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Wot No Teeth?

Denouement of Austin Seven starter ring removal

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martyn nutland09/02/2020 15:11:54
124 forum posts
7 photos
flywheel 2a.jpgflywheel 1.jpgIn the end I began by setting the flywheel vertically on the milling machine and, using a slitting saw (4" x 1" x 1/32), I undercut the teeth at the root in tangential increments. This is a laborious process as there are 80 teeth and the saw would only span 5 or 6 teeth at a time.
The tedium was relieved somewhat by the fact that, as we know, Bendix pinions of the pre-engagement era, are brutal devices. They bash their way into the ring gear usually in about the same place each time. In my case this meant that over about a third of the circumference of the flywheel the Bendix had destroyed around threequarters of the width of the tooth and I figured that could be removed by means other than the tangential cut process.
Having treated the teeth from the root end I chucked (three jaw self centring front fixing) the flywheel. horizontally on a rotary table. I then repeated the previous process but at the bottom side of the tooth. This isn't quite so tedious as I calculated I only needed a cut about 2mm deep on an undamaged tooth to reach the first cut. The theory was to end up with an 'L' shaped incision that 'voila' would part the teeth from the flywheel. This time I used a 1/16" thick slitting saw but the diameter was the same so I could still only treat 5 or 6 teeth at a time. I used 18° increments on the rotary table. There was no clever math about that, I just guessed that was the most I could rotate each time if the two cuts were to meet.
Naturally, the two cuts didn't meet! But I found it relatively easy to break away the teeth in short sections with a cold chisel after joining the slitting saw cuts with an ordinary hack saw.
I have a strong aversion to, and fear of, angle grinders but I used my Makita to take off the remains of the teeth that had been virtually destroyed by the brutality of the Bendix. I then gritted my teeth and used the grinder again to restore some degree of roundness to the denuded wheel.
Next I put the fmywheel in the lathe held on the tooth side in a four jaw independent chuck. This is the only side that has a decent boss on which to grip. I supported the opposite side on a rotating tube centre fitted to the tailstock. One has to work from the 'backside' of the job and I used left hand and right hand cutting tools to clean up and 'round-up' the wheel where the teeth had been. I got to 0.02mm run out on a dial indicator
The photos show the toothless wheel and the set-up on the lathe. The good news, apart from the wheel, looking 'half-decent' is that it has lost about 9 oz from its original 12 pounds.
The bad news is that I cut slightly too deeply on the tooth sides with the slitting saw leaving visible saw cuts around the periphery of the flywheel. You could revove these by continuing to machine away the area where the teeth had been, and although this would lighten the flywheel further, it might impinge on the bolt holes forthe clutch cover (see photo). Also I'm wary of heavily lightened flywheels as I've known them burst with nasty consequences!
Thanks again to everyone who suggested and advised. It really set me on a successful track.


Edited By JasonB on 09/02/2020 16:23:09

Brian H09/02/2020 15:16:43
1961 forum posts
108 photos

The reason you have had problems is that you've tried to do the job upside down!!!!

Glad it worked out and that, hopefully you will be back on the road for a super sunny summer.


Howard Lewis09/02/2020 17:46:23
4129 forum posts
3 photos

So the next task will be to find a suitable ring gear to shrink onto the toothless flywheel?

Sadly, ring gears do get worn in the same place, because the engine always comes to a stop in the same place..

It is galling to throw away a ring gear because five or six teeth are badly worn, when the others are in relatively good condition.

The ordinary Bendix engagement, where the rotating pinion goes against the ring gear, whether the teeth mesh or not is the worst offender. At least the solenoid pre engaged type of starter is much kinder in that it does not apply full power until the pinion has meshed with the ring gear.

But we have to live with what Herbert Austin though was best (cheapest? ) or was available at the time.


clogs09/02/2020 18:53:00
587 forum posts
12 photos

ring gears are quite cheap, easy to fit.........

the old days where bendix starters were used 1 replacement ring gear per life of the car......

not to bad really is it.....???

Mark Rand10/02/2020 00:08:37
945 forum posts
8 photos

Darn it!

I had always assumed that a pre-engaged starter drive would be kinder to the gears compared with the bendix system.

Charles P05/03/2020 10:39:57
10 forum posts

I'm late to this one but I cleaned up the OD of the flywheel by mounting it on a crank between centres. I then held it via the ID with a 4 jaw, trued it up with a dial gauge and just turned the teeth off (as shown). It's easier when the lathe is 1.5 tons of CVA but even so it was a filling loosening job!

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