Lotus Elan

Starter Lucas

PostPost by: geni » Sat Jun 01, 2019 7:16 pm

for Lucas Starter, use either the 9-tooth sprocket or the 10-tooth sprocket?
It seems to me that they are interchangeable without changing any other part
What does this change
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PostPost by: 2cams70 » Sun Jun 02, 2019 1:39 pm

It changes the gearing ratio. For a Lotus engine you need 9 tooth.
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PostPost by: geni » Sun Jun 02, 2019 2:28 pm

Cela ne m'explique pas le pourquoi de 9 a celui a 10dents !
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PostPost by: 2cams70 » Mon Jun 03, 2019 12:25 am

The Lucas M35 starter was used in many British cars throughout the '60's, '70's and early 80's. It'a a very simple design and quite ingenious. Anything from 850cc BMC Minis to the Lotus Twin Cam used the Lucas M35 starter.
As you can imagine the engine in an 850cc Mini requires a lot less torque than a Lotus Twin Cam to turn over and start. Using a pinion with fewer teeth means reduced cranking speed but also less torque required from the starter to crank the engine over. Having two pinion specifications available enabled Lucas to better optimize the the cranking speed versus cranking torque compromise across a wide variety of engines whilst still staying with the same basic starter design.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2015 Honda City 5spd.
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PostPost by: normanjsmith » Mon Jun 03, 2019 12:50 pm

My Plus 2, which I have owned since 1972 has a 10 tooth pinion.I cannot be certain it is original or not because the car had an engine change before I acquired it. It has always worked perfectly.
I have read that Lucas made a running change from 9 to 10 teeth but do not know when this was supposed to have taken place. Seems strange that both can mesh properly with the ring gear.
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PostPost by: nmauduit » Mon Jun 03, 2019 12:52 pm

geni wrote:Cela ne m'explique pas le pourquoi de 9 a celui a 10dents !

there are 2 versions, matching 110 (9 sprocket) and 135 (10 sprocket) teeth ring gears - I would think the dimension of the teeth is why they do not work well when interchanged...
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PostPost by: 2cams70 » Mon Jun 03, 2019 2:05 pm

From the Ford manual for the Escort we have the following:

Twin Cam: pinion 9 tooth, ring gear 110 tooth - so ratio = 12.2:1
1100/1300 crossflow: pinion 10 tooth, ring gear 110 tooth - so ratio = 11.0:1
1100/1300 crossflow auto models: pinion 11 tooth, ring gear 132 tooth - so ratio =12.0:1

Note both Twin Cam and 1100/1300 manual models used the Lucas M35 starter. The auto models used a totally different Lucas pre-engaged type starter. Not sure if the Elan was the same but one would presume it to be the same as the Twin Cam. Suggests that the pinions are physically interchangeable with the 110 tooth ring gear but doing so will give you the wrong ratio. Maybe the 4 speed Elan was the same as the Ford but the 5 speed was something different?
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2015 Honda City 5spd.
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PostPost by: RichardHawkins » Mon Jun 03, 2019 7:58 pm

In my student days I think I remember that if the gears were to mesh correctly you could not alter the number of teeth on one of the meshing pair without also altering the distance between the shafts that support and position the gears.

Starter and ring gear are fairly rough and ready and are not in continuous use like the differential. I suspect this could be how we manage with 9 & 10 tooth pinions on the same ring gear.

Does anyone have the deeper answer?

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PostPost by: nmauduit » Mon Jun 03, 2019 8:37 pm

2cams70 wrote:Note both Twin Cam and 1100/1300 manual models used the Lucas M35 starter.


are the diameter the same? I thought there was a difference between twinks and 1100/1300 crossflows...
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PostPost by: 2cams70 » Tue Jun 04, 2019 9:26 am

From parts book:
Same 110 tooth ring gear part number regardless of whether Twin Cam or crossflow. Originally Ford P/N 2733E-6384B.
The ring gear changed around the time the 711M and 701M blocks were introduced. Ford P/N 701M-6384AA. Still 110 tooth but I think that was when the ID changed slightly.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2015 Honda City 5spd.
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PostPost by: el-saturn » Tue Jun 04, 2019 2:38 pm

maybe unknown to many of you: there's a german copy made by hella (i'm 99% sure) which is much better than the lucas: even the ally bracket is of much higher design-quality (i broke 2 lucas brackets since 1981 and this german item has been in there for close to 10 years by now sandy
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