Tuesday, 30 July 2019

New carburetter for the W/NG

Updated from March 2019

I put a bid on this carburetter body (and won the auction!) thinking that I would have a go at sleeving a carburetter back to size, having some fun with my lathe and getting an original carburetter for the W/NG in the process. I know I can more easily go and buy a new 276 from Amal, jetted to suit my bike but where's the fun in that?

This 275B/1J came up on eBay at a good price, and is perfect for my W/NG:

For less than £20, I have a body, a slide, the jet block and the big union nut. There's a needle and a bent air intake bellmouth. It's all a bit fluffy, but we can attack it like we did the Solex.

It's actually in better shape than the 3HW 276 fitted to my bike, so I will get it up and running and see how it goes. Maybe I'll save the tired 276 for a bit of mini-lathe practice.

It will need an air valve, a mixing chamber top and a top ring, but most of the rest will transfer from the 276. The 5/045 air valves are available from Drags - the top and the ring might be more difficult...

Now to clean it up. With the bottom cap in the vice, we can use a large tube through the bore to provide some gentle leverage after the Plus-Gas has done it's job:

This is the first time I have seen the needle held in place with a bit of wire...

It's interesting how these things wear. That slide is nominally 1" OD; at the bottom, it's close to that:

It's very worn at the top, where the differential pressure pushes the slide against the body. It's about 0.965" here:

The top of the carburetter body is close to nominal:

The nations favourite carburetter cleaner. It's the fact that you are not supposed to use it on aluminium which makes it attractive - it's good at removing zinc oxides too, as well as old petrol deposits.

The brush on the right is called a 'file card' - it's for cleaning debris out of file teeth. It's also very good at cleaning threads in soft carburetter bodies:

Talking of threads, the throttle stop and air screw threads are 2 BA and are easily cleaned with a suitable plug tap. Don't force a taper tap into the air screw port though, or you will destroy the needle seat.

All the bits I have:

Rubbing the flange joint on some 120 grit sandpaper on a glass plate shows it is in pretty good shape:

Eventually I got a top and a threaded ring from eBay and I have just ordered a slide and an air valve from Drags, at vast cost. Here's the top ring and the top, of which both cable adjuster threads are intact. I'm happy about that; but not so much about the ding in the choke adjuster thread, which means the adjuster won't go in.

These threads are a little unusual - they are 7/32" x 40 tpi, which is a ME (Model Engineer's) series thread. These are a fine Whitworth form, and fortunately the taps and dies are readily available fromt the excellent Tracy Tools:

Next, while assembling the slide and choke into the carburetter top, I realise that the air valve guide is missing. I can turn that up from a bit of 10 mm brass round bar I have in stock - it's 6 mm on the OD, 7.6 mm where it goes into the top, and the spring is 4 mm OD. I drilled the ID 4.5 mm and then decided to open that up to 5 mm to ensure the spring does not bind.

Here's the air valve and guide from a 276, alongside the air valve for the 275 and the new guide I made:

Works beautifully, so it is on to reassembly.

Close observation of the parts diagram showed that the throttle slide has a split pin fitted to retain the cable. I've never seen that before:

I needed to shorten the cables by about 1/4", but other than that it's all back together. The fuel tap has a solid but old filter, and I have replaced the corks in both plungers; the return plunger has a new screw as well. Fuel tap repairs are shown in the first half of this post.

Monday, 22 July 2019

Petrol Tap Filters

Updated from December 2017

Many of the fuel tanks we have on our bikes are not in the best of condition and may be flaking rust or paint from inside, or worse, your tank liner may be in the process of falling to pieces. It's essential to have a good fuel filter.

Here are a few I made earlier:

Most of the fuel taps I have acquired have had either missing or holed filters, and, having had very limited success with the inline filters on the market (poor fuel resistance in plastics leading to cracking & cloudiness, or a ridiculous flow coefficient leading to fuel starvation) I have set about replacing the missing in-tank filters. This is typical of the damage you will find, if not a lot worse:

These are pretty simple to make if you are reasonably adept with a soldering iron. Start by removing the old one. I use a kitchen-type blow torch for this, which is plenty hot enough for sweating soft solder:

Hold the intake tube with a pair of pliers and twist it gently when the body is warm. It should come free quite easily

Look for the finest mesh you can find. The originals are a very fine copper mesh which is easy to obtain (though the mesh in the pictures is actually brass). Cut a suitable rectangle with scissors.

Start to form the cylindrical shape around a pencil.

You'll see that the final size for the filter on this double-plunger Ariel tap is very close to the diameter of an AAA battery:

I use a chamfered edge on an old credit card to form a tiny lap joint on both edges of the gauze, like I did with the oil strainer on the SQ4:

I then roll them around, mating up the lap joint and folding it down tight on the AAA former.

You can make a simpler lap joint like this:

Solder the joint with a small iron:

Flare the end to fit into the recess on top of the tap:

Have a good look at the recess on top of the tap. Make sure you clean out the joint of all goop, old fuel, rust and old solder. We are going to tin this area and sweat the new filter in.

Put the main feed pipe back in and trial fit the filter:

Now, push your AAA battery former up to the other end of the filter and form the closure:

Lay some solder onto the flare:

Lay a little more solder onto the end closure:

Flux the top of the tap and using a small blowtorch (the type you might use in the kitchen) apply some solder all around the joint, without the filter in place. Let it cool and clean it up and have a good look to see that it has run all the way around, then add the filter. Reheat the tap just sufficiently to melt the solder , and the heat should transfer to the solder ring around the filter flare allowing the two to fuse.

You might notice that this tap is fitted with a 3/8" BSP Dowty seal - makes a better job of sealing that joint than a fibre washer.

If you still have problems with your tap, check my post on replacing plungers here.

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

Saturday, 20 July 2019

Starting Young - Honda QR50

It seems to be a year for buying old red Hondas. First the 1978 CX500, now this:

Under that horrible red poster paint is a Honda QR50 from the early 1980's (initially I thought 1983 - overhauling the seat revealed the seat cover was made in 1988) which is a mini-crosser with Honda Express running gear. One day it may look like this:

It looks pretty scabby, and it looks like the rear suspension has collapsed. It is now in a pile of bits, but over the next few months son Thomas and I will get it ready for my grandchildren to ride!

There's an extra tube in that sub-frame

Break out the paint stripper!

Who cuts a chunk out of a tyre? no wait - I've done that myself. Must be rock hard

That cylinder head looks toast...

Why O why do people insist on stripping the engine and then leaving it for years?
This is the engine/transmission unit, assembled - not ours, a reference picture from Google. You can see the two 'swinging arm' bearings behind the cylinder:

Excellent parts lists here:


Monday, 15 July 2019

CX500 - Indicator Stems on the Mini-Lathe

Updated: First published 24th June 2019

The latest family acquisition is this 1978 Honda CX500, bought from eBay by son Thomas, and a very fine machine it is too.

The previous owner was, like me, quite short and had lowered the seat producing a very strange riding position; Tom has fixed that now with a new foam and cover.

You can see from the previous pictures that the bike is missing it's grab rail, which includes the proper mounts for the rear indicators and the tail piece. It's absence means the tail piece wobbles and the indicators don't earth properly.

So, a new grab rail appears from eBay but we need some indicator mounts. The ones fitted to the grab rail are wrecked:

We'll make some new ones from a stick of 19 mm grade 303 stainless round bar I have knocking about. We'll start with the end with the bolt recess:

I've drilled this part way through, 6 mm, for the indicator cable.

Then we'll swap it end for end in the collet chuck and machine the smaller diameter, which fits in two top-hat rubbers in the grab rail. We'll need a 10 mm diameter for the thread retaining the stem into the grab rail:

We'll thread these in the tailstock dieholder:

The tubes that carry the indicator stems have a small tongue, to stop the stem turning. The stem has a slot to receive that tongue which we can mill out:

That's two done, ready for the splines:

We'll cut 45 splines to match the original, using a tool ground at 80 degrees and taking 5 thou cuts to a depth of 15 thou. Here's the setup, using the indexing attachment I made; the lathe is used like a shaping tool in this configuration. The machine is out of gear and the E-Stop is locked off.

Here's a close-up of a few splines, cut to depth:

Here are the two stems, with splines complete and polished up with some 240 grit emery.

Next job was to turn up some isolation bushes in black acetal:

And here's the first one fitted to the grab rail:

And with an indicator test fitted: