameters showing beyond the jaws, to give you enough space to part off when you are done:

Turn the shank to the required diameter - a little over 5/16". This needs to be a loosish clearance fit in the tap body you just reamed.

Use a thin parting tool to form the O ring grooves. Space them so that they are at either end of the equivalent length of cork:

For those, like me, without a mill you can use the toolpost or a milling attachment to mill a 3/32" slot, about 1/16" deep in the tap shank. Since the loads involved in this operation are tiny, I didn't bother to set the lathe up for milling. I cut the slot at about 1500 rpm in two passes, with a 3/32" slot drill.

Once you have completed the milling, test the plunger in the body and make sure the plunger slides freely with the retaining screw in place. Next, put the bar back in the chuck and polish up the shank; then, before you part off, turn the shallow chamfer on the inside of the head. You can then part off.

Turn the plunger in the chuck, and skim the outside face of the head, cutting the shallow chamfer in the same setting. Polish the head and you are done.

And watch out - the reason that slot looks slightly ragged is because I broke a cutter in it. Go easy.

Next thing - you will want to smooth the edge of the ports in the tap. look at this:

See the sharp edges? Remove that with a burr in the Dremel, or a tiny grinding tool. If you leave it, the O ring will be damaged. Look:

That nick will cause a leak. You are not really supposed to use O rings in dynamic applications like this.

Thanks for reading, and I hope you found it useful.

Charlie's Shed - Fuel Tap Leaks

Updated from 2017

Following on from the replacement fuel filter I made here, I wanted to show you how I have renovated the double plunger taps fitted to my Ariels.

The plungers fitted to these taps are a simple design with a few variations - prewar, the plungers are adjustable and of about 3/4" diameter; post war, they reduce to about 5/8" and lose their adjustability. There is the plated knob, which may be round and knurled or hexagonal; the knob has a short shaft which has a milled groove, aligning with a peg in the tap body (to stop it coming out), and this groove is usually straight, but may be milled with a dog leg such that you can turn the knob to avoid inadvertently shutting off the tap. Fitted inside the knob is a brass inner shaft, of about 5/32" diameter for most of its length which is provided with a short section of larger diameter, to fit inside the tap body and to carry the cork.

Lastly there is the cork - a cylinder shape fitting tightly inside the tap body and around the inner shaft.

Here's a selection. These are all post war (so about 5/8" diameter; the hex is 0.600" across flats), and came to me from John Mitchell of the AOMCC.

You'll notice how some of these plungers have a straight slot for the retaining screw, and some have a slot with a 90 degree bend. These are the 'turn to lock' type, which are later than the ones with the straight slot:

Now, these taps are pretty reliable if you know what you are doing when you set them up. The corks wear, and they dry out leading to leakage but if you keep them in good condition they work well. If you have a leaky tap, first consider what you have been doing with the bike. If for example you drained the tank over winter, or the bike has been out of service for a while, or you just bought the tap off eBay try letting the plunger soak in a puddle of petrol for a while, or immerse it in a pot of boiling water for a few minutes to rejuvenate the cork. This approach has restored many taps to working order.

If you have to replace the corks, you need to remove the inner shaft using a punch - a 3 mm or 1/8" punch will be fine. Locate the mushroomed end of the inner shaft and place the knob, shaft down, in the jaws of a vice.

Tap the mushroomed end of the inner shaft with your punch and drive it out

You should have the plunger in two pieces:

Replace the cork. Check that the new cork has a hole that is on-centre all the way through, and that the ends are square - a lot of them are poor quality. Check that it is solid and does not have any dark grooves in the cork that are going to cause leaks.

Check also that it is the right length. The short length of MIG wire in the picture below has two bends in it - one to indicate the open end of the tap and one to indicate the location of the fuel port drilled through the tap - the port that the cork will shut off. You can see that the short cork fitted to the tap has no hope of covering up the holes, but the longer new cork will cover the holes nicely.

Reassembly is simple - fit the new cork over the inner shaft and press the tap together in the vice. Wet the cork in petrol and try it in a tap - it should slide but be quite stiff. Up end the plunger again, and use your punch with a hammer to slightly swell the small end of the inner shaft, retaining it in the tap.

Prewar, the tap plungers were made so that you could adjust the corks and the reassembly sequence is a bit different. This is a prewar plunger, though not in it's own tap; the inner shaft has a 5/32" BSW thread (yes, really) retaining it in the knob, and the hex is about 3/4" across flats.

The shaft has a screwdriver slot and a lock nut, so when you slacken the lock nut you can turn the shaft and knob independently and compress the cork, improving the seal. The lock nuts are often missing, but early Meccano nuts are identical and readily available from specialists; they are a 5/32 BSW thread, but the hex is designed (or maybe just fits) 4 BA spanners.

The shafts are sometimes too short - the screwdriver slot is easily broken if you try to adjust it without removing the locknut. In this case, the only option is to replace the shaft or the whole plunger. Replacement shafts are not available but can be made on the lathe, as I show in this post.

There is a note of caution here though. If the locknut is absent, the thread damaged or just not tight, my W/NG is perfectly capable of loosening the tap cork after a fast run. The result of this discrete self-destruction is a strong smell of petrol in the garage and a drip tray curiously full... The moral of the tale of course, like most things with old bikes, is that nothing is 'fit and forget'.

If after replacing or adjusting your plungers, your tap is still leaking there maybe excessive wear or damage to the tap bore; you may have had trouble adjusting the cork to get it to slide evenly. It's a good idea to remove both plungers and inspect the bore - if you suspect it is worn, run an adjustable reamer through it to skim the surface and restore a consistent diameter through the tap. The bore is normally about 11/32" ID - I use an 11/32" - 3/8" adjustable reamer. Your aim is to remove the minimum amount of material, but to true up the surface:

When you have passed it through, look and see if you have cleaned the whole surface of the bore:

But what if you have no plungers? If you have a lathe you can make them quite easily, as I show in this post. Indian-made plungers are readily available on eBay and the ones I have seen use long M4 screws for the inner shaft. These are again of highly variable quality - the ones I have are plated very well, and look good - but of the five I have, only three have the inner shaft hole in the centre and the corks are way too short...

Usefully though, they can also be made adjustable. I made this one using a long brass M4 screw, with a slotted head filed flat and an M4 lock nut.

Once refurbished, these taps are very reliable. Attach them to the tank with a Dowty sealing washer:

Here's a dual plunger tap beloved of Ariel, fitted with two pre-war (so large size), adjustable plungers.