By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th


All Topics | Latest Posts

Search for:  in Thread Title in  
john fletcher 103/12/2020 12:10:32
651 forum posts

Is there a way to access REME EMERs? A friend has a an old Rudge motor bike fitted with a BTH magneto and asked about overhauling it. When i was in REME more than 67 years ago there seem to be an EMER for so many things, was there one for magnetos? Alternatively, can any one point me in the right direction for information regarding the BTH magneto. I/we would like to know about these things rather than having it fixed, yes I/we can afford to have an expert restorer look at it. Like wise I could pay some one to do milling and turning for me, which I enjoy doing myself. John

Grindstone Cowboy03/12/2020 12:37:23
422 forum posts
36 photos

Seems to be plenty of info here


Speedy Builder503/12/2020 12:37:53
2182 forum posts
152 photos

I assume you have exhausted the net and come across this library of handbooks.


Speedy Builder503/12/2020 12:38:30
2182 forum posts
152 photos

GC, beat me to it !!

Maurice Taylor03/12/2020 13:20:49
162 forum posts
30 photos

1361d5cf-dead-44f3-933a-21eb985dcd5f.jpegHi,I’ve restored a Lucas K2F magneto ,changing internal capacitor etc ,wasn’t too difficult .

I made a simple test rig as it was hard to test it on the bike

l read somewhere that the spark needs to cross a 5mm gap in open air,which mine did.

Hope this helps


PS If you need to take the armature out ,try to find out if it will affect the magnetism in the stator, best to try to do work with armature left in place .





Edited By Maurice Taylor on 03/12/2020 13:50:26

Dave Wootton03/12/2020 15:52:09
108 forum posts
22 photos


If you remove the armature from a BTH magneto it will definitely lose it's magnetism unless you use a keeper, Lucas mags have a different magnetic material that holds it's magnetism.

Best source online for magneto information is as stated above the Brightspark magneto's site which has loads of information and how-to's on magneto repair and they also do remagnetising. I've used them in the past for parts and rewinds and there service is very good.




Edited By Dave Wootton on 03/12/2020 15:56:10

SillyOldDuffer03/12/2020 17:13:03
6653 forum posts
1499 photos
Posted by john fletcher 1 on 03/12/2020 12:10:32:

Is there a way to access REME EMERs? John

One of my Uncle's spoke fondly of what may be the same thing. Well written clear instructions for military vehicle maintenance? He reckoned they were tested on the thickest Pongos the British Army could provide and re-written until anyone could fix stuff during an emergency by following the instructions.

This is the same uncle who, only slightly too young to see the shooting part of WW2, drove an Army lorry from Aldershot to Greece without being taught to drive first. Done in a convoy with motor cycle outriders, and instructions starting: "At main gate turn right." No map, just a list of what to do at every road junction across what was left of Europe. 20mph max and a constant headache due to the whining gearbox. He enjoyed the Army so much he lied repeatedly about his age in order to stay in the Territorials. Being one of those lucky oldsters who look younger than they are, he served well beyond the age limit.


Peter Cook 603/12/2020 19:15:46
44 forum posts
3 photos

Reminds me of a story my father told about the TA(or whatever it was in the 1930's). At the time he worked as a mechanic for the firm that supplied and maintained the trucks. He was sent on an exercise in NWales with a big group.

The sargent in charge lined up the squaddies and after asking who could drive, added enough extra to give one per vehicle on the you, you and you principle. Father was then asked to give basic instructions. And off we go.

Some time later ascending a steep pass one truck was smoking very, very badly, think smokescreen! At the next stop they investigated. Oil was overflowing out of the engine. The sump was full to the pistons. When asked the squaddie said " You said to add oil if the oil pressure dropped. Every time I switched off the engine at rest stops the oil pressure dropped to zero - so I did as I was told".

john fletcher 104/12/2020 18:02:36
651 forum posts

I like your test rig Maurice a good idea. years ago I had a similar rig for testing dynamos. What my friend was concerned about was, when removing the armature to check the bearing how was he to arrange a keeper to the magnets. I'm pleased to say he has a good spark and I'll show him Maurice's set up. John

Oily Rag06/12/2020 20:43:05
264 forum posts
118 photos

Nice rig Maurice!

It looks like a re-cycled washing machine motor, do you have a speed control on it? For testing magnetos or other ignition systems it is also very handy to have a 'rotating spark gap', this is a asynchronous electric motor driving a spark gap, adjustable to give a range between 0.125" and 0.5" (the bigger gap is useful for high energy systems such as CD ignition ). If a misfire occurs due to breakdown of the system the spark gap immediately allows you to recognise the 'missing' spark as the sparks form a pattern such as a 3 point, 4 point, 5 point star etc as system speed increases.

We used these 'RSG's' as a way of setting the soft and hard ignition cut on the Lucas Race Ignition boxes, we set them up 60 rpm 'soft' and 20rpm 'hard' below the Monk limiter of the F3000 cars as the Monk denied for 2 secs and was a huge disadvantage if a driver triggered the Monk system. Very useful bit of kit which we recycled out of the Magneto service department.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest