The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Rgs-Bill on 17.03. 2014 17:21

Title: K-2F mags and K-2C for competition
Post by: Rgs-Bill on 17.03. 2014 17:21
Hi guys, any one here on the forum that can tell me what differences there are in the 2 magnetos, to make the competition model Lucas maggy any better than  the silver tagged street model maggy.  Musky used to race the A-7's and A-10's, (not sure on A-10)  Musky, our moderator said that externally the mag carbon pick ups are held in with a screw instead of a spring clamp, which could vibrate loose I am guessing.  Also the end cap is a threaded on end cap, but my 62 A-10  RGSS  has a threaded on end cap on a silver tagged maggy.  Does any one out there know what , if any, internal differences there might be to make the competition model any better ? 
Title: Re: K-2F mags and K-2C for competition
Post by: unclerob on 17.03. 2014 18:18
Hi Bill, I think a lot of ordinary mags have pickups held by screws and screw on end caps.....both mine do anyway! I've no idea if this is true or not but years ago I remember being told that when Lucas wound the armature they used to only use one continuous length of wire in the comp mags but often it was joined in the ordinary ones.....
Post by: groily on 17.03. 2014 18:35
Well  . . . the C mag has an end-housing held on by 3 1/4 x 20 screws, usually with deep hex heads drilled for wiring up. But many seem to have allen screws these days. Some are fixed camring, some manual. Fixed jobs can be modified if necessary, but you only get one chance at getting it right. 
The cb end bearing will be N3048 rather than than the stock E15, the points cover will be screw-on - like many others, indeed - but should have a breather built in with a little alloy tube coming off. With or without a kill button facility & brush/spring. I don't know, some early ones might have had an E15mm bearing at the drive end - but the 18mm is more common and a bit tougher and universally fitted on K series post '51.
Internally, it is said that more copper was applied to C coils than standard, and there is evidence of that, but most rewound jobs will be the same for Cs as for standard K2Fs.
The HT pick-up holes in the C body are smaller and the pick-ups are held on by 2 screws per side not by spring clips. Pick-ups aren't interchangeable.
In terms of normal performance, I'd be hard-put to say a C is 'better'. In fact, it can be a PITA if you want to get the pick-up next to the engine off in situ! Those screws HAVE to have a hex head or you need rt L scrooges with probably more than one angle on them.
Title: Re: K-2F mags and K-2C for competition
Post by: muskrat on 17.03. 2014 19:15
Thanks for that groily. I didn't know about the breather.
Title: Re: K-2F mags and K-2C for competition
Post by: groily on 17.03. 2014 19:55
KIFC looks spot-on Musky; K2FC is what it says, but a breather end cover (and a red name tag) would complete the 'ensemble' - not that it makes a scrap of difference in any practical way!  Greeny/ gold painted bodies speak 'R' as well maybe?, but I don't know what else sets them apart. Cheers.
Title: Re: K-2F mags and K-2C for competition
Post by: beezermacc on 28.03. 2014 07:11
In my experience there is no difference in performance between the competition mags and the standard ones. I have tested the resistance on most coils  coming through the workshop, just out of habit really as they all have to be rewound anyway. The resistance on all satisfactory coils is between 4500 and 5500 ohms. I have even counted the turns on some coils and there is a variation between about 7500 and 10000 turns but no correlation with either type of mag. I suspect the number of turns was dictated by the physical size of the coil. The more experienced coil winders, usually women in the Lucas factory, would be able to do a really neat job and get lots of turns on before the coil became max size. The less experienced staff might have had problems wrinkling the interleaving paper or snapping wire and creating soldered joints which causes air gaps and takes up space. I have no problem getting 10000 turns on a coil but 9000 is plenty to achieve the performance required. I don't believe the girls in the Lucas factory snapped the wires that often because it's a real PITA joing the wire again and very time consuming so a fail to be avoided! The trick is to use a good quality tensioner and not run the machine too quickly so you can see any potential snags as the wire comes off the spool. I can wind about three in a day from start to finish which includes stripping the old coil down. Some Triumphs (excuse me whilst I spit!) used mags which, at first glance, look like a K2FC; i.e they have screw-on pickups and the cam housing is attached with 1/4 whit hex head wire lock bolts, but these mags have a breather hole in the underside of the body which a genuine K2FC does not have. Also the Triumph mags often have the standard screw-on points cover. Some of the racing mags had a one-piece, stainless steel taper/capacitor housing (part of the armature) so that the drive shaft wouldn't separate from the capacitor housing (the bit the earth brush rubs on). The performance of the mag is mainly due to the construction of the armature and capacitor. Capacitor technology has moved on so much that there are a few capacitors which do the job really well, both ceramic and paper film dielectric epoxy insulated, all of which the mag restoring fraternity use widely depending upon application. Lucas used two types of capacitor in their K2F armatures, square cans and barrel type but both will fail over time due to the construction and materials available in those days. Surprisingly some mags are still working fine with capacitors which are 50+ years old. Going back to the original question, a K2FC will have a body without breather hole, a screw cap points cover with breather pipe, screw-on pickups, and a cam housing attached by 3 x 1/4 whit screws with wire lock holes but there will be no difference in performance between a K2FC and a good K2F........... in my opinion!
Title: Re: K-2F mags and K-2C for competition
Post by: muskrat on 28.03. 2014 09:04
Thanks for explaining all that beezermacc. So it's all show for no more go really. Screw on bits would be more secure for racing especially scrambles.
Title: Re: K-2F mags and K-2C for competition
Post by: Triton Thrasher on 28.03. 2014 09:43
Screw on bits would be more secure for racing especially scrambles.

That makes sense, for bouncing the bike around the fields.

For sustained high speed, I'd have more faith in the spring clips.