Monthly Archives: November 2013

The Gasworks

Next is to strip and clean the carburetter

No, that’s not a mis-spelling, the bike is fitted with an AMAL instrument and they have always used this spelling for their product so if it’s made by AMAL it’s a carburettEr and if it’s from an other manufacturer it’s a carburettOr.

Pre 1955 AMAL supplied their 276 and 289 series, these had a separate mixing chamber and float chamber and it’s this type that’s fitted to my Panther.

Strictly speaking I should be using an instrument from the even older 76 and 89 series as the 276 and 289 types came into use in 1940 when there was a design change in the pilot air inlet system but my bike has been fitted with this later type at some time in it’s life.

Amal carb

A complete Amal 276 carburetter

First step is to remove the float chamber.

This is attached to the main body by the nut at the base of that chamber, undo that and the fuel chamber comes away in your hand, exposing the main and needle jets, and can be put to one side for later.

The main body or “mixing chamber” is basically two tubes in a cross, the horizontal tube being the main airway and the vertical one contains a brass jet block held in place by a ring nut screwed onto its base and it also contains the throttle and choke control slides.


Mixing Chamber

This chamber comes apart by first unscrewing the knurled ring nut at the top of the vertical, (on mine the thread in this nut is worn and it has to be replaced).

You can now withdraw the choke and air slides from inside the body.

There is also a large ring nut at the bottom of the body, with a hexagon to take a spanner/wrench and removing this gives access to remove the jet block (but remove the main and needle jets first).


Jet block is retained by this ring-nut

This ring nut is the same thread form and diameter as the knurled ring nut at the top and so I used this to check that the threads at  the top of the body were sound.

The jet block is a light press-in fit into the zinc/alloy main body and will readily push out. Notice that there is a special composition washer goes between the base of the jet block and the nut and that the correct gasket MUST be fitted (some cheap, pattern, gasket sets supply a paper gasket for this that is too thin).

All that’s left in the main body are the pilot air screw and the slide stop screw so these were removed and the whole assembly of parts put into an ultra-sonic cleaning bath.

After a session in this bath the passages in both the jet block and the main body were blasted through with an aerosol carburettor cleaner and then the whole lot were given another session in the ultra-sonic bath before they were allowed to dry off.

Come re-assembly and first step is to fit the jet block into the main body, as this is a light press fit and I didn’t want to use force here the body was heated up in boiling water and then the jet block fitted.

You need a bit of attention to detail here as it is possible to put the jet block in in two ways and only one of them is right since when it’s 180 degrees out of phase the passageways in the body and the jet block don’t line up with each other.


Mixing chamber, jet block and ring nut

With the jet block fully home in the body you next fit a new composition washer and then the bottom cap nut, it’s a good idea to fit the needle and main jets now as well, you can fit the fuel chamber’s banjo bolt loosely here just to keep any muck out of the jets.

The throttle slide has the needle position checked that it’s in the correct notch and is then slid into place and its easy movement checked, you can also check for wear in the slide and body by trying to move it back and forwards in the body. If needs be it is possible to have the top of the body bore out to true again and the slide sleeved to fit the new body, if the whole length of the body is bored out then you’ll need to get the base of the jet block sleeved as well so make sure whoever does the work for you knows what he is doing.

Now is a good time to fit the slide stop screw since you can keep a finger on top of the slide while you fit it and so find the exact point at which the slide is being raised off the the mixing chamber’s floor.

Once it starts to lift give it one full turn more to give a “set up” position to the slide.


Throttle stop and mixture screws

The choke slide is next dropped into place along with it’s guide tube and spring,

Then the throttle slide spring and the mixing chamber top is fitted and secured with the knurled ring nut.

Only thing left to refit is the pilot air screw and this is screwed in until it bottoms and then turned back one and a half turns to the “set up”position.

While doing all this the float chamber had been quietly bubbling away in the ultrasonic bath so it was given a scrub with an old tooth brush to get the last of the muck off it, same as was done with the carburetter body.


Float Chamber

This is a bottom feed chamber so the float needle is dropped into place through the fuel inlet union and the float dropped onto it from the other end.

With an original float, it is held onto the needle by a spring clip fixed onto the top of the float so the clip has to be nipped between fingers and the float slid down the needle until it engages with the correct one of the two notches on it.

With a 276 carburetter you use the lower of the notches on the needle and you have to push the needle up at the same time as you slide the float down it until you feel the clip engage the notch.

The modern, plastic, replacement float uses a loose clip, the same part as secures the throttle needle in the throttle slide, to locate the float needle rather than having the clip as part of the float.

Now it’s just fit the float chamber top and tighten the locking screw on it and you then fit the float chamber onto the base of the mixing chamber, using a new fibre washer either side of the banjo, but don’t nip it up tight yet! and the assembled carburetter can be put on the shelf till it has to be fitted.

When you come to fit the carburetter to the bike first thing is to attach the throttle and choke cables to the two slides.

The cable inner wires fit through the adjuster screws on the chamber top.

Tthe choke cable then goes through both the upper guide tube and the spring for the choke slide and then, while the spring goes down inside the slide the end of the cable is slid down through the slot in the slide and then the nipple is seated in the bottom of the slide.


Fitting choke slide cable

The throttle cable goes through the throttle slide return spring, attaches to the socket in the outer edge of the throttle slide and is retained in place with a split cotter.


Fitting throttle slide

The two slides can then be slid into place in the mixing chamber, the top fitted in place and the ring nut screwed down.This is made easier if you set the choke slide to the open position and hold the throttle open so their springs are compressed.

The body is then bolted onto the inlet port adaptor with a heat-insulating washer between it and the inlet stub and the copper fuel feed pipe attached to the base of the float chamber.

NOW you can tighten the bolt attaching the float chamber to the mixing chamber.

Once this is done you can set up the free play in the throtle and choke cables using the adjuster screws on the mixing chamber top.

As the jetting has already been set up to the published figures all that’s left is to set the tick over and the pilot air adjustment, but this has to be done on a hot engine.

The basic settings, with the pilot screw one and a half turns out and throttle stop one turn open, will allow the engine to start and run, if it’s tickover is too fast you can turn back the throttle stop a bit but you now need to go for about a ten mile run to get everything warmed through.

Then, working quickly so the engine does not overheat, it’s just a case of reduce tick-over with the throttle stop until the engine begins to falter, you now adjust air screw till it speeds up, then slow it on the throttle screw again and repeat until it’s as slow as it will go, then screw in the air screw an eighth of a turn.

Check it now picks up cleanly when you add a bit of throttle and that’s the job done.

Pushing on

(This one is out of sequence as I forgot to post it, sorry.                                                                 It should appear between “Sod’s Law Strikes” and “On Tap”.)

Once I had the clutch assembled it needed adjusting and I ran into another snag, there was no free play in the mechanism.

The linkage consists of a lever inside the gearbox outer cover, a short connector piece it bears against, a 1/4 inch ball bearing and the pushrod itself.

It is not possible to mis-assemble at the lever/connector as if you do the outer cover of the gearbox will not go home and omitting the ball would leave too much play so suspicion fell on the pushrod.

Checking the books showed there were two slightly differing lengths available for the pushrod across the period when my bike was built but I found no reference as to when the change was made.

So it was a case of take off the clutch spring plate, remove the pushrod and check which one I had.

On removing the pushrod it was obviously a home made rod and rolling it on the bench showed it was bent so I decided to make up a new one to fit.

To do this I got a length of 1/4inch diameter silver steel rod. This is readily available, I got mine from Cromwell Tools

It comes in a 13 inch length and is diametrically accurate to within 0.00025 inch, not only that but it is easily heat treated to harden the ends.

First thing was to measure the old pushrod to determine its length, as it was very nearly correct in length I cut the silver steel to the same length and made a check assembly of the clutch.

Sure enough there was still no free play so I shortened the new pushrod by gripping it in padded jaws in the vice and filing the end back a bit.

Because it’s much easier to remove material than to add it I only removed a little then tried another check assembly then repeated the operation until I had the play I wanted.

The ends of the pushrod were then polished with a hand held oil-stone and the sharp edges taken off at the same time.

Now to harden the ends. Because of the composition of silver steel all you need to do is heat treat it, there’s no need for Kasenit treatment as it would if I had used bright mild steel to make the pushrod.

First stage was to heat one end until it was bright red-hot, about the colour of a cut carrot, and to hold it at that temperature for a couple of minutes.

The red-hot end was then plunged vertically into water and stirred round vigorously to quench it.

This hardens the heated metal to a “glass-hard” state, one where a file or a hacksaw will “skate” on the surface and will not cut it, downside is that at this state of “temper” the metal is brittle.

So I next “drew the temper down” so it was no longer as brittle but was still a good bearing surface on the ends.

To do this the now discoloured end was cleaned with some fine wet and dry paper and given a polish. The trick now is to apply heat to the rod about an inch in from the end and watch the colour change at the end.

As the metal was heated, at the heated point it turned blue and was kept at this.

Colour could be seen to move from the blue area down the pushrod and at the polished steel end it first showed a light yellow and when it had darkened to a yellow-brown it was again quenched.

This drew down the temper to the level you would use for making a punch which is what I wanted for this job.

If you want more details as to tempering steels a web search will throw up a number of sites such as this one;( be careful, this site is very moreish!).

Having done one end of the pushrod I then hardened the other in the same way and I had my new pushrod ready to fit.

Back Up

When I first made this sidecar I had a seat made for it, this seat is not really satisfactory but when I tried to have one made up properly I was told it could not be done at reasonable price, reason given was “No-one does it like that now-a-days”, which is why I’ve now made up a new one myself.

2 seats

The two seats, commercial one on the left.

As you can see the “professional seat” has been made by simply taking two blocks of foam and putting a cover on them and has a much thicker apron than the one I made, which is copied from an original Steib seat, the “bought in” looks like something you’d find on a bus!. This extra thickness reduced the knee clearance inside the cockpit and also made it a bit more difficult to get into and out  of the sidecar. As the apron lies on top of a set of tension springs set into the cockpit floor it does not need to be as thick as this hence the thinner apron on the genuine Steib seats.

Seat "aprons" compared.

Seat “aprons” compared.

First thing in making up the new seat was sorting out materials.

What’s needed is a new back-board, foam padding and covering materials.

The seat has a wooden back that hooks over a tongue on the top of the rear bulkhead of the cockpit and at the bottom is shaped to fit into the octagonal body.
seat back

This is the tongue the seat locates over

Onto this board is fixed a block of upholstery foam which is covered and held in place with heavy calico and over this goes the reeded top-cover with lower “apron” that goes on top of the support springs.

Under the seat

The springs that support the “apron”

On looking round the ‘net I found “Woolies” from whom I could source the foam and covering materials and I went down to the local DIY shop for some 12mm plywood from which to make the backboard.

I ordered up some 50mm and some 38mm foam along with the red vinyl covering material and calico.

To stitch the covering together I used an old-fashioned “Singer” hand-cranked sewing machine  fitted with a needle intended for sewing leather.

A modern electric machine baulks at sewing the multiple thicknesses of the materials I’m using.

The foam was supplied as a rectangular block and had to be cut to shape, this was easily done using an electric carving knife, bought as a special offer and afterwards donated to the kitchen.

First thing was to make up the backboard

The flat main board has a top “overlap” that is made up from another three pieces of plywood fixed to this board to allow it to locate over the tongue on the seat bulkhead.



The two pieces “A” and “B” were glued and screwed to the top of the backboard as in the sketch and then the long piece “C” glued and screwed on top of those.

The piece of 50mm foam was cut to fit onto the side of the backboard away from the overlap and then glued onto the board with PVA glue.

The foam was then covered with a piece of the calico which was taken round onto the back of the board and fixed there, PVA glue again and a staple gun used to secure it.

To be continued:-