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Failure to start after mag rebuild #713142
10/30/17 1:12 am
10/30/17 1:12 am
Joined: Aug 2016
Posts: 36
Canterbury, New Zealand
B
BevanC Offline OP
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BevanC  Offline OP
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Joined: Aug 2016
Posts: 36
Canterbury, New Zealand
Hi folks,
The plea below for help was posted on another forum, but has had no replies. Thought I'd try to help the bloke by posting it here. I'll pass on any suggestions.
Cheers,
Bevan

"My bike will not start. Please read all my post before responding

After having difficulty starting my BSA W32-6 4.99 hp side valve (1932) when it was hot I had the magneto professionally rebuilt. I was also advised by Tony Cooper who rebuilt the magneto that it would be more reliable to replace the original Lucas three brush dynamo with a later Lucas two brush dynamo; so I did. Hence I have a Lucas MS1 magdyno fitted, with a later Lucas dynamo.

Tony also advised me to replace the mechanical regulator, which was a coil on the back of the control panel switch (Control switch setting are off, charge, High beam and low beam). He told me it would be better if I replaced it with a Teb-tec solid state encapsulated regulator. Again I have done this.

When I replaced the magdyno I removed the cylinder head so that I could see that it was at Top Dead Centre, when the piston was at the top and both inlet and outlet valves where closed. I then located the magdyno into the sprocket with the ignition in fully retarded position. This is the method stated in the BSA Motor Cycle Instruction Book (All models 1930 to 1936 inclusive). The exact wording for all 1932 BSA motorcycle is:

Piston at T.D.C Ignition fully retarded, Contact Breaker points open .003”

Before locating the magdyno into the sprocket I had rotated the contact breaker assembly until a cigarette paper could just move between the points and left it where the cigarette paper just comes loose. I made sure that it was fully retarded by not connecting the cable to the leaver, hence the cable was loose.

Both the inlet and outlet valve (Tappet) clearances are correct, .004” inlet and .006” exhaust.

When I attempt to start the motorcycle it will not fire at all. I tired starting the bike fully advance, half advance and fully retarded; however the outcome was always the same it would not fire at all. So I did the usual check for air fuel mixture and spark at the spark plug. I removed the spark plug placed it against the engine and yes there was a spark, also fuel was gently dripping out of the carburettor which indicates that the fuel was getting through.

Then I tried spraying Easy Start down the carburetter mixing chamber, again I tried bike fully advance, half advance and fully retarded. It would only back fire sending the force back through the kick start.

My question is how do I diagnose and remedy this problem.

Thank you for your kind help"

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Re: Failure to start after mag rebuild [Re: BevanC] #713152
10/30/17 2:27 am
10/30/17 2:27 am
Joined: Aug 2009
Posts: 973
gastonia .. NC
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limeyrider Offline
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limeyrider  Offline
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Joined: Aug 2009
Posts: 973
gastonia .. NC
Have you made sure that you timed the ignition on the compression stroke? .....piston at TDC...and both valves closed?

Re: Failure to start after mag rebuild [Re: BevanC] #713192
10/30/17 12:50 pm
10/30/17 12:50 pm
Joined: May 2004
Posts: 3,728
Sydney Australia
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BSA_WM20 Offline
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Sydney Australia
As per Limey's reply, Pull the valve chest cover off and the mag end cap.
Rotate the engine to where the fag paper just pulls through the mag points then flip over to the other side and check you can turn both of the valve adjusters between your fingers indicating that the valves are closed.
Also check the valve lifter is not holding the exhaust valve open.


Bike Beesa
Trevor
Re: Failure to start after mag rebuild [Re: BSA_WM20] #713239
10/30/17 8:05 pm
10/30/17 8:05 pm
Joined: Aug 2016
Posts: 36
Canterbury, New Zealand
B
BevanC Offline OP
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BevanC  Offline OP
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Joined: Aug 2016
Posts: 36
Canterbury, New Zealand
Thanks guys, I'll pass the suggestions on.
Cheers,
Bevan

Re: Failure to start after mag rebuild [Re: BevanC] #713356
10/31/17 2:59 pm
10/31/17 2:59 pm
Joined: Sep 2015
Posts: 310
Kent, England
J
John Alexander Offline
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John Alexander  Offline
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J
Joined: Sep 2015
Posts: 310
Kent, England
Sounds like ignition timing, especially if it backfires using easy start. Don't use the easy start as their is a possibility of it catching fire when it backfires.
Goldie John.

Re: Failure to start after mag rebuild [Re: BevanC] #713372
10/31/17 5:00 pm
10/31/17 5:00 pm
Joined: Jun 2017
Posts: 24
CALIFORNIA
S
slow learner Offline
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slow learner  Offline
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Joined: Jun 2017
Posts: 24
CALIFORNIA
Maybe I'm reading the initial question wrong, but if you were setting the timing with the mag control cable loose isn't that the fully advanced position ? That's the way every English mag I've ever owned works (quite a few) but admittedly none as early as this. If I'm right it would explain what the owner is experiencing as fully advanced at tdc will not work.


Laurence Luce
Re: Failure to start after mag rebuild [Re: slow learner] #713382
10/31/17 5:44 pm
10/31/17 5:44 pm
Joined: Aug 2001
Posts: 7,432
scotland
triton thrasher Online content
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triton thrasher  Online Content
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Posts: 7,432
scotland
Originally Posted by slow learner
Maybe I'm reading the initial question wrong, but if you were setting the timing with the mag control cable loose isn't that the fully advanced position ? That's the way every English mag I've ever owned works (quite a few) but admittedly none as early as this. If I'm right it would explain what the owner is experiencing as fully advanced at tdc will not work.


Tight wire advance mags do exist too. They appeared on some 1950s singles.


Amateur Loctite enthusiast.
Re: Failure to start after mag rebuild [Re: BevanC] #713384
10/31/17 6:05 pm
10/31/17 6:05 pm
Joined: Aug 2016
Posts: 36
Canterbury, New Zealand
B
BevanC Offline OP
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BevanC  Offline OP
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Joined: Aug 2016
Posts: 36
Canterbury, New Zealand
The Lucas MDB1 mag on my 1929 Sloper and the MO1L on my 1960 Panther are both tight wire advance. It appears that this guys one is as well (assuming the points are rotating clockwise in his photo - I wonder if his rotates the other way ?). I set the timing on mine on full advance at the specified angle before tdc; seems safer to me since it prevents over-advancing when running.

Re: Failure to start after mag rebuild [Re: BevanC] #713528
11/02/17 12:23 am
11/02/17 12:23 am
Joined: May 2004
Posts: 3,728
Sydney Australia
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BSA_WM20 Offline
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Sydney Australia
Tight wire advance was the norm till around the 50's on BSA's.
M's remained that way AFAIK till the end of manual advance where the B's & A's got slack wire advance.

As for timing.
The .003" opening at TDC assumes that the points are .012" at full lift,and both sprockets are in the correct positions on the engine & magneto , if it is differnt then the timing will be out.
Now the easiest way to alter the timing is to change the max points opening, try it at .002" increments
IF you think the spark is too far advanced, close down the points gap a thou or two.
You can knock around .004" to .006" off the max opening and still get a spark, although it might break down at higher speeds so this is only done to quickly test the timing and not for running.
If the engine starts then the sprocket has slipped on the magneto.
If the magneto has just been overhauled then it should produce sufficient energy to spark at less than optimal flux opisition although it might brak down at higher revs.
From ( unreliable ) memory the magneto sprocket is on a plain taper and the engine sprocket is keyed.
Thus it is very easy to get the sprocket in the wrong position.

The opposite occurs when you enlargen the max opening so you can go each way very quickly to test if you have the timing right.

Last edited by BSA_WM20; 11/02/17 12:24 am.

Bike Beesa
Trevor
Re: Failure to start after mag rebuild [Re: BevanC] #714904
11/13/17 9:04 pm
11/13/17 9:04 pm
Joined: Jun 2017
Posts: 18
Germany
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Gui d'Orey Offline
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Gui d'Orey  Offline
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Joined: Jun 2017
Posts: 18
Germany
Sounds really stupid, but is the spark plug still good? Or the plug boot? I once lost days of fumbling with the mag, and in the end the plug was the culprit - when I changed to a new one the bike started on first kick.

I read somewhere that it can happen that one gets a spark with the plug out of the cylinder, but once it's in the head, the compression prevents a good spark from bridging the gap.

Cheers
Gui


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