05-08-2018, 06:50 PM
Some weeks ago, Ruairidh sent me a pair of the supplied dynamator gears and asked me to have a look at them and comment. So this is what I found with the main drive gear:
I Started by checking the Outer and root Diameters of an Austin and Dynamator gear -this is called the addendum and dedendum in gearspeak –which I will try to minimise in the rest of this screed. The dimensions are within a couple of thou’ on both, so no issue there. The Helix angle is the same on both gears too.
![[Image: 29977505018_3e5cef91a0_c.jpg]](https://farm1.staticflickr.com/854/29977505018_3e5cef91a0_c.jpg)
IMG_3197
However, when the dynamator gear was meshed with a good factory camshaft gear it could be seen that the camshaft gear was being ‘wiped’ by the top portion of the dynamator gear teeth as opposed to the Austin dynamo gear where the main contact was on the flank of the teeth as would be expected.
After seeing this I ‘printed’ each gear by rolling them along a fresh piece of Plasticine. This produces a ‘rack form’ i.e. straight sided tooth form in the modelling clay as the rolls across. It’s a good ‘quick and dirty’ way of seeing something called the pressure angle of a gear without needing to use sophisticated measuring equipment. The pressure angle of any gears in mesh with each other must match exactly for smooth running and reliability. It’s not easy to see in the photo here, but the angles formed (the pressure angle) are not the same between the Austin and dynamator gears.
![[Image: 29977513368_99ce6ba6b3_c.jpg]](https://farm1.staticflickr.com/938/29977513368_99ce6ba6b3_c.jpg)
IMG_3202
I didn't have a really good distributor gear to check the mesh of the dynamator distributor drive against. But from the wear pattern on the gear Ruairidh supplied it would appear to also have an issue with the pressure angle.
I Started by checking the Outer and root Diameters of an Austin and Dynamator gear -this is called the addendum and dedendum in gearspeak –which I will try to minimise in the rest of this screed. The dimensions are within a couple of thou’ on both, so no issue there. The Helix angle is the same on both gears too.
IMG_3197 However, when the dynamator gear was meshed with a good factory camshaft gear it could be seen that the camshaft gear was being ‘wiped’ by the top portion of the dynamator gear teeth as opposed to the Austin dynamo gear where the main contact was on the flank of the teeth as would be expected.
After seeing this I ‘printed’ each gear by rolling them along a fresh piece of Plasticine. This produces a ‘rack form’ i.e. straight sided tooth form in the modelling clay as the rolls across. It’s a good ‘quick and dirty’ way of seeing something called the pressure angle of a gear without needing to use sophisticated measuring equipment. The pressure angle of any gears in mesh with each other must match exactly for smooth running and reliability. It’s not easy to see in the photo here, but the angles formed (the pressure angle) are not the same between the Austin and dynamator gears.
IMG_3202 I didn't have a really good distributor gear to check the mesh of the dynamator distributor drive against. But from the wear pattern on the gear Ruairidh supplied it would appear to also have an issue with the pressure angle.