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ring gear teeth

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NutmegCT

NutmegCT

Great Pumpkin
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Calling all mathematicians and engineers ...

If I take my handy micrometer and measure the distance of my ring gear teeth (top of tooth to top of next tooth) I get .410 inch.

If I measure the same "gap" on my starter pinion gear teeth I get .520 inch.

Is that telling me the two don't match and thus don't mesh properly? Or is that not a problem?

I'm just imagining here - but if the teeth don't "match", then eventually the head of one ring gear tooth will crash down on the *head* of one pinion gear tooth, right?

And thus put a *lot* of radial pressure on the pinion gear shaft? Remember, the original starter had been welded so there was no rubber cushioning around that shaft.

And thus put so much pressure on the pinion bearing that the hood will crack and/or snap off?

I would have thought the tooth spacing on both pinion gear and ring gear should be exactly the same.

Thanks.
Tom
 
You have to measure the "gap" half way down between two teeth on the pinion gear and the same on the ring gear. Theoretically, gear teeth only touch one another as they mesh at the "pitch circle diameter". To demontrate this, extend the 4 fingers on both your hands in front of you and "mesh" them like the teeth on two gears. Then rotate your hands like two gear wheels so the fingers fit deeply together (engaging the teeth). They would only touch each other half way down (at the knuckles). When you have a large gear (ring) and a small gear (pinion) the gap at the tip has to be different so the teeth only touch at the pitch line.
 
Don Elliott said:
"pitch circle diameter". To demontrate this, extend the 4 fingers on both your hands in front of you and "mesh" them like the teeth on two gears. Then rotate your hands like two gear wheels so the fingers fit deeply together (engaging the teeth). They would only touch each other half way down (at the knuckles). When you have a large gear (ring) and a small gear (pinion) the gap at the tip has to be different so the teeth only touch at the pitch line.
Click to expand...

Hmmmmmmm....a fellow machinist I believe. Not only knows the term but is able to give an excellent explanation in plain English! /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
Thank you Don! I've never understood that before. Your explanation is excellent.

Tom
(6:38pm - waiting for this page to load. The 'net seems very slow right now ...)
 
Tom, you don't have that car running yet??

I thought that by now, you'd be sending us pictures of you sliding it sideways down your driveway and into the garage.
 
Tom,
I have a vague recollection of me having problems when I rebuilt by early TR3A. The ring gear on the cars with the "bomb" type starter motors has a different number of teeth from the ring gear on later cars. It isn't much of a difference, but the problem will slowly manifest itself over the years.
I am sure that someone more knowledgeable than me will be able to confirm the number of teeth on each.
Nick
 
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