Lotus Elan

Lotus Sprint Rev limiter

PostPost by: bloodknock » Thu Oct 05, 2017 12:22 pm

My car came with a mechanical centrifugal rev limiter formed as part of the rotor arm in the distributor.
dsc04368.jpg and

Does anyone else retain one of these fitted? Do the proprietary electronic ignition systems sensor assemblies work / interfere with this?
dsc04371.jpg and


CRASH!!!!
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PostPost by: nmauduit » Thu Oct 05, 2017 1:15 pm

these period rev limiters work by increasing the gap due to centrifugal force at a certain rev level determined by the springs and the weight on the sliding contact : if your electronic ignition does not like firing blank, you may prefer avoiding to use them, though usually they do not enter operation often on a road car where you rarely reach the red line (you may use a modern electronic rev limiter as a protection for loaning your car to overly enthusiastic friends, since obviously you are not limited to period correct items as you are using electronic ignition).

Exact calibration may be difficult to ensure with aging springs, wear and dirt... but on the positive side they act as a last resort : they just remove the spark at the wire. I have seen standard ones (Lucas 54422688 3250 = 6500 rpm) and fast ones (Lucas 54424982 = 7000 rpm).
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PostPost by: bloodknock » Thu Oct 05, 2017 1:42 pm

The electronic ignition was my only concession to modernity since access to the distibutor and hence the points is at best difficult.
I do have a lucas period solid state rev limiter but its a box that would have to be mounted somewhere.
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PostPost by: ericbushby » Thu Oct 05, 2017 4:52 pm

I bought one of those because at the time I thought it was a good idea. Unfortunately as you can see above it will not fit if you have the electronic ignition module fitted.
As far as I can tell it works by the silver coloured weight coming out on springs to touch the vertical post which is connected to the shaft underneath thus short circuiting the rotor arm to earth.
If anyone wants to try this I am very happy to sell it for ?12.00 including postage to the UK only. I will not post this abroad. I paid ?16.00 for it.
It is new in box and looks much the same as the one above, except for the detail shape of the weight.
Part No 5520839 3325 RPM which of course is distributor speed, so 6650 crankshaft speed.
The box is marked Lucas DRB118C Rotor Arm 888Y
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PostPost by: iancockshull » Thu Oct 05, 2017 6:10 pm

Eric
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PostPost by: bloodknock » Thu Oct 05, 2017 6:14 pm

You are correct Eric, the centrifugal weight actuall shorts the HT to the distributor shaft, so the ignition is firing into a short at tha point, theres no open circuit involved. The line impedances of the coil cable etc absorb the sall ammount of energy developed and limit the peak voltage so should not damage the ignition circuitry. i think its like a lot of "Vintage" systems, simple and effective.
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PostPost by: snowyelan » Thu Oct 05, 2017 6:44 pm

The old luminition systems fit under these limiting rotor arms. The downside is the external control box with only the sensor under the cap.
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PostPost by: bloodknock » Fri Oct 06, 2017 7:35 am

Yes thats the problem. It seems that if I want to retaing the centrifugal rev limiter then ive got to use a product with an external box, which is not what I want. If I were prepared to use a standard rotor arm I have a number of ignition mudules to choose from that would fit inside the distributor, but then an external rev limiter would be required and I dont want external boxes because of originality appearance.CATCH22
Ill have another look at where an external rev limiter could be located.
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PostPost by: nmauduit » Fri Oct 06, 2017 8:32 am

if you want a modern electronic ignition and rev limiter all enclosed within the distributor body, there is a product offered by a dutch company (123ignition.nl - no affiliation). I've had one fitted a couple years ago, only good things to say about it so far...
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PostPost by: ericbushby » Fri Oct 06, 2017 8:38 am

Rev. limiter rotor arm sold.
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PostPost by: bloodknock » Fri Oct 06, 2017 5:20 pm

new-092_1.jpg and
Has anyone experience of this unit? Ive had it kicking about for years
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PostPost by: billwill » Fri Oct 06, 2017 6:00 pm

It's definitely a good idea to have some sort of Rev Limiter.

As I understood it, the Elans came with this centrifugal rotor arm limiters originally, but many probably wore out & were replaced with solid rotor arms.

Mine was a solid rotor for many years, but then someone on this forum spotted a dealer selling the centrifugal limiters on eBay and many of use bought new ones from him. I think they were 'officially' Land Rover ones (?). The seller was amazed at the heavy demand from us and raised his prices. :-) :D

So I now run with this traditional limiter. I do have a form of electronic ignition but it is the simplest type still using the points and merely acting as a fast transistor amplifier to give faster switching, which reduces the wear on the points and yet also makes better sparks. Its a Maplin (wellerman) kit circuit with some enhanced components.
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PostPost by: bloodknock » Sat Oct 07, 2017 7:25 am

I once owned an MGB and the throttle springs broke away on the route perifique with the throttle wide open (Driving the Parisien way!) fortunately I managed to turn off the ignition rather rapidly. I think the locals thought the style was quite normal! :roll:
So I think Rev Limiters are rather a good idea especially on a Twinc.
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PostPost by: saildrive2001 » Sat Oct 07, 2017 9:37 pm

I have a Petronix electronic rev limiter & I hid it away attached to the metal brace that is inside the car & ahead of the drivers door & up high. I will try to take a photo & post it.
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PostPost by: bloodknock » Mon Oct 09, 2017 8:57 am

Thanks Keith
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