Advice and assistance sought - kickstart gear quadrant

Hi folks, first post, but been looking in for a few years.

I need to make a kickstart for a vintage motorcycle as per the photo (haven't put this in vehicle resto section as it's more about metals and processes than vehicles).

I'll probably make it in 3 or 4 parts and weld together. Concerned about the teeth being hard/tough enough. Maybe case hardening by kasenit? Certainly don't want to go for any professional heat treatment if at all possible. I have oxy acetylene, if I heat after the teeth are cut, does the hardening require a length of time at temp before immersion in the powder, and a length of time soaking?

I thought EN8 for all parts.

Next, I only have a vertical mill, and don't have a dividing head, would anyone be interested in milling the teeth for me (might want 2 doing)? 10DP, radius to o/d of teeth approx 83mm.

EN8 is a poor choice for case hardening, but you can flame harden it by heating and quenching. It won't be as hard as a high carbon steel but should be good enough for your application.

Neil

buy a commercially made wheel and cut to make 2 ? Noel.

My Chief has a kicker similar to that but according to the Indian spares people they should be made from a ductile iron mine is, it’s supposed to withstand shocks better and lets face it hard or soft you are never going to wear it out. Plus one for fabrication. Starter ring gears are soft and they last ok.

Edited By bernard towers on 27/01/2022 22:36:51

I'd consider getting the three spokes and gear segment laser or waterjet cut as one then weld on the hub and crank.

You would need to get your radius a bit more exact as 83mm radius with 10dp would give 63 1/3rd teeth

I've added "gear" to the thread title which may draw the eye of a couple of our members who take on a bit of gear cutting.

Edited By JasonB on 28/01/2022 07:53:41

I would turn up a small plug for the central bush with a small centre or spotting drill hole in it to use a pair of dividers to get an accurate gear diameter measurement. To get the exact number of teeth, I would scribe a circle to match the od of the gear on some card and mark the teeth positions in stages around it.

If you can get a complete gear made, two quadrants could be made from it and the welding heat would not have to be near the teeth.

 And, by the way, welcome to the forum.

Edited By old mart on 29/01/2022 18:57:03

Edited By old mart on 29/01/2022 18:58:36

Find a ring gear of the right tooth form (mini ?) cut into 3 or 4 lengths and alter radius to suit this job,reduce width if need be, and braze onto the rest of the assembly that could be welded construction. Noel.

Remember - the loads on a gear like this are serious, if ever the engine is tried without proper attention to the advance-&-retard lever. Legs have been broken, as well as gear teeth.

Tim

YES ! I have a 500 bullet, kick start, It is only likely to kick you if your careless ! Decompressor in, turn the ignition on slowly turn engine over and watch for the ampmeter to drop to zero, release decompressor and kick her over ! Noel.

I'd be reluctant to heat treat a spindly shape like that kicker quadrant. It looks likely to distort all over the place.

Is the original sample in your photo hardened? Can you rub a file over the edge of one tooth and see if it is hardened or not? It quite possibly was not hardened, just made from a good quality cast steel, the kind of tough stuff that quality vices were made from.

And what sort of bike is it off? It's one thing to kickstart an 1100cc JAP OHV V-twin, and another to kick over a 350 side valve single with 4:1 compression. On the latter, you could probably get away without hardening the teeth. Not so much the former.

If you have a mill but not dividing head, you could still make that quadrant by using direct indexing off the sample quadrant or even off a lathe change gear etc of the right number of teeth. It would need the same number of teeth as a full circle of that quadrant would have. Easily calculated from the accurate radius and the DP if you have a DP gauge to confirm that.

You can set the gear blank up on a common shaft with the sample quadrant or gear and use a spring loaded plunger as a detente. The shaft can be mounted on an angle plate or suitable large block/s of metal.

Of course it would take longer to make the direct indexing set up than to cut the gear, but that's the fun of it all. If you wanted easy, you would go to the nearest dealership and buy a brand new Triumph.

Edited By Hopper on 30/01/2022 09:16:57

.

An interesting observation

Given the hammering that the various ‘manhole covers’ on our road take without breakage … it seems entirely reasonable to me.

MichaelG.

With Indian's 5 to 1 compression, you could just about make it out of butter and it would do the job. (Sorry, as a Harley rider I couldn't resist.)

On a more serious note, my 750cc sidevalve Harley with (the high-performance) 6:1 compression can readily be "kicked" over by hand so the stress on the kicker gear is not great, certainly nothing like that on the transmission gears delivering the engine's massive 32 horsepower to the rear chain.

So I am sure ductile iron would work on a lower compression engine like the old sidevalves. (And butter on those Indians.) But for machining one from scratch I would use a good steel, just to be sure.

Edited By Hopper on 30/01/2022 09:49:23

Edited By Hopper on 30/01/2022 09:50:43

Thanks for all the responses guys.

I think that on balance, I will go with the reasonable steel/unhardened approach. My application is not highly stressed (as compared with a hi comp engine). Photo of the bike accompanying - all of 2.75 horse power - yes that's 2 point 75, not 275. It's a 1927 Ladies model Royal Enfield of 225cc (2 stroke). I have only used my vertical mill in the upright mode, but understand it is possible to swivel by 45 (not sure if I can get 90 deg, to turn the spindle horizontal). If I can, then maybe I can bolt the kickstart quadrant to the blank and carefully work from there.

The teeth profile is 10 DP, and from a quick scan on ebay, I can see something referred to as 'pressure angle' comes into play (I thought these were straight cut, so angles wouldn't be an issue). Can anyone enlighten me? I see (if applicable) there are 2 angles, 14.5 and 20 degrees, the former being used in 'olden days', and probably applicable to my situation.

If I find an 'involute'? cutter they seem to be number of teeth related, so that would refer to the full circumference (in my case 63/64 teeth)?

They will (almost certainly) be 14.5 Degree pressure angle, but that is not really important at the speed they will operate at! Wear on the driven gear might be considerable.

That is a fairly poor output for a motor of 225cc. I had a post-war (1950s?) moped of 49cc. That was a 4-stroke with overhead valves but still produced 2HP. 50cc Hondas were rated at 4 1/2 HP, I think?

Correct, the range of teeth listed on a given cutter refers to the full circumference, ie, a complete gear. Any given cutter is correct for the lower tooth count, the errors as the tooth count increases get larger, until the next cutter in the sequence is needed. As the number of teeth increases the involute curve becomes more like a line, until, with an infinite count, you get a rack with straight sides. A rack is just a gear of infinite diameter.

Andrew

Cool. A sort of ancestor the Flying Flea. And at that whopping power, probably no need for hardened gears.

Pressure angle refers to the profile of the gear teeth when viewed side on. The teeth are still straight cut at 90 degrees across the gear blank. It has to do with the angle of contact between the two meshing gear teeth. 14.5 degrees was standard in the good old days of 2.75hp motorbikes. 20 degrees is standard in the modern era. The two profiles use two different gear cutters. But as NDIY said, for your low speed low power purposes, a 20 degree cutter might work ok.

You don't need to tilt the mill head, it can be done with the gear vertically and the cutter horizontal

.

Here is an oft-quoted demonstration of ‘pressure angle’

Post #21 in this thread includes a nice animation:

https://www.chiefdelphi.com/forums/showthread.php?t=129632&page=2

MichaelG.

The horsepower referred too in Kie4ths post is probably the RAC rating which was applied to early motorcycles. These were used to define how much road tax you had to pay. I have a couple of 2.49 h.P. numbers that definitely are more than that they are probably around 12-15 H.P. The little Enfield will probably be around 10 HP.

EN24T - 34CrNiMo6, can be bought in rectangular bar, find some one who can waterjet it. Harden and temper, in the past all the gears I had made were induction hardened 40-45Rc.