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Lucas SR2 magneto end caps #522450 01/11/14 11:49 am
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57nortonmodel77 Offline OP
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I dont often get to work on SR2 mags, but have noticed a shortage of vendors who sell the end caps. My regular supplier is in process of making some for me & asked this question:

" I have looked at an original cap I have in stock and it has 3 HT pickups inside the cap one at 10 o’clock and one at 5 o’clock plus an extra at 2 o'clock which is not drilled for an HT cable, why? it must be for use on different engines running at different speeds or maybe 2 and four stroke engines? "

I wonder if he has an odd agricultural end cap, but I dont recall that situation on the last SR2 I worked on. Anyone have a comment, or a pic of the inside of an SR2 endcap?

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Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #522463 01/11/14 12:39 pm
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triton thrasher Online Content
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I'm sure this isn't much help, but this is the inside of my 4-cylinder agricultural magneto end cap.

I expect it's an SR4, but there's no label.

[Linked Image]

The 180 degree twin cylinder John Deere could use two adjacent (not opposite) HT terminals, if I remember rightly.

Last edited by triton thrasher; 01/11/14 12:44 pm.

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Re: Lucas SR2 magneto end caps [Re: triton thrasher] #522544 01/11/14 9:47 pm
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57nortonmodel77 Offline OP
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Thank you!
I was looking at an SR1 cap today & it has no brass posts, just the single thin copper strip

http://www.klempfsbritishparts.com/COVER--END--MAGNETO--SR1-0

I just had a SR2 in the shop for a rebuild on a '59 Indian Chief (Royal Enfield) , but I really didnt pay attention to the brass posts, other than to clean them.


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1948 Norton 500T Trials bike
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Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #522573 01/12/14 7:09 am
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Yeah, the single type is slimmer, not having to cover a rotor arm. Common on AMC singles, for some reason.

I've never even seen an SR2. Is it more or less the same as a 4-cyl?

Thinking about it, the magnet of the 4 must turn at engine speed, to give two pulses per crankshaft revolution and the rotor arm must be geared down to half speed, to pass each terminal once per two crankshaft revolutions.

The SR2 won't need a geared rotor arm, because its magnet turns at half crankshaft speed, as will the rotor arm (does it have a rotor arm?).


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Re: Lucas SR2 magneto end caps [Re: triton thrasher] #522592 01/12/14 10:11 am
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57nortonmodel77 Offline OP
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Yes, the SR2 I worked on had a rotor arm , but it mounted directly on the armature shaft. After looking at the first paragraph of the workshop manual, it seems they offered the SR2 in engine speed & 1/2 engine speed varieties, so some had a gear on the armature shaft that drove a gear on the rotor. These mags were used on motorcycles, farm equipment, marine, & industrial engines, so there were a lot of different options.
Here is a copy of the workshop manual:

http://www.brightsparkmagnetos.com/library/LWImags/Lucas%20SR%20Magnetos.pdf

parts list:

http://www.brightsparkmagnetos.com/...36-57/G09-23%20Magnetos%20and%20ATDs.pdf



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Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #522600 01/12/14 11:00 am
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triton thrasher Online Content
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Engine speed SR2, with geared rotor arm ("electrode" in the book), would have been for things like the twin cyl Deere, with uneven firing intervals. There would have to be four HT terminals in the plastic end cap, with two of them somehow shorted to the casing.

I was right though. My pic of an SR4 end cap was no help!


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Re: Lucas SR2 magneto end caps [Re: triton thrasher] #522650 01/12/14 3:48 pm
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Hi!
As I understand it, the SR series was initially an Industrial magneto in many different configurations, hence the platform mounting capability not used on Enfield singles & twins. Sure looks like a knock-off of a Fairbanks-Morse tractor magneto. I've seen/had many variants over the years. Right now, I am pondering 2 SR-2 caps from Twins, but the brass pick-ups are located/clocked differently from one another. Ah, the mystery of these things! Anyway, single (blade type), 2, 3 and 4 cylinder variants with brass pick-ups are out there. I still argue that the SR series was the best magneto produced by Lucas. Certainly more reliable than the K- series over the years. That is yet another argument, though.

REgards!

Bigtwin

Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #522671 01/12/14 5:34 pm
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57nortonmodel77 Offline OP
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Many bikes used platform mounted mags, like The MO1 mag/dyno as an example. The SR2 and other rotating magnet mags have pro's & con's versus the K series Lucas. I wouldnt say the SR2 was more reliable, but it sure was easier to change the capacitor on (until recently).

I think the problem I started the post with is, the vendor may have a end cap that Lucas manufactured in such a way that would fit different applications based on which terminals the factory hooked into???? It would be great if someone could snap a pic of the inside of a SR2 cap. If we can work this problem out, I will probably need to purchase a tons of these SR2 caps to make it worth production, but I cant find anyone else who makes them (at least ones that are good quality). I already stock the red electrical varnish for the interiors, so that part is not too difficult smile

All the best,
Skip


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My Bikes
1948 Norton 500T Trials bike
1950 Norton Model 7
1952 Norton ES2
1957 Norton Model 77
1960 Norton Nomad 600cc Desert sled
1961 Norton ES2 (slimline)
1964 Norton Atlas Scrambler
1972 Bultaco Alpina
Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #522682 01/12/14 6:09 pm
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triton thrasher Online Content
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There was a legend that the SR2 made Enfields hard to start.

Wonder if the cap with HT terminals and the rotor arm made it more susceptible to dampness, than the K2F. I find the K2F to be proof against all weather.



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Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #522683 01/12/14 6:10 pm
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There's really no mystery about the cap for the SR2: it's just like an automotive distributor cap grafted onto the back of the SR mag.

[Linked Image]

As has been suggested, there are numerous versions depending on the intended application, and the one for a single is a simple cover which connects the HT lead direct to the coil.

The one above is from an Enfield twin, and in concept is just like an automotive distributor: the output of the coil is fed to the center of the rotor, which aims the timed spark at the appropriate brass post.

I've seen caps with various schemes for venting, suggesting that condensation was a real problem. I had an NOS cap about two years ago, which had fairly large screened ventsjust above the domed portion.

Whereas this cap has the HT leads 180 degrees apart and connected directly to the brass posts, I've seen at least one which had both HT leads high up, wiht the one on the left connected to its brass post via an internal conductor.

...gREgg


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Re: Lucas SR2 magneto end caps [Re: gREgg-K] #522867 01/13/14 6:59 pm
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Hello, all!
Funny how we all have had different experiences/luck with Enfield magnetos over the years. For me,anyhow, it has been less problematic to replace a troublesome K-series Mag with an SR-2. Moisture can be a problem for any mag... & I have K-2 mags that have died due to internal corrosion, as well. How many of ya'll have found bikes running without cap gaskets & or cracked caps from over tightening screws? Owner abuse! The SR-2 caps with the vents were used on the Apache performance engines. Naturally, water could go both ways! BTW, I run condensers from a Kohler generator mounted externally with no problems on the SR-2s. The benefit/failing of the SR Mag was the simplicity. They certainly are not "high performance" in comparison to the K-2f Competition magnetos... but then they have that armature with all the wires spinning around... Hmmm?
I would like to try a good one of K-2f competition mags, though. I don't know they were ever standard on the Twins...Anyone know for sure? Interesting thread!

REgards!!!

Bigtwin

Re: Lucas SR2 magneto end caps [Re: gREgg-K] #522890 01/13/14 11:26 pm
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57nortonmodel77 Offline OP
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Thank you very much for the pic Gregg, It's how I remembered it, now it is confirmed! My supplier is in the UK & uses only very high quality materials & precision machinery, so if these SR2 caps are as good as the slip rings & pic-ups, these should be pretty nice. I'll keep you all updated.

As to the "vents", the vent holes in mag caps are not to let out condensation but to create an air flow through the cap to stop the air becoming ionised due to the high voltage. The rotor arm is used as a fan, if you look at BTH JD magnetos or ML CG4’s you can see the blades cast into the shape. The vents have gauzes in them to stop any fuel vapour catching fire working on the same principle as a miners safety lamp.

There is pro & con about rotating magnet versus rotating coil, but if set up correctly, both will work perfectly reliably.

Skip


Magneto & Dynamo restorations & supplies

My Bikes
1948 Norton 500T Trials bike
1950 Norton Model 7
1952 Norton ES2
1957 Norton Model 77
1960 Norton Nomad 600cc Desert sled
1961 Norton ES2 (slimline)
1964 Norton Atlas Scrambler
1972 Bultaco Alpina
Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #522971 01/14/14 1:34 pm
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The way I heard it, the vent stops a buildup of corrosive ozone, formed by sparking at the points.


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Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #772908 05/07/19 1:31 pm
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Sorry to dig this up, but I was curious if you were able to get the end caps manufactured. I have an SR2 that fires great (borrowed end cap from another SR2), but I don't have an end cap.

Re: Lucas SR2 magneto end caps [Re: 57nortonmodel77] #772911 05/07/19 1:54 pm
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USNFC, I have a used Lucas cap for an SR2 I'd be willing to sell. It is in pretty nice shape cosmetically, but lowest of the 3 fastening bosses (inside) needs repair. If you're good with plastic and JB Weld, it should be an easy repair. If you're interested, send me a PM and I'll shoot you a couple pictures.

..gREgg


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Re: Lucas SR2 magneto end caps [Re: gREgg-K] #773148 05/09/19 2:23 pm
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Thanks gREgg-K, but I actually got a PM about one and picked it up. It should be on it's way from England now. I appreciate the response though.


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