Replace Stator?

[KerryAJS]

Thanks Duncan.
It's been a long time, and I mean a long time since I played with the bike, over 40 years... WOW, that a long time when you write it down!
I don't remember any "box of tricks" other than the regulator under the saddle. What I do remember is trying to start the bike with a flat battery and switching to emergency on the ignition switch. The bike would start, but, after a while, when the bike would begin to backfire, I would revert to the normal position on the ignition switch and away we'd go! Does this sound right or are my memories clouded?

[Duncan]

Thanks Duncan.
It's been a long time, and I mean a long time since I played with the bike, over 40 years... WOW, that a long time when you write it down!
I don't remember any "box of tricks" other than the regulator under the saddle. What I do remember is trying to start the bike with a flat battery and switching to emergency on the ignition switch. The bike would start, but, after a while, when the bike would begin to backfire, I would revert to the normal position on the ignition switch and away we'd go! Does this sound right or are my memories clouded?

That's my memory too, you cant run on EMG only start and get a little over tickover before the bike starts misfiring.

[Groily]

[/quote]
That's my memory too, you cant run on EMG only start and get a little over tickover before the bike starts misfiring.
[/quote]

That's right. The Em Ign position relied on a direct AC feed from the alternator. When the engine started the AC fought the DC coming from the battery. As revs rose and the battery started to come back to life, it misfired and you had to switch across to 'normal' ign.
Only available with a 3 wire stator and with things configured accordingly, with primitive 'regulation' managed by switching alternator coils in - or out - depending on what was switched on - or off. Not that I used to find the Em Ign function was exactly reliable, but then they were on bikes I had as a very callow youth blessed with all sorts of other imperfections including no doubt horrors at the back of the slightly complicated switches used to do all this!
The alternator rotor needs to be 'timed' to deliver the pulse at the right moment though, so 'peak pulse' comes just as the points open. OK if everything is keyed on I think - but a faff on, say, plain tapered magnetic flywheels without keyways, eg as on an LE Velocette. (DAMHIK)

With the capacitor, yup, it's supposed to store charge sufficient to fire up the engine on the later two wire / 12v systems, and I suppose it probably does - usually! But have to say, not something that has given me great confidence either over the years, and I believe they can be responsible for battery leakage in certain cases as they deteriorate. But perhaps I'm too pessimistic on this! Also, don't know if they are up to operating with systems like Boyer Bransden or whether they're only good with traditional contact breakers?

Dr James Smith's book Classic Motorcycle Electrics (big plug for this bible) goes into this quite thoroughly on pp 142 and 143 and also on p 217 for those who have a copy handy. (That's the James of 'Matchless Clueless' fame.)

On the 'should one go electronic?' point, I think it's a good plan frankly, as it consigns points wear, condenser worries, gap adjustment and all the floppiness of worn point plates to history, and in some (all?) cases the mechanical advance mechanism too if the system has a programmed curve built-in. Not sure what's the 'best' option or best value, but there be much expertise here and I'm sure advice will be forthcoming.

On preserving the Lion Crest lamp, there are tungsten and halogen options, also LEDs as mentioned. But not sure about high wattage availability in BP-F, if you are aiming for 60/55W for example. H4s are easier in that regard certainly, and available from auto shops of course, which makes life easier if replacements are ever needed.

[jackstringer]

Capacitor, remember you can buy them from the likes of RS or Farnell for not a lot, don't worry about the voltage just search for 4700uF. If you wanted it would be a good thing to have after the rectification anyway as it does smooth the Voltage a little, not by much but it is visible on a sillyscope.

Talking WAV, Watts = A x V, V = W/A, A=W/V its all very straightforward. Things to watch out for with SOB is that the wires would have broken down over the years and this will create resistance at connections and along the wire, this can be a big cause of Voltage drop. What starts off at the battery as 6V ends up as 5.4V at the bulb. For example, you have a 120W alternator at 6V which means it can pump out 20A, but with 12V its now down to 10A, still the same amount of Watts.

Let us say you are on high beam and you hit the brakes, 30+4+21+5+2 = 62 W and that is 10.4A which is quite a bit of current and depending on the wire it can be 3/4 of the rating of the wire. But if the voltage is dropping due to poor connections, and old wire then it creeps up to 11.5A.

Code: Select all

             6 V       12 V
---------------------------
Main Beam   30 W       60 W
Dipped Beam 24 W       55 W
Pilot        4 W        4 W
Speedo       2 W        2 W
Brake       21 W       21 W
Tail         5 W        5 W
            -----     -----
            86 W      147 W
            -----     -----
            14 A       12 A

These are just rough numbers but you can see that there is a fair amount of power being used and this is assuming your stator is putting out the full 120 W, at idle etc it is not. Yes I know I have it with main and dipped on the same time but this is just to make a point the bike is using its power.

So what to do, I suggest simple things like making up a new loom with 2mm2 wire and good connectors, also add another wire to the headlight and earth it to the shell, don't rely on the chassis to be a good earth. If you want to take it to the next level then a relay for main and dipped will save the power having to go though the switch and loosing current though there (also stops the switch getting warm). Look at changing stuff like Speedo, Sidelight and Tail to LED that should shave off a few Watts in power and free them up to go towards the headlight bulb.

I must get around to doing some tests to see the kind of output I get from mine at standstill and at speed on the road. As a meteorologist I love to measure stuff just for fun.

[Groily]

jackstringer's post illustrates nicely how a 120W stator can be marginal at low revs, with a big bulb, even forgetting the fact that main and dip won't be on at once. With coil ignition an extra couple of amps have to be added in for the sparks department, which the table for a magneto bike doesn't include.
While the actual current needed should be a bit less at engine-running system voltages of 7ish or 14ish, the point remains (reverting to earlier posts in the thread) that 120W max output (which isn't there at low revs) isn't perhaps enough for coil and battery ignition plus a chunky headlamp for riding round town.
And poor wiring or bad connections with unwanted resistances make things worse if not addressed in the mix.

[KerryAJS]

Thanks everyone for your replies, I'm traveling at the moment, along with a not so smart, smart phone... You have generated some questions that'll ask when I get back to base next week.. thanks again
Dan

[KerryAJS]

Hello Folks, back to the thread again!
Can someone explain the meaning of "SOB" as used by Jacksringer above, (that is, if he's not about to explain)

Just to clarify, having gone through all the advise given and PG's site, I'm now leaning towards the 3 phase stator, as a future proof for later "add-ons" like 55/60 watt halogen bulb, electronic ignition and (not sure if I would) indictors. Also the bike will be ridden in built-up areas quiet a bit... low revs.
Please pick faults in my theory.. if there are any.
One other point, the number on the rotor/magnet doesn't seem to match the available ones.. any ideas?

[Groily]

https://www.classicmotorcyclespares.com ... lucas.html
From the above link it seems you have a welded rotor - and yours looks good.

If going 3 phase I'd speak to PG and follow his advice. That rotor might be just fine, but I honestly don't know not having "been there, done that or got that T shirt".
It does seem, however, that you are going to need good low rev performance, and indicators are - I'd have thought - very highly recommended if not essential these days for regular riding in town and 'staying alive'.

The 200W single phase option would do the job probably, but the whole point about the 3 phase version was to deliver good low speed performance with a decent safety margin - as well as enhance the safety of the bloke on the seat. I've heard folk say now and then that it's a bit OTT, but its horses for courses. Big lights, not a magneto, indicators, maybe sat nav, heated grips even (VERY tasty) . . . there are lots of good ways of using up all that power.

Not quite sure what SOB means in that context either - although we all do a lot of it when things go wrong!

[jackstringer]

Sorry SOB is a term used by a mailing list I have been on for 20 years. It's a habit that will

SOB, Sh*te Old Bike (often used in jest and not to be taken seriously).
RCT, Ridiculous Childs Toy (bicycles).
SMIDSY (yes that was our robot), Sorry mate I didnt see you.
DAMHIKIJDOK, Don't ask me how I know I just do OK (example, don't spend 2 hrs trying to kick a bike over without first checking that the spark plug cap was put back on DAMHIKIJDOK).

[KerryAJS]

Thanks Groily.. I think we're on the same wavelength
What can I say Jackstinger.. you made made me laugh out loud! All that was miss was a pint of Guinness Infront of us all