Dommie magneto chain tension

I have a problem
When I test fitted the magneto chain with the idler and auto- advance fitted to the mag shaft the tension, if set to the "tight" spot, was too loose at the slackest spot. Too bad, I thought - needs a new chain. New one arrived today (RGM) and when fitted still has excessive variation in chain tension.
So I tried, 90 degrees at a time, advancing the idler (WRT to chain) to see if anything changed. It did but not consistently. So I tried shifting the chain 10 or so links on the auto-advance and repeated the idler process. Again no pattern that I could discern (my only point of reference thus far being the white marks on the gear teeth of the new idler - everything else too oily/greasy to put reference marks on). My next step will be to degrease and paint white + numbers on chain and auto-advance and go through the process of finding what's wrong.
I Just thought I'd check here to see if anyone else has had this pain and can simplify my trouble shooting.
One point I found - when I first tightened my homemade idler shaft support (see pic below) it clamped the idler sprocket solid - silly me - no gasket. Put a couple of pieces of cardboard in and voila - no probs. I'll decide if I file down the idler shaft support boss or glue gasket to the "tool" - the former seem more foolproof.
Anyway - any advice (nice, helpful stuff) out there in Norton land?
Cheers
Rob

By the way - I've tried two idler gears and two auto advances, all with sprockets that don't appear to have any appreciable wear.
Same/similar result with all.
Cheers
Rob

Have you checked drive side magneto bearing?

Although you said you tried two auto advance units, have you checked for internal play in the AAU assembly?

Slick

Thanks Slick
The magneto bearing(s) have no play at all radially and about 0.001" axially.
The potential culprits are one or more of:
1. idler sprocket eccentric to its shaft CL
2. magneto sprocket eccentric to mag shaft CL
3. taper end on mag shaft eccentric (almost certainly not this alone)
4. new chain has uneven pitch
5. something else I haven't thought of that someone here may enlighten me about
I'll commence spot degreasing and numbering and work out a method to measure and record results to find the source
Cheers

No. 2 would be in the AAU assembly. My guess is this is where it is, but you tried two AA Units ..... ??

No's 3 and 4 are highly doubtful, IMO.

It sounds like you are methodically in pursuit of the problem. I am sure you will find the answer.

BTW .... while you are rotating the system, checking for slack and binding, manually advance the AAU and check if the unit returns to retard position freely. Binding in the AAU assembly might be somehow related to your chain tension problem.

Slick

Maybe something or nothing but your chain on the bottom run looks as though a couple
of links are tight (slight kink in chain).

These chains are riveted from stock lengths and this can happen.

It would give the problem you describe.

Andy

Thanks Andy & Slick
After putting numbers on the chain and both sprockets (see pics) and looking at the data (chain slack ranging from 6mm to 16mm each test) it is looking like the problem may be a bent magneto shaft.
Eyeballing the sprockets against the casing of 2 AAUs shows a "wobble" in the sprockets each revolution.
I hope I'm wrong but will confirm with a dial indicator as I get time.
Let you know
Cheers
Rob

Between the 15 & 12 the chain is kinked slightly when it should be hanging down.

It might help to degrease the chain completely. But I am of the opinion a bent shaft or
if the sprockets are new, they might have been machined i little off.

Andy

In any case if it isnt catching the cases then run it.

Unfortunately, at its loosest, it is catching the cases at the dowel boss near "12" (on the chain), so something has to be done.
Well - I methodically varied each of the sprockets positions and the chain position - one at a time but nothing consistent other than the maximum and minimum amount of chain slack (14mm & 6mm)
In desperation I checked the position of the points plate (using the leading edge of the "heel" as reference) and bingo - loose happens at 3 o'clock and tight happens at 9 o'clock, regardless of how I vary sprockets and chain.
So, how much shaft eccentricity will cause this 8mm (320 thou) in chain slack? My meanderings below point to 14 thou eccentricity - any comments on my logic?

So my freshly refurbed (2 years ago but unused) magneto has a problem. My fault - bought it on evilbay (100% positive feedback, many sales??) so my redress options probably don't exist.
The big issue though is if anyone hasn on how I get this fixed?
Cheers
Rob

Been trying to follow the process with interest. I can suggest that the mag armatures are built from 3 components... the coil armature and two shaft ends screwed together. One piece of crap trapped in the assembly could cause a wobble in the final bolt up. Only on a dial indicator spin measurement of the armature removed from the mag will this be evident. Of course it should run true or you will continue to have problems.
It probably should be run/held on the bearing surfaces not supported on centers from the ends. Maybe pull the bearings off and hold each end of the armature in a collet in a lathe and measure for wobble at the other end.

+1 on dynodave's post.

I would add that while you most likely have the skills to disassemble the mag, inspect, and reassemble armature properly so it runs true on bearing surfaces as Dave suggests, overall reassembly of K2's requires skill and equipment that is best left to professional magneto rebuilders, IMO.

Specifically, the bearing housings must be aligned so the armature runs axially true within the housing. The mag will most likely require a magnetic boost after assembly .... that requires equipment not likely in your shop.

Although the mag was refurbished, the quality of the work is suspect. It is your call, but if the mag was mine, I would send it out to a professional re-builder with a detailed explanation of what you have found.

Good luck with it

Slick

texasSlick said:

+1 on dynodave's post.

I would add that while you most likely have the skills to disassemble the mag, inspect, and reassemble armature properly so it runs true on bearing surfaces as Dave suggests, overall reassembly of K2's requires skill and equipment that is best left to professional magneto rebuilders, IMO.

Specifically, the bearing housings must be aligned so the armature runs axially true within the housing. The mag will most likely require a magnetic boost after assembly .... that requires equipment not likely in your shop.

Although the mag was refurbished, the quality of the work is suspect. It is your call, but if the mag was mine, I would send it out to a professional re-builder with a detailed explanation of what you have found.

Good luck with it

Slick

Click to expand...

Terminology ... Being nit picky with words (not you Slick :mrgreen: )
Professional magneto rebuilder means getting paid $$$$$$$$$$ and not necessarily level of quality!
relate-able story:
(Long time ago) Guy near NYC had a mag rebuilt by one of the "big name" mag re-builders in England. Did not start his BSA A-10 real good. He was not happy. Wanted me to inspect it. I did not like the capacitor he used in the armature. So I changed it. Also the magnetic gauss I measured was only at 60% of the "average" old K2F.
Side story...having worked in a high voltage/radar/electromagnetic physics environment for over 40 years ...I just happened to build a gausser (for home/shop, out of industrial surplus-yeah baby) to refresh my magnets in my BSA's and Norton mags. I also machined all the pullers and tooling to play with them instead of destroying them during disassembly. Banged the magnetism to the roof.
NYC BSA guy was super happy, he got a deal for $100, and best of all I learned something about mags and Professional Rebuilders. This is all well before the PHD did his big article on britbike.com.
I will probably do a mag for my friends 650 Manxman that I am putting together.
After that one, its one more mag for my fake 62 88SS.

Good luck with yours

I would agree Dave, that the quantity of $$$$ paid does not necessarily translate to a quality job.

One of the great things about this forum is the sharing of experiences with suppliers. Rob needs to "put it out there" to find a reputable, endorsed, recommended, and respected re-builder in Oz. My use of the word "professional" was a shorthand catch-all for the adjectives in the previous sentence.

I hope Rob notes your phrase " all the pullers and tooling to play with them instead of destroying them during disassembly." It is tooling such as this that makes me advise re-building a K2 mag is not a DIY project for most individuals (and then there is that Gausser not many of us have in our shops!).

Slick

Slick & Dave
Thanks for the helpful comments
I'v run a dial indicator on the shaft - turned it by point plate. Confirmed the run-out - you can actually see it with naked eye now that I'm looking for it.
My concern is - if this is wrong, what else is that I don't know about yet?
As you suggest I need to find a trustworthy maggie repairer - hopefully in Oz. Anyone have recommendations?
A quick internet search yielded:
Peter Scott Motorcycles (Sydney) - 1400 km south
Antique Auto-Electrics (Ballarat) - 2100 km south
Les McKiterick (Brisbane) - 600km south
Looking forward to replies
Cheers
Rob

Is Les still doing maggies commercially ?
Last I heard he had been banned from the shed, on medical grounds.
He was looking to retire when he gave me the tour of his works, about 15 years ago.
That winding lathe - for +1 km of wire !! - looked to be the key to the whole show.
Lotta processes to do a full refurb of a maggie, even had a little electroplating works,
ovens to bake the epoxy sealing coats, heat test the windings, etc etc.
He had enough work lined up for several lifetimes too...

robs ss said:

snip
Confirmed the run-out - you can actually see it with naked eye now that I'm looking for it.
My concern is - if this is wrong, what else is that I don't know about yet?
Anyone have recommendations?
A quick internet search yielded:
Peter Scott Motorcycles (Sydney) - 1400 km south
Antique Auto-Electrics (Ballarat) - 2100 km south
Les McKiterick (Brisbane) - 600km south
Looking forward to replies
Cheers
Rob

Click to expand...

My first suggestion is possibly get a "rear points" housing, fixed drive sprocket and run an EI.
If you've got lots of time then search on OZ forums for mag rebuild recommendations at home.

Other problems besides the out of line armature, is a very very high probability of a non centered armature as TS alluded to. It is SO highly misunderstood and seemingly improperly compensated for instead of being correctly set up. It's likely since the overlooked armature straightness will go hand in hand with out of line armature. There may be 2-3 hours for teardown, armature correction-trueing then armature housing bearing centering and final assembly. Assuming no other problems... like ground brush burn on the ground slip ring

Not to mention, and this is very, very important getting to mag to fire at 0 and 180 degrees

Yes Berhard - this may be a sore point
They were not equal so I used the method recommended by Slick in his K2F magneto thread - dutifully ground and packed the cam ring so that gaps were equal.
The sore point is that I've been thinking that this may not have been necessary with a straight shaft. Once the shaft is straight may have to redo
Sigh.....!
Rob

I'd comment that that chain looks rather dry in those pics ?,
its always worth oiling them and keeping them oiled to avoid stiff or dry spots...

The armature would have to have been set up in a lathe - is there any other way to do them ? - so may have had a misadventure since then ?? You see them come out of old maggies in all sorts of conditions, they don't seem too robust a design for how they were designed to operate.
And the book does say they should be inspected and serviced every year !!

robs ss said:

Yes Berhard - this may be a sore point
They were not equal so I used the method recommended by Slick in his K2F magneto thread - dutifully ground and packed the cam ring so that gaps were equal.
The sore point is that I've been thinking that this may not have been necessary with a straight shaft. Once the shaft is straight may have to redo
Sigh.....!
Rob

Click to expand...

Sorry Rob, but I agree you most likely will have to redo after getting the armature properly aligned. A conscientious rebuilder should deliver the mag with the points close to equal on each ramp. I suspect most rebuilders are satisfied with "within 0.002 in." I have measured 4 degrees difference in firing with 0.002 gap difference, so I would "tweek" it in.

Slick