Well, yesterday it was finished. The cotter pin went in way too far and would need replacing, but it worked. However, there was an itch...
I suppose I am a bit obsessive, but I couldn't put up with having to remake the cotter because I had machined the shaft wrongly. I filled the slot up with weld.
A few minutes later, I had re-machined the slot; the shaft is 3/4" within the kickstart lever and the slot has a maximum depth of 0.150" - the easiest way to measure this accurately is from the bottom of the cotter slot to the opposite side of the 0.75" diameter, so you measure 0.600". The slot is bang on the correct depth, and the 0.375" cotter pin fits perfectly.
All I need to do now is cut the spare length off the cotter pin and radius the end.
The last step in the long story of the kickstart shaft project is to machine the flat for the lever cotter pin. We are back on the lathe with the vertical slide and will use this setup to machine the slot:
The cotter pin is about 3/8 diameter so we will use this 3/8 end mill to cut the slot.
This is the last pass of 3/8 end mill - and it's a pass I wish I hadn't made. I was very near the end and used a trial fit to find that the slot I was milling was about 1/32" too shallow. For some reason I decided that it would need another full turn of the lead screw to finish the cut - completely forgetting that the lead screw pitch is 1/16". So now that slot is too deep.
I could weld this up and re-machine it, but the cotter pin still fits and stays in place properly. I guess I will leave this until it becomes a problem - I can't get a 3/8" bolt in there, which would be possible if the slot was any deeper.
With the kickstart shaft nearly finished, we need to think about the bush for the lay shaft. This fits in a bore in the end of the kickstart shaft:
The bush will be a top hat shape to accommodate the end of the layshaft and to determine the end float of the low gear pinion. It's going to be made from this piece of SAE660 bronze:
First job is to reduce the diameter to nominally 1” to pass into the shaft with a few thousandths clearance:
Next, we reduce the diameter such that we have a few thousandths interference fit in the 7/8" bore, and add a small chamfer to aid assembly. That done, we can bore it in steps up to 5/8" - our shaft is 11/16", but we will do that last bore in situ.
Parting off the bush. The hang out here is not ideal at all, and I believe I may have knocked the stock out of square in the chuck - it would have been far better to do this job with the revolving steady.
No matter though, this does not affect the working diameters and we can face off the end of the bush if necessary.
The top hat bush, mostly finished aside from the layshaft bore.
It's not as tight as I would have liked, so I have fitted it with Loctite 603 retainer. This won't be cured until tomorrow.
This is the last job for the lay shaft bush - it's been fixed in place and the Loctite has cured overnight so it is now being bored too 0.6875" for the layshaft. Notice that the shaft is in the fixed steady - it is essential that the shaft is bored concentric to the kickstart bush in the outer gearbox cover:
Some while back I had left a little excess material on the major diameter of the shaft thinking that I might need to play with the first gear pinion end float, and so it proved. As machined the shaft is a little overlength and I used this setup to remove around 0.020" from the end of the shaft which provided the necessary clearance.
I'm pleased to say that assembly and testing of the gearbox proved that everything works as expected. The next step, and final step, is to machine the recess for the kickstart lever cotter pin.
Back home after a few days away fitting a new front door and frame at my daughter's house in Kent, I find a few minutes to move the kickstart shaft project along a little bit.
When I left a few days ago I had the shaft set up in the pillar drill just waiting for final adjustment and the fitting of a centre drill to start the hole for the pawl.
That done, we move on to the 9/32" hole on the outside of the shaft. I have discovered that the pin is retained in place by the low gear pinion and cannot come out in service. I bought a pair of long series drills for this job and it makes it a little easier to set the work up on the pillar drill. We go right the way through both sides with this one:
We follow the 9/32" with a 5/16" drill which only goes through the inside web. I'm pleased that the pin fits very well in these two holes and with a little fettling (the pawl was rather ragged) the pawl goes in as well.
I'm a bit concerned by the shape of the pawl where it engages the pinion as the surface, perhaps not surprisingly, is rather worn. A further problem is that the cam which pushes the pawl back into place actually jams the shaft. This is due to the lack of wear in the new shaft I think since dimensionally it is identical to the old one.
Working on the pawl a little to square it up and refine the edges sorts out the problem and we have a pawl that goes nicely into the retracted position:
The video shows it working in both positions:
A dose of heat and a pot of case hardening compound will give us a pawl that fits and has sharp edges giving it plenty of life. We'll have to see if it still works with the bush in place - that might require a bit more fettling, so we will leave the case hardening until that is done.
As we get towards the end of the kickstart shaft project, it's time to think about where the lever will sit and where the flat for the cotter needs to be machined. This picture mocks up what it will look like eventually:
The key to success here is to understand the relationship between the mating face of the cotter and the flat on the shaft, all of which combine to determine the position of the lever. The last thing we want to do is to have the lever too vertical or too low in relation to the rest of the machine - worst still that it sits forward of the gearbox!
We'll use the old shaft to understand this relationship.
What you see here is two pictures of the lever, the cotter and the old shaft. I have used a Sharpie to show the relationship between the shaft and the lever.
We can see that the cotter fits in either direction without affecting the relationship between the shaft and the lever.
This next rather blurred picture - it looks like it's focused on the bench top - shows the Sharpie mark against the flat on the old lever and confirms that the flat is perpendicular to the axis of the lever.
We can use this information when we machine the flat on the new shaft. We'll have a look at some of the reference pictures and get a feel for where the lever should be.
