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jdunmyer
06-21-2010, 04:21 PM
What's a good material for making ignitor points for make & break ignition systems? We've always used Nickle welding rod (for welding cast iron) to make the points and been pretty sucsessful, but the Star is driving me crazy. The problems are almost certainly the ignitor.

I chatted with one fella a CoolSpring PA this past week who uses Tungsten, but a buddy tried that and said he couldn't machine it, and couldn't peen it into a hole in the ignitor lever. Dunno if it'll silver solder or not.

As you gas engine experts know, problems can easily be seperated out to be one of three things: Ignition, Carburation, or Something Else.

JCHannum
06-21-2010, 04:31 PM
I silver soldered the tungsten from a set of points to the moveable point for the ignitor on my half scale Deere engine & used SS welding rod for the fixed. I have a good spark, carburetion is not the best as we were talking about the other day.

gbritnell
06-21-2010, 04:32 PM
Either use a piece of tungsten from a TIG welding electrode or get an old set of ignition points and use the tungsten from them. Yes it will silver solder. If you use an old set of points it's virtually impossible to unfuse the tungsten from the point arm so just cut it off, silver solder it to your arm and then grind away the excess material.
gbritnell

Fasttrack
06-21-2010, 06:32 PM
Plus one for brazing (silver soldering) tungsten welding electrodes. That's a popular choice among tesla coil enthusiasts where rotary spark gaps have to handle high voltages and extremely large currents. You won't be able to "machine it", even grinding it can be a challenge but it works well for contacts!

darryl
06-22-2010, 01:40 AM
Probably wouldn't be good enough for this app, but I've hacked common light switches to use the contacts in other applications. Switches are cheap, and the contacts are some kind of appropriate metal.

Evan
06-22-2010, 02:37 AM
Copper/silver alloy works very well. I made a battery switching assembly for my electrotrike using contacts made from sheet Triflo silver solder. It is a 50% silver/copper alloy on the outer layers and is showing no burning switching over 100 amps at 48 volts. It is the actual recommended alloy for high current contacts that arc because of inductive loads.

jdunmyer
06-22-2010, 07:27 AM
Perhaps some points out of a motor starter or heavy-duty relay?

Evan
06-22-2010, 07:42 AM
Sure, they should work. The reason that copper/silver alloy works so well is that even if the contacts become burnt they still work because silver oxide is just about as conductive as pure silver. Pure silver is a poor choice though because it will easily vaporize when arcing while copper does not.

Another possibility is to use graphite to copper. It works fine in electric motors. To maintain the correct clearance the graphite contact should be spring loaded against a stop.

Whichever material you use the contact should be arranged to provide a slight wiping action when it closes and opens. Imagine contacts on parallel arms on separate side by side pivots at the same end. Push one against the other and continue a slight amount after contact and they will wipe.

Duffy
06-22-2010, 08:37 AM
How about coin silver? A Canadian dime or quarter are 85% silver, if pre-1967. I think that older US coinage is 90%. And spare us all the prattle about defacing coinage; it only had meaning when the coins had intrinsic value. Now they are just tokens and anyway a dime will make your points and wont affect either the balamce of payments OR defecit.

Evan
06-22-2010, 08:54 AM
Not enough copper. The copper prevents fast erosion of the silver. The standard alloy is 50/50 as I said. I suppose it would work well though if the short lifetime isn't an issue. It might cause a problem from the vaporized silver plating nearby surfaces, which it will. It has a particular affinity for steel.

BTW, defacing coinage isn't illegal unless intent to deceive can be proven.

JCHannum
06-22-2010, 10:23 AM
When I was resurrecting a Fairbanks Z engine I asked what to use on the Smokstak board and was told to just use a nail. I did and it worked. I cannot attest to it's longevity, but it worked reliably as long as I owned the engine.

These are not exotic systems as they were among the first electric ignition systems. The Deere plans called for tungsten and that is what I used. Any good conductor should work initially as long as it is clean and has good contact. The more exotic materials will hold up better in the long run. My biggest problem with the Deere engine was getting a good contact and a good snap to separate the points. It can't be sluggish when it trips.

What are you using for a coil?

Herm Williams
06-22-2010, 11:30 AM
I use dimes in mig welders (hobart) they switch 100++amps about four years with eight or ten hours a day use before being vaporized. go to globalspec type in repaceable relay contacts. last time I checked alot were listed.
re

jdunmyer
06-22-2010, 08:55 PM
Jim,
I'm using the coil I got from Debolt, it's a custom-made choke. We've experimented with lots of different inductors in an attempt to duplicate the performance of that coil and haven't really been successful.

Mind you, this Star is our third engine, and all use similar ignitor points. In fact, the Olds is nearly identical.

Observing the ignitor when it's out of the engine, I noticed that when the points just close, I can see a bit of "sizzle" at the contact point. The points are closed by a tripper that cocks a spring, and that spring seems to not apply enough pressure to have the points make real good contact. In fact, putting an ammeter in series verifies that: the meter will show NO current when the points first close and will finally show close to "shorted" just before the tripper slips off to fire the engine. The points are naturally sooted up from the combustion process, but no more so than my other engines. Although a wiping action would be nice, I don't see how to implement it.

I've had limited success with rotating the points a few degrees to get new surfaces in play, but am not getting a lengthy run out of the "new" points. The points consist of 2, 1/8" diameter nickle welding rods, about 3/8" long, situated at right angles to one another. One is fixed and insulated from ground, the other is mounted on a pivoting shaft so as to touch and snap away from the first one. Go to: http://bbs.homeshopmachinist.net/showthread.php?t=41522&highlight=Star and you can see a pic of the ignitor; insulated point on the left, pivoting point shaft on the right.

I just thought of something that I'll try: maybe the movable point isn't being grounded well enough through just the shaft in the ignitor housing. It should be easy enough to afix a wire to the shaft and connect it to ground.

The engine ran fine during its first show, maybe putting 25 hours on the clock. When at Coolspring, PA this past week, it started acting up, and I'm having little success in getting it going reliably again. It's going to Wauseon, OH tomorrow, and I'm hoping to run it for the usual 30 hours or thereabouts. If you get out there, I'll be in the Model Building behind the grandstand.

Evan
06-22-2010, 09:15 PM
If you have a piece of sterling silver that can be scrapped without causing a "problem" then try replacing the points with that. You can also use graphite from a standard non rechargeable D cell battery centre electrode. Graphite will reduce the current surge as the coil is charged but will break the circuit just as fast as any other conductor. That may actually improve the spark.

JCHannum
06-22-2010, 09:36 PM
I am sure you have more experience with these than I do, seeing the success you have had with the Olds particularly. A lot of modelers dispense with the ignitors and go to a spark plug because of the problems with getting the small ones to work, they are touchy.

I played with the Deere for quite a while before I got it working. I even resorted to working in the dark to see the spark. Your sizzle might be a sign of a problem. I have a pretty good assortment of music wire if you want to try winding a stouter spring.

Just another thought, what kind of compression do you have? I seem to recall somewhere that too high of a cylinder pressure can also have an effect. As I recall, someone solved his problems by taking a cut off the piston top to reduce cylinder pressure. I don't know if I saw this on HMEM or Smokstak.

I'll probably be going to Wauseon Friday, the Model Building is always my first stop.

EddyCurr
06-22-2010, 10:24 PM
Observing the ignitor when it's out of the engine, I noticed that when
the points just close, I can see a bit of "sizzle" at the contact point.

I've had limited success with rotating the points a few degrees to
get new surfaces in play, but am not getting a lengthy run out of
the "new" points.Is there an appropriately sized condenser in the primary side of the
ignition circuit?

.

Evan
06-22-2010, 10:25 PM
Just another thought, what kind of compression do you have? I seem to recall somewhere that too high of a cylinder pressure can also have an effect.

Definitely. The higher the pressure the higher the voltage it takes to make a spark. It also affects the timing since it takes time for the voltage to build.

jdunmyer
06-23-2010, 09:31 AM
Is there an appropriately sized condenser in the primary side of the
ignition circuit?

Eddie,
There is no condenser in a make & break ignition.



A lot of modelers dispense with the ignitors and go to a spark plug because of the problems with getting the small ones to work, they are touchy.

Jim,
I'm aware of that, but prefer the ignitor. The Vaughn has nearly 800 hours on it and has had the ignitor rebuilt maybe 3 times, the Olds has had the ignitor out only once in over 900 hours. Of course, the Olds has a blockout, so the ignitor only operates when it's going to fire.

The compression shouldn't be "too high", but we did make the piston slightly taller than called for. I think it's something like .100" taller, so that shouldn't affect it much. The problem appears to be failure of the points to make good contact every single time. I'm unsure if it's due to soot/carbon buildup or the slight burning that takes place naturally.

Interestingly, the Olds gave me trouble while at Zolfo Springs this past Winter. Although it passed the "knife switch test", the engine simply wouldn't run. I pulled the ignitor and found a slight groove worn in both the fixed and movable points, so I rotated them about 90* to get a new surface. The thing started and ran great, and I have no good idea as to why.

Will do some more experimentation this w/e.

EddyCurr
06-24-2010, 12:53 AM
Eddie,
There is no condenser in a make & break ignition.Why not?

Ahh.


GAS ENGINE IGNITERS (Make and Break) (http://www.old-engine.com/magign.htm)

An igniter is made up of a set of mechanical points, much like the
points in early vintage automobiles, except they are located INSIDE
the combustion chamber. One side is insulated, the other side is at
frame ground and they are mounted to an assembly that PROTRUDES
INTO the combustion chamber. A capacitor (condenser) is NOT used
across these points because sparking across the points is WANTED,
unlike in a car where the heat and metal consumption of sparks would
wear away the surface of the points needlessly. When the igniter
points "make" or close, a current will build up in an inductive coil that
is in a series circuit. Then at the appropriate time, the points "break"
and an inductive "kick" causes an arc to draw across the opening points.
The gap opening is about 1/16". Even battery voltage itself will cause
a small spark, but the more coil inductance that is in series with the
points and battery, the hotter and bluer the arc created.

.