From a previous post by Craig Taylor a few years back.
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Lets go over this again:
1. Gear manufacturing industry standard is to mark the gear with its own number of teeth followed by the number of teeth of its mate. Hence the driver gear (internally splined) would be marked 21:31, and its driven gear mate (with dog lugs) would be marked 31:20. Hewland chose to deviate from the standard marking in the hopes of reducing confusion with racers. Webster chose to use the industry standard.
2. Gears must be run as a matched pair. A 21-tooth driver gear from a 21:30 set must not be run with a driven gear from a 21:31 or 21:29 set. At best it will not assemble in the gearbox because of difference in diameter. At worst is a broken gear. This is why gears are sold in matched pairs.
3. What you can learn from gear names Webster and Hewland:
20:31 No other markings Hewland gear of early lineage. Material English versions of 8620 or 9310 if late. However no marking identifiers.
20W31 Webster Gearset, prior to 1986 material 8620
20W31 with date (11/87 example) Webster gearset post 1986, 8620 material.
20W31S with date 1991 or later Webster "s" gearset, upgraded machining, hobbing and grinding facilities introduced. Material 8620.
20M31S (also dated 1993 or later) Webster "s" gearset with material change to 9310.
20 31 M Hewland gearset late tooth design, English version of 9310 steel.
20 31 N Hewland gearset with latest tooth design,english version of 9310 steel. (These are still rare, except in MK5)
For FF 1600 any MK gearset is suitable because of the restricted power. For F/S2000, SV, or any car over 120 HP, only the Webster M or Hewland M or N gears are suitable. Others WILL BE BROKEN.
Craig, I hope that this helps.
Craig
tayrace1@airmail.net
Taylor Race Engineering, Inc.