Author Topic: Starting problem after magneto rebuild  (Read 163 times)

Offline Billington

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Starting problem after magneto rebuild
« on: October 28, 2017, 10:31:29 PM »
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.







Offline R

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Re: Starting problem after magneto rebuild
« Reply #1 on: October 28, 2017, 11:57:32 PM »
Are you sure though that you have timed the spark on the compression stroke, and not on the exhaust stroke ?

I'd suspect it is 360 degrees out ??
You wouldn't be the 1st to ever do this either.
(At least with a twin, you can just swap the plug leads over)

And, have you spun the maggie (by hand even) and verified it gives a nice big fat blue spark.
And that it smells of petrol on the plug after all these efforts.
(and have tried a new plug, just in case).
Hopethishelps.

Offline iansoady

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Re: Starting problem after magneto rebuild
« Reply #2 on: October 29, 2017, 10:06:52 AM »
Agree fully.

As you may (or may not) know, the dynamo, control box etc are irrelevant when it comes to whether the engine starts or runs. However, you need to make sure that you have correctly wired up the 2 brush dynamo as it's completely different to the 3 brush one.

Were you not on her a few months ago with similar problems?
Ian
1952 Norton ES2
1962 Ariel Arrow
1982 Moto Guzzi V50

Offline Billington

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Re: Starting problem after magneto rebuild
« Reply #3 on: October 29, 2017, 02:31:29 PM »
Thank you both iansoady and R for you kind help. You are right I need to go back and double check the things that I believed I checked the first time around. I know that the problem lies with me the bike is simply at combination of mechanical and electrical components that I need to assemble correctly. Part of the problem is that I've been attempting these tasks while feeling mental burnt out from my day job, hence not correctly interpreting what the bike is telling me.

Also iansoady, Yes, your right I was on this forum a few months ago with a similar problem. With the great help from members of this forum I was able to diagnose that the magneto primary wiring had broken down and needed rewinding. I've got the rebuilt magdyno back, hence the new chapter in my learning journey as a new vintage bike owner and the new post.