Challenger crankshaft puzzle?

[46T Sprocket]

I purchased this crankshaft some time ago and recently I sent it to Simon Batemen (Nametab) to have a new big and small end fitted. The crank came back with the job duly done with a nice new connecting rod fitted. I was about to split the crankcases to fit this crank when I noticed the original Challenger 24 tooth primary drive sprocket was not going to fit. How I didn't notice this when I first received this crank baffles me? I didn't though - so I have to find a solution.

Perhaps a member knows something about this odd crank? The standard sprocket fits a 0.790" diameter shaft. The shaft where the sprocket fits on this crankshaft is 0.60" diameter.

I could of course split the current crank and remove the drive side and do the same with this odd crank and then fit the original drive side to this latest crank. I could also machine up in my lathe a sleeve to bring the shaft up to the diameter needed and then organise two keyway's to locate both the sprocket and the sleeve. Either way that's a lot of work and it would be nicer to find a sprocket that fits.

All suggestions welcome.

Thanks,
David.

[johnrunnacles]

Have you queried it with Simon? I have always found him to be most approachable, and may well be able to save you all that extra work.

[46T Sprocket]

Yes I have contacted him. No doubt he will get back to me.

[46T Sprocket]

My own thinking is that this possibly isn't a Greeves crank but something ALPHA have made for a different engine. ALPHA made engines with a similar crank with the same stroke as Greeves engines.

[druid]

Greeves didn't, to my knowledge fit any Challengers with a 24T sprocket, it was either 21T or 25T. Instead of re-using the old sprocket on the new crank get a replacement sprocket of the correct type.
Druid

[46T Sprocket]

It's 25 I miscounted.
I'm still looking for a solution to fitting that sprocket to this smaller diameter shaft?

[46T Sprocket]

Simon has come back to me. It looks like it isn't a Greeves crank as I suspected - The crank is probably from an Alpha or Dot set of crankcases designed to be mated to a standard villiers "A" series gearbox. He said a standard Villiers sprocket will fit the shaft. That's no use with my Griffon duplex drive though.

[John Wakefield]

If you make up a steel sleeve as per my drawing with a slot cut to suit the woodruff key and length of bush to suit the sprocket, you can them make a wider key to go through both the sleeve and the sprocket and job should be a good un but you need to check alignment, and also that the shaft on the opposite side will accommodate the flywheel

[46T Sprocket]

Very good John, I'll give it some thought.

Only slight doubt is will the key be strong enough. The keyway on the shaft is much narrower than the Greeves keyway by about a third. I've done a lot of work on the porting and it's a very powerful motor now.

Regards,
David.

[John Wakefield]

Maybe, but it wont do any damage if it does shear, should be ok as long as its a good fit in the slot so that the sleeve supports it, and the nut is done up really tight. It would also help if sleeve was a press fit into sprocket.

[johnrunnacles]

I have (somewhere?) a duplex sprocket to fit the standard Villiers shaft. Not sure of the number of teeth but I will get back when I have found it. What size is your primary chain?

[46T Sprocket]

Thanks for the post. I can't remember offhand. I'll check in the morning.

[46T Sprocket]

I have (somewhere?) a duplex sprocket to fit the standard Villiers shaft. Not sure of the number of teeth but I will get back when I have found it. What size is your primary chain?

It's a 70 pitch chain John.

[johnrunnacles]

Duplex sprocket has only 20 teeth, David, but everything else about it looks to be Villiers-compatible.

[46T Sprocket]

Thanks for your efforts John.