K2F Uneven Spark on 650SS

Hi all
This issue comes up a lot, without the mag in my hand its hard to troubleshoot, but this is what my experience has been (over 100 Lucas & BTH mags).
It is rare that the camring is worn unevenly. An easy check is to remove the camring & with a set of verneer calipers ( they have a knife edge) measure each side in the exact opposite locations (ramp to ramp, low side to low side) & you will probably find them to be equal. if so, the cam ring is not your problem.

Keep in mind, the armature is made of 3 main parts screwed together with 2 slotted screws with the heads located under the slip ring. There is a procedure to aligning the 3 parts of the armature to be sure it is running true. This is where I most often find the fault & the "nose" of the armature is running out of line, causing the entire points plate to not run concentric with the cam.

The guys at Brightspark Magnetos have a nice step by step direction page with photos:
http://www.brightsparkmagnetos.com/cond ... mature.htm

This may seem odd, but sometimes I just swap out the new points arm (just the rocking section, not the threaded piece) & often the problem goes away (I don't Know why)

Lastly, and as a last resort, there is an eccentric screw hidden behind the welch plug at the bottom of the end casting. If this screw is turned, it will move the cam ring so that you can "re-center" the cam ring in its range.

All the best!

Skip Brolund

I totally agree that the cam ring is rarely the problem (unless someone has been in there stoning it).In any case,you can still easily fix it without resorting to stoning;even if there is an error in the cam ring.
I don't put much faith in changing the points,or in any way changing the radial distance from the armature axis to the points heel.Any change there will have the same effect at both lobes (either retarding or advancing both).

Read this fully before you decide to do anything:http://www.britbike.com/forums/ubbt...in=46330&Words=magneto&Search=true#Post421297

X-file said:

I totally agree that the cam ring is rarely the problem (unless someone has been in there stoning it).In any case,you can still easily fix it without resorting to stoning;even if there is an error in the cam ring.
I don't put much faith in changing the points,or in any way changing the radial distance from the armature axis to the points heel.Any change there will have the same effect at both lobes (either retarding or advancing both).

Read this fully before you decide to do anything:http://www.britbike.com/forums/ubbt...in=46330&Words=magneto&Search=true#Post421297

Click to expand...

Re; "I totally agree that the cam ring is rarely the problem”
Absolute b/s in my own personal experience, in the early 1970 when Norton was still in business, I purchased a brand new Lucas cam ring in a genuine Lucas box, took said new cam ring to work and clocked it up true in a milling machine dividing head then ran a .001 thou clock gauge on the internal cam-it was checked 3 times - 4 1/2 degrees out, so it appeared to me Lucas was flogging off inferior goods to unsuspecting buyers, using worn out machinery .

I cannot say if this method works, but I would need to check with a timing disc and battery & bulb method, with the a/ r jammed fully open if doing it on the bike;

"
Firstly I closely compared the new cam ring with the old one. Having said that the bike is now 52 years old so any cam ring might have been fitted over this timescale.
However looking at the old ring it was so worn that there was no line across it where the points should open and close along the track of the points heel---so it might well have been the original cam ring!
Comparing the new and old rings they were virtually identical by eye in terms of:
a) The relationship of the advance/retard range cut out to the control shuttle cut out and
b) The relationship of the advance/retard range cut out to the can opening and closing lines transversely across the rings.
I then measured the "thickness" of the cam ring at each end of the cam lobe on each cam on the new ring.
The measurements were:
1st cam 0.154" and 0.153"
2nd cam 0.154" and 0.155".
On the basis of the above I concluded that the new cam ring was good.
I then set the cam ring to the fully advanced position and measured the points gap on each cam. They were 0.010" on the first cam and 0.024" on the second cam.
I then started shimming between the main housing and the cam ring housing.
I started by taking the difference in the gaps and dividing by 2 and putting a shim of 7 thou on the side opposite the cam giving the larger gap. This swung the gap comparison way over in the other direction. This meant that due to leverage effects a small shim thickness gave a much bigger difference in points gap.
By trial and error I found that by putting in a 3 thou shim the gaps became 0.018" on the first cam and 0.018" on the second cam.
Eureka!
I then adjusted the points gap to 0.012" on the first cam and this gave a gap of 0.012" on the second cam.
I then finally retightened all the screws and rotated the mag a few times and remeasured the gaps. They were 0.013" on the first cam and 0.012" on the second cam.
Within the limits of repeatability and my measurement accuracy I think I now have equal gaps on the two cams."

Hey Guys....

At the risk of belaboring this thread, the last three posts need some clarifications. All contain truth, but need further explanation.

First, Skip and X-file write that the cam ring is rarely the problem....TRUE if we are dealing with newly made CNC cam rings. They should be dead nuts regarding ramp thickness and angular displacement .

Next, Bernhard writes his NOS Lucas was nearly junk....TRUE...do not compare NOS to new CNC. Bernhard also writes he found a worn cam ring that had the ramp bump worn to a gentle slope rather than the bump....I also found one such cam ring, but the ramp thickness was identical to the other ramp which had a normal bump...why one ramp wore so and not the other, who knows? This condition will mis-match the timing, but not the point gap.

Bernhard describes the procedure to shim a cam ring to equalize point gaps.....very good how-to-do-it explanation , but it should be noted this procedure should be done to extend the life of a worn cam ring. Moreover, equalizing the gaps with this technique may still yield mis-matched timing (see paragraph above regarding worn bump profile on one ramp) . If you have a NEW CNC made ring, and have 12 - 15 thou unequal gap, it is bass-ackwards to botch up a $100 cam ring because, like Skip & X-file said....the cam ring is NOT the problem. The housing centering is the problem, and this should be left to a Pro. There are two or three things that can be horribly screwed up when centering the housing. If you don't know what they are, take that as proof you should not DIY.

Skip tells of an offset cam ring locator screw that can be used to tweek the timing. I have heard of these but was of the opinion they were a one-off modification (I could be wrong on that). I want to make the point that these rotate the ring +/- a few degrees and will not fix any between cylinder timing mis-match, but eliminate the need to break the taper at the maggie drive side to make a small timing change.

Slick

texasSlick said:

Bernhard describes the procedure to shim a cam ring to equalize point gaps.....very good how-to-do-it explanation , but it should be noted this procedure should be done to extend the life of a worn cam ring. Moreover, equalizing the gaps with this technique may still yield mis-matched timing .


If you have Skip & X-file said....the cam ring is NOT the problem. The housing centering is the problem, and this should be left to a Pro. There are two or three things that can be horribly screwed up when centering the housing. If you don't know what they are, take that as proof you should not DIY.

Click to expand...

Apart from his unfortunate finding of one bad cam ring in the earlier post,
in his next post Bernhard is merely reciting some of what was contained in my previous link.

Read the link.It's not about extending the life of a worn cam ring.If you get unequal timing with equal gaps,you can just add another shim to get equal timing with unequal gaps.That's rare,but possible.Someone may have even previously stoned a cam ring so equal gaps won't work.

It doesn't take a team of scientists or any high-tech equipment to correct timing errors like this.Just loosen the 2 screws that hold the cam housing to the main body until you have a gap between the 2.Put a shim in between the cam housing and main body approximately in line with more retarded opening ramp on the cam.If you want a thin shim,the plastic wrapper on a cigarette pack is 0.00075" thick.

You guys must have very thick cigarette papers over there ?

The paper I put through a computer printer is about 0.002 each - a ream of 500 is about an inch thick.
The cigarette paper i have here for magnetos is about 1/2 a thou in ricepaper, I'd guesstimate.
(it barely measures on a micrometer, and crushes..)
That makes it accurate to within a degree for magneto timing ?
That foil thickness quoted of 0.00075 sounds similarly useful...

A quick look through the 850 Workshop Manual didn't find that static timing method.
Wouldn't this risk something moving if the centre clamp bolt is loosened ??

Thanks people, the machine is 100 miles away at a friends house, I couldn't ride it anymore with that pinging... So I gotta pick her up on the weekend. I can't wait to get her back to the workshop and do these tests you've mentioned..... Thanks

Our ciggy paper here in Australia is about half a thou.... I think trying to roll a smoke with a 002" paper may be hard to achieve! I remember trying to roll one with newspaper and tea leaves when I was a kid....what an abortion!
But I like the idea of the buzz or light bulb method because after all it is electrical contact that we are dealing with?

The points spin, so quite how alligator clips are going to handle that isn't quite clear to me. ?

Aircraft maggies have stationary points and coils, and rotating magnets,
so those buzzer thingies are a neat little box that you just clip on , and bobs your uncle...

Rohan said:

The points spin, so quite how alligator clips are going to handle that isn't quite clear to me. ?
.

Click to expand...

The clips stay on for about 1/2 turn of the contact block....plenty of rotation to approach break point on one ramp and rock engine back and forth checking break point multiple times to get an average. Then rotate 180 (clips will likely pop off) replace clips and check other ramp.

Someone questioned if removing center screw would cause movement to create error....the taper on the contact block will hold it firmly if first tighten screw to press block into taper, then remove screw. The block is keyed so it will not rotate on the armature shaft.

Slick

Got another one, the reason for removing the centre screw is to remove all continuity that exists (5 ohms) back through the Maggie when points are open, so you can use te buzzer or light?

TBolt said:

Got another one, the reason for removing the centre screw is to remove all continuity that exists (5 ohms) back through the Maggie when points are open, so you can use te buzzer or light?

Click to expand...

If you're asking a question, then yes.

Yes, sorry that was a question

TBolt said:

Got another one, the reason for removing the centre screw is to remove all continuity that exists (5 ohms) back through the Maggie when points are open, so you can use te buzzer or light?

Click to expand...

Yes....with center bolt/screw in place, meter will read continuity thru the armature. You will not get indication of points opening.

Clip one meter or light lead onto tab with spring.....check around other places on contact block to find place with continuity when points closed and open circuit when points open (don't remember....might be adjusting screw head).

Slick

Theres No Such Thing as a uneven spark ! :lol:



O. K. worth having a look at the SLIP RING as its rotateing . The thing in there that the HT lead pick up / carbon brushes run against .
It should be ROUND . Light Wear can be lated true . Horrendous ravines mean a new ones needed .

If thats ok , Belt it with a hammer ! . 8) RIGHT , the CENTRE of the Rotateing Points Plate . On the Brass adjacent the retaining bolt .
Its on a tapered seat with a fixing groove for radial indexing .
Points gap should be .014 to .016 . , unusual to get both at .015 and DEAD EVEN fireing point . BUT YOU WILL GET EXACT DEGREES ON BOTH .
only a womble wouldnt .

The idea is to TAP the thing lightly with a drift ( Alumn. ) & hammer . Very Lightly , Almost - you still have to tap it to get it to shift A THOU.

Unless the slip ring is junk , setting from T.D.C. on BOTH CYLINDERS , and checking , and persevereing , will get it SPOT ON on BOTH ,
within the parameters for the GAP , ( points ) described . If you want to wreck it , run it 4 degrees out .
Wonder if this works on 4CA c/b sets . :lol:

3/8 " b.t.d.c. is likely RIGHT . You can see why manual advance isnt a bad idea . But get exact timing on all cylinders . Or its of to the salt mines for you .

Theres No Such Thing as a uneven spark ! :lol:



O. K. worth having a look at the SLIP RING as its rotateing . The thing in there that the HT lead pick up / carbon brushes run against .
It should be ROUND . Light Wear can be lated true . Horrendous ravines mean a new ones needed .

If thats ok , Belt it with a hammer ! . 8) RIGHT , the CENTRE of the Rotateing Points Plate . On the Brass adjacent the retaining bolt .
Its on a tapered seat with a fixing groove for radial indexing .
Points gap should be .014 to .016 . , unusual to get both at .015 and DEAD EVEN fireing point . BUT YOU WILL GET EXACT DEGREES ON BOTH .
only a womble wouldnt .

The idea is to TAP the thing lightly with a drift ( Alumn. ) & hammer . Very Lightly , Almost - you still have to tap it to get it to shift A THOU.

Unless the slip ring is junk , setting from T.D.C. on BOTH CYLINDERS , and checking , and persevereing , will get it SPOT ON on BOTH ,
within the parameters for the GAP , ( points ) described . If you want to wreck it , run it 4 degrees out .
Wonder if this works on 4CA c/b sets . :lol:

3/8 " b.t.d.c. is likely RIGHT . You can see why manual advance isnt a bad idea . But get exact timing on all cylinders . Or its of to the salt mines for you .

If we catch you wombling, or hitting a magneto with a large hammer, its off to the salt mines for you Matt. !
Do not pass go, do not collect $200.
No alcohol either...

Apart from the salt mines,knocking the points to move the points heel to a bigger or smaller radius from the armature axis,will have the same effect at BOTH lobes.
If it advances one cylinder,it must also advance the other cylinder an equal amount.

Matt- correct points gap is 12 thou. 15 thou is for distributors.

As said above, you can't correct the timing difference by bending the rotating parts. If you force the points heel closer to one lobe, it is then closer to the other lobe as well, when the assembly rotates 180 degrees.

The lobes of the cam ring (not the bloody slip ring!) must be moved, radially, in relation to the centre of rotation.

This can be done by moving the cam ring, or altering the shape of a cam ring lobe. In theory, the centre of rotation could be moved toward one or other cam lobe, but that's not easy.

Triton Thrasher said:

Matt- correct points gap is 12 thou. 15 thou is for distributors.

As said above, you can't correct the timing difference by bending the rotating parts. If you force the points heel closer to one lobe, it is then closer to the other lobe as well, when the assembly rotates 180 degrees.

The lobes of the cam ring (not the bloody slip ring!) must be moved, radially, in relation to the centre of rotation.

This can be done by moving the cam ring, or altering the shape of a cam ring lobe. In theory, the centre of rotation could be moved toward one or other cam lobe, but that's not easy.

Click to expand...

Agree! Don't apply undue force....there is a delicate bearing under the housing! I especially agree with the last sentence above....send the mag to a pro to move cam ring housing.