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Old 14-03-18, 06:35 PM   #11
Dan_pt
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Thanks again guys. One issue with the HPC gear is its bore size. At .625" I reckon it will be too big for the magneto shaft. I'll call them tomorrow to see if they can supply one with a smaller bore in it.

Dan.
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Old 14-03-18, 08:19 PM   #12
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You could sleeve the bore....not ideal but if HPC cant do one with a smaller bore, then its an alternative....
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Old 14-03-18, 08:22 PM   #13
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As far as I remember HPC will make gears to order and charge accordingly and if you go to their website you can order a catalogue.

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Old 14-03-18, 09:47 PM   #14
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Quote:
Originally Posted by Dan_pt View Post
Thanks again guys. One issue with the HPC gear is its bore size. At .625" I reckon it will be too big for the magneto shaft. I'll call them tomorrow to see if they can supply one with a smaller bore in it.

Dan.

Or machine the outside off your old one, and open the new one up to take the new 'teeth' as a press fit ?

Neil.
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Old 15-03-18, 08:03 PM   #15
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If you give hpc a ring they may be able to give you measurements over pins. If you drop dowels (of whatever size they say) in between opposite teeth then you can measure the distance over the pins more accurately than measuring just the outside diameter etc. This also works for gears with odd teeth numbers if they have a method to provide those dimensions.

I found and hacked an involute curve generator macro for my cad system. This allows me to draw out the teeth shape correctly, and pins and measurements. It works well.

You need to watch out for things like starter motor pinions with only about 9 or 10 teeth. They use one diametric pitch number for the base circle and tooth form and use another pitch number to define the root and tip diameters. Thats why you get very "triangular" looking teeth that nearly come to a point at the tooth tip.

I have done accurate cad models of a starter pinion and ring gear and did a kinematic (moving) model of them to check it. It is clever how the faces roll together.
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Old 16-03-18, 08:30 AM   #16
mervyn cloake
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Dan,
If the rest of the gear is in reasonable shape, why not look at repairing the one you have.
There are ways of doing that. If the teeth are only damaged they can be built up and very carefully shaped with a fine cutting disk. I have done this. if the teeth have completely broken off then a new piece can be dovetailed in and the the new teeth cut to suit. Both methods are not difficult and will work.

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Old 16-03-18, 12:53 PM   #17
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I did consider building up and reprofiling the teeth but they look to have been bent over slightly so decided against it. I have ordered a gear from HPC and I will think about the best way to proceed once it arrives.

Dan.
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Old 16-03-18, 01:07 PM   #18
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Neil's suggestion sounds good - like fitting a new starter ring on a flywheel.

NHH
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Old 20-03-18, 09:45 PM   #19
Dan_pt
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Quote:
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Neil's suggestion sounds good - like fitting a new starter ring on a flywheel.

NHH
And ultimately, that is what has been done.
A colleague made up a tapered holding tool for the old gear and then turned it down until only around an inch of it was left, the new HPC gear that was over an inch wide was parted off and bored to suit. The two pieces were then pressed and welded together. The result is perfect and I now have a nice and quiet engine.
I also have enough of the new gear left over to make another one should the need arise.

Dan.
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Old 20-03-18, 10:05 PM   #20
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I did say they tend to be quite wide!

Good job!

MP
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