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E: Engine Half time pinion specification


Well Known and Active Website User
VOC Member
Could someone please fill me in on the following for the half time pinion:

pitch diameter (Standard size only)
pressure angle

I think the answers are 16, 1-1/2, and 14-1/2 but I hope someone can correct or confirm this. It looks like the Comet dynamo pinion is the same size except for bore?



Well Known and Active Website User
VOC Member
Craig, do you really believe you can accurately measure down to 0.001" using digital calipers?
The screen migh read down to half thous but by their construction cannot deliver this level of accuracy.

Robert Watson

Well Known and Active Website User
VOC Member
First: I think that is not Craig's doing but the Spares Co trying to get a customer to close, so that they only have to send 3 1/2T pinions and not the whole box!

Second: and that's why they are called "Verynear" calipers!

Third: I have a collection, probably around 30-40 various new and used 1/2T pinions. I have learned not to trust the stampings on them. Only proper way is to use thread wires (I think .120 Dia, Mistake should be the .108 thread wires!) and measure the pitch dia of each gear, with a micrometer.
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chankly bore

Well Known and Active Website User
Non-VOC Member
I think .108" diameter is preferred, but using anything close, say, shanks of 3mm. or 1/8" drill bits will get you moving in the right direction. Another thing to be aware of is a snug fit on the E81 key while you're playing in this particular sandpit. I seem to recall exhaustive listings, with frequent emendations in "Forty Years On". For memory, all figures were obtained with .108" shanks and micrometers. Laurie Binns replicated the findings here in Victoria. Very few of the stamped numbers were correct.
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