Lotus Elan

Ring gear diameter

PostPost by: Donels » Fri Apr 12, 2019 1:28 pm

I am about to have the flywheel refaced, lightened and a new ring gear fitted. The workshop has asked for spigot diameter to machine the flywheel for the ring gear. I am a little confused as I thought it was a simple heat and shrink operation so have gone back to them asking "why". Does anyone know what size the spigot diameter should be for a standard, road going cast iron flywheel for a 110 tooth ring gear?

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PostPost by: Craven » Fri Apr 12, 2019 4:20 pm

I can probably look it up if no one else comes back but be careful as there are two similar ring gears for Ford flywheels.
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PostPost by: types26/36 » Fri Apr 12, 2019 6:10 pm

I have these diamensions as I presume it is the same for the preXflow engines but it would be better to get a confirmation from another source.
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PostPost by: avro » Fri Apr 12, 2019 7:00 pm

Dave
I can confirm that Brian’s dimensions are correct. The Lotus flywheel along with the pre 1970 pushrod engines had a spigot diameter of 10.048” (S110/10FR) . Post 1970 Pushrod engines had a larger Spigot diameter of 10.167” (A110/10R) although the Lotus flywheel remained the same until the end of production.
Having spent many years lightening and balancing engine components my advice would be not to have the original Lotus Flywheel lightened. Compared to some of the Ford Pushrod flywheels the Lotus flywheels are much lighter in their standard form. The small amount that you would be able to remove safely would have a negligible effect on engine performance .

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PostPost by: Donels » Fri Apr 12, 2019 9:17 pm

Thanks all for the input. A quick measure confirms its closer to 10.048 rather than 10.167.

Nick, have you had bad experience with a lightened cast flywheel?

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PostPost by: avro » Fri Apr 12, 2019 10:34 pm

Donels wrote:Thanks all for the input. A quick measure confirms its closer to 10.048 rather than 10.167.

Nick, have you had bad experience with a lightened cast flywheel?

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Not personally but many years ago l was asked to inspect a cast flywheel assembly ( or what was left of it) . It had been lightened to the extreme and had been used on a race Mini engine. The flywheel assembly exploded during a race. It came through the aluminium bellhousing , through the car bulkhead and the driver sustained serious injury.
I had on occasions after that refused to balance some flywheels, including Fords if l felt that they had been over lightened.

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PostPost by: Donels » Sat Apr 13, 2019 7:53 am

Thanks for the warning, I maybe need a steel flywheel.

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PostPost by: englishmaninwales » Sat Apr 13, 2019 1:37 pm

Ouch! Doesn’t bear thinking about, given the orientation of the flywheel in a Mini (provided the car wasn’t LHD) :shock:
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