Nothing new with the 1958 Tomahawk. So many other projects going on right now.
But the Interceptor has been getting some much needed attention. It quit running on it's maiden voyage. Turned out to be a failed magneto.
I'm clean out of usable magnetos, and I don't want to run up my credit card again until I've got it back to a zero balance. So I have to get creative.
There's this little Lucas DKX2 distributor, which came off the Tomahawk. I'd been planning on installing one of my K2F magnetos on that bike when it's ready for an ignition system. I like being able to run with no battery and a dead alternator, given the record I've had with those Lucas alternators.
Now I've got to get two of them refurbished or replaced with one of the electronic ignition replacements. That will happen, but not for awhile.
In the meantime, I need to get the Interceptor running. It's been sitting since early June, when it quit running.
I have to find a place to put a battery in my modified battery box, which was chopped up years ago to accomodate some air filters. I haven't ever had a battery in that bike since I first got it, and years ago, decided that it needed air filters more than space to put a battery, so I altered the box so that some air filters would fit.
The solution, now that I need a battery, is to find the smallest sealed battery I can find. The one I ended up with, from Batteries Plus, measures one inch by two inches by three inches.
It only puts out 2 AH at 12 volts. Not much, but it will at least live long enough to get the motor running.
Then I needed a coil. That was easy, I bought a 6 volt coil from one of the Domi-Racer sale catalogs years ago.
And a switch. There's a Lucas "long arm" light switch that came with the Tomahawk which looks like it will do the job, and has nice screw-terminals to connect to. I found another one just like it on ebay for $28.00.
This switch is set up so that it has three positions; OFF, LOW, HIGH. I found that I could bring the main 12V line up to the center of the switch, then connect the headlamp (no high/low, just low beam) to the 3rd terminal, and the ignition coil to the second terminal.
With the switch in the OFF postion, it's not making contact with either the 2nd or 3rd terminals, and power is disconnected completely. Switch to the LOW position, and I get power only to the ignition coil, and switched to the HIGH position, I get power to the ignition coil and the headlamp. Perfect.
The next trick is to find a ballast resistor to reduce the voltage seen by the coil down to 6 volts to limit the amount of heat it dissipates. I found a nice 2 watt resistor with a cast aluminum body forming a finned heat sink. Checking the resistance through the coil, I find that it's exactly 1.8 ohms. Almost a perfect voltage divider, maybe just a little more dropped across the coil than the resistor, but pretty close.
I connected the coil, resistor, and distributor up to a large battery charger with an ammeter, and found the total current draw was a bit less than 3 amps, with about 4 volts dropped on the resistor, and 5 point something dropped on the coil.
On twisting the distributor, I got a nice, fat spark out of each sparkplug. I left the whole thing connected to the charger for about an hour with the points closed, and checked the resistor and coil periodically to see how warm they got.
They both seemed to reach a maximum temperature that was reasonable; I could pick them up without burning my fingers.
In looking around for a way to install the resistor, I came across a piece of 1 inch aluminum angle "iron". This could mount to the vertical piece inside the battery box which holds the battery strap in place (which I'm using to hold the ignition coil in place, because the battery is now in the other side of the box). I pop-riveted the resistor to this, and hooked everything back up to the battery charger. The resistor was now running noticably cooler, while the aluminum drew heat off of it.
Another issue with this setup is that the K2F magneto on Royal Enfields is driven by a double row chain, while the KDX distributor is driven by a single row chain. Both chains seem to have the same pitch, but the sprockets don't align, and in addition, the distributor drive sprockets are smaller than the magneto drive sprockets.
This means I have to use the Tomahawk's intake cam sprocket, because the intake sprocket also carries the ignition drive sprocket.
Also, on inspecting the single row chain that came out of the Tomahawk, I found one link plate had broken. This bike was parked just before a major failure, apparently. I don't seen how that chain could last 10 minutes in a running engine.
Fortunately, those are available from Hitchcock's in England. While I ordered that, I decided to get a new timing chain as well. The one I had in there is pretty stretched.