Pick-up brushes (again)

[CheeserBeezer]

Hi. I know this has been mentioned before on numerous occasions but it seems a reminder is necessary. If your bike is a twin cylinder and you buy replacement pickups, then your bike starts misfiring and only running on one side and generally becomes a pain, then you have fallen victim to the cr4ppy pick-up brushes which have been on the market for ever! These pick-ups are usually supplied in plain white boxes. If you really do need to buy new pickups and/or brushes please buy them from a reputable person who does not sell stuff that they know is cr4p! I restored a magneto a few weeks ago and needed to replace the pickups so I used old original Lucas ones and fitted new brushes which I know are good. The customer, on receipt of his newly restored magneto decided, unilaterally, that he'd fit some shiny new pick-ups as shininess is more important than reliability. After about a 30 mile round trip he picked the phone up and ranted at me that I'd done a lousy job. His bike was misfiring and had become difficult to start. He insisted that he hadn't fiddled or interfered with it in any way and was hotfooting it down to the local post office with mag in box on its way back to me. On opening the box the new pick-ups were evident, along with a filthy black carbon coated slip ring which which had been converted from a twin to a single by the filthy black pick-up brushes. The customer wasn't too chuffed when I explained to him why his failed mag wasn't covered by the warranty. I understand he is now trying to recover his costs by ranting at the dealer who supplied the pick-ups! I'm please that the customer was not a forum member! Anyway, rant over!

[groily]

What a familiar story and timely reminder CB. All those 'I never touched it mate' tales, spittle running from corner of mouth, teeth bared.
WHat IS incredible is that the useless bits are STILL being sold despite a zillion bad experiences and a fair amount of bad press, which you'd think those who sell these duff items must have picked up on. It's not as if it's just the occasional rogue part - grief is 100% Guaranteed.

[BSA500]

Hasn't there in recent years been fake lucas stuff in fake lucas boxes with pretend greasy fingerprints

[Bsareg]

The 'genuine' lucas has printed boxes with the oily prints.

[Triton Thrasher]

The 'genuine' lucas has printed boxes with the oily prints.

Are they good?

[Bsareg]

No. I found the 'Lucas' ones crap. I buy mine from the easycap people, perfect, just the right hardness.

[BSA500]

Those 'Lucas' ones I wouldn't touch unless you know without a doubt they are NOS, which lets be honest you can never know unless you bought them 30 odd years ago  . I just buy from Priory Magnetos he rebuilt my mag and I use what he would use.

[Triton Thrasher]

Why does the magneto use carbon brushes, instead of an air gap as found in a distributor?

[groily]

An Interesting Q TT.

Car mags initially used 'carbon wipe' dizzy heads, and they're 'OK'. But quite soon - well pre-WW2 - Lucas, BTH and other largely British manufacturers pioneered the spark gap rotor arm set-up as per coil ignition. Much better for cleanliness in the dizzy head, air gaps came into their own when nickel electrodes became a thing, and they also, it is said, extended spark plug life (or at least the intervals between having to clean them). Which probably made it less critical than it had been to test magnetos using various 'utility factors' (big unwelcome resistances) to try to replicate real-life situations in tired dirty engines, although test equipment always retained that facility.

As to 'Why Not?' in non-distributor types, dunno, but I absolutely can't imagine that Lucas, or particularly BTH and Bosch, others too maybe like ML and CAV, hadn't thought about it. I'd guess it was an idea discarded as opposed to one never thought of, but WTHDIK? Some of the folk who wrote Learned Papers on ignition systems for the various learned societies were extraordinarily clever.

Don't think 'speed of rotation' comes into it because two cam-lobe ringcam 4 cyl car mags run at engine speed, 6cyl at 2/3rds etc, and 'camshaft mags' (a straight swap for a distributor and running at 1/2 engine like ours) used however many lobes there were cylinders, obviously. So sparks galore. And slipring diameters on most rotating coil magnetos are not far off the internal dimensions of many distributors of the day.

Could it be that the risk of spark erosion on sliprings that aren't that easy to replace (the way rotor arms are) has anything to do with it? None of the above manufacturers used an air gap on rotating coil magnetos to get the spark from sliprings to the distributor HT feeds. Or maybe 2 gaps to jump would be a step too far at low rpm when the mag is at its feeblest. Not a non-dizzy mag issue though.

I think I'll amuse myself with an experiment when I get A Round Tuit. I no longer have a good means of measuring HT voltages at my disposal, but at least I'd be able to see what size gap any sparks would jump which is a pretty good proxy for voltage - and compare to the same mag running with the standard bits. Worth a try just for curiosity's sake. (We all know what happened to the cat though.)

[Rex]

There was always that "Ten Bob Tip" in the old car/bike mags from pre-war where it was suggested that to "up the voltage" on a failing ign system (or it's components) a coat button would be spliced into the plug lead to create an air gap.
Maybe the rotating cam design inherently created this air gap to hopefully maximise the spark quality?
Plus it was cheaper...as ever.

[BigJim]

Just to throw some nonsense onto the end of this thread. My self and a friend were returning from an Irish rally a million years ago. He was riding a heavy weight Panther and was a bit weary after all the partying and decided to take his brush out of the mag and call the AA to save the slog back across Wales. I being of stupider stuff slogged off and left him to it. Point being the bike fired up and ran really well when the AA gent eventually arrived! Snigger. Sad to say he got his comfy lift back anyway because the mechanic had never heard such a rattling old beast before and was easily convinced that something was amiss!
 

[chaterlea25]

Hi All,
Not adding to the above but a quizzical ignition related question i was asked a while ago. It took me a few minutes to come up with an answer on which I'm fairly sure I am correct
The question related to a straight 8 cylinder petrol Rolls Royce fire pump engine that lives in the Cork City Hall. ( a friend worked there and was asked to look it over)
OK,
So how does an 8 cylinder distributer work when there are only 4 lobes on the shaft , but  they work  two sets of points 

John

[CheeserBeezer]

There is a bit of confusion on here, probably my fault. The yellow boxes with pre-printed thumb prints are modern Hepolite brand which are nothing to do with the original Hepolite. I'm not aware of anything else with pre-printed thumb prints. Hepolite don't do pick-up brushes and never did. The green boxes with Lucas on are mostly products distributed by Wassell which, generally, I find to be of good quality and much better than the stuff Wassells used to sell (and maybe still do) in white boxes. This applies to the pickup brushes as well. By far the best brushes are new-old-stock original Lucas which were sold in red and white boxes and the brushes were wrapped in tissue paper. However, the 'Lucas' pick-up brushes sold new in green and white Lucas boxes are fine. I use them all the time and my bikes don't suffer pick-up brush problems. When using them it is worth rubbing the tips to remove loose residue before fitting. Other than that, they're fine. The brushes which are cr4p are only sold as part of a complete pick-up set in a white box. Some unscrupulous dealers might be swapping things around so beware. The dodgy brushes have a polished appearance and you can draw all day with them. The 'Lucas' brushes release a small amount of fine dust when first put to use but, once this is rubbed off, they're fine, which is why I give them a rub before fitting. The only brushes I'm aware of that are sold new today are the 'Lucas' ones. If that is not the case, please let me know!

[berger]

Jim my dad did a test for a trainee back in the late 1930's that was supposed to help the lad find out what was wrong with the engine ,my dad pulled the wire cores out of the leads and much to everyone's surprise the engine fired up , it must have left traces in the old rubber outer insulation

[groily]

An Interesting Q TT.

I think I'll amuse myself with an experiment when I get A Round Tuit.

I have amused myself this morning. Little things and little minds.
Result of a brief play showed equivalent performance of air gap and carbon brush on a K2F, in the sense that sparks up to 6mm were available in line with the Lucas test specs. Fat sparks every time at the flick of a wrist too.

A slightly fiddly job to try to get a, say, 2-3 thou gap between not-a-brush and slipring using a standard Bob Culver-quality pick-up and a light interference fit of a brass rod with shiny nose, at 5.13mm. Not the exact same setting in the pick-up for both rods and gasket choice obvs critical, so we'd have to be careful. If the makers had ever gone this route they'd have made the not-a-brush adjustable for depth I think and issued appropriate fitting instructions to avoid a foul-up.

Didn't run at high speed for long as didn't want to risk a problem on my best spare K2F, so dunno if there'd be dimples or tracking problems on the slipring segment in prolonged use owing to the arcing.

Given that a mag will run with a disintegrated carbon brush quite often, arcing away to the spring if that hasn't fallen out, I wasn't expecting it not to work, but was quite surprised at how 'the same' both sides of the mag performed when running it with one brush and one not-a-brush.

But, not wanting to risk the new slipring, or even maybe stress the rewound coil's insulation, toys are now back in their cupboard.
Does say though that if a brush fails on the road, a bit of something metallic rammed tight up the pick-up will at least get you home.

And thanks to you TT for raising the question.