The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Stevie1262 on 12.07. 2018 22:05

Title: No spark ....could it be points?
Post by: Stevie1262 on 12.07. 2018 22:05
After nearly 38 years got hold of another A10 ...it’s been sitting a while and needed auto adv retard mag fibre pinion replaced ...a replacement came with the bike....before setting up the Timing I thought I would check for a spark ....spinning the mag by hand or in a drill and earthing HT Leads nothing seen ....had a look at the points opening and shutting ok but I am confused ...using a meter testing at each side they are showing continuity to earth whether open or closed ...is this right or is there a problem I would have expected one side to be insulated....although it’s been a long time since I worked on a Mag ....the fact that it’s not run in a while throws doubt in my mind about the state of the Mag ....any advice appreciated
Title: Re: No spark ....could it be points?
Post by: a10gf on 12.07. 2018 22:59
Take a look here > Magneto Circuit Diagram (https://www.a7a10.net/forum/index.php?topic=8138.0)

In practice you try to measure the primary winding which is around 0.5 ohm, so needs a damn good meter :O)
But what looks like continuity at least shows there's no open circuit in the primary.
Secondary if ok should be approx 5 kohm.

And a post in 'Pictures, Stories & Introductions' is always appreciated.
Title: Re: No spark ....could it be points?
Post by: Stevie1262 on 13.07. 2018 08:37
Cheers will do ...this is about 5th A10 or A7 I have owned within last 40 years not had one in a while ...(and most had Mag issues at some point) so that’s always on my thoughts ....broke all my rules buying this one as a non runner especially when it was sitting with the Mag Pinion off and spare HT leads lying about ....the chap said it was sparking I’ll have to double check ... but heart ruled the head and I bought it ...mags  I remember spinning them by hand and getting a spark ...I have good meters I’ll test today ....Cheers
Title: Re: No spark ....could it be points?
Post by: JulianS on 13.07. 2018 08:55
If original Lucas windings and capacitor expect them to be us.

But worth carefuly checking the points assembly.

 If steel backed points make sure the spring does not touch the cam ring shorting it and make sure the little backing spring is in the correct position and not shorting.

I dont think simple meters are much good for mag testing.
Title: Re: No spark ....could it be points?
Post by: Triton Thrasher on 13.07. 2018 09:20
Are you turning it the right way?

If you loosen the centre screw and leave the points plate held on by the taper, then one point should show as electrically isolated from the casing when the points are open and should conduct to the casing when the points are closed.
Title: Re: No spark ....could it be points?
Post by: duTch on 13.07. 2018 09:30

Hola Stevie- In addition to the above, can we assume you've checked the points, slipring/brushes and the earth brush/es and pickup brushes is/are clean ?

 Good luck with it if it's been parked up for a while ....(how long?)
Title: Re: No spark ....could it be points?
Post by: Stevie1262 on 13.07. 2018 13:45
Yep will check today Mag is in good nick bearings feel good and it spins fine points were gapped ok looked clean not checked the pick ups I’ll pull the Mag off today for a better look my gut feeling is the points set up needs investigated the chap who sold me Bike confirmed he didn’t check for spark as it wouldn’t run and they found mag pinion all worn out...didnt do much more ...rest of engine put together well ....hey ho joys of Old Bikes 😆
Title: Re: No spark ....could it be points?
Post by: Stevie1262 on 14.07. 2018 22:57
Nope no luck ..windings seem to test ok and points give correct continuity readings to earth when centre bolt removed as suggested, so may be the condenser... beyond my scope now ...it will have to go off for testing and repair ...located a working one to try many thanks for all the advice ....nothing changes,  just like the old days always try and have a spare Mag handy 😆