Other Notes:
MW, EP, SB etc = Special Application or Vehicle. i.e. E115F - suitable for Alvis, EP115F - suitable for Perkins
/10, /12, 12/14, 2 ½ = Pitch or Number of Module
Part number example G138NE = 7/8” wide, 138 teeth, no entry
Fitting Instructions for ‘Shrunk-on’ Ring Gears Reproduced from an Original Catalogue
Replacement of starter ring gears should only be undertaken by professionals with the proper equipment
Damaged flywheel gear teeth not only cause noisy engagement and running, with the possibility of a blind spot at which the teeth are so bad that the starter pinion fails to engage altogether, but also entail a likely risk of the starter-pinion being wedged and resulting in breakage of drive-end bracket and bent armature shaft.
In some cars the gears are integral with the flywheel, but it is not necessary to scrap the flywheel when gear teeth are hopelessly damaged. Replacement ring gears can be fitted on the flywheel when the old teeth have been machined off, and an accurate spigot turned to receive the ring.
The flywheel should be mounted in the lathe chuck, with particular care that it is dead central. The old teeth are then machined off flush and the spigot turned to the dimensions specified. The diameter of the spigot is usually .020" greater than the bore of the ring, but the ring bore should not be measured for the diameter required, as it may be slightly out of round. A micrometer gauge to measure up to 24" can be used with advantage or a fixed gauge can be made for each of the spigot diameters specified for popular vehicles.
When a gear has been fitted previously to a flywheel, it is very important that care is exercised in its removal. To attempt to remove simply by knocking off is destructive, in that this action may seriously damage the small lip which is present on a number of flywheels. It is recommended that the old gear be first split by drilling or hacksaw, finally by a chisel, thus enabling the gear to be easily removed over any lip. Care must be taken to see that the starter pinion clears the teeth adequately when in the restricted position, and that slight backlash is present when engaged.
Whatever method be used to expand the gear before fitting it must be heated slowly and uniformly, and on no account to a greater temperature than 290°C., or 554°F. A thermostatically controlled muffle or heater fired by gas or electricity is the one method by which a safe and efficient expansion is obtained. The use of a blow lamp or similar is not recommended.
After placing the ring in position on the spigot it should be tapped well home against the shoulder with a copper mallet or soft drift and then left to cool gradually in air. If cooling is hurried by quenching with water or by air jet, uneven stresses will result and the ring may crack. No concern need be felt about tapping the gear into position, because any slight " ovality" which makes this necessary disappears whilst the gear shrinks on the flywheel.
The correct position for the chamfer on the ring teeth must be carefully observed. The chamfer should be on the leading edge of the teeth in the direction of rotation, and should be on the side of the ring to which the starter pinion approaches. The leading edge of the pinion teeth will then engage the chamfer and enable the pinion to slide easily into mesh, even when the teeth meet end on.
It is always advisable to examine the pinion shaft to see that it is not bent, and also that the starter pinion is free from damage and that it can move freely into the engaged position with the ring gear.
Special Note - Where a gear is used that is narrower than the original teeth on the flywheel, special care should be taken that the entry side of the replacement gear is in the same position as the entry side of the original teeth on the flywheel. For example, if using a gear 11/16" wide to replace flywheel teeth 1" wide, first turn off flywheel teeth to root diameter (bottom of teeth) and then turn flywheel back 11/16" from the original entry side of the flywheel teeth and to the turn-diameter marked on the bore of the replacement gear. This will put the entry side of the replacement gear in the same position as the entry side of the original teeth in the flywheel.
