The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: mikeb on 19.01. 2017 02:34

Title: magneto bearing removal
Post by: mikeb on 19.01. 2017 02:34
I've read the old forum threads but the problem is some of the photos have disappeared so...

what are some tips and tricks for removing the bearings from a k2f (or a mo1n if that's not a rude question.

obviously take to the pros is an option, or copy the 'brightspark' suggestions here: (

but what else can you get by with in the shed?

Title: Re: magneto bearing removal
Post by: groily on 19.01. 2017 08:53
It depends which race is being bothersome Mike.
For the inner races, there are some simpler ways than making profile clamping tools or finding access to an 'Octopus' extractor. One not-so-good wheeze which can work is to wrap a strand of thick single-strand copper wire in the ball track and squeeze the race in a vice, and tap the shaft to see if the bearing will slide off. But caution! it's not a great plan as races can crack with too much vice pressure and some bearings are just too well stuck on. (OK if the bearing is to be replaced though.)
A better plan is a simpler extractor - a plate of steel with a hole the size of the diameter of the race, with three or four grub screws disposed radially to engage the track for the balls. Small allen screws with their noses ground 'rounded' can work well. Then hoick the thing off with a typical puller. This will almost always work. But protect the end of the brass taper for the cb assembly if using a puller which bears in that area.
You mention the brightspark tools, which we made because we do a lot of this. But I don't actually use, for extractions, the large push-me pull-me tool for inner races that is shown on the site, with its collets etc. I use a simpler clamp tool I made from steel years and years ago, with the profiles for 15mm and 18mm bearings cut into a single reversible lump, with steel arms and a chunky thread on the extractor bolt. It has served me half a life-time and is capable of exerting a lot more pressure than the larger and more sophisticated item with the collets. But it won't refit the race, which was the point of the sexier weapon.

For the outer races, it's harder sometimes. At the drive end, a heat gun or immersion in boiling water and then a drift against the oil seal on a K2F can sometimes shift them. A screwdriver with a bend put on the extreme end and used as a lever can sometimes do it. Or, in many cases I've seen mag bodies with two small holes drilled from the outside to enable access with a small drift to the rear of the race. This isn't elegant, but really does no great harm as the race and insulator (and oil seal on a K) will not let oil in; or tap and thread for a bit of threaded rod, like 6BA or something, to plug the holes again.
At the cb end, the race is easier to get a bent lever onto. With some heat and some careful prising they will probably come.
However, there's no doubt that using an expanding weapon with sharp edges and a 'camming' action makes it a heck of a lot easier. If doing them more than infrequently, it's worth making something or buying enough beers to get a mate with a lathe to make one.

Maybe folk have come up with other, smarter, ways to do this without the need for special kit?

It is a surprise to me that a profile clamp puller isn't actually commercially available for these inner races (as far as I know), because I'd have thought there would be a market for them judging from the number of people who happily replace their sliprings and bearings themselves. There may be 'knife' extractors, similar to but miles smaller than, the items used to get drive side main bearing races etc off. At one point, I made a dozen sets of pullers for getting 15mm races and also sliprings off. The idea was to have a 'toolpack' for customers to use. But in 5 years only two people had asked, by which time we had given them away to mates. They were made according to the downloadable drawing you refer to Mike.
Title: Re: magneto bearing removal
Post by: mikeb on 19.01. 2017 09:35
thanks groily that's some great tips - its the inner race so I'm going to try the steel plate/grubscrew approach or some variant of it. i also thought of two pieces of suitable size chain links cut and put around the inner race and put in the vice and then a tap.  i'm currently working on a spare mo1n from the b33 (dead capacitor) but considering it a practice run for doing the slipring on the super rocket next.

one thing around I've seen commercially is as per the pic below. while its supposed to go behind the race i figured it could well go in the race and if I soften its jaws the race may even survive. do you think that would work?
Title: Re: magneto bearing removal
Post by: Bsareg on 19.01. 2017 10:47
If you are sure it's a dead capacitor why not go for one of Brightsparks caps. No need to remove bearings, just snip wires, saves finding a way to hold contact breaker nut. Fits under the breaker itself
Title: Re: magneto bearing removal
Post by: groily on 19.01. 2017 11:58
It's hard to do a quick job on the MO1 condenser 'cos the thing is the cb end of the armature, while the K is the drive side and therefore has an accessible doubled-up live lead that traverses the coil from condenser to points. So you just cut off and insulate the double strand at the condenser and leave the earth side alone (as long as the coil tests good that is).

The knife extractor might do the job on the inner race using the ball track I guess - depends how tight the darn race is on the shaft. Races usually survive the grubscrew trick unmarked (I use that 'method' now and again on 13mm and 14mm id bearings - for which I haven't made full profile tools because they are rarely encountered and I am too lazy). But I am usually going replace those bearings anyway, so don't worry too much. Not sure about the chain-link squeeze - neat idea if it works though!
Title: Re: magneto bearing removal
Post by: Caretaker on 19.01. 2017 12:10

I've read the old forum threads but the problem is some of the photos have disappeared so...

Yes, (very probably) not forum's own pictures (uploaded as attachments), but links to pictures on external hosting where the owner has changed hosting or rearranged pictures and setup, thus killing off any and all previous posted links all over the net, and destroying some post or topic's informational content. Have been fighting this plague for a long time.

A reminder to NOT use any external image hosting services here. Use only the 'attachment' feature from the forum, maybe not the most flexible of attachment handling, but the pictures will always be there when needed.  See
Title: Re: magneto bearing removal
Post by: mikeb on 19.01. 2017 21:22
why not go for one of Brightsparks caps
tried that but with this maggie it started fine when cold but not when hot  - as i understand it that kind of the cap problem means the cap has to go.

links to pictures on external hosting where the owner has changed hosting
yes that's exactly the problem - externally hosted pic that have now disappeared. the ones within the forum are good.

so far I've tried a bit of plasticized 3mm wire (as chain too thick) bent around the ball track and held in the vice, then some taps on the (protected) shaft. but no luck so far - the bearing inner is really tight. being next to the slipring, how much heat can these things handle to loosen them up?

groily - on the mo1n has anyone succeeded in just dremmeling out the capacitor earth tag with it all in place and still assembled? i can remove the earth screw and could re-solder a tag to the wire and screw it back, and if the cap is going to stay in there but be disconnected electrically then could i just snap the tag off somehow or dremmel a great hole in the cap's side to remove the tag -- all with armature and bearings and slipring in place???
Title: Re: magneto bearing removal
Post by: groily on 20.01. 2017 08:36
Starting cold and not hot is a pretty typical condenser problem (or coil in worse cases of course) - but yes, the cap has to 'go' - or be disabled. You don't want a duff one and a new one both connected - no gain. Very few condensers fail 'open circuit' - it would be handier if they did!

Heat and the slipring - hmm. How long's a piece of string? No harm applying a hairdryer or a heatgun on 'low' probably, the slipring can take a fair temperature without anything bad happening. Think I'd move on to the steel plate and grubscrew option myself though, as that will work.
(I should say that if the slipring is an original one, it's a 50:50 whether it is leaky at elevated temperatures anyway - in which case damaging it wouldn't matter.)

As for doing an MO1 in situ  . . . it's been done, but I haven't tried it. If you can get the earth tag off and then run just that low tension wire from the coil to earth without  touching anything else, it would work. The stud on the old condenser (that its earth tag is attached to) mustn't be able to touch the brass end cheek. So yes, you probably could get in there with mini-tools. It is do-able in theory, and has been done at least once.

Assuming in all this that you are happy with the HT coil? From slipring brass strip to armature shaft (with the earth tag connected at the condo!) you want to see something around 4-6000 ohms in round numbers. If it's Open Line, then either the slipring isn't connecting properly to the coil, or the coil has a break and further investigation is essential.
Title: Re: magneto bearing removal
Post by: mikeb on 21.01. 2017 04:42
success getting the mo1 bearing inner off with a variation on the grub-screw method. see the pic - a piece of pipe lying around conveniently with an id of 21-22mm, some M4 screws with rounded ends and threaded into the pipe, an M12 nut welded in the other end and a bolt pushing against an old nut (off an a10 maggie) on the end of the maggie shaft. nothing broke in the process. extracting the cap easy as was grinding off its earth lug. i'll stick some silicone in the gap (where the lug was) when i reassemble to ensure no conduction.

at this stage I can't find a resistance on the secondary (HT) winding which is surprising as it was sparking fine when it came off the bike, so I'll clean it all up and try again. probably worth a new slip ring if I'm in this far and new bearings.

now i have some confidence for when i get to the k2f. thanks for your help groily
Title: Re: magneto bearing removal
Post by: kiwipom on 21.01. 2017 08:05
hi guys, Mikeb nice work good idea,cheers
Title: Re: magneto bearing removal
Post by: groily on 21.01. 2017 10:02
Good progress Mike.
Slipring is always a good idea, and bearings if the tracks are marked, pitted or dulled. (That will bring you to the 'outer race' question where more resourcefulness will be needed!)
Re the HT coil  . . . if you scrape clean the spike on the end that goes into the slipring, you might find continuity. But you might well not, to be honest. If the coil has a small break in it, it will still spark - the spark will jump a small gap but it will slowly get bigger until the spark can't. Might last for a reasonable while, or it might not. I wouldn't proceed too far without knowing whether it's good -as you might find yourself having to go through the whole rigmarole again! Also worth heating it up (50°C is good) and seeing whether it goes soft to the squeeze - if it does the insulation is breaking down/has oozed out over the years.
Title: Re: magneto bearing removal
Post by: trevinoz on 22.01. 2017 20:32
Also get a 1mm drill and clean out the slip ring connection.
Title: Re: magneto bearing removal
Post by: mikeb on 22.01. 2017 21:04
hmmm... i cleaned up the HT spike and even tho it sparked fine on the bike (when cold) its likely there's a small break in the HT winding as currently open circuit between the spike and ground. and the slipring connection looks  a bit melted and similarly hard to find a connection. so i wish I'd figured this out before struggling with bearings etc. the one on the bike currently is said to be reconditioned but is a hard starter (especially cold) and misses occasionally. may have to pull that one down next. *sad2* lucky my a10 is (currently) reliable
Title: Re: magneto bearing removal
Post by: chaterlea25 on 22.01. 2017 22:24
Hi Mike
HT winding as currently open circuit between the spike and ground

That's not the correct way to check *ex*
Check from winding spike to the points centre bolt,
The inner end of the HT winding is connected onto the LT winding

Title: Re: magneto bearing removal
Post by: mikeb on 22.01. 2017 23:25
good point John. tho with the inner end of the HT winding connected onto the LT winding, and the LT winding being less than one ohm, then the HT spike should also show a circuit through to ground?

either way tested again and i cant find any circuit between the HT spike and anything; I even put the points assembly back in to double check. so... dead HT?
Title: Re: magneto bearing removal
Post by: groily on 23.01. 2017 08:07
Just for clarity  . . . You can check the continuity in various ways depending on what's been taken apart.
With the bare detached coil on the bench you should see continuity between the HT spike and either low tension tail. About 5000 ohms. You should see half an ohm between the two low tension leads.
With the slipring on the armature and the low tension wires connected you should see the 5000-odd between the brass strip and the spindle of the armature or between brass strip and the centre screw, and you should see the half ohm of the primary between the cb centre screw and the spindle.
Primary and secondary windings share a common earth because the two windings are connected directly, as John stated.
With the armature refitted to the mag and all wired up and the earth brush fitted you should see the 5000 between slipring and body, or from slipring to centre screw.
(What you see on an assembled mag on the low tension side may not be meaningful with the contact breaker refitted, as it depends on whether the points are open or shut and on the effect of having the condenser in circuit.)
But if you can't see the 5000-odd in any circs, then the HT side is unfortunately open line and the bobbin needs a rewind.
Title: Re: magneto bearing removal
Post by: chaterlea25 on 23.01. 2017 23:00
Hi All
I really should not post replies after coming home from the pub  *red*

Title: Re: magneto bearing removal
Post by: mikeb on 29.01. 2017 23:16
I really should not post replies after coming home from the pub
well it proves you make it home John, which could have forensic value one day. all comments appreciated as I stumble thru the dark arts of lucas. I probably have to conclude this maggie needs rewind *sad2* even if it can produce a spark.