BTH Magneto pinion
- Thread starter redbloke1956
- Start date
Hi John , It has a Taper just like the original
Kevin
Kevin
Ed,
Thanks for the info on availability of the parts from VOC. I am running a Newby belt drive so I can easily mark the engine sprocket using a degree wheel and check it with a strobe. I know that Grosset makes a degree wheel that allows the passage of oil so that you can use a strobe.
It is best when you mount the BT-H that you position the slots so they are most useable to you. I am running a twin plug and moving the magneto 2 degrees at a time I started at 26 degrees and I ran out of "slot" after a few runs, but the bike was still gaining power with each movement. This position turned out to be 19 BTDC degrees, but I had to re index the slots, so I will have to wait for the next session before I can test it further.
Finally, a check with a strobe can also tell you if the advance is working. Mine appears to have lost its ability to retard and is now fixed. It may be that I am just not getting low enough in the revs to check it properly. It is not an issue on this bike, but it would be on a street bike and it is probably worth checking occaisionally.
David
Thanks for the info on availability of the parts from VOC. I am running a Newby belt drive so I can easily mark the engine sprocket using a degree wheel and check it with a strobe. I know that Grosset makes a degree wheel that allows the passage of oil so that you can use a strobe.
It is best when you mount the BT-H that you position the slots so they are most useable to you. I am running a twin plug and moving the magneto 2 degrees at a time I started at 26 degrees and I ran out of "slot" after a few runs, but the bike was still gaining power with each movement. This position turned out to be 19 BTDC degrees, but I had to re index the slots, so I will have to wait for the next session before I can test it further.
Finally, a check with a strobe can also tell you if the advance is working. Mine appears to have lost its ability to retard and is now fixed. It may be that I am just not getting low enough in the revs to check it properly. It is not an issue on this bike, but it would be on a street bike and it is probably worth checking occaisionally.
David
Dear David,
I couldn't get the Grosset adapter for use with a strobe to function satisfactorily but that may have been down to me as I have met Mr. Grosset and admire his work. I have a "Heath Robinson" (Rube Goldberg?) device that I mount onto the mag pinion window that I can use to strobe a degree disc. It is of course half engine speed so I have to double the reading but does give me the strobe facility.
Your engine uses a very small advance so I guess that it is set up very well maybe with quite high compression, squish bands, etc.
The combination of adjustment using the taper and the slots does give you almost infinite adjustment so it will be interesting to see what your final optimum advance figure is.
Have you ever seen the ignition advance using the BT-H mag? It is possible to specify fixed ignition at the build stage. Is it possible that this is what you have or are you operating above 3000 rpm when the MK1 CDI has finished advancing?
I couldn't get the Grosset adapter for use with a strobe to function satisfactorily but that may have been down to me as I have met Mr. Grosset and admire his work. I have a "Heath Robinson" (Rube Goldberg?) device that I mount onto the mag pinion window that I can use to strobe a degree disc. It is of course half engine speed so I have to double the reading but does give me the strobe facility.
Your engine uses a very small advance so I guess that it is set up very well maybe with quite high compression, squish bands, etc.
The combination of adjustment using the taper and the slots does give you almost infinite adjustment so it will be interesting to see what your final optimum advance figure is.
Have you ever seen the ignition advance using the BT-H mag? It is possible to specify fixed ignition at the build stage. Is it possible that this is what you have or are you operating above 3000 rpm when the MK1 CDI has finished advancing?
to Davidd,
just out of interest, I have fitted a twinspark ignition to my Comet with a 600 cc TP topendkit. I was told the best start for ignition timing was 28 degrees compared to a standard 34 degrees. Now you write about 19, am I misunderstanding something?
Bernd
just out of interest, I have fitted a twinspark ignition to my Comet with a 600 cc TP topendkit. I was told the best start for ignition timing was 28 degrees compared to a standard 34 degrees. Now you write about 19, am I misunderstanding something?
Bernd
No, I started at 34 degrees assuming that it would do no harm, at worst I would not have good power. This was before I strobed the bike. I raced at Roebling Road and the bike ran but did not make good power. I then went to 26 degrees and raced at Texas. The bike was much worse, but I was convinced it was something else. A leakdown test showed something wrong with the rings. Disassembly showed a shattered compression ring. I installed a new piston and rings, strobed the ignition at 26 degrees and went to the dyno. After several runs to change the main jet and the needle position and tighten up the float bowl that was flooding at high rpm we went to work on the timing. I went towards TDC bit by bit and gained HP every time. I finally ran out of slot on the magneto and had used up most of the day. I returned to the shop and checked to see where I ended up with the ignition by using the degree wheel and it was 19 degrees. I probably gained 1/2 hp going from 26 to 19 degrees. Not much but the trend was still up. Carleton Palmer had done the same on his racer. He started at 26 and went down to 20 or 22, he did not measure it as he routinely used the dyno, but he made three runs going lower each time. So 19 did not bother me as a number.
I also was reading a Kevin Cameron article about timing and it became apparent to me that the timing number is determined on the dyno. The printed numbers can give you a rough guide, but the real question is how fast is the combustion chamber processing the fuel. If your highest power is at 60 degrees, the combustion is incredibly slow. If the power is in the teens and twenties, the combustion is much faster. The numbers in Richardson were most likely developed based on the dyno tests for best power with as single plug and pool petrol.
Ed, I have the MK2, as I remember, and I did not specify fixed timing. Justin Mackay-Smith was operating the strobe and I was trying to let the revs drop as low as possible. The BT-H has worked well for me, so I do not want to criticize it. Based on the curve that is published on the website I thought it would be very dramatic, but he had difficulty seeing it operate. With electronic equipment I think it is worth getting a base line or control, because when you are trying to diagnose a problem it is impossible to check the electronic items on their own, but you can check to see if things you noted have changed.
David
I also was reading a Kevin Cameron article about timing and it became apparent to me that the timing number is determined on the dyno. The printed numbers can give you a rough guide, but the real question is how fast is the combustion chamber processing the fuel. If your highest power is at 60 degrees, the combustion is incredibly slow. If the power is in the teens and twenties, the combustion is much faster. The numbers in Richardson were most likely developed based on the dyno tests for best power with as single plug and pool petrol.
Ed, I have the MK2, as I remember, and I did not specify fixed timing. Justin Mackay-Smith was operating the strobe and I was trying to let the revs drop as low as possible. The BT-H has worked well for me, so I do not want to criticize it. Based on the curve that is published on the website I thought it would be very dramatic, but he had difficulty seeing it operate. With electronic equipment I think it is worth getting a base line or control, because when you are trying to diagnose a problem it is impossible to check the electronic items on their own, but you can check to see if things you noted have changed.
David
all this dyno work has its uses but remember to retard a tad when done-the machine is not affected by wind resistance until it "hits the street" then you will find the ideal dyno figures to be "bollards". I ran a dyno centre for 20+years and this is only the start of my accumulated knowledge.
I had my magneto rebuilt by Dave Linsley about 4 years ago. Nothing further to report... And I wouldn't (and didn't) attempt to refurb the Lucas ATD. I found I had five old ones in a box, most of which could be dismantled by vigorous shaking, which told its own story. I went the Roy Price route, and have never had cause to regret it. Even with a Shadow first gear it trundles around town at walking pace with a complete absence of drama, which remains absent accelerating back up to warp speed.
My experience of self-generating electronic systems (like B-TH, or is it BT-H?) goes back to Femsa units on TZ Yamahas, and is that 1) the first sign of impending trouble is that they stop working and 2) the only cure is replacement.
They're rather like the little girl with the curl on her forehead:
When she was good, she was very, very good.
And when she was bad, she was horrid.
My experience of self-generating electronic systems (like B-TH, or is it BT-H?) goes back to Femsa units on TZ Yamahas, and is that 1) the first sign of impending trouble is that they stop working and 2) the only cure is replacement.
They're rather like the little girl with the curl on her forehead:
When she was good, she was very, very good.
And when she was bad, she was horrid.
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