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ET49 sizing information


Well Known and Active Forum Website User
Non-VOC Member
I have come across several ET49 half-time pinions, some of them marked and some not.

The ET49 is sized from, I think, -10 to +10. Is the sizing done using the
outside diameter or the base of the teeth?

What size is the 0 pinion and what is the amount of the increment to +1 etc?

John Mead


Well Known and Active Forum Website User
VOC Member
There was a series of articles in MPH about measuring across pins. Maybe it is in Another Ten Years. I would look, but we are still unpacking from our move.


Well Known and Active Forum Website User
VOC Member

Neville Higgins did an article on this and as I remember he had an additional series of articles correcting the first. He used two drill rods measuring .108" to measure the various gears and came up with 1.645" over the rods for the zero half time pinion. The articles are in 578-585 excluding 581 and 583, which is roughly March through October of 1997 if I am correct. I would read all the items before using the above figures. They are not all articles, some are letters to the Ed. with corrections and some are letters from Dave Molloy.


chankly bore

Well Known and Active Forum Website User
Non-VOC Member
I assume you want this information to set up the timing gears. While there was an exhaustive series of articles as mentioned above, the main requirement is to have a simple practical method of differentiating the sizes of your collection of pinions. I assume you are setting up a Twin, and that your spindles are parallel, tight and unworn.I further hope you have a ROUND steel large idler and the camshaft pinions are ditto. Set up your one-piece or steel large idler boss and large idler against each cam pinion in turn to check for tight spots. If none is found, dress the key E81 to be a tidy fit in the half-time pinion slot. If you want to be rigorous, make new E87 studs 1/8" longer and use Aerotight or Nyloc nuts instead of punchlocking. Offer up the large idler and mesh it with the cam pinions. Slide in an apparently sloppy half-time pinion. Have a look at the backlash. Take out the sloppy pinion and put the shank portion of two 1/8" drill bits diametrically opposite each other. Measure this, and all the others across with a micrometer. Line them up in a graduated row and "suck it and see" as my apple-cheeked old grandmother used to say! It may help to make a sloppy E81 for starters and a tighter one for final assembly so as to aid frequent extraction and insertion. If you are using an alloy large idler or a two piece alloy/steel idler boss, God help you, 'cos after 60 years they are past breaking time. If you are setting up a Single WITH a timed breather and a Lucas or Miller generator, set the generator central in the seal first as if it were a cam pinion. If you are using an ALTON and an atmospheric breather on a Single any old (new) half-time pinion will do, but please use a steel small idler.
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