FH - rocker box refurbishment

With the cylinder head coming on, it’s time to take a look at the rocker box. We won’t be doing too much, as a number of folk have told me how a BSA A10 rocker box fits straight on and is a much better design - but I don’t have one of those.

We’ll start by stripping out the rocker shafts and cleaning the box.

While the lathe is in action, we’ll replace the 5/16" BSW stud that wasn’t holding the cover on - the covers are held on with a special 1/4" CEI sleeve nut. What we need is a stepped stud, like the original in the inlet side but with a 5/16" BSW thread to go in the aluminium casting. Somebody has already recut the thread in the casting to suit the replacement stud.

We'll start with a bit of 5/16" mild steel round bar. Because it's 1/4" in diameter for most of its length we'll need to be careful when we turn it. What we will do is use the travelling steady on the lathe to support the slender quarter inch section as we turn it to size.

 This turns out pretty well especially when we make a finishing cut with a round nose tool. Cutting the 5/16 BSW thread, I've set the die to its largest diameter such that the thread is a little oversize.

This is where the oversized thread pays off - when it's fitted in the box the the stud fits quite tightly and hopefully won't back out.

The next step is to get the box in the cleaning tank for degreasing; we'll then examine it for damage and polish the outside.

Mini-lathe - boring bar

 

My 0XA boring bar holder fits 1/2" bars or 3/8" bars with an adapter sleeve. Shame my boring bar is 10mm! It currently resides in a 250-001 tool holder, which is a bit of a waste.

Mini-lathe to the rescue! The sleeve on the left is turned from a bit of 1/2" round bar, with a 10mm reamed hole and a slit. Works perfectly, and liberates another 250-001 tool holder!

SQ4 - fuel tank

 Some years ago the Square Four got a new fuel tank in original paint from Yeoman’s Motorcycles. It was pretty shabby but it still had the coach lines picked out in gold paint to show where the Ariel craftsmen put them all those years ago.

As you can see the paint is very faded. The Square Four wore this tank for several years but eventually I decided that it was really too far gone. I didn’t really want to repaint the whole tank and lose all the patina, so inspired by Graham Ham’s book about his Speed Twin ‘Daisy’ I resolved to clean up the paint as best I could and enhance the gold lines a little bit.

The areas that were worse affected were around too weld repairs where the tank badge carriers had been refitted. The paint here was burnt and discoloured and no amount of rubbing down was going to bring that back. I used a matching spray paint (from stock I had accumulated years ago) to blend these areas in to the rest of the paint. Rubbing all the paint back with various grades of wet and dry from 240 to 2000 brought the tank back to life enough. 

I then used some old jet black gold lacquer and some 3 mm PVC masking tape to put the lines back in. When these were mostly dry I rubbed over them with a dirty glove to dull them down. This works reasonably well when I timed it correctly but if the paint was too dry it didn't pick up the dirt from my gloves.

It needs more work of course, but it's getting there for sure.

Mini-lathe - manual drive

 It's useful sometimes to be able to manually turn the lathe chuck, particularly on these little lathes which don't have a lot of low speed torque, for example when thread cutting. Usually I just haul the chuck around by hand, using the chuck key or a bit of bar like this:

It works, but it's a bit ugly and the chuck guard gets in the way.

There are a few designs around for cranks that can be used with an expanding arbour, or the crank can be expanded into a full wheel for better control.

I made this expanding mandrel years ago as part of a dividing setup for the lathe. I used it to make a number of splined shafts and the graduated collars for the tailstock and the saddle hand wheel.

The mandrel features a journal at one end to carry a gear which provides the dividing index. An M6 threaded rod passes through the mandrel which connects with the expanding plug at the inner end.

With this mandrel already in the tool box, it makes little sense to repeat the exercise for a crank with an expanding arbour so we'll adapt the one we've got. I've made this boss for the hand wheel - it registers with the expanding mandrel on the journal where the indexing gear normally fits, but I have added a pinhole to that mandrel to enable the boss to drive the mandrel. The boss is provided with a drive pin at one end and a 1/2" BSP thread at the other, to which I fitted a pipe flange to carry the wooden wheel itself.

Here's the wheel - it's simply cut from a scrap of 3/4" plywood. The M6 threaded rod that expands the mandrel passes through the hand wheel boss into a recess on the other side such that the same threaded rod can be used both for the hand wheel and the dividing set.

The nut in the first picture is replaced with this special threaded widget which reaches down inside the boss to mate with the threaded rod and lift the expanding plug, specially designed so that the dividing setup and the handwheel setup can use the same expanding plug and threaded rod.

Here's the manual hand wheel in place with the special nut holding the expanding plug wedged into the mandrel and providing a rigid drive for the chuck.

Here's the other side. It does of course fit with the gear train cover in place.

I've stored the wheel on a little post screwed to the wall - oh all right, it's just a screw in the wall that the wheel sits on:

Lathe - lead screw handwheel

 I made a lead screw hand wheel for my mini-lathe a few years ago. It works, but it's generally a bit wobbly because it's fitted to a very short M8 thread on the end of the lead screw.

You can see it here. The plain section is the tail end bearing for the lead screw and that short M8 thread you can see is the thread for the lead screw end float adjustment. It's very short, probably about 10 mm.

What I've decided to do is to replace this section entirely with a much longer piece that carries the bearing and passes much further into the short shaft I have my hand wheel mounted on.

The first step is to part off the old 8mm section and drill out 7.5 mm, reaming for 8 mm.

Next we will let in a short piece of 8 mm round bar into the reamed hole and we'll retain it with high strength Loctite retainer. This would have been very straightforward had the first piece I selected not been 5/16" rather than 8 mm! Measure twice, cut once as they say.

I put a longer thread on the new piece of rod to retain it solidly into my hand wheel axle.

Here it is in place. It's retained by an M4 grub screw into the plain section of shaft at a point where the end float is minimised. Actually there is no end float measurable in the installation at all.

There are a couple of modifications to the old handwheel here that may be obvious or may not. The wheel fitted in the later pictures is much larger than the old one for better control; there is also a small piece of rubber fitted into a 4 mm hole in the axle which provides a bit of extra friction to the graduated collar.

The collar, by the way, is divided into 62. The lead screw is 16 TPI, or alternatively has a pitch of 1/16" or 0.0625". This means that each division of the collar has an error that amounts to 0.0005" per turn.