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Misc: Ignition KVF Cam Rings


LoneStar

Website User
VOC Member
Hello all,

I'm needing to replace the cam ring on my KVF magneto. The situation is a bit cloudy, though, as there are at least two versions:

the Vincent Spares list shows

PR22Q: Lucas 458661 - used on models 42134A, 42134B, 42134C, 42134D only
PR22Q1: Lucas 459155 - used on models 42134E, 42134F only

The Lucas catalog (1936-57) also shows 459155 for the E & F magnetos, but 455460 for A through D versions. The Vincent-listed number 458661 isn't shown at all.

My magneto is the F series, so I need 459155 - but suppliers generally refer only to a KVF cam ring. Does anyone know the differences between the two (or three) versions of the cam ring?
 

Robert Watson

Well Known and Active Website User
VOC Member
Well there is a can of worms.

As the catalog shows 1936 to 1957 AND prewar twins and other bikes used similar cam rings albeit 47 degrees but others used 50 deg and these in the base mount type mags and with manual advance I think these would be unlikely for a post was twin.

I have a couple of new ones on the shelf and I recall they were different. I look and see what's what and I think one may even still be in the lucas box.

stay tuned
 

greg brillus

Well Known and Active Website User
VOC Member
The only variation with the post war twin magneto cam ring's would be the type to suit manual advance, this type having a machined groove for the "Wine glass" cable abutment, and another groove to accommodate the travel of the cam for full advance and retard position. It is pretty rare that the cam ring gives any trouble, more likely the alloy housing itself. A significant split in the timing from the rear to front cylinder is usually in this housing, and/or the armature shaft is bent or similar. I've seen some out by nearly 10 degrees.........
 

LoneStar

Website User
VOC Member
I'm replacing mine because it shows scoring and wear; a bit odd as I keep it lubricated and it's presumably hardened, but it's been on the bike since I bought it in 1998.

The Series B/C Spares List says this about the magneto, PR22, for Rapide and Black Shadow:

Lucas Magneto KVF/G.M.1 - 42134. 1948 Models 42134A, 42134B, 42134C, 42134D; 1949-1954 Models 42134E,42134F.

I doubt the difference relates to manual advance - didn't all the postwar twins come with ATDs, except the Black Lightning?

The Lucas catalog has the same breakdown of magneto versions / Vincent model years.

040.jpg 20191228_183929.jpg
 

greg brillus

Well Known and Active Website User
VOC Member
The only other thing I can think of is the small cut out in the cam ring that locates it in the end housing. Some have a peg at the top or bottom that would suit the cam ring shown in your picture above. The other type uses a small slot about 10 mm in width, and this type locates in the end housing via 2 very small machine head screws that are set this same distance apart in the vertical face of the end housing. I think the later type also suits a manual advance magneto where this slot in the cam ring allows for the range of advance from full retard to full advance. The positioning of these locating slots is important to the internal timing of the mag, and the timing can be retarded quite a bit, whereas it can only be advanced so far until the output from the mag will stop quite abruptly. The same point at which the mag is at maximum magnetic flux verses when the contact points open.
 

Robert Watson

Well Known and Active Website User
VOC Member
Here are the two I have,

One is a 459155 and in the original box. The other looks to be new but has a wider slot obviously hand ground and does not have the little hole on the internal face with the bit of fabric which I am guessing would be soaked in oil to give a tiny bit of lubrication to the points shoe. 20200101_140308.jpg20200101_140426.jpg
 

greg brillus

Well Known and Active Website User
VOC Member
Those are the 2 types I meant in my last post, the end housings are different as well. The lower one will suit a manual advance mag if the slot is machined for the cable abutment to locate from.
 

LoneStar

Website User
VOC Member
Thanks for the ideas. Mine looks to be a 459155, per the photo - it does have the hole with felt wick for oil, and a narrow slot (.154").

Not sure about the other, but it seems unlikely to be one of the two numbers claimed to be used with magnetos A through D. As Greg says, the wide slot only makes sense if it needs to rotate, and no KVF came with manual advance. (Side note - why was the slot for the abutment omitted if it's intended for manual advance?). Probably post-Lucas production, or for a different mag?

I'm still puzzled by what could be the difference between the early and late KVF cam rings. It's the only part that's unique to the E & F magnetos. The end housing, "screw, cam fixing" and "pin, special, cam timing screw" are the same in all versions. (Not sure what both those last are - mine appears to have a single screw, threaded but unslotted, that engages the cam notch.)

Maybe it's something trivial like the lubrication hole?

Anyway, I've ordered a new one and we'll see how it looks - the vendor had no info on the two variants. I expect it will be a replica of the later one, as that was used on more machines.

20200101_211157.jpg096.jpg
 

greg brillus

Well Known and Active Website User
VOC Member
Some mags had a different end housing that use the cam ring in the lower photo that Robert posted above. Instead of a pin at the top, they had 2 tiny screws with heads about 2 mm in diameter, and a gap between them, I think more towards the bottom of the mag........It is possible this may have been done on mags after 1950 when the larger 18 mm drive end bearing became the norm, pre 1950 mags had 15 mm bearings both ends.
 

LoneStar

Website User
VOC Member
Greg,

Possible, but it's not reflected in the Lucas catalog - the drive-end bearing does change part number on the F version, but not the housing or cam-related parts. Have you seen KVFs with the two pins and wider slot?
 

greg brillus

Well Known and Active Website User
VOC Member
I've just looked at one in the shed, off a late 1950 Black Shadow that has the two small screws and the wide slot in the cam ring, so some are definitely like it. That is not to say they are original as many years have passed since. I have seen both types on many machines, plus at one point I was overhauling magnetos, about 4 per week, of many types and models over a period of about 7 months.
 

LoneStar

Website User
VOC Member
Interesting stuff, thanks. The Official Documentation doesn't always reflect the details of actual production.
 

peter holmes

Well Known and Active Website User
VOC Member
When I purchased my Rapide in 1965 the KVF magneto had had a modification done to it by a previous owner, they had drilled and tapped two small threads round the circumference of the aluminium cam ring end cover, at the time I presumed the purpose was to distort the cam ring a little to get the firing degrees spot on, an alternative to stoning the ramps a little I supposed, then the mag packed up and I gave to a Lucas electrical shop in Edgware, I have a feeling it came back to as a service exchange unit without the tapped holes, has anyone else come across this modification/bodge.
 

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