I 've been compiling these articles for almost three years now, and so far I've carefully avoided one particular subject: Magnetos.
That's because all the firsthand knowledge I have about this harmless-looking component was gained long ago when I witnessed an incident involving my husband and his brother while restoring their first engine. As they examined the magneto closely and tested it out, our dog had the misfortune to be standing a little too close. There was a small blue flash, followed by a shout of surprise from the human members of the group while the canine one yelped and shot to the far end of the garden - where he remained shivering with fear for some time. He's a very intelligent dog, and I decided to take his advice on this one.
Thanks to his wise counsel, I've never fallen for the 'just hold this wire while I make a test' trick, but when it came to choosing a subject for this month's article, he was more interested in his biscuit box than offering constructive suggestions. But, given that the advice on the Stationary Engine List came from two of the most respected sources we have in our group on the subject of igniters and magnetos, namely Ted Brookover and Bill Lopoulos, I decided I would be safe in pursuing this subject.
With something of the same feeling of trepidation I had beginning this article, the question that started this all came from someone taking his first serious look inside a magneto.
I've decided to venture into the world of electromagnetic flux and disassemble an igniter and Webster magneto. This one got real wet, and the igniter was puffing around the rotating shaft, too, so it seems like a good thing to jump into it.
I successfully fixed the leaking shaft with a dab of valve lapping compound and some oil on the tapered fit. Next, I thought I would take one of the end plates off the Webster to see what makes it tick and to check for a damp coil(s).
I decided the spring end might be the best end to remove. I pulled the springs off and was surprised to find that the spring rocker was not located at magnetic center. In other words, the pins on the spring rocker are not horizontal when the poles and coils line up to their natural magnetic alignment.
To get the end plate off I need to remove the spring rocker. Is this a tapered, self-locking fit? Mo pins or keys? When I reassemble this, should the spring rocker be aligned with magnetic center, or is there some special angle at which it should be installed?
The first response was from Ted:
Try moving the movable electrode in the igniter side to side. If there is any movement at all, you might as well fix it because the mag and the igniter are going to be out of time. The magneto inductor has a woodruff key on each end of the shaft to locate the spring arm and the push finger. The keyway can be hard to find if the key is sheared off, but it is there. - Ted
Judging by the feel of it, I would say there is 0.002-0.003 clearance between the movable electrode and the igniter body. Is this okay?
When removing the spring arm and/or the push finger, is this fit a tapered fit or a cylindrical press fit? I had no luck removing it last night, but I am treading gently. I may need to make a small puller.
If side-to-side movement is visible, it is too much. The problem is that when the push finger on the magneto is released and strikes the movable electrode lever the first - and only - movement should be a rotary one that opens the points. If the shaft is worn, the first movement of the movable electrode shaft when struck will be lateral (to take up the wear) and the second movement will be rotary (to open the points).
Unfortunately, peak voltage in a Webster only occurs for a fraction of a second, so by the time the secondary movement of a worn shaft opens the points, the voltage peak has passed. It is at this point that many Webster mags are declared junk; and out come the batteries and coil.
'It must be the mag, the engine runs fine on a battery and coil.' That's what I hear all the time. Sure it does, the voltage from a battery and coil is constant and controlled by the points making contact and breaking contact. The really sad part here is that every time a Webster rig fires on a battery and coil, it suffers damage! The points on Websters are soft (as are all low tension magneto points) and the voltage of a battery and coil will burn them.
Every time the rig fires with that coil lying right under the magneto it builds a huge (several feet in diameter) magnetic field. If that field is strong enough, and if the polarity is opposite that of the magnets on the magneto, the magneto magnets can suffer. Disconnecting the wire does no good; this is magnetism not electricity - they are as different as air and water.
Yes, you must use a puller on the spring arm and the push finger. They are a tapered fit with woodruff keys and the side plates are very fragile. - Ted
I have found the battery terminal puller available from Sears works very well. Of the countless Websters I have serviced, only one or two have been so stuck that this puller will not do the job.
You want to back the nut off the shaft until it is flush with the end of the shaft (this is to protect the threads when the puller is attached). Put on the puller, tighten the jaws, then tighten the puller lead screw. You will need to give the end of the puller several sharp raps with a hammer to loosen the push finger/return arm/bump arm. When pulling the ends off the armature shaft, be careful you don't crack the pot-metal bearing plates.
When rebuilding an igniter with a worn movable electrode you frequently have to replace both the shaft and the seat/guide. This ensures a good seal. Make sure you cut a 45-degree seat on the electrode after replacing the shaft. After cutting, seat the electrode with valve grinding compound. - Bill
The 'professionals' are not the only ones to take a look inside a Webster.
I completely disassembled my Webster, removing (very carefully) the coils off the iron cores. I also removed the oil wicks and cleaned them. It went back together easily. By the way, I also checked the armature to make sure it hadn't contacted the fields.
Ted, adjusting the movable igniter contact on mine doesn't seem to make any difference. It seems to run okay, especially after I got the cam gear timed in the general ball park. Is there any way I can put a meter or something on it to tweak it?
Also, I just remembered that pushing in against the spring on the moveable contact scrubs the contacts clean. I read that somewhere. I try to remember to do that before starting my Galloway. I've also got to find a better way to lube the moveable shaft.
Use new lock washers. The one on the moveable contact on mine was tired and the nut came off after running for 15 minutes. I got new hardware, new rollers and a new trip lever.
Do your magnets bottom out on the laminated sheets? On my two-magnet Webster the outer 'U' magnet is about 1/8-inch from touching the laminates. Finally, I would advise checking the north/south alignment on the magnets with a compass in case someone has turned them around in the past. - Rick
It is the inside face of the magnets touching the laminations that counts, not the bottom edge. Most multi-magnet Webster mags have a small gap at the bottom. -Bill
Thank you all for the Webster and igniter tips. I'll pick up that battery terminal puller on the way home tonight. Can't wait to see what's inside!
One of the fun aspects of communicating by e-mail is that things get updated quickly, and by the following day we heard how the project was going:
Picked up a battery terminal puller last night and removed the spring arm and disassembled the Webster. Pretty simple in there -just two coils and the rotor. Why are there four poles on the rotor when only two are ever used?
I de-oiled everything and disconnected the ground on the coil set and checked insulation leakage - it measured infinity on the megohm setting. Total coil set resistance is about nine ohms. Is this about right?
The bushings in the end plates were in good shape, so I put her all back together and got a pretty blue spark again. I put it back on the engine and fired it up late last night.
I didn't mess with the set-screw adjustment on the igniter arm the trip arm hits because it is working so well. Is this gap setting a constant on all Webster/igniter setups? What should the setting be, or is it simply 'tweaked' to give the best spark? Thanks again for all the great support.
I'm not sure what the narrow poles are used for. They might act as magnet keepers in case the armature snaps too far, which would allow the magnets to partially discharge. As for the bump arm setting, I have seen some literature say it should just touch the push finger. Some literature says there should be a 0.010 gap. I would just adjust for maximum spark.
Nine ohms is about right for coil resistance, but I would never expect there to be a break in the coils. The way that they fail is two-part. First, the varnish insulation cracks and they spark between layers when the voltage builds up. Second, they spark through the insulation on the wire that goes to the terminal block, again due to cracks in the insulation. You will never be able to detect these problems with a meter. I always just replace the coils. You go through so much work disassembling the mag, you should just put in new coils, especially with type M and MM mags - those coils are never any good. Type K and L coils aren't too bad. Regardless, if you remove the coils for any reason don't even think of putting them back in, because disturbing them results in too many cracks in the insulation. - Bill
So, there you have it, the advice of experts. And if this article isn't helpful, just blame the dog!
Engine enthusiast Helen French lives in Leicester, England. Contact her via e-mail at: Helen@insulate.co.uk You can join the Stationary Engine List on the Internet at: www.atis.net