04-02-2019, 09:11 PM
Greetings Bob
Here's what my 1953 edition of "Modern Motor Engineering" has to say:
"When a bevel drive gear is dismantled, cleaned and examined, the condition of the mating faces of gear teeth present a clear indication of how the gears have been meshing. Similarly, by using engineer's marking paste on newly assembled gears one is readily able to check these for correct meshing.
In this connection it should be mentioned that when the engine is driving the rear wheels, the driving faces on the pinion and crown-wheel teeth are different from those in driving contact when the rear wheels are driving the car, as during coasting operations.
Referring to Figure 35, which shows tooth contacts under different conditions, Fig 35 (2) shows the ideal meshing contact for well-made new bevel pinion and crown-wheel gears. To check this contact, paint the faces of the teeth of the crown-wheel at three or four different places around the circumference with white lead, using this sparingly. With the pinion in position relative to the crown wheel so that its heel is flush with the outward circumference of the crown-wheel, the latter should be adjusted so that the white lead will be wiped off its teeth, as shown in Fig 35 (2). This may be done by rotating the crown wheel several times in a direction opposite to normal rotation on forward speeds. (My Italics) This will cause the white lead to be wiped off the gear teeth sufficiently to indicate the contact region"
I can't easily reproduce Fig 35 (2) here, but suffice to say it shows an ideal line of contact which sits evenly between the face (outward extremity) and the flank (root) of the tooth, and not biased to either the heel (large end) or toe (small end) of the tooth.
My interpretation of this is that you could either rotate the pinion in the normal direction for forward drive, or rotate the crown wheel in the opposite direction. However, given the natural friction in the assembly, rotating the crown-wheel might produce higher pressure between the teeth, and thus give a better marking ?
Here's what my 1953 edition of "Modern Motor Engineering" has to say:
"When a bevel drive gear is dismantled, cleaned and examined, the condition of the mating faces of gear teeth present a clear indication of how the gears have been meshing. Similarly, by using engineer's marking paste on newly assembled gears one is readily able to check these for correct meshing.
In this connection it should be mentioned that when the engine is driving the rear wheels, the driving faces on the pinion and crown-wheel teeth are different from those in driving contact when the rear wheels are driving the car, as during coasting operations.
Referring to Figure 35, which shows tooth contacts under different conditions, Fig 35 (2) shows the ideal meshing contact for well-made new bevel pinion and crown-wheel gears. To check this contact, paint the faces of the teeth of the crown-wheel at three or four different places around the circumference with white lead, using this sparingly. With the pinion in position relative to the crown wheel so that its heel is flush with the outward circumference of the crown-wheel, the latter should be adjusted so that the white lead will be wiped off its teeth, as shown in Fig 35 (2). This may be done by rotating the crown wheel several times in a direction opposite to normal rotation on forward speeds. (My Italics) This will cause the white lead to be wiped off the gear teeth sufficiently to indicate the contact region"
I can't easily reproduce Fig 35 (2) here, but suffice to say it shows an ideal line of contact which sits evenly between the face (outward extremity) and the flank (root) of the tooth, and not biased to either the heel (large end) or toe (small end) of the tooth.
My interpretation of this is that you could either rotate the pinion in the normal direction for forward drive, or rotate the crown wheel in the opposite direction. However, given the natural friction in the assembly, rotating the crown-wheel might produce higher pressure between the teeth, and thus give a better marking ?