Girostarter help needed.

[NickPoll]

Hello, I'm just about to take an Inter engine apart. I've been told that the gear that engages the starter to the crank is worn, so it doesn't engage properly. Does anyone on this forum know the part I mean and is it available anywhere ?           Nick.

[NickPoll]

My son Daniel has removed the Girostarter and as expected the teeth that engage with the crank are very badly worn. Any ideas ?      Nick.

[Jim Janecek]

could you build up the tips with some weld and then use a rotary table with your mill to shape them to the correct size?
just a thought.
not as easy as finding a replacement part tho

[Bob Purton]

Hi Nick. Is it the teeth on the back of the gyrostarter that have gone, the ones on the crankshaft end or both? Either way a very difficult problem to solve. I think old Westinghouse literature calls them wolves teeth or something like that, will look it up again. Best bet is Club Ydral, there are busted engines out there and the part that usually goes is the clutch spring, I guess the centre bolt has come loose on your customers one and hence wrecked the teeth. Have you PMed Jean Do?

[NickPoll]

Hello Jim & Bob,   Thanks for the responses. It could be built up with weld and remachined, but I'm no expert with my mill. It's both parts that are worn badly, the crank & the Girostarter teeth. I'm visiting Jean-Do early next week, so will ask his advice. The engine I'm working on belongs to Giles Deloge. I think you're right Bob when you suggested the central bolt had been loose.     regards, Nick.

[Bob Purton]

Hi Nick. I think your best bet is still to find donor parts, the machining of those teeth would have to be a perfect mesh, in the gyrostarter manual to engine manufacturers it stresses that accuracy is crutial and even if you could get it done you would have to get the whole piece case hardened again. The more I think about it , it would be easier to bin the old shaft and make a new one rather than welding it. Then there is the other part with the gyrostarter spring diaphragm riveted to it, another nightmare! I have a spare engine with good teeth on the shaft end but is missing the other part. It was always my intension to one day convert this engine to siba dynastart, not easy but not impossible either and once sussed could be a solution to getting a lot of broken inters back on the road. . Let us know how you get on Nick.

[Barry]

It would be very interesting to see a good picture of the offending gears on both parts.

[Bob Purton]

Barry, Its called Wolves teeth Hirth notching, twelve tapered teeth sections cut straight on the end on a shaft with a 60 degree pitch to the teeth but the teeth also slope
 in to the centre at 12.56 degrees. Could be done on a CNC I guess. I have a detailed diagram but it was on old fax paper which has faded to almost nothing. I'm going to try and trace over it in pen and will post a scan.

[Bob Purton]

Here it is

[Barry]

Here it is

Thanks Bob

The two files are the same?  Is that right or an error?

[Jim Janecek]

perhaps time to try this place:

http://www.emachineshop.com

[Bob Purton]

It was just one document Barry, loaded up twice for some strange reason.

emachineshop? Hmm, I think I would rather present a pattern to the machinist myself. I would be sure to make a mistake with the software and then end up with an expensive part that didn't fit.

[Barry]

It was just one document Barry, loaded up twice for some strange reason.

emachineshop? Hmm, I think I would rather present a pattern to the machinist myself. I would be sure to make a mistake with the software and then end up with an expensive part that didn't fit.

Cheers Bob.  I didn't realise we could post pdf files.

It would still be good to see some photos.  You must have investigated alternative solutions, not just the dynostart.  Something in between perhaps?

If the gears were separate 'pressed-on' parts etc. it would be helpful.
The idea would be to draw up the gears in 3D CAD then make SLA rapid prototypes to see if all is well.
These rapid prototypes may be suitable for use as casting patterns but castings may not be tough enough?

The CAD could be supplied direct to the machine shop - Jims contact or others.

I am still a bit worried about the specification of the metal and the hardening required.

All this is quite a bit of work $£$£$£$.

An alternative solution could be cheaper and easier but I suppose the original designers thought theirs  was the best idea.

[NickPoll]

Hello all,  Thanks for the advice and tips, but a miracle has happened ! I've been offered a good set of parts that have been stored in a garage for years in France. It's another Inter owner who has offered them, so we know the parts are correct. Yipeeeee 
Anyway, here's a couple of photos of the bad parts that came from the engine I'm working on.                      Nick.

[NickPoll]

And here are the parts I've been offered. Pretty lucky I think.             Nick.