BSA Owners' Club Forum

The BSA Workshop => Pre War => Topic started by: BILLINGTON on 28 October, 2017, 22:41:09

Title: Starting problem after magneto rebuild
Post by: BILLINGTON on 28 October, 2017, 22:41:09
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.


Title: Re: Starting problem after magneto rebuild
Post by: BEVANC on 30 October, 2017, 01:05:37
I have posted your query on another forum and will let you know of any advice. 

I'm by no means an expert, but my Sloper has a similar carb to your bike.  Just because fuel drips from the carb does not guarantee the jets are clear.  I would take the carb apart, ensure the jets are clean, and the float level is correct.  Although kick back is often due to the timing being incorrect, I think that too lean a mixture could also be a cause.
Title: Re: Starting problem after magneto rebuild
Post by: STAR TWIN on 30 October, 2017, 06:15:12
Granny and eggs comes to mind but are you absolutely sure you have set the timing at TDC on compression? We have all been there...
Title: Re: Starting problem after magneto rebuild
Post by: BEVANC on 30 October, 2017, 13:09:00
A much more experienced Sloper owner than myself has the following comments\queries:

1/ From the photo, the magneto does appear to be tight wire advance, so the timing procedure you described should be correct. When tightened, the cable is definitely rotating the cam in the direction opposite to engine rotation, isn't it ?  If not, then the ignition could be way, way, advanced and would cause the symptoms you describe.

2/ Is there any chance that one of the valve timing gears could have been moved by even 1 tooth during the the magneto replacement ? This would also cause starting problems.
Title: Re: Starting problem after magneto rebuild
Post by: BEVANC on 30 October, 2017, 17:51:41
A suggestion posted in reply on another forum:

"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"

Best of luck :)
Title: Re: Starting problem after magneto rebuild
Post by: BILLINGTON on 30 October, 2017, 19:05:56
Thank you everyone you have given me some great pearl of your wisdom. I will try them out and let you know the results.
Title: Re: Starting problem after magneto rebuild
Post by: BEVANC on 02 November, 2017, 00:47:46
A further comment from another forum:

"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."