BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
JWood Auction JRC Engineering dealers JWood Auction
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Photo posting tutorial

Member Spotlight
BritTwit
BritTwit
Kansas City area
Posts: 534
Joined: December 2005
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
200 registered members (1xfatboy), 1,877 guests, and 550 spiders.
Key: Admin, Global Mod, Mod
Newest Members
Doug Valley, tim_v7, BosBSA, Ron 1973 TR7RV, barnett468
10030 Registered Users
Top Posters(30 Days)
Lannis 146
Stuart 67
Popular Topics(Views)
475,652 mail-order LSR
Forum Statistics
Forums33
Topics65,697
Posts635,023
Members10,029
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
Help with Lucas Magneto #699562
06/25/17 3:03 pm
06/25/17 3:03 pm
Joined: Jun 2017
Posts: 18
Germany
G
Gui d'Orey Offline OP
BritBike Forum member
Gui d'Orey  Offline OP
BritBike Forum member
G
Joined: Jun 2017
Posts: 18
Germany
Hi chaps,
I've just spent a very frustrating weekend fighting with a magneto on my BSA 1930's Sloper. It's a MDB1 and it was actually working fine, but I decided to give it a clean and set timing which was a bit off.

After setting everything and testing it on the bench, turning it with a drill, I was happy to see a fat, healthy spark, and reassembled it on the bike. Only now there wasn't any spark anymore! After checking everything and not having found anything suspect, I took the magneto off the bike and tested it on the bench again. Again a fit big spark was there. I set it back on the machine, and before assembling the sprocket or tightening anything down, did the test again with the drill and still hat a good spark. But afer reassembling everything and setting the timing, I get no spark when I use the kickstarter, not even a weak one!

Anyone has any ideas what could be wrong or what to check? I'm at my witts end...

Any help would be greatly appreciated!

Cheers,
Gui

Support Your #1 BritBike Forum!
Membership Type! Free
Member
Premium
Member
Premium Life
Member
Vendor
Member
Site
Sponsor
Recognition No Premium Member Premium Life member (5 years) Vendor Member Site Sponsor Membership
Post commercial threads No No No Yes Yes
Custom title No Yes Yes Yes Yes
Upload avatar & photos No Yes Yes Yes Yes
Link avatar & photos Yes Yes Yes Yes Yes
Private Message Storage: 10 100 100 100 100
Length of signatures 255 600 600 600 600
Removes this very advert island between post 1&2 No Yes Yes Yes Yes
Price Free $12.90/year $105.00 No End
$55.00/5 years
$210.00/year
($17.50/month)
Email
Click on button >>
  Premium Member Premium Life member Vendor Member Site Sponsor Membership
Re: Help with Lucas Magneto [Re: Gui d'Orey] #699575
06/25/17 5:03 pm
06/25/17 5:03 pm
Joined: Jun 2017
Posts: 18
Germany
G
Gui d'Orey Offline OP
BritBike Forum member
Gui d'Orey  Offline OP
BritBike Forum member
G
Joined: Jun 2017
Posts: 18
Germany
Well, I suppose I was attacked by gremlins today. The problem is solved, although I have no idea what was the cause and what actually solved it....

I pulled out the mag sprocket again and tried it with my drill once more. A nice big fat spark was there again! After scratching my head some more, there was nothing left to do , but to assemble the sprocket and try the kick starter. The spark was still there.... after closing the timing case, kicked her a few times and the old sloper was running again! Unfortunately due to the excitement I set the timing too early. When I advance the ignition, she starts spitting and at full advance the motor dies. So I'll have to reopen the case and set it properly....

Anyway I would still love to know what was wrong and why I wasn't getting a spark, so any ideas are still welcome. Hate these types of mysteries.

Cheers,
Gui

Re: Help with Lucas Magneto [Re: Gui d'Orey] #699585
06/25/17 7:42 pm
06/25/17 7:42 pm
Joined: Oct 2003
Posts: 11,138
North Georgia, USA
RF Whatley Offline
BritBike Forum member
RF Whatley  Offline
BritBike Forum member
Joined: Oct 2003
Posts: 11,138
North Georgia, USA
This post could do with some photos.

Just saying.


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA

"Shop Boy" at Rodi British Bikes
Re: Help with Lucas Magneto [Re: Gui d'Orey] #699663
06/26/17 2:42 pm
06/26/17 2:42 pm
Joined: Feb 2007
Posts: 486
Ewing. NJ
E
edunham Online content
BritBike Forum member
edunham  Online Content
BritBike Forum member
E
Joined: Feb 2007
Posts: 486
Ewing. NJ
I am sure that the drill is spinning your mag over a lot faster than your kick starter. The mag should spark just spinning it with your fingers. My guess is that your mag is operating somewhat marginally, and that the reason it is sparking now is because you are kicking it harder because you are frustrated, and thus spinning the motor faster.

Ed from NJ

Re: Help with Lucas Magneto [Re: edunham] #699673
06/26/17 4:36 pm
06/26/17 4:36 pm
Joined: Jun 2017
Posts: 18
Germany
G
Gui d'Orey Offline OP
BritBike Forum member
Gui d'Orey  Offline OP
BritBike Forum member
G
Joined: Jun 2017
Posts: 18
Germany
Hi Ed,

Yes, that also occurred to me, but she now sparks with a slow easy kick. The mag is due for an overhaul, surely, but I was hoping to leave it for next winter, nad enjoy the rest of the riding season. Let's see how the old girl holds through.

I also set the points gap to 0,003" according to the BSA owner's manual, which is smaller than what was previously set to, and now she runs rougher. Probably another sign that something's not quite right...

Re: Help with Lucas Magneto [Re: Gui d'Orey] #699681
06/26/17 5:19 pm
06/26/17 5:19 pm
Joined: Sep 2013
Posts: 1,631
Pacific northwest
Q
quinten Online content
BritBike Forum member
quinten  Online Content
BritBike Forum member
Q
Joined: Sep 2013
Posts: 1,631
Pacific northwest

knowing little about magnetos ... I would look into ... whether the final tightening down of the mag
is somehow pulling something out of alignment ?
gear lash or end float pushing on the points cam or brushes ... just far enough to cause mechanical binding or a short ?

... is the points cover causing a short ?
... or with the cover off , is the points-arm opening and closing normally ?

Re: Help with Lucas Magneto [Re: Gui d'Orey] #699683
06/26/17 5:32 pm
06/26/17 5:32 pm
Joined: Aug 2001
Posts: 2,531
New Hampshier USA
MikeG Online content
BritBike Forum member
MikeG  Online Content
BritBike Forum member
Joined: Aug 2001
Posts: 2,531
New Hampshier USA
Originally Posted by Gui d'Orey
Hi Ed,

Yes, that also occurred to me, but she now sparks with a slow easy kick. The mag is due for an overhaul, surely, but I was hoping to leave it for next winter, nad enjoy the rest of the riding season. Let's see how the old girl holds through.

I also set the points gap to 0,003" according to the BSA owner's manual, which is smaller than what was previously set to, and now she runs rougher. Probably another sign that something's not quite right...


They quote .003 thou for a point gap? hardly seems like enough, I have the K2f on my A10 at .012 I think


1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
Re: Help with Lucas Magneto [Re: MikeG] #699710
06/26/17 8:55 pm
06/26/17 8:55 pm
Joined: Jun 2017
Posts: 18
Germany
G
Gui d'Orey Offline OP
BritBike Forum member
Gui d'Orey  Offline OP
BritBike Forum member
G
Joined: Jun 2017
Posts: 18
Germany
Originally Posted by MikeG
Originally Posted by Gui d'Orey
Hi Ed,

Yes, that also occurred to me, but she now sparks with a slow easy kick. The mag is due for an overhaul, surely, but I was hoping to leave it for next winter, nad enjoy the rest of the riding season. Let's see how the old girl holds through.

I also set the points gap to 0,003" according to the BSA owner's manual, which is smaller than what was previously set to, and now she runs rougher. Probably another sign that something's not quite right...


They quote .003 thou for a point gap? hardly seems like enough, I have the K2f on my A10 at .012 I think



Yup, it is indeed specified as 0.003" on two different versions of the BSA Mortor Cycle Instruction Book for 1930 Models smile

After further analysis, I moved my suspicions to the spark plug itself. If I take the cap off the HT Lead I always get a nice spark, but with the plug attached it is really sporadic. Unfortunately, it's an old 18mm plug which is not readily available, so I'll have to order one online and will take a few days until I can confirm if the plug is the culprit.

Re: Help with Lucas Magneto [Re: Gui d'Orey] #699724
06/26/17 10:20 pm
06/26/17 10:20 pm
Joined: Feb 2014
Posts: 382
Cork Ireland
C
chaterlea25 Online content
BritBike Forum member
chaterlea25  Online Content
BritBike Forum member
C
Joined: Feb 2014
Posts: 382
Cork Ireland
Hi,
0.003 in is definitely not correct
0.012in = 0.30mm is the correct gap at max opening
Maybe 0,003 is the max gap when the piston is at the firing point (cigarette paper thickness) ????

John

Re: Help with Lucas Magneto [Re: chaterlea25] #699795
06/27/17 12:50 pm
06/27/17 12:50 pm
Joined: Aug 2001
Posts: 2,531
New Hampshier USA
MikeG Online content
BritBike Forum member
MikeG  Online Content
BritBike Forum member
Joined: Aug 2001
Posts: 2,531
New Hampshier USA
Originally Posted by chaterlea25
Hi,
0.003 in is definitely not correct
0.012in = 0.30mm is the correct gap at max opening
Maybe 0,003 is the max gap when the piston is at the firing point (cigarette paper thickness) ????

John


this makes more sense to me


1960 BSA A10
2007 Suzuki Bandit
1957 A10
(Used to be a Triumph here)
71 Norton Commando
Re: Help with Lucas Magneto [Re: Gui d'Orey] #699805
06/27/17 3:07 pm
06/27/17 3:07 pm
Joined: Nov 2011
Posts: 4,067
U.S.
Magnetoman Online content

BritBike Forum member
Magnetoman  Online Content

BritBike Forum member
Joined: Nov 2011
Posts: 4,067
U.S.
Originally Posted by Gui d'Orey
I also set the points gap to 0,003" according to the BSA owner's manual, which is smaller than what was previously set to, and now she runs rougher. Probably another sign that something's not quite right...
What's not right is you have the gap set much too low. Yes, I know you say that value is given in two different manuals, but even if it is given as 0.003", it's wrong.

The rough running you experience at this incorrectly-low gap is a direct consequence of a 19th Century discovery known as Paschen's Law. AC currents are much easier to interrupt than DC because the arc is quenched during half the cycle of the voltage oscillation during which time the contacts have moved far enough apart that the voltage is insufficient to restart the arc. Although it takes kV to initiate an an arc across the 0.020" gap of a plug, it takes less across a 0.003" gap.

According to Paschen's measurements it takes ~400 V to initiate an arc across a gap of 0.001", and this much voltage is present in the primary of the magneto. But, you say, your gap is 3x larger so there shouldn't be a problem. Even if there were no radial run out in the bearing (and with up to 0.005" end float allowed, there will be a similar amount of radial run out), setting the gap at 0.003" means it only opens at the "top" of the cam where the slope is minimal. Whereas with a proper gap of 0.012" the slope is ~0.002" per degree of rotation, at the "top" of the cam it is much less than this. This means that it takes many degrees of rotation of your armature before the points open to that 0.003" value. In the mean time the separation is much less than this and Paschen creates the rough running you experience by allowing arcing across the points which both alters the timing and dissipates much of the energy that no longer is available for the spark plug.

Again, even if you've read those manuals correctly, 0.003" is wrong. Set the points at 0.012"

Re: Help with Lucas Magneto [Re: chaterlea25] #699858
06/27/17 9:39 pm
06/27/17 9:39 pm
Joined: Jun 2017
Posts: 18
Germany
G
Gui d'Orey Offline OP
BritBike Forum member
Gui d'Orey  Offline OP
BritBike Forum member
G
Joined: Jun 2017
Posts: 18
Germany
Originally Posted by chaterlea25
Hi,
0.003 in is definitely not correct
0.012in = 0.30mm is the correct gap at max opening
Maybe 0,003 is the max gap when the piston is at the firing point (cigarette paper thickness) ????

John


That does seem more correct. It's strange that BSA mentions it specifically, but then doesn't go on to specify the maximum gap. The "instruction book" is very basic and just gives a veeery general overview of the bike, not like a more modern manual. I suppose any rider in the 30's was expected to be mechanically fit. One of the best quotes in the book is something like this " ... the gearbox has three gears. They are there to be used, so do use them as the speed and load requires it."

Re: Help with Lucas Magneto [Re: Gui d'Orey] #699880
06/28/17 1:43 am
06/28/17 1:43 am
Joined: Mar 2014
Posts: 563
Denver CO
J
Jerry Roy Online content
BritBike Forum member
Jerry Roy  Online Content
BritBike Forum member
J
Joined: Mar 2014
Posts: 563
Denver CO
Originally Posted by Gui d'Orey


I suppose any rider in the 30's was expected to be mechanically fit. One of the best quotes in the book is something like this " ... the gearbox has three gears. They are there to be used, so do use them as the speed and load requires it."



Musing along, the bicycle was one of the prime methods of wheeled transport back then, so the person supplying the power was well acquainted with the type and speed of the power required to keep going under various conditions. So it is probable that an astute someone who obtained a powered machine would apply a bit of what might be termed a mechanical version of anthropomorphism to the engine, and pick a gear that allowed it to operate in its "sweet spot'.

Just a thought. smile

CZ

Last edited by Jerry Roy; 06/28/17 1:45 am.
Re: Help with Lucas Magneto [Re: Gui d'Orey] #702895
07/26/17 7:45 pm
07/26/17 7:45 pm
Joined: Jun 2017
Posts: 18
Germany
G
Gui d'Orey Offline OP
BritBike Forum member
Gui d'Orey  Offline OP
BritBike Forum member
G
Joined: Jun 2017
Posts: 18
Germany
Hi everyone,

just an update on the issue. The problem is solved!

It was indeed a bad spark plug. After a few weeks hollidays, I got a new plug, and big,fat, happy sparks! The bike startet after a few kicks, and runs nicely again. It happens every time, doesn't it? we look at everything else, suspect big, complicated problems, and forget to check the simplest and obvious things?

Regarding the points gap, you were all right of course. The BSA manual do specify .003" just as the points open - the proverbial fag paper. Strangely enough, BSA never mentions what the gap should be when fully open. I dug out some old books on Lucas electrics for classic bikes, and took a look of some manuals I had for later BSAs and Ariels and the gap should be 0.012-0.015". It's been a while, nearly 20 yrs, since my last restoration, and my skills are rusty smile I should have spoted it right away.

Anyway, I'm very happy she is running again, and that there was nothing serious to ruin the rest of the riding season.

Thanks for all the inputs!

Cheers
Gui

Last edited by Gui d'Orey; 07/26/17 8:02 pm.
Re: Help with Lucas Magneto [Re: Gui d'Orey] #702908
07/26/17 9:30 pm
07/26/17 9:30 pm
Joined: Aug 2001
Posts: 372
Iowa
konon Online content

BritBike Forum member
konon  Online Content

BritBike Forum member
Joined: Aug 2001
Posts: 372
Iowa
The .003 gap might be for setting the timing , as the points break open .


1968 BSA Firebird
1200 HD
XS 1100
1972 Rickman 125

Moderated by  Alan_nc 


Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.6.1.1