B.T.H Mag-Dyno

delboy

Well Known and Active Forum User
VOC Member
A little snippet more folks.
Out of interest, I just found a note I made from a 2013 conversation with Tony Harris about his early Bth/Lucas Magdyno look-alike, saying that "It fires at 100 RPM, so should start okay".

None of the Vincent's I've ever worked on, have I ever needed to know how fast it spins over.
Okay people with a calculator or a maths degree, how fast do "A" Rap's turn over when kickstarting?
Sorry,
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Delboy.
 

oexing

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When you believe the kickstart speed is too low for electronics, simple advice: Kick it faster ! When you cannot, well, this is a matter of leg strength and driver´s weight, no ? So no hope for faster kickover speed with a different ratio of gears, you just get faced with even tougher force from the lever as a higher ratio makes things harder.
Alternative: A real powerful magneto - not a rotating coil type . Or go for coil ignition with a more powerful dynamo or alternator. There are some ways to success but I would definitely NOT want a CDI ignition from a magnetic source.

Vic
 

vibrac

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Thats true about a different way to kick an AMC box on a Comet I read it on here last year and found a long push halfway down the stroke followed by a kick did the trick as said above not like the Burman routine at all
 

billirwinnz

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With the old magneto fitted it is now starting as it should :)

I have spun the BTH in the lathe in a darkened room. I don't have continuously variable speed but at 190rpm there is a weak spark that doesn't look reliable. Put a piece of normal copier paper between the plug points and it kills the spark. It's likely that it doesn't produce a spark under compression pressure at this speed. At the next step up, 300rpm, there's a strong very visible spark that has no problem making holes in the paper.

From this it seems that unless the motor spins at 400rpm or perhaps more the spark is going to be weak. I haven't been able to measure cranking speed but on a cold engine it is very sluggish and probably well below 400rpm.

Thanks to all for your help and suggestions.

Bill
 
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