My latest acquisition was a 2 HP model K Stover engine, in borderline "parts engine" condition complete with cracked head, broken rocker arm and frozen piston. Missing were one of the flyweights on the governor, gas tank, igniter, magneto and the entire magneto trip mechanism that attaches to the push rod. At first, I relegated this basket-case to the parts department. However, the more I looked at the 2 HP Model K Stover engine the more of a challenge it became to restore it, even though it is a common and not particularly desirable engine from a collector's standpoint. Not wishing to spend any money on it for missing parts, I decided to fabricate all those missing items and repair the broken ones. Upon disassembling the Stover engine I found the cylinder, rings, valves and bearings to be in quite good condition. I welded the head with Utectric wire, honed out the cylinder, ground the valves and lapped them in and fitted all the bearings. With a hacksaw, grinder and cape chisel, I fashioned a new governor flyweight from a cast iron pipe plug to match the existing one. The usual cleaning, sandblasting, painting and assembly followed.
Now, the ignition system and the main purpose of this article: at the various meets around New England, I have seen all sorts of Rube Goldberg ignition setups ranging from a wire rubbing on a bolt screwed into the cam gear, to elaborate and extremely cumbersome automotive distributor setups. Wipers rigged up to the valve push rod were prevalent. These, unfortunately, made contact both on the forward and return stroke of the push rod, causing an unwanted spark during the intake stroke. Most of these makeshift arrangements had no provision for advance or retard and many of them were unsightly as well.
About now I can imagine the hair raising on the necks of those of you who have thought out these various systems. Don't get me wrong, I am not criticizing your efforts to "make do." After all your engine is chugging merrily away and you are having fun and are proud of the results of your efforts. That is good and it is what this hobby is all about. Please accept my apologies as no offense was intended.
I have developed a non-authentic system that provides all the necessary functions, works extremely well, is quite obscure, is fairly simple to make, looks factory-made and in no way will butcher the original parts on the engine. Being a model T Ford enthusiast as well, I chose to go the timer and high tension spark coil route. Use of the timing gear shaft as a mounting base for the rotor lends itself well to the four stroke cycle engine. On a two stroke cycle, one would work off the crankshaft.
This brings to mind the many remarks made by various hobbyists relative to the poor quality of Ford spark coils. This is not true. They can be easily rebuilt by installing a new 0.5MF. capacitor rated at 400 volts minimum across the points. This can be accomplished by sliding the side panel off the box, digging out a little tar and soldering the new capacitor across the points, leaving the old one in place. Providing the secondary coil windings have not been broken, and installation of a new set of K-W points available at most antique auto parts houses, the Ford coils will work as well as any. Adjust the points to 0.032" clearance and an additional 0.005" on the cushion spring. Bend the rear point mounting platform up or down to attain a good, hot spark. I have had a set of these old rebuilt coils in my Model T for eight years and about 20,000 miles and have never touched them since they were installed. I have detailed instructions available for rebuilding these coils if anyone is interested. This I will grant, however; a nicely varnished and polished Kingston coil box properly mounted on the truck does have more asthetic appeal than a taped-up Ford coil lying on the ground beside the engine.
Back to my timer setup. First I shaped a spark plug boss from 5/8" mild steel and drilled holes to fit at the igniter opening of the cylinder. This was drilled and tapped for a 5/8" pipe thread Champion X sparkplug and provided with an asbestos gasket. Figure A-1 details the general setup for the timing mechanism.
The timer wheel (1) and wiper support arm (2) must be made of insulating material. I chose to use an old automotive fiber cam gear which I machined on a lathe to the dimensions shows: 2-1/2" O.D. x 15/8 I.D. x 1/2" thick. To the back of this disc I bolted a #14GA steel washer approximately 23/8 O.D. with a center hole bored to fit the engine timing gear shaft. A contact tab of #14GA steel 9/16" wide x 5/8" long was curved to match the O.D. of the fibre disc, inlayed into the face of fibre disc and welded to the #14GA backing washer. The whole assembly was then chucked in a lathe and turned to a smooth O.D. concentric with the center cam gear shaft hole. The unit was then slipped onto the cam gear shaft and the nut was tightened. (Timing will come later.)
A mounting bracket (3) and an advance lever (4) were now fashioned of #14GA steel. Dimensions must be worked out to suit your engine and give the wiper an arc movement of approximately 20° to 30° on the O.D. of the timer wheel approximately 1/2" for a 2-1/2" Ø wheel. The advance lever was pivoted with a rivet to the mounting bracket and the assembly bolted to the engine. The wiper arm (2) was made as shown of scrap fibre material left over from the auto cam gear used to make the timing wheel. One end was slotted to pivot freely on a rivet through the upper end of the advance lever. A thin strip of brass or old clock spring 1/2 wide was inserted into a hacksaw slot in the other end of the wiper arm as shown. I bent the end into a "U" shape as shown so it would ride smoothly on the face of the timing wheel. An undersized hole was drilled through the assembly and I turned in a machine screw, making sure that the screw made good contact with the wiper strip. Nuts were provided on top for attaching the low tension wire from the battery. A light tension spring (8) was now attached between the insulated portion of the wiper arm (2) and the advance lever (4) to assure positive contact between the wiper and the timing wheel. I now reassembled all parts to engine and made sure that there was sufficient clearance between these protruding parts and the engine flywheel. For this reason all parts must be kept as thin and as close to the original engine parts as possible. After checking for free movement on all linkages, the assembly was wired up to a battery and a good working spark coil. The entire assembly was now nothing more than a rotary switch between the battery, spark coil and back to ground at the engine through the cam gear shaft. The next step was to time the engine ignition.
First, one must find the inner dead center up on compression stroke. To do this accurately I made a cardboard disc about 12" in diameter marked off in degrees with a 0° point and 50° either way from this mark and a 180° mark to indicate outer dead center. This disc was slipped tightly over the engine crankshaft and a pointer was attached at some convenient solid point on the engine. Inner dead center of piston travel was located with a dial indicator attached to the cylinder with the head off or with a pointer arrangement through the spark plug hole. After locating true inner dead center the cardboard disc was then rotated on the crank shaft until the 0° mark lined up with the pointer. I secured the disc with tape so it would no longer rotate on the shaft. At this point the crankshaft could be moved and easily returned to inner dead center point by lining the pointer up with the 0° mark on the degree disc. I turned the crankshaft in the direction of rotation until the piston came in on compression stroke and continued past inner dead center stopping 1° to 5° after the 0° mark on the degree disc. I moved the timer lever arm (4) back to a retarded position and marked the bracket (3) with a scribe. I loosened the timing gear shaft nut and rotated the timing wheel (1) counter clockwise until the wiper (5) just contacted the steel tab on the wheel and the coil buzzed. I tightened the cam gear shaft nut, making sure that the timing wheel did not move. I checked the timer contact again by backing off the crankshaft and rotating it again toward the firing point until the coil buzzed. I checked to see if the pointer was 1° to 5° after inner dead center on the degree wheel. When I determined that the timing was okay, I drilled and tapped through the timing wheel backing plate into one of the cam gear spokes for a 10-32 locking screw (7). I installed a stop pin (6) in the bracket (3) to locate the full retard position of the lever arm (4).
To locate advance position I backed the crankshaft up, then rotated in the normal direction with the piston coming in on compression stopping at 15° to 30° before inner dead center on the degree wheel. I then moved the timer lever in the advance direction until the coil just buzzed and scribed the face of the bracket. I checked the location by backing off the crankshaft and rotating it in again to see if the coil buzzed at the proper point on the degree wheel. When it was okay, I installed a stop pin in the bracket as before.
I now had a completed custom igniter assembly. I removed all parts and painted them to match my color scheme. I reassembled the parts and tested them once more to be sure I would not break an arm when the engine fired for the first time. I removed the degree card and pointer and installed the flywheel. The timer device was neatly camouflaged behind the flywheel. I ran a small brass push-pull rod (9) out to an inconspicuous but convenient location to facilitate advancing and retarding the spark.
Have a happy season making smoke rings and, who knows, I may spot a homemade timer like this at one of the upcoming meets this summer.