1961 Norton Model-50 Crankshaft Pinion Markings

Just checked mine which as expected are different.Only the two dots are evidenf.

I suspect your other marks are home made,perhaps an attempt at using different timing?

The marks are stamped during the manufacture of the pinion. In the 40s, 50s and 60s making such items was not as accurate as it is today. The marks indicate how much deviation there is from the desired timing point/mark.

The attachment shows some early Dominator crankshaft pinions with similar markings. Anyone tuning the engine for optimum power would probably have a collection.

Just checked mine which as expected are different.Only the two dots are evidenf.

I suspect your other marks are home made,perhaps an attempt at using different timing?

Hi Steve,

Your are correct about the 2 timing marks for meshing with the cam wheels. To the best of my knowledge the other marks indicate the thickness of the teeth. This is necessary because of the inconsistency in the machining accuracy of the casings. I think the unmarked pinions are the standard thickness and to achieve the correct back-lash ( clearance between the teeth ) the engine builder would need to fit a plus or minus thickness pinion to adjust to the correct fit. The numbers, for instance, +3 would probably be .003" thicker where your pinion looks like -1 or .001" thinner. Regards, Richard.

I can shed some light on this having been in theengineering industry for a long time.

Norton gear drawings would haveincluded dimensions for a centreless ground pin. These could be made very accurately even a long time ago. Two such pins, usually about the same diameter as the tooth thickness, were placed inopposing gaps. A micrometer was used to measure the diameter over the pins.

The design engineers would calculate the optimum 'over the pins' dimension assuming everything to mid tolerance dimension.

If the teeth are oversize, or the pitch circle too large, the micrometer measurement will be oversize by + XX thou. This is stamped on the gear. Some gears will be undersize, hence the -XX

Two unused gears with zero, or no marking, will run with the correct (to the designer)backlash if the gear centres are correct. A +2 gear mated with a -2 gear will also run with correct backlash. Theory says it will mesh incorrectly but you can ignore this.

In this way selective assembly in the factory can be used to produce geartrains with the correct backlash, even if there are errors in gear cutting and gear centres.

You will find these marks on otherNorton timing gears. I have a whole bunch of lightweight timing gears from -5 to +5.

Auxillary gearboxes on aircraft engines were assembled in the same way.

Once the gears have been run for 50 years the markings lose their relevance, but you can be sure a +5 started life larger than a -5, and it may help you reduce engine noise if you can reduce backlash.

Cheers

Peter

Previously Phil Hannam wrote:

The marks are stamped during the manufacture of the pinion. In the 40s, 50s and 60s making such items was not as accurate as it is today. The marks indicate how much deviation there is from the desired timing point/mark.

The attachment shows some early Dominator crankshaft pinions with similar markings. Anyone tuning the engine for optimum power would probably have a collection.