Lotus Elan

Cut out rotor

PostPost by: seniorchristo » Tue Jul 02, 2019 4:42 pm

I remember the original cut out rotor as being fairly effective in consistently limiting RPM’s to 6500. Is anybody still using these rotors?
Thanks :)
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PostPost by: elancoupe » Tue Jul 02, 2019 4:54 pm

I used them for many years until recently. Never had any issues.

How many of em do you want ? :)
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PostPost by: bitsobrits » Tue Jul 02, 2019 11:03 pm

While these were the hot ticket "in the day", I wouldn't trust a motor I cared about to a 50 year old part that was likely not all that consistent to begin with. Worse yet, you may get a repro part where the weight and spring strength may or may not yield a correct cut out rpm. How would you know until it's too late? There are many modern and reliable rev limiters available these days, most being adjustable to any desired rpm, and with "soft cut" technology to boot.

This is my current favorite as it mounts on a standard coil and isn't too obtrusive.

rev-l.jpg
rev-l.jpg (16.01 KiB) Viewed 1036 times


Others will likely have their favorites as well, or may weigh in and say the factory centrifugal rotor is just fine!
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Formerly:
Elan S1 1964
Elan S3 1966 FHC pre airflow
Elan S3 1967 FHC airflow
Elan S4 1969 FHC
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PostPost by: alan.barker » Wed Jul 03, 2019 12:23 pm

Imho when you start to wind up the revs you watch the tacho with a 50 year old Engine.
Just for info the big valve is 6750 rpm
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PostPost by: Craven » Wed Jul 03, 2019 12:27 pm

Changing down a gear at too high engine revs is not a good idea with any rev limiter!!
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PostPost by: JonB » Wed Jul 03, 2019 12:29 pm

Sorry, this might seem a stupid question but does the Big Valve engine actually have a rev limiter? Mine has a 23D distributor..
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PostPost by: rgh0 » Wed Jul 03, 2019 1:12 pm

The rev limiter was installed as standard on all twin cams originally - 6500 rpm in the standard and S/E engines and 6750 rpm in the later sprint engines. if regularly used at above 7000 rpm the standard cranks break so the continued use of a rev limiter either the original type with a cut out rotor or a modern electronic limiter is strongly advised :shock:

cheers
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PostPost by: JonB » Wed Jul 03, 2019 1:16 pm

Thanks Rohan! How can I confirm I have one (other than attempting to thrash it to 7000k)?

[Edit: Ah, it is built into the HT rotor arm.. silly me.. so I need to take a look at mine for sliding parts.]
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PostPost by: MarkDa » Wed Jul 03, 2019 10:09 pm

Yes Jon - the limiting rotor arm is a full disc with a spring loaded weight that moves out to break the circuit.
Obviously springs can weaken reduced break rpm or the screw in additional weights could have been removed to increase rpm.
Given all this and normal erosion of the spark electrode theres no way I'd re-use the one i took out after a 30 year lay up.
Modern soft rev limited are the way to go.


https://images.app.goo.gl/w1gDdAaVC4o7wDud6
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PostPost by: billwill » Thu Jul 04, 2019 2:35 pm

A seller on eBay found a stash of the standard limiter rotor arms some years ago and one of our members here spotted his advert (which was not for Twink cars). A number of us members hastily bought some and the vendor reaslised they suited the Elan and put his price up.

I think they were actually originally for a Land Rover. Anyway the limiting rev is engraved on the brass bit (in distributor RPM, hence half the engine RPM).

New Old Stock is fine if you can find them.

There is a topic about this on the forum somewhere but I haven't yet refound it.
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PostPost by: billwill » Thu Jul 04, 2019 2:42 pm

Here's one of the former topics, but not the original one.

viewtopic.php?t=40404&p=282044

and another, but still not the one I meant above.

viewtopic.php?f=38&t=20756
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PostPost by: JonB » Thu Jul 04, 2019 2:57 pm

MarkDa wrote:Yes Jon - the limiting rotor arm is a full disc with a spring loaded weight that moves out to break the circuit.
Obviously springs can weaken reduced break rpm or the screw in additional weights could have been removed to increase rpm.
Given all this and normal erosion of the spark electrode theres no way I'd re-use the one i took out after a 30 year lay up.
Modern soft rev limited are the way to go.


https://images.app.goo.gl/w1gDdAaVC4o7wDud6


Well I definitely do not have one of those in my distributor. Engine was rebuilt by QED in 1992 and seems to have done 50,000 miles since. It's very strong and seems to like a good thrashing, but it only takes one part to let go at speed.. The soft limiters look good but at 25% the price of a 123 distributor, maybe I'll save for one of those.
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