B.T.H Mag-Dyno

[Simon Dinsdale]

I recall Bob Stafford saying that the kickstart quadrant 199x and 38BA was offered in different ratios by Burman depending on the bike it was fitted to and he thought the Rapide used different ratio to the singles. This would all influence the kickstart RPM.

See "Back to A" pg 125 for several articles about this where its stated the A Rapides used 19 teeth ratchet gear and appropriate quadrant (so did Ariel Sq 4) but the std for singles and most Burman gearboxes was 17 teeth ratchet.

 

[vibrac]

I will clarify my BTH pin hole in fag paper comment by saying that was my experience with a single early mag (first year production) with the original maker on his test rig and as I say I never saw a spark . The mag business has been sold since so I have no idea if its design has been changed I have sourced a twin one since and thats OK, I am saving up my pennies to get the single one refurbished after many years of racing they do go rusty internally.

 

[delboy]

I recall Bob Stafford saying that the kickstart quadrant 199x and 38BA was offered in different ratios by Burman depending on the bike it was fitted to and he thought the Rapide used different ratio to the singles. This would all influence the kickstart RPM.

See "Back to A" pg 125 for several articles about this where its stated the A Rapides used 19 teeth ratchet gear and appropriate quadrant (so did Ariel Sq 4) but the std for singles and most Burman gearboxes was 17 teeth ratchet.

Very interesting.
Has anyone out there ever seen a Burman 19 tooth ratchet and matching quadrant?
I spoke once to a [supposed] Sq4 "expert" who said he'd never heard of them.
I'm trying to visualise it in my head, but wouldn't a smaller quadrant and bigger ratchet slow things down?
Where's my Meccano?
cheers,
Delboy.

 

[Simon Dinsdale]

Very interesting.
Has anyone out there ever seen a Burman 19 tooth ratchet and matching quadrant?
I spoke once to a [supposed] Sq4 "expert" who said he'd never heard of them.
I'm trying to visualise it in my head, but wouldn't a smaller quadrant and bigger ratchet slow things down?
Where's my Meccano?
cheers,
Delboy.

I have a Burman quadrant in the box of spares that is a slightly smaller radius and number of teeth which cannot be used on the std 17 tooth ratchet and would need to mesh with a larger ratchet which 19 teeth would work. I thought I had the matching ratchet but I cannot find it in the parts box at the moment.

Simon

 

[delboy]

Aha,
If I'd looked beyond my nose, I would've seen the Burman parts list in "Back to A" lists the ratchet 38BA and quadrant199X

I have a Burman quadrant in the box of spares that is a slightly smaller radius and number of teeth which cannot be used on the std 17 tooth ratchet and would need to mesh with a larger ratchet which 19 teeth would work. I thought I had the matching ratchet but I cannot find it in the parts box at the moment.

Simon

 

[delboy]

Aha,
If I'd looked beyond my nose, I would've seen the Burman parts list in "Back to A" lists the ratchet 38BA and quadrant199X

Oh, something weird going on with my internet? The rest of the last post went missing.
Anyhow-
The Burman parts list shows parts with the same part No.s, but listed for [1000 Square four] Annoyingly doesn't tell us the difference.
With no little wheels to hand to play with, my brain cell still tells me it would kickstart slower with a 19 t ratchet and smaller quadrant?
regards,
Delboy.

 

[delboy]

Oh, something weird going on with my internet? The rest of the last post went missing.
Anyhow-
The Burman parts list shows parts with the same part No.s, but listed for [1000 Square four] Annoyingly doesn't tell us the difference.
With no little wheels to hand to play with, my brain cell still tells me it would kickstart slower with a 19 t ratchet and smaller quadrant?
regards,
Delboy.

My nose must be getting really short!
On the Draganfly motorcycles website it lists in the Ariel Burman bits:- 3190-31 Kickstart ratchet pinion 17T [Not sq4] and 3190-37 kickstart ratchet pinion 19T.
Also, 3325-31 Kickstart quadrant [Not Sq 4] and 3325-37 Kickstart quadrant Sq.4.
The Square 4, 19T pinion and matching quadrant are noted as not available.
Curious-er and curious-er.
Delboy.

 

[Simon Dinsdale]

Oh, something weird going on with my internet? The rest of the last post went missing.
Anyhow-
The Burman parts list shows parts with the same part No.s, but listed for [1000 Square four] Annoyingly doesn't tell us the difference.
With no little wheels to hand to play with, my brain cell still tells me it would kickstart slower with a 19 t ratchet and smaller quadrant?
regards,
Delboy.

I agree a larger 19t ratchet would be slower, but easier to kick over with a larger engine. You may think slower is bad but if its easier to kickover then you may get a higher initial burst of speed on the kickstart which would help as you don't need multiple RPM to get a mag to spark, just initial speed if you know what I mean. You can find this by flicking a mag over peak magnetism by hand and get a spark.

Anyway as I don't have an A twin this is all theory.

Simon

 

[oexing]

CDI ignitions seem to produce only very poor sparks at kickover speeds, so I would not accept them on big engines. Better try to have some coil ignition, electronic or contact breaker is your choice. This hooked onto a twin spark coil on the twin or a single coil on a single breaker. BUT you need a decent dynamo or alternator, another matter then, Alton or my choice one of the BLDC motors from Ali plus a converter from 48 V to 13.8 V, sizes to your liking, 400 W , 300 W or under 100, could be fitted on top of a magdyno I think. All available for less than € 100.- but you need some time on a machine for adapting the lot.

Vic

 

[billirwinnz]

When I had a modern BTH cdi kit on my Comet I had problems starting. Eventually I phoned the BTH folk to be told that the output below 250 rpm was zero, and it needed at least 400 rpm for reliable operation. Having full retard at 4 to 6 BTDC is also a big help.

Hi Martyn
Yes. I think speed is the problem. I re-timed it to 38 degrees instead of 34 so that I'd have 6 degrees of advance on starting to no avail. I'm going to put the repaired mag back in. I'll test the speed versus spark of the BTH in my lathe. I'm also going to try to determine the speed of rotation by filming a kick on my iPhone and counting frames. I'll fit a degree disc to see how far it rotates on a single kick.

Cheers Bill