Charlie's shed - adjusting primary & rear chains

 The Huntmaster clicked over 400 miles on a run recently and is bedding down nicely. Checking it over in the workshop revealed a front chain that was rather loose, and of course one of the issues that you learn when dealing with these old bikes is that if the front chain is loose the rear chain will probably be tight as sometimes the gearbox will move. 

It's time to have a look at both chains, and for this we will use the on board toolkit:

First stop is under the oil tank where we find the gearbox top bolt and the chain adjuster. Loosen the nut on the right a little bit and then use the chain adjuster to draw the gearbox backwards or push it forwards.

Next you need to gain access to the primary case so that you can inspect the tension on the primary chain and later top up the oil. If this is tight use a big flat spanner to undo the inspection cover:

Now you can see the chain. This should have about 3/8" up and down movement and this should be slack movement - the chain should not be stretched tight and you should not be putting much effort into moving it. If the chain is too tight you will be putting undue pressure on the engine main and gearbox bearings, not to mention the chain itself and the clutch basket bearing. Typically the chain will get looser as it wears and you will use the gearbox adjuster to draw the gearbox backwards by a little bit to tighten the chain. When you are done, leave the gearbox adjuster where it is and tighten up the gearbox top bolt.

Turn the engine over on the kickstart and test the chain in a couple of places to ensure it's not over tight anywhere.

Once the front chain is done, we can look at the rear chain. The Huntmaster has a fully enclosed rear chain case and the inspection point is behind a grommet which itself is behind the left hand side silencer. It's easiest to remove the silencer to gain access to the chain:

This is much easier on bikes with only a simple chainguard, but on this one we can enjoy the fact that the rear chain oiler is doing it's thing in keeping the chain clean and lubricated.

Once you can access the chain, slacken off both the wheel nuts and the lock nuts on the chain adjusters shown by the spanner in this next picture. When you tighten the rear chain you must make sure that both adjusters are turned by the same amount - count the flats - to make sure that the rear wheel alignment is maintained. Be really careful with this because setting up the rear wheel alignment is a bit of a pain. Do the lock nuts up when you're done and tighten up the wheel nuts again.

When checking the rear chain it's best to turn the wheel and sit on the bike, because a swinging arm bike will always tighten the chain when the swinging arm deflects upwards. Ariel recommend 5/8" chain movement with the swinging arm deflected to normal riding position and 1 1/4" to 1 1/2" with the bike on the stand. That's quite a difference and comes from the frame geometry - the swinging arm pivot is a long way from the mainshaft centre.

Model A - drilling holes

 With the space for the pawl milled out, the next step is to drill some holes for the pawl spring and the pivot pin. When that is done we can function test part of the mechanism.

To drill for the pawl spring we keep the vertical slide setup in the lathe. Getting the height is straightforward because we can use the old shaft to line the vice up with the drill and thus ensure the angle of the hole is correct. 

Since this is going to be drilled in a surface that isn't perpendicular to the drill, I start the hole with a 1/4" slot drill and cut for a few millimetres, finishing the hole to depth with a twist drill.

The twist drill is marked to depth with a bit of tape. A 1/4" drill isn't quite enough - I drill it 6.5 mm to clear the spring and it's plunger:

The holes for the pivot pin aren't quite so easy. I'm going to make a small deviation from the original design here - The original pin is stepped, it's a 5/16" pin reduced to 9/32" for part of its length. Strangely the larger size is inboard, so the step prevents it moving outboard. I want to make the smaller size inboard so that there is no possibility of the pin coming loose and interfering with the layshaft first gear. 

The problem with this approach is that there is no way a conventional twist drill can reach.

I ordered some long series twist drills from the excellent Tracy Tools. They will be here in a few days.

Model A - milling the kickstart shaft

 I can't believe that it's over 2 months since I started work on this kickstart shaft, but I guess plenty of other things have been going on at the same time including railway stuff, making the parts to exchange for the 3D printed gears and other things. However, we are well on the way and this latest post is about milling in the vertical slide set up for the kickstart shaft shaft stops and the platform for the kickstart pawl. 

Milling the end stop took two attempts to get the angle right but I'm very satisfied with where this is now:

This is the other end which is a bit more difficult because it's a completely enclosed corner. I started this with a 3/8" end mill and finished with a 1/4"  slot drill to remove as much material as I could. It may yet need to clean up with the Dremel.

The next step is to rotate the shaft and start with the flat area where the pawl sits. I've marked the edges of the area using the original shaft as a guide and I've tried to set up the new shaft in the vice such that the virtual area defined by these lines is in a vertical plane. I used a pointer in the collet to line up the marks as shown below - this is a later picture, but it gives you an idea:

Cutting at around 0.5 mm per pass, we start to define the flat area:

Many passes later and we are nearly there. The finish is fine, despite the grumbling vibration from the lathe. I tightened up the gib strips during this operation, but I really must look at the saddle retaining strips.

Soon afterwards, we are done. The platform for the pawl is 10 thou narrower than the original.

Next step is the holes for the pawl and the pawl spring.

Model A - a bit of turning

 We're back on the lathe for a small job between milling operations. The first is to skim a couple of thou off the 1.125" section to give it a bit more clearance, and the second is to remove the flange we used to hold the shaft to the rotary table.

The cardboard templates we made confirmed that the milling operations on the rotary table were finished.

This is the part ready for the next step. The reduced section on the left is now small enough to fit in the fixed steady which we need for drilling, and the 1.125" section fits in the bush in the outer cover.

Model A - changing setup

 I do believe we have come to the end of the milling that we are doing on the rotary table. Both the slots are finished as far as I can tell at the moment, so we need to have a look, have a measure, and think about the next steps. 

Fitting the shaft into the gearbox cover this time, I have discovered that the inner 1 in or so of the shaft is around 0.002" oversize - it is dead on 1.125 in, but needs a little bit of clearance. The main part of the shaft is 1.122 in and fits perfectly.

Again both ends of the slot that the stop fits into will change shape when we get the shaft onto the vertical slide.

You can see here the vast difference in length of these two parts!

Comparing old and new:

I've made some simple stiff card templates to make sure that the shapes of the slots are correct and to help me place the beginning and end of the flat area the pawl sits on: