TR2/3/3A starter conundrum

I just finished getting an A OD transmission ready to use. Only now am I discovering that this transmission that I bought is an early "bullnose" transmission. All of my starters are for later cars. I'm looking at Nippodenso Hi Torque starters from BritishStarters.com I have a technical question that is giving them a little pause. I have a hodge-podge of parts. I am using a TR4a engine with a TR3a flywheel/clutch and (apparently) an early TR3 transmission. My question is: Is the ring gear tooth count the same on the press on ring gears for the early TR3 (with bullnose "bomb" Starter) the same as the bolt on flywheel for the TR3a and later cars? If it is I should be fine. I assume (maybe I shouldn't) that I can use the high torque starter with the bullnose transmission, as the pinion gear of the starter engages the ring gear by throwing the pinion away from the starter like the bull nose starter as opposed to the later TR starters which pull the pinion gear into the ring gear. I am I as clear as mud? Advice please
Joe ('58/'59) TR3A

Hi Joe,

That is a bit of a conundrum.

I could be wrong, but I think the ring gear tooth counts are different early vs late as there are two different pinion gears available on the high torque starters depending on what set up you have.

Cheers
Tush

I'm thinking the tooth count is the same and the change was the later flywheel being a bolt-on with the tooth bevel on the rear side.

Just because I didn't know any better for years - I am running the early starter with the late flywheel. Looks like a PO installed a post TS50000 engine (& flywheel) but used the starter from the original engine since the original gearbox bell housing lacked the extra bulge required by the late starter.

It works fine, possibly because the teeth have been beaten into submission though the years.

The ring gears are not the same and you should use the correct starter for the gear. It will work for awhile but will fail over time. If you identify the ring gear BS should tell you what one to use they used to have them both.

Use the high torque starter for the later (post-50K TR3A through TR4A) cars. Looks identical to the unit for the early ring gear, but has an extra tooth on the pinion gear. (I forget offhand whether it's 9 vs 10 or 10 vs 11, but something like that.) The later ring gear is smaller than the early one.

It will work fine even though it is going into the "wrong" side of the ring gear. The high torque starter is a pre-engaged design, meaning the pinion is moved into mesh with the ring gear before the starter motor begins turning. It doesn't need the bevel on the other side of the ring gear.

The original starters used a Bendix drive, where the torque of the motor is what moves the pinion gear to engage with the ring gear. Obviously the pinion is already turning when that happens, so they do need the beveled teeth.

PS, it might depend on manufacturing tolerances or whatever, but I have seen exactly what Keith describes. A friend was working on restoring a TR2 he bought as a project, but the PO had apparently substituted a later flywheel. Starter worked at first, but then started slipping sometimes. By the time I saw it, it wouldn't turn the engine at all.

Got a new starter from BS and have the bolt on ring gear. Not installed in the car so I can count the teeth.
Ring gear has 90 teeth. Pinion gear 10 teeth.

David

Once you have this sorted out...you'll need to move onto which clutch to use!

I had my spare starters on the bench and took a moment to count the teeth. The early (pre-TS50000) has 9 teeth on the pinion, the later one (used on my TR4 for example) has 10 teeth.

But I noticed that (at least w/i the limits of my ability to measure) the spacing of the teeth is the same on both. This is because the 9-tooth version of the pinion has a much smaller outside diameter that the 10-tooth style.

That may account for how I have been able to use an early starter with a bolt-on ring gear with no problems for 36 years. The bevels on the ring gear may be wrong but there is a pretty fair bevel on the pinion that is still on the impact side. I am not recommending anyone try this and it does seem like an invitation to have a problem, just relaying my experience.

So if the pinion gears have different outside diameters, does that mean that the ring gears are also of differing diameters? And would that preclude swapping starters? It might be best to just buy the starter that's actually meant for your style ring gear.

Yes, yes and yes. There may be times when you can "get away" with using an early starter with a later ring gear, but usually it won't work, at least not for long.

If you somehow wound up with a later flywheel inside an early bellhousing, just get the later gear drive starter.

BTW, this solution also works if you are trying to install aftermarket headers on a TR2/3 with the early ring gear. The headers typically will interfere with the early starter, but not with the shorter gear drive version.

PS, thanks for the tooth count, Geo. I'll try to remember next time You're also quite right, the gears are the same diametral pitch (tooth spacing is the same), so they would work fine if you could somehow adjust the center-to-center distance.

TR3driver said:

...the gears are the same diametral pitch (tooth spacing is the same), so they would work fine if you could somehow adjust the center-to-center distance.

Click to expand...

Good point. My back-of-the-envelope calculation suggests I am getting .08" less engagement using the early starter & later flywheel. I am sure neither the starter teeth nor the flywheel teeth are very pretty by now -- just one of those things I'll resolve 'someday'.