The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Terryb on 09.06. 2014 17:31
-
Hi All,
I have a sick Shooter, after a 150 mike ride yesterday the bike started to miss fire at low rev's and then eventually stalled. Managed to get it home, but now there is no spark. Before this run, it was running sweet as a nut, first kick starter.
Have had a look at the end cap on the Mag, the only thing that looks doggy is the length of the carbon contact which makes with the centre screw. This is worn down to the brass retainer. Could this be the problem?
-
G'day Terry.
The bike should run without the end cover on (if the camring stays put), it won't turn off. But the dust from it may have fouled something, earthing a bit that's not meant to be. Give the points area a spray with electric contact cleaner and a blast of compressed air and try again. Note if the bridge in the end cap doesn't make contact with the center screw your kill switch won't work.
Cheers
-
I had the same problem on my 1954 GF been out for a ride then started to misfire, what had happened was the cam ring had turned and the blade spring on the points were touching . the problem was the rivet that holds the cam ring in its position had come out a little and allowed the cam ring to turn.
Pull the rivet out and inside you will find a piece of shaped steel, turn it around so it fits the cutout in the cam ring then knock the rivet back in. If it does it again put a bit of shim in then knock the rivet in.
Victor
-
Always do the obvious first.
Are the plugs clean and gapped?
Are the points clean and gapped?
Do the points open and shut as they rotate?
-
Had an email from a gent, which I've lost, regarding the end cap and possibility of the carbon shorting out on the brass. Surely, the carbon and brass are conductors, therefore they are connected. I thimk its more blikely that the carbon is so worn down, that its not making contact with the points centre screw.
-
the carbon is so worn down, that its not making contact with the points centre screw.
that would stop it stopping, would not stop it running, the carbon brush runs against the central screw and is wired (or should be) to a switch (push button) to earth, when pushed the switch completes a circuit from the central screw to earth thereby killing the spark, so maybe check the pushbutton and as has been said anything in the points that shorts them to earth
your right about the brass/carbon
would check as Triton Thrasher suggests, eliminate
-
If they're steel points this can happen. (https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg3%2Ftakka22%2F001_zpsa069537d.jpg&hash=254a3a41e131c545da22dea2ad79f8866b88e199) (http://s244.photobucket.com/user/takka22/media/001_zpsa069537d.jpg.html)
-
Hi All,
Checked all of the obvious things. Cleaned slip ring, points adjusted, plugs re-set and still no spark. Looks like its going in for a re-con. Strange thing is that its only done 2K since the last one. Thanks for the advice.
-
Well there are refurbs and refurbs I guess, while the mechanics of the thing don't change the quality of parts used is out of your hands once the postie takes it away, I had both mine done at the same place based on the fact that the first one goes fine on my Flash so sent the second one to same place.
However it refused to start my Rocket type so swapped them , result both work fine on my Flash but neither of the two will start the Rocket (higher compression) .
Lesson learnt but disappointing, when time and cash allow I'll send it to one of the guys here for a check over and fix, suggest you ask for a private quote from the guys here they both (might be more than two) seem genuine blokes
-
Hiya Terry- I had a similar thing happen a couple of months ago, did all he obvious clean-ups and checks, but really nothing- had a couple of tongue lubes and ran out of daylight.
Next day it fired up like nothing happened... *conf*
Have you done a finger on the slip-ring/plug leads..?
Change plugs?
-
Change plugs?
good one Dutch, probably the most obvious but missed by all so far unless Terry has tried a new pair.
quite a few here (me too) have experienced plugs go on strike - blaming Modern fuel and unvarnished inner porcelain bits in the plug for them shorting out so no spark,(wet soot = carbon = conductor = short) just an opinion held by many , may be right or maybe something else but a new plug generally solves it
-
Change plugs?
.....probably the most obvious but missed by all so far....
Oh, he'll have tried new plugs before asking on the internet!
-
Hi Guy's,
Problem solved. Not easy to see, but the contact centre screw had come undone, enough so that at speed the points assembly was stable, but when the rev's dropped the spring was shorting out. Hence no spark on kick over.
Gave the whole assembly a good clean, checked all the insulation. Re-fitted them and checked the gap and it all works fine. Just need to renew the end cap some time. Anyway thank you all for your help and suggestions.
Terryb
-
Interesting that you say it was recently overhauled.
Mag specialists aren't the best at tightening screws, in my experience.
The centre screw is part of the LT circuit. If it's loose, you'll have problems even if the points stay in place.
-
I think I'm tending to agree with you TT about this Mag specialist, but in his defence, the recon was done in 2008.
However, the bike has stood around for the last 6 years and 600 miles of the 2K has been done by me in the last 3 months. Never the less the centre screw should not have come loose enough to stop the bike.
Did a 25 mile run yesterday and she ran OK
-
I had that happen to me on the way home from southport ,right on a dark stretch of road the bloody thing cut ,one moment motion the next dead , my mate and pushed her home nearly 5 miles outfit by the way , stayed at his knackered 6am next day pulled the cap of and the ponits fell out pushed home and tightened purred away again me with ten ton of egg all over my mug , stupid or what !! but I was only 16 cheers BobH
-
In defence of mag restorers everywhere! I thought I'd throw in a bit of information about the points centre screw. Obviously it does need to be tight enough to hold the points in place but........ the threaded part of the screw screws into the primary windings connection from the ignition coil. This connection is essentially a square nut insulated from the armature body by a piece of flat fibre material (a bit like the material fibre washers are made from). The square nut is prevented from spinning by its location in a square hole in a plastic insulator tube. If the screw is overtightened two things can happen, 1) the square nut can punch a hole in the fibre insulator and make contact with the armature body, or 2) the square nut can burst the shoulders off the plastic insulator tube. Provided the mag restorer has done a good job with the armature and bearings most other matters are within the scope of most owners. The aforementioned problems are often caused by the plastic insulator tube being manufactured a little too short thereby allowing the nut to travel too far before it tightens, by which time it has guillotined the fibre insulator. The plastic insulator tubes don't seem to be available anywhere so I make my own, to the correct length, and I supply some of the other magneto restorers with them. So, tightening the points centre screw is a slightly more delicate operation than many realise - I have come across plenty of mags where the overtightening of the screw is what has stopped the mag. I can understand why a mag restorer (and I honestly don't think it was me!) might be a bit cautious because, if the screw is overtightened and the fibre insulator is chopped, the mag and the armature have to be dismantled to fix the problem.
-
Sounds like a good reason to shorten the screw a pinch for peace of mind then.
-
thanks for the info Beezermacc.. *good3*
-
Sounds like a good reason to shorten the screw a pinch for peace of mind then.
Unfortunately this won't make any difference. The screw isn't the problem, it's the fact that the screw draws the nut through the fibre insulator.
-
Sounds like a periodical check on the centre screw is a must maintenance task. I'll keep a check on mine in future.
2 hours sitting on the Madejski round-about (M4) waiting for the brake down wagon, was not my idea of fun.
Thanks anyway.