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RING GEAR REPLACEMENT #2 - FT-101B

If you think the BBQ grill and oil is too messy, try this. Many people also report success using a kitchen oven to heat the ring gear at 400-450dF for half an hour. In this case there is no chance of overheating to loose the temper, so after installation it can air cool with no need for a messy oil bath. Risk kitchen privileges at your own digression.

At 03:13 AM 1/13/2007 +0000, Martin (b57mormaz) wrote:
>Freezing your flywheel will do as much as heating your gear ring.
>Easy to do and no burned fingers.


For a steel flywheel, it won't work.
For an aluminum flywheel, maybe.

I just went through the engineering bit on interference fit of the ring gear. For the FN2 fit on 10.75 diameter mounting diameter interference should be .0040-.0072 inch. With maximum interference, to get from interference to zero clearance you need to change the size by at least 0.0072 inch.

Coefficient of thermal expansion for steel is 0.00000633 per degree Fahrenheit.
Ring gear mounting diameter is 10.75"
Heating or cooling 1 degree changes diameter of ring gear or flywheel
10.75" x 0.00000633 = 0.000068"
Required minimum temperature change is then
0.0072 / 0.000068 = 106 dF

From room temperature of 70 dF you would have to chill the flywheel to -36 dF just to get to zero clearance. Home freezers don't get that cold. If anyone has done this with a steel flywheel, and it worked, then the part dimensions are wrong, the ring gear is too loose and may come off in operation. For standard parts you would need to go colder. Dry ice would work.

Coefficient of thermal expansion for aluminum is 0.00001244 per degree Fahrenheit. The same calculation for an aluminum flywheel gives a minimum required temperature change of 54 dF. You can to that with a home freezer. Chilling the aluminum flywheel from 70 dF to 0 dF shrinks it 0.00936", giving about .002" minimum clearance to slip on the room temperature ring gear. But you better be really quick about it before temperature of the parts will converge. If you don't get it fully seated on the first try you're screwed.

On the other hand, heating the steel ring gear from 70 dF room temperature to 323 dF in a home oven will expand it 0.0172" giving 0.010" minimum clearance to drop it onto a room temperature flywheel. Maybe it's time for baking up the steel angle cake.

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