Mag for 1930 TT Rep

[Orgasmatron]

What model magneto was fitted to a 1930 TT Rep without lighs?

[chstorm]

On my 1930 TT Rep there is a British Thompson Houston (BTH) magneto. I believe that this was fitted as standard on the TT rep. It is a very good magneto.

Cheers!

[Orgasmatron]

Carl,
Thanks for the info. Is there a particular model number on the magneto?
Regards.
Chris.

[Orgasmatron]

Looking at thr mag/dyno currently on my TT Rep it is a Lucas E3HM-LO/MN2E-Type AX950 combination.
Would I be correct in assuming that these would be a later addition to my bike (the headlamp is A later Lucas type with the switch and ammeter mounted on a removable plate like a MU42- can’t see a model number though – rather than a Lucas H52)?

[chstorm]

You are undoubtedly correct in assuming that the Lucas MagDyno is a later addition. Such additions were often made after WW2 to make the bike more useful for road transportation
A TT rep was made for sporting use – grass track racing etc., and lights were irrelevant.

I will have a look at my TT rep during the weekend. It is garaged together with 8 other bikes and I have to dig it out to look at the BTH magneto and try to find the model/type number.
I may take a photo or two and send it to you as an e-mail attachment if you can give me your e-mail address. I have not yet found out how to put photos directly on the forum.

Kind regards,

Carl

[Orgasmatron]

Many thanks Carl.
My email address is :- pm.smith(at)o2.co.uk
Regards.
Chris.

[Anonymous]

TT Reps were available from the factory with lighting kit – I’ve got one and it is noted in the factory dispatch records as being fitted with magdyno and lighting kit. That runs an MDA2 magdyno date stamped 1929 so I have every reason to believe it is the original one for the bike that the Scott works fitted. Later ones (as in mid 30’s onwards) were usually MN2E or MS2E versions from the ones I have and have seen and have myself. Non lighting kit ones seem to have mostly been fitted with BTH but I also have a Lucas magneto from that period that is mag only.

Cheers,
Richard

[chstorm]

Hi,

I have sent photos of the BTH magneto to your e-mail address. As you will see, the type is KCV50 A1. Serial number is 1F 307922.
I am using a replica BTH electronic magneto on my Vincent Black Shadow, and I am very satisfied with it. I have two other BTH replica magnetos made for Scott. One of them is the new type where you can put the Lucas generator on top. It will then look a lot like the ordinary Lucas MagDyno. I have not used any of them yet, but will try the new type magneto on my 1936 Scott, which I use as a test bed. The 1936 Scott has a Roger Moss tuned engine with a tungsten-balanced crankshaft, hi-compression head and flow tuned transfer ports, Silk pistons with “windows” etc. It goes very well with the original (overhauled) MagDyno, but it is a fact that the magneto is one of two Achilles-heels on a Scott (the other is the clutch). The magneto runs at engine speed on a Scott and has a hard life. On an “ordinary” bike it would run at a half of engine speed.
With the original magneto, everything is well up to ca. 4000 rpm. Then the magneto starts giving erratic sparks, and the power drops. There will be violent vibrations in the engine until it gives up around 4.400 rpm. On a Moss-tuned engine the torque/power curve rises steeply from 3.500 to 4.000 rpm, and power would undoubtedly continue to rise if the magneto could cope with the engine speed. This is where the electronic BTH “magneto” allegedly is superior. It will function normally with much higher engine speeds than the Lucas magneto. In addition it will give a “fatter” spark at low revolutions, making starting easier.
My TT-rep 1930 is not Moss-tuned, but has been used for grass-track racing etc. in the 1930’s and functions very well with the original BTH magneto – at least well enough for my use. It seems to me that the BTH was a better magneto than the Lucas, but this is only based on subjective observation.

On my Henderson 1928 DeLuxe, there Is a BTH magneto, probably from a Tiger Moth or Gypsy Moth. A beautiful piece of work. I have just overhauled it, and I was impressed with the quality of both mechanical and electrical parts.

Cheers!

Carl

Kind regards,

Carl

[Orgasmatron]

Many thanks to both Richard and Carl.
The factory records for my bike indicate that it was fitted with lights and a mag/dyno when it left the factory. However, it appears that a later headlight and mag/dyno has been fitted and I thought that I might as well get everthing as correct as I can whilst I am rebuilding. I don’t mind doing without the lights initially but, ultimately, I would like to get the bike back to how it left the factory.
Thanks again.
Chris.

[Roger Moss]

My 28 built 500 Replica was specified to have battery lights and a BTH M2 small taper magneto. The battery carrier was clamped to the frame under LH leg and could be quickly removed for competition. The front and rear lights were also QD. This mag was also fitted to late 20’s Douglas machines that are the same hand as a Scott with a mag platform mounted mag driven from the flywheel. I set one to Gary Schultz in USA this year. I have pics if you need. The BTH is a better quality mag than a Lucas, but mag windings have a finite life and the speed the Scott runs at is more than the contact breaker system will comfortably tolerate. If you use higher revs, you will think the engine has reached its limit of power, whereas what is usually happening is that the points are bouncing and you are losing spark timing. If all components are in good condition this will not effect normal modest use, but if the components of the cam and breaker are in poor condition then the onset of problems just starts earlier. I tried hard to get the best out of a BTH mag for racing, but if you run a good mag on a test rig with a strobe, you see what was a somewhat dithering line dissolve into a cloud as the timing becomes highly random. I made my own electronic mag initially that Richard still uses, but then used one of Tony Harris’s early BTH mags which has been exemplary.

[Orgasmatron]

Many thanks for that Roger.
I have been seriously considering a new BT-H electronic magneto, as an alternative to the as-supplied set up.
It depends on what I can find.
Perhaps converting an original BT-H magneto to electronic function would be best, if that is possible (I would then have an original unit with modern internals).
Regards.
Chris.

[Roger Moss]

I was restricted to the components I could get at the time which were PVL and they would not go in a BTH mag body. I put a pair of car alternator bearings in the mag body and made a new center shaft with two tapers on. The first to take the PVL rotor and the second the drive which in my case was a belt pulley as my mag drives from a pulley on the clutch drum.
I had long since abandoned driving the mag with chains.
The coils were mounted concentric with the rotor externally, outrigger to the mag body but then it was all covered with a sheet metal cover / guard so is not obvious. When I costed it all out at normal rate as the hours would otherwise would be earning hours, then it cost me £1000, but it worked. When Tony Harris devised his mag, he used 4 high energy button magnets on a small rotating disc although the body still had to be bigger to accommodate it. This cost me about £350 as a special price as a prototype research and development unit as if there were faults in the design or construction, then the unusually arduous duty on a Scott, especially a racer, would show faults up quicker than anything else. I have not seen the last incarnation which was a Lucas magdyno body copy with the Lucas friction drive to a dynamo. In this case you can put on a traditional dynamo or an AC generator as you prefer, but the mag side should be bombproof. I do understand that this is not the cheap option and it may well be beyond the comfortable means of many, but the brutal truth is that you get what you pay for in this life and if you want quality you have to pay a fair price for it. Final comment, some of the available AC alternators are very “Notchy” as they have four powerful magnets and the result is like lifting the valves of a four stroke which gives the drive a much harder time than it was originally designed for. My preference is to use a traditional Lucas dynamo with an electronic controller from Hawker or Boyer and then use LED bulbs where possible to cut down on power consumption. This combination gives a smooth, long lasting and efficient combination. However, from my present knowledge, there is not enough room in a normal BTH mag body to get the rotating magnets and coils in, but if you have the time and knowledge to try it, good luck to you. If you need parts and info, I suggest you talk to Rex Caunt who makes special ignition systems. See Rex Caunt Racing on the net http://www.rexcauntracing.com Kind Regards Roger
Roger

[Orgasmatron]

Thanks again Roger.
Regards.
Chris.

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