Author Topic: K2F magneto  (Read 762 times)

Offline a101960

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K2F magneto
« on: 17.01. 2017 13:51 »
As a matter of interest are all K2F mags the same? That is to say can you mix and match parts? I want to convert from auto to manual A/R can I just buy a manual A/R housing and associated parts (drive wheel etc) or is there more than just that involved?

John

Offline bsa-bill

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Re: K2F magneto
« Reply #1 on: 17.01. 2017 16:00 »
Quote
I just buy a manual A/R housing and associated parts

I believe I have read  the housing for our A s is smaller at the point nearest the engine ( is the shoulder ground off ?) so might be you need one for BSA A, other than that I think you might need to change the other end to accommodate the cable, someone will have done this and know more
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online groily

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Re: K2F magneto
« Reply #2 on: 17.01. 2017 18:18 »
There is a host of small differences between mags in the K2F range, but to do the conversion only really requires:

* a manual cb end-housing (unless you already have one with a blank undrilled/untapped casting for the cable mechanism - which can be modded)
*  the notch in the camring that engages the peg enlarging to provide camring movement (but careful - this needs doing with some precision to ensure the correct internal timing of the mag at full advance) and
*a notch grinding to take the cable plunger.

There are several different versions of the cb end housings - for large screw-on points covers, for plastic clip-on ones, for alloy domes secured by small studs and nuts, etc.

Manual end housings come with the entry point for the advance/retard cable on either side ('slack' or 'tight' advance).

The chamfer on the mag body found on many BSAs isn't extended to the cb housing, so there shouldn't be a problem there.

The ATD could still be used, rather than replacing the drive - there are quite a few folk who have "manual + atd". Some lock the atd in a fixed position, others let it do its job regardless, as it will self-retard at low revs. (What choice is made here affects how the basic ignition timing is set.)

One other thing: it is surprising (scary in fact) how big a difference the replacement of the end housing and the bearing race can make to the firing interval between cylinders. If at all possible it is highly advisable to check the interval by using a strobe on both cylinders. Variations between cylinders of well over 5° at the mag are not unknown with 'mix 'n match', and that's 10° on the crank. (Piston-damaging territory in extreme cases.)
Bill

Offline a101960

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Re: K2F magneto
« Reply #3 on: 17.01. 2017 19:29 »
Groily, thanks for a helpfull reply. I have done a bit of research and it seems that I need to careful about what end housing I buy, because the earlier type have different bearings fitted. Is there anyway to check for this? And does it actually make any difference?

Online trevinoz

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Re: K2F magneto
« Reply #4 on: 17.01. 2017 20:13 »
The early type has a 15mm bearing on the drive end. The points end is the same on them all, 15mm.

Online groily

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Re: K2F magneto
« Reply #5 on: 17.01. 2017 22:34 »
Should indeed be standard 15mm on all K2F cb end-housings, as Trevinoz says.
The only 'won't fit' part is a K2FC end-housing. It's similar from a couple of paces, but square not rectangular, has bigger holes for 1/4 BSF (not 2BA) screws to pass through, and most of them use a different version 15mm ('N3048' so-called) bearing from the standard 'E15' item. The difference is the greater width of the outer race.
The drive end bearing went up from 15mm id to 18mm (with larger oil seal to suit) around 1951(ish).

Bill

Online trevinoz

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Re: K2F magneto
« Reply #6 on: 18.01. 2017 20:15 »
That slipped my mind, Bill. Must be a case of Oldtimers.

Offline a101960

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Re: K2F magneto
« Reply #7 on: 21.01. 2017 16:36 »
I found a manual advance casting on ebay. Only problem is it looks like some clown has opened out the hole indicated by the red arrow. So, can this be sleeved? The other two holes are unmolested. Also does anyone know where I can buy the plug that limits the cam ring movement. It looks like it screws in is that the correct assumption? There appears to be to holes that look like they are designed to to accomadate the plug, one at the top and one at the bottom. Does it matter wich one is used?
John

Online groily

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Re: K2F magneto
« Reply #8 on: 21.01. 2017 21:15 »
It looks quite 'well-used' as they say, but as long as the camring isn't a sloppy fit it ought to serve.
You can sleeve the enlarged hole - probably bodged to allow the use of a larger screw than original into the thread on the body on that corner  . . . they can strip. The housing should register OK on the other holes though - so not a huge prob for fitting it.

The missing pin is a 1/4BSF screw with an eccentric tit on its nose - and it has a hole in its head for a small pin to be tapped in when it's set in position to lock it there.
What it does is offer fine adjustment of the camring position, to get the ring in the optimal position at full advance of the instrument.
Any 1/4 BSF screw with the nose filed to about half diameter, and a slim locknut on the outside to lock it, will work fine - or you will need to fiddle about with a drill and make a pin to replicate the original.
When setting the camring, you want the points to just start to open a few degrees after the flip point of the armature, with the plunger at full advance (in this case, fully 'down' the 'ole as it's for 'slack advance' on an anti-clockwise drive magneto). 
It is very important that the points don't start to open before the flip point (or right on it for that matter) because the mag is not ready to discharge until it passes the flip point.
If the camring is set far too far advanced, there'll be no sparks; if it's a bit too advanced  the mag will spark at low revs but you'll lose the sparks as revs rise as the lines of magnetic flux 'bend' with speed. Usually, with the eccentric tit set at about mid-point, things will work quite well, but the newness of the heel on the contact breaker and wear on the camring influence when the points actually start to open. It is worth playing to get what seems to be the best low speed spark at full advance, by spinning the mag by hand on the bench, and then checking that the sparks don't disappear when you spin it under power. If you can measure the speed of rotation, you ought to get all sparks, across large gaps (grind the earth electrodes off a couple of old spark plugs to obtain 4mm+) from somewhere not very far north of 100rpm. Lucas said '90% of sparks across 5.5mm test gaps with three sharpened points at 130rpm' for the K2F.
The eccentric can go in on the top or the bottom if there are two threaded holes to choose from, as the camring is symmetrical. But you need to choose which before grinding a notch for the cable plunger on one side, and enlarging the slot that allows the advance/retard.
As a point of note, the large slot for the AR movement in a manual camring is usually about 10.5mm/11mm from side to side, which would give you about 20° movement on the magneto, or 40° on the crankshaft. Less is plenty though - and the worst thing to do would be to make it too wide - because then the plunger might disengage from its notch at full stretch one way or t'other and the operating mechanism jam in the housing. On my own machines I usually restrict the movement to a bit less than standard, as we don't really need massive amounts of retard IMHO.
Bill