Lotus Elan

Ring Gear and Starter Pinion

PostPost by: RichardHawkins » Wed Dec 04, 2013 8:53 pm

Dear All,

We recently had a discussion about high torque starters, I was away from my garage and could not make sensible comments.

I am installing an MT75 gear box from a Scorpio into my S4 Elan. When I took the box from the scrap yard I also took the flywheel and ring gear. I left the starter which I now regret.

I am using a modified cross flow flywheel to join gearbox and engine.

Scorpio has pre-engaged 135 tooth ring gear. Cross flow has 110 tooth ring gear (pre-engaged I think). My old Lotus ring gear is also 110 tooth with a 9 tooth inertia starter.

I have chosen a LRS 736 pre-engaged starter ( which I think will clear the chassis) with a 10 tooth pinion and am using the 135 tooth ring gear, on the cross flow flywheel, as I already have it. The Scorpio and cross flow flywheels are the same diameter (10.167") where the ring gears fit.

The 10 tooth pinion looks a good fit with the 135 tooth ring gear and a bad fit with the 110 tooth ring gear. The old 9 tooth pinion looks a good fit with the 110 tooth ring gear and a terrible fit with the 135 tooth ring gear.

Burton Performance sell ring gears and starters. On page 26 paper catalogue there is a 135 tooth pre engaged ring gear 10.167" diameter for cross flow, BDA & Lotus Twin Cam Part No FT275B. There is also a 132 tooth pre-engaged ring gear for a 10.048" flywheel.

On page 109 Burton catalogue starters are listed with 9, 10, & 11 tooth pinions, but only inertia type for cross flow BDA & Lotus Twin Cam. So Burton sell a pre-engaged ring gear but do not seem to sell a matching starter.

I think the 9 tooth pinion is designed for the 110 tooth ring gear, and the 10 tooth pinion for the 135 tooth ring gear.

Does anyone know if I am correct? Does anyone know how many teeth are on a Scorpio starter pinion?

Richard Hawkins
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PostPost by: avro » Wed Dec 04, 2013 11:50 pm

Hi Richard

As you thought you will require a 10 tooth pinion to go with your 135 tooth ring gear.

The Lotus Twin Cam engine has a 110 tooth ring gear and a 9 tooth pinion and has the same diameter flywheel as the pre crossflow engine ( 10.048"), however the crossflow engine from 1970 onwards also uses a 110 tooth ring gear but the flywheel on the crossflow has a larger diameter(10.167").
When using a pre-engaged starter the 132 tooth ring gear fits the Twin Cam and pre-crossflow flywheel. The
135 tooth ring gear fits the Crossflow , Ford OHC (Pinto) and CVH etc

Cheers

Nick Stagg
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PostPost by: RichardHawkins » Thu Dec 05, 2013 9:18 pm

Nick,

Thanks for the confirmation.

Richard Hawkins
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PostPost by: garyhois » Mon Dec 09, 2013 9:26 pm

Not to upset the apple cart, but sounds like a dilemma I had a few months ago when getting a replacement.
I have hi torque starters on all my twincams, I also carry a spare starter (they don't last long on high compression engines).
I have 9 tooth and a 10 tooth 29mm versions, what the advise I was finally given you can use either 9 or 10, BUT always replace with the same on an old ring gear.
Just to confirm I have a mixture of inertia 9 and 10 tooth taken off elans.

BTW, I read all ring gear gearings it confused me

Two final notes,
for the baby elan be careful, get the wrong twincam starter and it wont fit, the space is limited
The hi torque starters are actually Toyota, cost ?60, new. You will need the engine adaptor tough

Gary
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PostPost by: pharriso » Wed Dec 11, 2013 1:56 am

garyhois wrote:The hi torque starters are actually Toyota, cost ?60, new. You will need the engine adaptor tough

Gary


That is the value delivered by Gustafson etc.
Phil Harrison
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