Help Please, with my Magneto

[BSA Biker]

Hi all, last year my Lucas K2F magneto was playing up so it was sent to Dranganfly to be rebuilt. Turns out they use a sub-contratctor to rebuild them so more expense incurred using a middleman.
At the same time I reduced the piston comp to 7.25:1  from 8:1 for my A7SS as my R/H knee is not able to be used for kicking over the engine anymore and it seems strange using my left leg.
So on rebuilding the engine it just started and then stopped after running (roughly) for a few minutes. Thinking that the tappets had closed up, they were readjusted and the timing re done. It then would not start again even after many (40plus) attempts to reset the timing. Now after going down to 6.6:1 comp pistons it fires up but only on one cylinder, first RH then another time LH. But at the sparking plugs when checked on top of the cylinder, both plugs in their HT leads spark correctly. The carb. was renewed some time ago as the old one was slightly distorted (bought at a auto jumble secondhand). Today changed back to the old one without any change.

Any suggestions, please don't say that the HT leads are the wrong way as that was checked a long time ago. Both at the mag and the cylinder.
Failing that, does anyone know of another person (who is an expert) to repair another magneto which was bought off Ebay not working properly.

[RoyC]

Could be duff spark plug/s that spark out of the engine but not under compression.

[Bsareg]

Try drawing on a piece of paper with a pickup brush. If it leaves somthing like a pencil mark, it's too soft and could leave a ring of carbon on the slip ring. Plugs will fire but may not fire corectly when under compression. There's a lot of crap ones out there. I've had no problems with the Brightsparks ones.

[morris]

Sounds like your mag has been badly restored. Send it to Brightspark for a proper job.  Highly recommended. And he’s based in Normandy France so from Spain won’t cost you to much on sending costs.

[BSA Biker]

Well thank you all,

Today after giving the slip ring a good clean, changing the very soft carbon pick-up brushes, and giving it another quick ignition re-time, it finally fired up and sounded like the old bike thats been loved (and cursed) for the last fifty plus years.

When the temperatures go down later tonight it will be given a trial run before cleaning, checking over and then the ITV test, (Spanish MOT).

It will be good to use it again after almost a year of problems, didn't even give the carbon brushes a thought, Chinese again?.

[BSA Biker]

Well, when the temperature dropped to about 80*F last night I took it for a ride, great progress until the magneto got hot from the engine (about 3 miles) then it started the odd misfiring again. This happened with the mag before it was rebuilt and to another that was bought on eBay as a "good one". Whats the chances of that happening to three mags? the soft carbon brushes were fitted all the time so am going to give the slip ring yet another clean tomorrow and then se what happens.

The carburettor is a new remake of the Amal monobloc (made in Salisbury) with all the correct jets etc so not thinking its that, any suggestion if the slip ring is clean.

[stanwhite]

Any chance it could be a valve sticking when hot?

A useful diagnostic if it is ignition:  Reduce the plug gaps. A lot!!! Run gently. If all is OK, this could indicate an insulation breakdown somewhere. The higher the cylinder pressure (high comp pistons, large throttle) the more volts you need to spark, and if there is a "better" gap someplace else, it sparks there, and not at the plug. Temporary very small gaps may help prove the point. The engine won't run right, so be gentle, and not for too long...

Whatever it is had transferred across all three mags. I assume you didn't change the plug leads, caps, and plugs?

I got caught out a year back with a VW car. It had leads that needed the small cap screwed on the end of the spark plug. These were not fitted, resulting in an extra gap in the HT circuit, higher than normal HT voltage, (a lot higher, 45kV!) and arcing all over the place. Funny thing, it had been like this for some years before it gave trouble. New leads and plugs, happy car...

Are your plugs too "cold", and oiling up shortly after setting out. (Pull one out at the roadside and check, and if it is "black and oily" that is not good...).

HTH,

 Stan.

[BSA Biker]

Hi Stan,

When I cleaned up the slip ring etc the new HT leads and pick ups with hard carbon brushes were changed over from the other set with the soft brushes which had been there for some time.

Normally the plugs are  B8ES but the other day I changed them to B7ES to see if it made any difference, but all of them are black and oiled up a bit, not helped by me changing the pistons to 6.6 :1 compression from7.25 : 1 after not being able to kick them over anymore. Carb has been jetted for them though.

[stanwhite]

Sounds like you have two choices...  Even hotter plugs, or ride harder...

If you have a spare set, ride until it starts to misfire, then change the plugs. If then OK for a few miles, a hotter plug is probably called for and black and oily does indicate insufficient plug temperature.

Higher cylinder pressures mean higher temperatures. You reduced the compression, lowering temperatures, so that suggests a hotter plug is needed to burn off the contaminants.

HTH,

 Stan.

[duTch]

 B-B, I've been running B6ES with 7.25:1 (Ally head/Flat-Top) pistons, and it seems to be ok after a fewK miles (air temp range 10˚C- 42˚C), maybe try it

[Worty]

B6HS for me, work well but can be a tad sooty at times - not oily though.  Found riding it hard was fun and changed the plugs to a nice tan colour   I reckon you've checked the points gap hasn't closed up - this resulted in lousy running for me.  Other than that it's going through everything bit by bit - pain in the a**e

[BSA Biker]

Thanks to all your help the old gal is finally going like it should. Tuesday last it passed the Spanish ITV test (MOT) they even did the noise test which worried me no end, but the chap very slowly gave it a little bit of throttle and then stopped, hey presto it passed. After all the other parts were completed and it was time to go, I forgot myself and gave it a handful to pull away, it rather loud then, but the test was over and the money paid etc I was gone before he could say anything. 21.21 Euros, not too bad for two years, but it would be unnecessary in the UK and France.

Returning to my magneto problems, it was very soft carbon pickups that caused the problems. There was so much deposited on the slipping that it must have been arching all over the place. Lots of meths and clean rag and eventually okay. But why do the suppliers allow this rubbish to be imported from China or Taiwan, must be very cheap to them I suppose.

My spare magneto will be used when it eventually comes back from Brightsparks, thanks Bill.  But at least the bike now starts first kick every time, just like in the old days. Only trouble now is that its too hot to use it for very long periods.

[RogerSB]

it was very soft carbon pickups that caused the problems. There was so much deposited on the slipping that it must have been arching all over the place.

Glad to hear that with the help on here you've sorted it.

Here's a warning to others when replacing magneto pick ups and brushes

Coincidentally, earlier this week I thought I'd treat my 1960 GF to a new set of magneto pick ups, ht leads and plug caps. I bought Lucas pick ups and tested the brushes before fitting and was disappointed to find them very soft. Attached is a photo showing the difference in the new Lucas ones and my old ones (blue arrow) when I tested them on the inside of the Lucas box lid. Needless to say I changed the brushes over for my (luckily) very little worn old brushes. Unfortunately I can't remember where I bought the original good brushes.

Also there is no groove on the Lucas brushes for the spring to locate in - hence the carbon brush easily drops out of the spring when fitting (absolute rubbish)  .

Photo attached of brushes and the box label.

[a101960]

I bought Lucas pick ups and tested the brushes before fitting and was disappointed to find them very soft. Also there is no groove on the Lucas brushes for the spring to locate in - hence the carbon brush easily drops out of the spring when fitting (absolute rubbish)

How appalling. I trust you have sent a snotogram to Lucas. I shall be interested to see their response.

[BSA Biker]

 As usual someone is trading on a once good company name having bought just that, the company name. Then goes on to buy cheap rubbish from China or Taiwan and charge over the top prices for it, making out that it is the genuine British stuff. We have all been caught out like this.

What is going to happen when the chap working from an industrial unit gives up and finally retires. Will this be the end of using old motorcycles, or will we be too old ourselves to care?.