Tuesday, 15 June 2021

SQ4 - bushing the saddle nose

Since I've had it on the road, the Square Four has felt a bit wayward around the rear end. Since I had rebuilt the rear suspension and knew that it had no wear, I suspected the tyre and wheel though they were both new and rebuilt - until I realised the problem was closer to home. Literally much closer, to my backside.

The saddle nose bracket on an Ariel frame is quite small, giving little bearing area. Coupled with a bolt with an over-long thread, used a s a bearing surface produces this effect after a few years:

This picture shows the saddle removed, but with the bolt in position. The red circle shows a portion of the thread used as a bearing - a very poor idea:

So, the first job is to make those worn holes round again. The bolt is 5/16" (0.312", or around 8mm), and they are both worn to over 0.350". I used an adjustable reamer on them to remove the ovality.

Ovality in the frame holes is not the only problem - the holes in the saddle frame are also very large. I have another problem in this area in that the fuel tank has very little clearance around the saddle nose bolt and I have solved both these problems in one go. In this picture, the original bolt has had it's head thickness reduced to produce a shoulder which fits in the saddle frame hole with very little clearance, and the full nut used at the other end has been reduced to the thickness of a half nut, again with a shoulder. This enabled the bolt length to be reduced, to get more clearance for the tank, and removed the whole assembly to the right to move the thread out of the bearing area.

Next job was to make two shouldered bushes to fit in the holes:

The bushes pass right through the fixed frame lugs, to provide maximum bearing area; there is a minimal shoulder to allow the bush to be retained in place (or removed).

This repair has removed virtually all the play from the saddle nose bearing.

Thursday, 10 June 2021

Model A - new bits from club spares

 I had a nice little present from AOMCC Black Ariel Spares this morning:

Here we see a pair of footrests, a brake pedal spring, the gearbox adjuster and a valve cap spanner.

Monday, 7 June 2021

Model A - Rear Brake Rod

 The rear brake rod is a much simpler affair than the front - it has a clevis at the rear end and this just needs a new pin, which is easy to make on the mini-lathe using a tailstock V-block:

The brake rod is just a bit of 1/4 round bar, threaded 1/4 CEI for the adjuster. The clevis is there, though very worn and we can find a spring from stock. The adjusting knob is missing, so we will turn that from a bit of 303 round bar, 1 OD:

It's reduced to 1/2" at the rear end, and the front appears to be domed but other than that is is similar to the front one. Same straight knurl:

Dome is made after parting off, with a combination of turning and a bit of filing:

We can mill a shallow groove in the rear to accommodate the clevis using an end mill.

Job done, though I think that clevis will need replacing.

Friday, 28 May 2021

Model A - front brake rod

 The Model A came with its original front brake rod, but none of the fittings. It's an odd design - the rod is 3/16" (0.1875") but, to prevent rotation in the brake arm, it's flattened at the end. This makes it larger - it's actually threaded 1 BA, on a major diameter of 0.209".

Of course, cleaning up the thread is a bit of a challenge with the flat since many dies will not bite having three sets of flutes, or very narrow flutes, as the thin rod disappears into the gaps. 

Here's my stock 1BA die:

See the narrow flutes? This next picture is another I bought:

The flutes are much wider on this one, and I managed to recover the thread and get my newly-turned adjuster knob to fit. It's made from 303 stainless steel on the lathe, milled for detent on a 1 BA mandrel in the toolpost:

The outside is cut with a deep straight knurl, slightly chamfered:

The next lathe job is the spring housing, copied from the one on the W/NG. It's a bit of 1/2" 303 round bar with a 1/4" CEI thread in one end, bored 9.5 mm for clearance on the 3/8" brake rod end:

Tuesday, 18 May 2021

Charlie's Shed - 276 air filter adapter

This is an exercise in turning as a favour for fellow AOMCC member Lee who is currently building a KH - a 500 cc twin. One of the delightful things that happen in the AOMCC is that members trade bits and information with each other - Lee gave me a new clutch adjuster for the W/NG recently, so it's my turn to return the favour and get some good turning and screw cutting practise at the same time.

His KH has a Vokes pancake air filter, which he wants to attach to a 276 carburetter. These are the dimensions:

They will be a 60° form - it's a CEI thread but in a non-preferred diameter.

We'll need a bit of this 2" brass bar:

I've faced this both ends and turned a section down to the required outside diameter of the larger thread: 

Next job it to cut the bore to the minor diameter of the inside thread, starting with drills up to 3/4" and finishing with a boring bar:

I'll cut the outside thread first - it's easier and I can test the setup. In this picture, you can see the thread is not fully formed - it's flat on the peaks:

I obviously didn't take too many pictures - I have finished both threads in this shot and have test fitted ot to a 276 of my own. I did actually turn a 1/2" length of the inner thread from a bit of thick wall tube to test it properly - this carburetter is in very poor shape so it's not a very good test.

Here's the finished adapter ring:

And here it is on Lee's carburetter. He says the thread into the filter is a bit tight - but we don't want it falling off now do we!