Meshing Crown Wheel and Pinion
Correct meshing of the crown wheel and pinion is of vital importance from the point of view of silence in operation and the life that can be expected from the gears.
Crown wheels and pinions should be stored and used in the original pairs. When the parts are dismantled their relative positions should be carefully noted and each part marked to ensure correct reassembly.
Replacement of a crown wheel and pinion.
Correct meshing between the crown wheel and pinion is obtained by finding the area and line of contact from one gear to the teeth of the other, as revealed by the transference of a marking compound. In the first place, the pinion shaft and bearings should be correctly assembled into the torque tube using new bearings if necessary.
The crown wheel, pinion and differential assembly can then be placed in position, and initial adjustment made, so that there is between 0.006 in. and 0.010 in. clearance or backlash between the teeth of the two gears (measured by feeler gauge)*. This is done by turning the nearside serrated adjusting ring located behind a small plate at the back of the axle casing close to the differential. Lever it round by pulling the serrations downwards
Correct meshing of the crown wheel and pinion is of vital importance from the point of view of silence in operation and the life that can be expected from the gears.
Crown wheels and pinions should be stored and used in the original pairs. When the parts are dismantled their relative positions should be carefully noted and each part marked to ensure correct reassembly.
Replacement of a crown wheel and pinion.
Correct meshing between the crown wheel and pinion is obtained by finding the area and line of contact from one gear to the teeth of the other, as revealed by the transference of a marking compound. In the first place, the pinion shaft and bearings should be correctly assembled into the torque tube using new bearings if necessary.
The crown wheel, pinion and differential assembly can then be placed in position, and initial adjustment made, so that there is between 0.006 in. and 0.010 in. clearance or backlash between the teeth of the two gears (measured by feeler gauge)*. This is done by turning the nearside serrated adjusting ring located behind a small plate at the back of the axle casing close to the differential. Lever it round by pulling the serrations downwards
with a tommy bar until it bears tightly against the inner bearing. The adjusting ring will then need to be turned back about two serrations to obtain the required clearance. The offside adjuster may then be tightened by levering upwards in a similar manner, but must only be “hand tight.” Over tightening will cause the bearings to over heat and be damaged.
At the same time, correct bearing contact on the faces of the gear teeth should be aimed at. This is checked and corrected in the following manner: The teeth of the crown wheel should be given a light marking of engineer's blue, in two or three sections, covering at least six teeth in each place. The crown wheel is then rotated in both directions while a light loading is maintained on the pinion by lightly gripping the driving flanges. The marking which are obtained both on the face and flank of the teeth should conform to the shading as depicted below in figure A when the gears are correctly meshed. It may be queried that marking shows contact for only about three-quarters of the face from the toes of the teeth, but under working conditions of load, contact across the full length of the teeth will be made.
If correct marking (as shown) is not obtained, use should be made of such adjustments as are provided for positioning the pinion and/or crown wheel. By use of shims of different thickness (usually two steel shims are used giving a spacing of 0.005”) or the screw in adjustment, refit the pinion shaft so that it enters the axle casing either slightly less or more. Again make the initial adjustment, so that there is between 0.006 in. and 0.010 in. clearance or backlash, apply marking past and check the contact again. If the contact has not been improved, adjust the pinion location in the opposite direction and try again until the best contact possible is obtained. The book Austin Seven Specials” by Bill Williams contains further information of the subject of axle rebuilding.
At the same time, correct bearing contact on the faces of the gear teeth should be aimed at. This is checked and corrected in the following manner: The teeth of the crown wheel should be given a light marking of engineer's blue, in two or three sections, covering at least six teeth in each place. The crown wheel is then rotated in both directions while a light loading is maintained on the pinion by lightly gripping the driving flanges. The marking which are obtained both on the face and flank of the teeth should conform to the shading as depicted below in figure A when the gears are correctly meshed. It may be queried that marking shows contact for only about three-
If correct marking (as shown) is not obtained, use should be made of such adjustments as are provided for positioning the pinion and/or crown wheel. By use of shims of different thickness (usually two steel shims are used giving a spacing of 0.005”) or the screw in adjustment, refit the pinion shaft so that it enters the axle casing either slightly less or more. Again make the initial adjustment, so that there is between 0.006 in. and 0.010 in. clearance or backlash, apply marking past and check the contact again. If the contact has not been improved, adjust the pinion location in the opposite direction and try again until the best contact possible is obtained. The book Austin Seven Specials” by Bill Williams contains further information of the subject of axle rebuilding.
* An alternative way to set the correct backlash: Bolt a 12” length of steel strip to the pinion drive and mark off a point 7” from the centre of the pinion. Clamp a steel bar to the axle casing with one end ground to a point. The point should line up as near as possible to the mark on the strip. Turn the flange back and forth feeling the backlash. At the 7” radius there needs to be not less than 1/16” movement which represents 0.005” clearance at the pinion. These measurements MUST be carried out with the same paper gaskets that will be used in the final assembly.
Pinion