The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: duTch on 29.05. 2017 10:20
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What am I missing?? (I know that's been asked before)
A couple of weeks ago, I did stuff (cleaned slip ring++) that made mine run real good (good Inglish hey?)...then I ran into some folk at the pub I hadn't seen for a while, and girl buddy Kym says " I always hear you coming and know it's you..." >:D... and I said "yeah it's runnin' real... (at this point she punched in the gob and said 'don't say it- but I said it anyway..) ...good, hey "...and then I +*beer*+ left..
Next morning started up to go to a job, and a bit rough- nothing untoward, usually evens out, but not that day...only had to go a few K's, but dinae git inny better...conked out on the left, and occasionally fired but right plug was ok, then conked out altogether at the lights and had to push it past the copshop to the job *smile*... had to truck it back to the (very) Low Chaparral...
So I have fuel which comes through the idle/main circuits if i blow air in the pilot intake (cough-spit)..spark on new plugs x2 sets = *????* sometimes is good on both, and sometimes better on one, and fires up on the left, but not the right and dies after a few rounds.
Points gap varies ~12/~14 thou, but always been ok...spring not touching cam ring...earth brushes cleaned- 2 sets new plugs B6ES/BP6ES
Slip-ring looks a bit 'crazed'...I'm wondering if that's playing up.
Maggie has done ~10K miles since rebuild (20 years ago), and ol' mate assured me it'll last me out...no reason to doubt that..
I've swapped the (new) pickups/brushes/leads/caps/plugs.....why would it run on one side and not the other with various combos of that??
*pull hair out* *pull hair out* *pull hair out*
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G'day duTch.
Wot didya use to clean the slipring? May have smeared a bit of carbon around causing kayos. Clean it again with electrick contact cleaner.
Cheers
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First I used metho- or was it the beer *eek* well oneof'em...maybe that's why I fell over *dunno*
nah not really- but somewhere along I might've used brake or carby cleaner or cable lube....I know I was doing the Gutzzi clutch cable concurrently *conf2* or maybe the Bakers ZnOH soldering flux ....or...maybe the beetroot juice *dunno*
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I'd say I was joking, but that's about how it went ^^^-truthful-ish without being serious
Like nothing changed overnight- *dunno*
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Grasping at straws, of course, to explain the change between the morning and the trip home from the pub.
Here are some maybe's (maybe all remote):
- One (or both) of the pickup brush holder clips was not quite in position and slipped off, allowing the holder to slip out.
- Wire has come loose from the contact inside the pickup brush holder.
- Contaminated fuel, maybe by malicious prank while you were in the pub.
OK, if history repeats itself, someone in Australia or Ireland or someplace else will now provide the simple and correct cause of the problem.
Richard L.
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Sounds like the magneto is crying out for attention. A good indication of a failing mag is it running only one one side or the other, but not both. Crazing on the slip ring might indicate tracking there. If the brushes are soft carbon (as so many aftermarket ones are these days), cleaning the slip ring may well have spread a thin film of carbon round the slip ring. Take out the brushes, make sure they are really clean, clean the slip ring thoroughly and dry it and maybe, just maybe all will be well again.
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When I started this topic, I wasn't sure whether to start this in this section, but just have to see what transpires from here...
Just had another look at the Maggie as per Groilies post here;
Re: K2K Magneto - no spark
« Reply #3 on: March 28, 2017, 19:19:20 »
Quote As Beezermacc and Wozza say.
If you wanted, you could test for basic HT continuity by sticking a meter from the brass segment of the slipring to the mag body having removed a pick-up - should be a few thousand ohms. An infinite reading means trouble, probably because the coil is open line or, best case, is not connected properly to the slipring (or earth). At least you'd then know you had a real problem on your hands.
You should see the same K ohms from the contact breaker centre screw to the slipring, and should have (almost for sure will have), less than 1 ohm from the cb screw to the mag body with the points held open. This will show the low tension primary winding is OK and will also tell you that the coil is indeed earthed as both primary and HT winding are earthed in common.
Suspect you need to talk to Beezermacc!
So I did that on three different meters (40K & 20K scales) and;
"brass segment of the slipring to the mag body" reads 18.9KΩ- (sounds a bit high?) on *20KΩ scale* and,
" cb screw to the mag body with the points held open" reads 1.8Ω-2.0Ω (also too high?) *ex* EDIT; (on 400 Ω scale)*ex*
I also have the same 18.9K reading from the slipring through the leads to the plug tips (both sides)
Now I'll go kick it in the guts and see what happens, and hope no-one tells me I'm wasting my time.
As I think I said, it was refurbished 10K miles ago by a renowned engineer dude Les McKitterick (now retired)
Slip-ring also cleaned and fitted with new (never been used) aftermarket pickups...stay tuned I guess *dunno*
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Sorry Richard I forgot to answer you questions. The fuel is only a couple of weeks old (when the saga started) but due for .. *ex*..oh I just remembered I almost ran dry and used some I had in a jerry-can from January, but surely that should be ok... might just run out and buy some fresh stuff anyway...but I'd find it hard to believe it'd go off overnight.
I doubt it was spiked at the pub or otherwise, as I park up the back in a corner, and was only there for two beers (2x 10 Imp.Oz= 1.25 US pint)
All the leads were/are connected ok
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.........Sounds like the magneto is crying out for attention. A good indication of a failing mag is it running only one one side or the other, but not both. Crazing on the slip ring might indicate tracking there. .....
Yo that's what I'm thinking, weird thing is that it was mis/not firing on the Left and fully running on the Right, but now it fires on the Left only, but only a few revs and dies....but on Saturday, I had what I thought was nice regular fat blue sparks both sides... am wondering if an 'Easycap' might rectify things *conf2* *dunno*
I've been trawling the site for similar issues, closest I can find thus far is this from Richard (and I like that little opening pun *wink2*)- but I'm sure there's more;
Recapping, for clarification, this goes back to your June 8, 2016 post regarding easy starting cold and hard starting with warm engine. I have just started having this same issue, so I am telling a bit of my story hoping you get something from it and, also, tagging along for whatever advice is offered.
My immediate suspicion was magneto problems, either a bad cap or LT windings leaking with heat. My cap is a new EasyCap, so that is very doubtful. To test the issue I went out for a ride that was long enough to warm everything up. On getting home, I immediately pulled the plugs and tested for spark across about a 0.150" gap. No problem leaping that gap. I also tested with the plugs that I had just pulled from the bike and the result was a good hot spark. Tested compression on both sides. All good. This was all just yesterday, so I have yet to check timing and look for possible carb issues.
Richard L.
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Dutch, The problem here is that I can't remember what the actual fix turned out to be for that topic and it's not discussed in a later post. While wracking my brain, I remembered a diferent time when I rotated the cam ring housing 180 deg. in order to get access to the cam ring adjuster. This messed up the symetry of the points opening and one side was barely opening, if at all, and starting was impossible.
Gotta send before running out of battery.
Richard L.
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Thinking further on this, I believe it turned out to be timing. All this was happening right when the T-shirt issues were getting resolved. Then, a week or two later I discovered shims in the sump, one week before the DGR ride. So, I forgot to post a followup in the tear-down frenzy.
Richard L.
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Thanks Richard- I actually had tree-compose that because I lost my initial draft when I returned to the 'reply' page after going back to copy your post *bash*.
My intention was to check is which 'Easycap' is needed bit I just did some research and found by my reckoning the CO1 is the part/alternatively CO4, (they sound like Carbon gasses)
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So I did that on three different meters (40K & 20K scales) and;
"brass segment of the slipring to the mag body" reads 18.9KΩ- (sounds a bit high?) and,
" cb screw to the mag body with the points held open" reads 1.8Ω-2.0Ω (also too high?) *ex* EDIT; (on 400 Ω scale)*ex*
I also have the same 18.9K reading from the slipring through the leads to the plug tips (both sides)
Now I'll go kick it in the guts and see what happens, and hope no-one tells me I'm wasting my time.
Your 18.9K is def high on the HT if you were getting good clean contact on the slipring and assuming the earth brush - under the screw on top of the mag - is also making decent contact (and that the meter is OK too). It's a slightly 'funny' number to me, as more often with a continuity problem we're talking Mega ohms or infinite resistance than a kilo-ohms thing,
Could 'just' be your slipring to coil connection is bad though - the attachment is not the greatest engineering design on the planet by a long shot, with just a spiky bit of wire going into a small hole in the ring and hopefully making a good contact inside. Or that the earth connection of the low tension lead is poor at the condenser due to a dry joint or something - that connection earths both the HT and LT windings. Much less likely that though - because if it was a bad joint, you'd see a high reading on the LT too.
Your reading on the low tension is probably fine - meters aren't that good at very low readings sometimes.
New pick-ups and brushes . . . Probably not your problem here although the symptoms do match, as all is brand new and things are squeaky clean still. BUT there are, as often stated here, a lot of really crap brushes out there that are too soft, cause dust to form on the slipring and then cause erratic running and misfiring on one or both sides. In any event, I'd check the brushes aren't soft enough to 'write like a pencil' and chuck them over the hedge if they are as it will be a problem later. And I'd check that there are no tingles coming off the HT pick-ups with the engine running - the dielectric strength of some of the stuff being sold out there is pathetic.
For me, though, the number one thing here is to see why that HT reading is three times higher than we'd expect, because whatever else you do, if there's something not right in the coil/slipring department, the problem won't go away. As long as the earth wiring connection is sound, the condenser won't affect those readings although it could be dead or dying and would also cause erratic running etc if it were.
(Btw, C01 for anti-clockwise drive mag with brass contact breaker; C04 for the later low inertia steel cb assembly if you go there)
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Thanks groily- funny, I've reaad lots of your posts, but I think maybe never actually interacted (?)
I just finished ordering two CO1's as a precaution anyway.
The New pickups are from a swap stall, so unsure of quality, and 90º ones that I had to cut a corner off to sit ok *work*
One of the meters I used is a 'Amprobe 33XR-A', cost me ~$150 bucks a while back for other dangerous explorations *eek*.
There was about 0.4 - 0.5 Ω residual on the LT side with a reading of ~ 2.4Ω (by my reckoning).
I wonder if I should hunt down Les, and ask him if there's any chance he may have wound the HT side high- if that's possible ?
I cleaned up the earth brushes again (one under CB plate & one in the body which had a fibre washer that I ditched), but made no difference (I cleaned them all the other week with the slip ring, which was significant to it running as well as it was that I was skyting about- irony).
Is there any reason I can't pull the CB end off the maggie in situ and have a dekko - nah forget that- remembered the whatzit screws?
I'm about to head up the road for a feed, and will post a pic (or two?) of the slip-ring that I took the other week- finally found 'em. Can't think much else just now, cheers
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Piccie of my slip ring, and I thought the points spring may have been a bit close to the post , so jammed a bit of cardboard in there to pack it out- but made no difference
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I would not have much faith in that slip ring, especially in a bike that appears to have magneto trouble.
I believe they must be made from pretty well flawless plastic for long term reliability, or else internal tracking can occur and then get worse as it carbonises plastic and traces of oil in the cracks.
(https://www.a7a10.net/forum/index.php?action=dlattach;topic=11747.0;attach=36504;image)
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Is it possible that the high HT resistance has been caused by it being rewound in a non-standard way?
After all, 18-19 kOhm would be correct on some ignition coils.
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I would not have much faith in that slip ring, especially in a bike that appears to have magneto trouble.
I believe they must be made from pretty well flawless plastic for long term reliability, or else internal tracking can occur and then get worse as it carbonises plastic and traces of oil in the cracks.
I looks better than it did at first... *eek*
Is it possible that the high HT resistance has been caused by it being rewound in a non-standard way?
It did cross my mind, but no idea of its functionality or otherwise- way outta my league. I'll see if Les is still around, and can enlighten me.
Slip-ring has worked fine for four years *dunno*, I'm thinking to rustle up a whole replacement spare maggie for emergencies like now
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Hi All,
The pic of the slipring looks all to familiar *sad2*
Well and truly Fkd!!
Test resistance from one plug lead to the other, if theres any reading other than infinity on a low voltage meter = dead
I use a 500v Megger to test the sliprings, that will soon show any problems
There have been a lot of crap sliprings on the market, I had two fail on the A10 before I modified a proper BTH mag to fit
John
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Maybe not the cause of the failure, but for future reliability I would do a bit to the contact breaker assembly - replace the spring which retains the moving contact in position, move the little backing spring to the post side of the main spring and replace the card with a suitable diameter hard fibre washer.
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As Julian says, where is your moving point retaining arm?
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi254.photobucket.com%2Falbums%2Fhh116%2Fludwig_020%2FKF2_1.jpg&hash=88111b048f10d29e2102fc827b0fc74ac0561504)
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Busted off TT by the looks of it. I wonder if there is a lot of slop on the pivot post too - it's another job worth sorting if the thing is coming to bits anyway, although a fiddly one. The problem is that wear there causes poor opening, promotes arcing at the points and very often upsets the firing interval between the two sparks by several degrees.
The buffer spring needs sorting, the fixed point is 'unusual' in having had its hex turned into a knurl(!) and it really should have its retaining clip and little titty thing to help keep things straight. The clips can often be had - or in the worst case a bit of junior hacksaw blade cut & ground to suit, punched through to make an 'ole and clouted carefully to make a register for the tit does a neat job that's almost indistinguishable from the original (with a bit of patience!). The pin may also be available, or a small (6 or so BA) screw and shallow nut can serve if the pinhole is tapped, although it may be tight if there is an (optional) auxiliary earth brush meeting things from the other direction.
As to winding recipes and TT's query above . . . very occasionally I have seen (rotating) mag coils wound to produce a simple HT resistance as high as 8000 ohms, but never anything like 19K. But I agree there are car-type coils which show much higher figures, certainly, and static coils are quite often close to 5 figures on some magnetos. 'Normal', if there is such a thing, seems to be from 4500 to maybe 6000 ohms depending on who's done it. Commonly, 5000, near enough spot-on. Some of the competition windings seem to have had a bit more wire on back in the day judging from from some of the readings, but AFAIK the majority of winders treat all K series coils pretty much the same these days.
The slipring isn't worth persevering with. It probably leaks, will almost certainly be prone to tracking and so on, and its surface is rough enough to eat brushes I'd guess. I wouldn't be at all surprised if connectivity inside was poor and responsible for the poor HT reading, but the only way to find out is to get it off and measure from the bare spike of the coil.
I think the mag needs a fresh going over to be honest, to eliminate the risk factors one by one and get it back to full health!
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I'm still a little hung up on the fact that the night before the problem started, Dutch left the pub, gave it a couple of kicks, and got home with no apparent issues. Sometimes lurking problems turn on like a switch, but it seems to me that this slip-ring thing would show up progrescsively, if it's indeed the problem. This said, it does seem that this might be one of those times when the problem, whatever it turns out to be, turned on like a switch.
Oops, edited: I am interpreting Groily to mean that leaks lead to the crazing on the surface of the slip ring, so I went looking for images to show other cases. I came accross this video from Brightspark Magnetos (Groily, you may have heard of them): https://m.youtube.com/watch?v=Jeq1h9dOoKo . So, assuming leaks are the issue, did they just want one more trip to the pub before passing out?
Richard L.
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Ha! Hadn't seen that one for ages Richard. But I do remember we had fun doing the mods to make the bits and then watching the effects. Good of you to dig it up!
But like you, I'm not sure about the 'switch' thing either. There are several things that aren't exactly optimal with the offending instrument, so it could be a combination, or maybe just one thing that has been holding up, just, but now got to the point of being obstinate. Everything works until it doesn't, and the reason for 'doesn't' won't always or necessarily be a breakage as such, especially where the thing does still work, at least some of the time and/or badly. Basically, I dunno! But I'd still go for an overhaul even if it comes back to life for peace of mind.
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Thanks guys, but first some credits;
As Julian says, where is your moving point retaining arm?
I think it's in a box somewhere- jumped ship about four years ago, and I keep forgetting about it, but seems they hard to find... but groily's idea sounds sound, and thinking different ideas to fabricate a 'Pip' (moulding one with a two pack?)
........left the pub, gave it a couple of kicks, .......
*eek* how about just one *smile*
...The buffer spring needs sorting, the fixed point is 'unusual' in having had its hex turned into a knurl(!)...
If the 'Buffer spring' is he one Julian mentioned, I was looking at that wondering that it didn't look right- probably from when I took the moving points of to dab some grease on the pivot a while ago....The knurled fixed point is not mine, but in TT's pic.
John; Test resistance from one plug lead to the other, if theres any reading other than infinity on a low voltage meter = dead
I use a 500v Megger to test the sliprings, that will soon show any problems
At first I thought 'Megger' you meant a 'Growler' for testing armatures- so what's a Megger?
I tested right through from one plug tip to the other and turned the engine slowly, to have a reading of '1' (where I presume 1 = infinity?) removed the leads at the pickups, and same result and at the same time rechecked the resistance to the centre bolt and today have a read of 14.6 KΩ both sides (through the pickups, which didn't affect the values yesterday compared to straight to slip-ring)
So thanks guys, I guess I'll be doing today what I wasn't planning to do......maybe
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So thanks guys, I guess I'll be doing today what I wasn't planning to do......maybe
Of course you mean taking the wife to dinner and a movie.
Richard L.
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Hi Dutch,
Megger is a name (like Hoover) of a brand of insulation tester,
I suppose Megger were the original of the species,
Its an instrument that applies a high(250,500,1000v or higher) DC test voltage to a piece of equipment to test the "quality" of the insulation
https://uk.megger.com/products/insulation-testing
Any sparkie worth the name will have one *ex*
John
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My dad, who was an electrician on submarines in the '20s, had a Megger for testing motors in his (later) electrical contracting business. Wish I had had the awareness to claim it before he closed shop in the late '80s.
Richard L.
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Dutch,
Is it my computer or does the slip ring look pretty bad? Almost like the copper pad is breaking apart or something.
Lee
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Of course you mean taking the wife to dinner and a movie.
I don't have one of them, and generally do those thing if and when I want (or need), but I could possibly borrow one if I needed the interference *smile*
Its an instrument that applies a high(250,500,1000v or higher) DC test voltage to a piece of equipment to test the "quality" of the insulation
Ok thanks ....obviously I don't have one or similar and I haven't found that function on any of my multi-meters.. *conf*
So yesterday I didn't achieve much other than in the process of tracking down Les McKitterick (magneto rebuilder- so I could ask about extra resistance/technique) , I discovered that he's no longer with us, but a guy who worked with him for his last two years has apparently bought all his stuff and now doing the work.
I have his number so will call him later and if anyone in Brizzo needs him I'll pass it on (he's in Kallangur).
Through a search result (Noturn Owners), I also found there's a guy in Adelaide who does K2F rebuilding too.
Is it my computer or does the slip ring look pretty bad? Almost like the copper pad is breaking apart or something.
Consensus says it's farqued, but seems odd that would make it play up suddenly and only one side. *pull hair out*
ok I've work to do *work*
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My dad, who was an electrician on submarines in the '20s, ......
Can't help imaging extension cables plugged in the back of the Sub *eek*
Anyway-today's update;
I ripped the Maggie out and found lateral play in the drive -side bearing, so called ol' matte at Kallangur and he said to bring it up for a squizz, which I've done. Was keen to dissect it but figured best to leave it intact. ..at that stage
A quick look showed a hairline crack running the length of the body- probably not good. ...he'll do surgery on it and let me know iin a day or two..... *dunno2*....$$$$
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Todays update; had a message from Daven who had a look at the Maggy...
D/S bearing had spun in the housing, burn/break in winding (hence the high resistance-x3+), slip-ring is shot and condensor(s) appear to be shot.
Reckons he has the bits to repair, but could be a couple of weeks..
Nothing much good except that when Les did it, he said it'd outlast me, maybe he thought I looked a bit ragged *eek* ....guess I got one up and outlasted it *smile*
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It should have lasted a lot longer than 10,000 miles.
How long was it in years?
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It should have lasted a lot longer than 10,000 miles.
I'd've thought the same, and expected lifespan was a pending question, considering Les said 'it'll outlast me'...
I had it rebuilt mid-90's, and used it only basically once a year to get to the local bike show for the wheel change race, as by the time I had the Maggy fixed the rest had gone to crap- no rego or anything, then domestic bliss went pooposideon, and it parked up from ~97/8 until I dug it out in 2010. Add a couple of years to rebuild ( early '13).
So basically about 20 years
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It should have lasted a lot longer than 10,000 miles.
How long was it in years?
Maybe it is like dog years?
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Ah well, when you get the mag back you are gonna love the easy starting. Whatever it costs, it's worth it.
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The K2F magnetos on my bikes A7, A10 & Norton were rebuilt about 30 years ago and each has covered a minimum of 30,000 miles. Hopefully your next magneto rebuild will be to this standard.
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I'm struggling with the question: What became of the lubrication in the D/S bearing?
Richard L.
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........ you are gonna love the easy starting. Whatever it costs, it's worth it.
yea, but It's generally been a one or two kick starter anyway- even the day it stopped, hot or cold, no choke (doesn't exist) doesn't need a tickle- just do it from habit *eek*
The K2F magnetos on my bikes A7, A10 & Norton were rebuilt about 30 years ago and each has covered a minimum of 30,000 miles. Hopefully your next magneto rebuild will be to this standard.
At least what I expected. *conf2*
I'm struggling with the question: What became of the lubrication in the D/S bearing?
Maybe I missed that- but am also struggling with it *conf2*
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D/S bearing had spun in the housing, burn/break in winding (hence the high resistance-x3+), slip-ring is shot and condensor(s) appear to be shot.
And still running? ::hh::
Are we sometimes not a bit harsh on our dear old friend George Lucas...
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Are we sometimes not a bit harsh on our dear old friend George Lucas...
Yes, it was Joseph Lucas's successors who threw these things together with paper daisies wrapped around the bearings.
George Lucas is innocent!
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Are we sometimes not a bit harsh on our dear old friend George Lucas...
Yes, it was Joseph Lucas's successors who threw these things together with paper daisies wrapped around the bearings.
George Lucas is innocent!
Yeah, I know. was thinking Joseph and typed George. That bloody star wars thing... *conf2*
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Ok Folks, so I have a favourable resolution *smile*
Collected the rebuilt Maggy, and stuck it in and I reckon would've started first kick except I'd messed with the carby settings the other week, as when it did fire after 3 or 4 kicks blew some black smoke...but not for long.
Photos;
#1 The bits he replaced, including new looking windings with burnt bits, and condensers with possible signs of overheating
#2 very small burnt bits at end of arrow,
He said it had the wrong slip-ring for K2F, as the brass ring runs from 90º before spike hole to 90º after spike hole = 180º, and the new whitiesh one he installed is ~120º- spike position unknown *dunno*.
These two pics are just aids as part of the process;
#3 Timing cover drain hole mod; to drain the timing chest oil before pulling the cover- maybe I just like to live dangerous
#4 Street sweeper bristle; used it to slide the washers down to the bottom stud with the 'extended nut' (and for a shitload of other things)
haven't been far yet full test tomorrow, ran outta daylight, so just to the bottle-O, for more suds
Cheery days *smile*
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Hard to believe all of that came out of one magneto. *smile*
Drain hole sems is a good idea. Any trouble with leakage around the screw? No moreso than the primary cover, I suppose.
We will now begin a contest for naming the best use of a street-sweeper bristle.
----back scratcher.
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I have taken 3 different types of slip ring from anticlockwise K2F mags. I wonder if your old ones like any of the photos?
First photo slip ring on left is from a K2FC marked part 456727. Next to it is a standard K2F item(yes a bit abused) which shows the difference in brass segment length.
Second photo a different view of the same two slip rings.
Third shows one I took from a K2FR (marked 493198 and 35KV) on left next to a standard K2F item marked part 455361. The former having a slightly longer brass segment than the standard item and slightly shorter than the K2FC item.
Anyone know the reason for the different brass segments?
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duTch, glad you got it sorted ,with all that lot changed it's got to be good for a good few yrs now !!
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Firstly I forgot to thanks all for their input and forcing me out of the two-week denial that it could be a Maggy problem- last time I was in denial for ten years *bash* *bash*
yo Bob, I'm not sure if it's best it outlives me or I outlive it *smile*
Julian, I can't find any number on mine, but I did find a couple of hairline cracks starting...my only thought on the longer bass segment is maybe longer spark duration if that's possible- think I'll leave that up to the Gurus
Yes Richard, does look a lot, but I guess it's now fluffed up a bit...I did the hole a while ago and forgot to mention it seems fairly good so far, but will talk about that elsewhere, as with the 'back scratcher'....I started using them a while ago for a host of different things.... *smile*
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Ref JulianS' query on sliprings . . . it's true there were some modest variations in the length of the brass strips on different rings. Quite why I don't know for sure, but the single critical thing is that an HT brush - one only! - must be fully on the brass at the firing point for that cylinder.
With manual advance and retard, the brush will be on a different spot on the ring according to the position of the camring (the position of which relative to the armature controls the exact moment at which the contact breaker opens). That variable may explain the use of slightly longer segments on some models, especially if using more advance and retard than is typically found on a standard K2F (which is around 18-20° on the mag via a notch c. 11mm wide limiting the camring's movement).
As long as one HT brush is in full contact with the brass segment at all positions of a manual camring (set correctly in its housing) when the points open, and as long as there is no possibility of the spark's trying to hop across to the other brush at the same time (owing to an overlong brass segment connecting both brushes, or nearly doing so), all will be well.
The sliprings made by the best UK supplier for both clockwise and anti-clockwise rotation twins use a strip of about 90° or a bit more maybe of the circumference, handed accordingly. This is adequate for correct operation of any manual K series mag I have seen, and also works perfectly OK on 50° V twins with an ATD. Haven't had the opportunity to see if there's enough brass on them to work in all circs on a pre-ATD V twin, like an HRD, but suspect there is probably just enough provided there isn't too much movement available on the camring or that the movement is slightly restricted to avoid under- or over-shooting the brass at the firing points.
The 35Kv marking refers to the dielectric strength of the material - ie its resistance to leakage at high voltage.
While it is common to see 25° or even 30° sometimes of advance/retard on single cylinder mags (which in most cases have a continuous brass strip through 360°), there isn't any real need for it I don't think except possibly for trials riders, and no Lucas twin I have seen has that much.
So the modern replacements available can be reckoned to work on all the models we're likely to encounter, with the possible caveat concerning manual advance V twin engines, and their resistance to leakage is as good as we'll ever need. Testing them at elevated temperatures linked in series with ignition coils operating at considerably higher voltage than your average magneto has revealed no problems that I am aware of, and I don't know of a manufacturer whose slipring products reflect the variations shown in the pix. Which isn't to say there isn't such a guru out there, natch, but I don't think there is any need for the different length segments for normal purposes. In cases where it is important to be able to position a brass segment in a specific way, there is a manufacturer in the Netherlands who supplies very handy kit-form sliprings which can be assembled with the brass strip wherever you like. The ones I have used are for Bosch instruments, and cater for parallel twin and V twin engines.
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I've been reading through this thread to take advantage of the wisdom of the forum after my 59 GF that previously was a one/two kick starter died (luckily in the shed prior to a ride) and now refuses to start. The magneto that previously provided bright blue sparks to both cylinders is now providing nothing. I've worked through the advice already provided on the thread and the clincher seems to be the infinite resistance between the slip ring brass section and magneto body. If I've read Groily's advice correctly this indicates problems that are beyond my capabilities - can anyone point me in the direction of a magneto specialist in Australia who can help?
cheers
Tim
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Tim, the guru in Sydney is Chris Zoch.
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Thanks Shark, I've given Chris a call and will be putting my magneto in the post tomorrow.
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Tim, the guru in Sydney is Chris Zoch.
+1 to that. Chris did a nice job and was super helpful rewinding my Mo1 earlier this year