Dear Karlos/Harit ji,
Recently and just by chance I happened to see this thread. I have gained some experience with magnetos the hard way, so I thought of sharing it with Team bhp friends.
You see, I have worked with and restored several vintage outboard engines, mainly Johnson and Elgin makes. These have two cylinders but distributor is not used, there is flywheel magneto, i.e. rotating magnets with two sets of ignition coils and CB points spaced 180 degrees apart. I think the advantage of this arrangement is that there are practically two separate parallel ignition systems, one for each cylinder, so if there is any problem with one, at least one cylinder will continue firing and get you home !
I also restored a Dutch cycle motor called Bernini M13, also known as 'The Egg' because of its egg shaped 1 litre fuel tank. This uses a Wico Pacy series 90 flywheel magneto, which was standard fitment in small engines in the 50's. This magneto had two serious problems- one that its permanent (Alnico) magnets had become weak after 70 years, and the magneto spark was too weak to run the engine. The second problem was that the ignition coil was burnt out(secondary shorted). I could not find anyone in Lucknow or nearby with the expertise or equipment required to recharge(remagnetise) the flywheel magnets. But I was able to find a very unorthodox, easy, cheap, and effective solution. I wrote to Mr Andrew Prattle of Globalnet, UK, and he was kind enough to add it to his website as my solutions may be of use to others. If you permit, I am quoting my letter below-
Bantamag update
by Akhilesh Agarwal
Dear Mr Andrew Pattle,
I am a retired mechanical engineer living in Lucknow, India, and have a lifelong interest in engines, vintage cars, clocks, and cycle motors. Over the years, I have acquired and restored a rare, hard to find Lohmann cycle motor to perfect running condition, as well as a Berini M13 cyclemotor. They are both quite rare and the ones I have may be the only ones of their kind in India.
The Berini I restored recently has a Wico Pacy Series 90 (Bantamag) magneto, which had some basic problems due to which it gave a weak spark, preventing the engine from starting. The major problem was weak flywheel magnets. I refer to Wilfred’s article on Wico Pacy Bantamag, which says there is no known solution to this problem. Since I have found a way around this problem, I would like to share it with you as it may be of use and interest to others. I am giving below a copy of a letter I wrote to my friend David, who lives in the UK, about my restoration work:
Dear David,
It is very kind of you to say that ‘failure’ is not in my vocabulary, but the story of the Berini is not without failures! I think I wrote that I had purchased it second-hand from a mechanic about 45 years back when I was doing my engineering. I fitted it on my bicycle and tried very hard to get it going, which it did on rare occasions, but I could not diagnose the faults correctly due to lack of knowledge and experience. The Berini was lost for 45 long years and rediscovered recently when I demolished our old house. The taste of my past failure was still fresh in my mind and rankled, so I wanted to restore it now to erase the stigma.
It proved to be easier said than done. It was not in bad shape mechanically. I replaced the bearings. Then I found the crankcase oil seal was damaged, and so was the rotary valve plate. Crankcase compression is vital in two-stroke engines because primary compression takes place in the crankcase before transfer to the cylinder. I purchased the required oil seals during a visit to, of all places, Singapore, and carefully lapped the valve plate/seat, thus resolving the crankcase compression problem.
The major problem was the magneto which gave a weak spark. Although a Dutch product (designed by German ex-DKW engineers), the magneto is made by Wipac, Bletchley, UK. I wrote to them but did not get any response. The magneto had multiple problems, making it hard to diagnose. Firstly, the magnets had become weak and no recharging facility is available. So I got around it by drilling holes from the outside and fitting Chinese Neodymium magnets. They are very strong and recharge the original magnets by induction. But there is a polarity issue. The original pole layout was unknown. Much research on the internet and study of magneto design and function did not clear the issue, I used my own logic. I followed unipole alternate polarity rather that dipole or tripole polarity more commonly used. The Neodymium magnets I used were of 10mm diameter × 10mmmm length. Round magnets are better because you can drill holes from the outside of the flywheel just up to the outer surface of the original magnets, fit the Neodymium magnets so they are in contact and fix them in place with Cyano Acrylate. The glue should be used only after getting the polarity right, once glued the magnets are impossible to remove! It does not matter if the magnets protrude above the flywheel.
Then there was an ignition coil problem. The original coil showed low resistance in the primary but OK in secondary, showing shorting in the primary. I took it apart but found it was not shorted, I suspect actually the secondary was shorted, but not detected by the multimeter! New coils were available in the UK for an unaffordable £50(the Berini was originally purchased for £2.50!). Secondary coils are very hard to rewind at home due to large number of turns of very fine wire, so I decided to use an external ignition coil. But that needs a power coil in the magneto to power the external ignition coil primary. Conventional wisdom says that the voltage induced is proportional to the number of turns, so I wound a home made coil of 450 turns compared to only 120 in the original, but it didn’t work well. I increased the turns to 600, there was slight improvement in the spark, not still not good enough! I had some wire left over, so I wound another coil of just 150 turns, based on a different design—two coils in parallel, the first power coil driving the primary of the external coil. This reduced the resistance from 1.5 to 0.5 Ohms. In this arrangement, called energy transfer system, power transfer is maximised. It is a slight modification to the original design, but it worked! The rest is history!
Here’s a video of the Berini running.
Please let me know if I can be any further service to you.
Best regards
Akhilesh Agarwal
Pl see the following links-
Technical back ground on Wico Pacy Series 90 magnetos-
http://www.icenicam.org.uk/library/W...structions.pdf
Global net website-
http://www.users.globalnet.co.uk/~pattle/nacc/arc0126.
Video of M13 running, please hear the purring sound-