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Old 11-19-2019, 03:44 PM   #1
PC/SR
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Default Flywheel ring gear pin

What type or source do guys use as a pin for the ring gear to the flywheel. Can't get specs or measurements of the ones I see online. Thanks
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Old 11-19-2019, 04:53 PM   #2
BRENT in 10-uh-C
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Default Re: Flywheel ring gear pin

A stock flywheel with a reproduction ring gear is actually installed with a 0.0015" interference fit. The ring gear is heated and then slipped onto the flywheel so that when it cools, it will shrink to fit tightly.

If you find yourself with an issue of a ring gear trying to slip on a flywheel, here is a trick that you can do. I install electric starters on early brass-era stuff that did not come with an electric starter. I make the flywheel ring gears for these engines and mount them onto flywheels (that never had an electric starter nor a provision for a ring gear). On those, I roll the ring and then weld it together. Then I slip the ring gear over the flywheel and drill down into the ring gear and the flywheel at the same time. One half of the diameter of the drill bit is drilling into the flywheel and the other half is drilling into the ring gear. I drill these holes 90 apart and thread them to install -28 set screws. These act as a sprag to keep the ring gear from rotating on the flywheel.
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Old 11-19-2019, 05:01 PM   #3
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Default Re: Flywheel ring gear pin

IMO, a pin is the hard way to go. I had a ring gear slipping on my Tudor and fixed it without even removing the motor. Through the starter motor opening in the flywheel housing, I put a few drops of Loctite #290 on it. That was many tens of thousnads of miles ago and no trouble since.
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Old 11-19-2019, 07:41 PM   #4
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Default Re: Flywheel ring gear pin

The attached article may be of help.

Some of the reproduction flywheel ring gears do not mount with a proper interference press fit on the flywheel. Each time the starter engages it tries to jerk the ring gear away from the stop. A better design would have been to place the stop on the flywheel in front of the gear instead of behind it. But, who am I to question Henry?

A few years ago I had a reproduction flywheel ring gear work its way forward until it jammed things up. I had to remove the starter and tediously tap the gear back into place using a drift as I manually rotated the engine. After going through this drill several times I removed the flywheel (a fun job) and took it to a machine shop and had it mounted to the flywheel and locked into place with screws and lock-tight. The article addresses that activity.

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File Type: pdf flywheel ring gear.pdf (132.3 KB, 67 views)
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Old 11-19-2019, 09:30 PM   #5
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Default Re: Flywheel ring gear pin

Thanks for the info. I am installing a flywheel now and want to prevent problems by pinning it now. I guess any set screw would do the trick per Brent, but like the screws shown in Tom's article. Do you have info on getting those Tom? Thanks
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Old 11-20-2019, 01:20 AM   #6
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Default Re: Flywheel ring gear pin

Quote:
Originally Posted by PC/SR View Post
Thanks for the info. I am installing a flywheel now and want to prevent problems by pinning it now. I guess any set screw would do the trick per Brent, but like the screws shown in Tom's article. Do you have info on getting those Tom? Thanks
They were supplied by the machine shop where I took the flywheel. Download the article and show the photo to where you take yours.

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Old 11-20-2019, 02:26 AM   #7
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Default Re: Flywheel ring gear pin

Here is a picture of what I did. I used a countersunk cap screw but a simple grub screw is all that is needed, since it is the threads forming a "Scotch key" that hold the parts together and the head holds nothing, should the threads strip. I used 4 screws, and the ring gear is actually moving forward between them (bending) after many thousand miles. I think 6 screws is better.
The ring gear was shrunk on and loctited after cooling. Starter is 6 volt. It still overcame the loctite and shrink fit.
We have had to do 3 other cars recently too. I drilled mine through the starter hole. I had to use a titanium nitride coated drill since a high speed steel one would not cut. The TiN one was just a cheap import but did all 4 holes really easily. It surprises me that the drill goes in very centrally between hardened ring gear and much softer cast iron, without wandering further into the cast iron.
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File Type: jpg pinned ring gear roadster.jpg (60.5 KB, 70 views)
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Old 11-20-2019, 05:33 AM   #8
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Default Re: Flywheel ring gear pin

That would have to be one of the few jobs that is easier on a RHD car.
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Old 11-21-2019, 02:11 PM   #9
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Default Re: Flywheel ring gear pin

The hardness tempering may only extend a little inboard of the ring teeth. It just depends on the method the manufacturer used to harden the ring. The type of steel has a lot to do with it as well. Induction hardening can be controlled pretty well and is the more common way to harden stuff like this. It also relieves stresses by normalizing to some extent.
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Old 11-21-2019, 03:31 PM   #10
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Default Re: Flywheel ring gear pin

Rotorwrench, I agree they looked to be induction hardened by the coloured rings radiating from the teeth. But the back of the ring gear was still too hard for a standard high speed drill. It was interesting to me that a cheap titanium nitride coated Chinese drill bit worked really well, and did all 4 holes with coating still visible on the drill tip when I finished. A standard countersinking bit would not cut the metal either and I had to use a tungsten carbide one.
I see in Tom Endy's post the screws look like button head -countersunk or maybe counterbored. They look neater than my ones, but I used what I had handy at the time. Mine were metric too, and I usually try not to use metric on my non-metric cars.
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