(GASP) I’m actually going to continue this series! A whole year after the engine was completed! Crazy huh?
Well since I’ve waited such a long time, I am going to have to resort to looking at my pictures and trying to remember what I did. Hopefully I don’t leave out too much good content!
By “Upper Assembly” I am going to refer to the parts that are left to be written about: crank case cover, head and valves, rocker arm, mag, valve rod and ignitor. This will be a loooooong post.
When I removed the head, it had a fair amount of rust and sludge buildup inside the water jacket. Using a hefty piece of wire, I was able to scrape it all out and blow the dust and loose chunks out with a compressor. Other than the water jacket, the other critical part of the head is the valve seats and guides. I checked the guides for play and the valves did not wiggle enough to worry about so I started into grinding them.
Grinding valves is easy to do on an antiqe engine- no crazy equipment or computer controled cnc machine. The only things needed are a valve grinding tool and a can of grinding compound. If you don’t have a valve grinding tool a screw driver can be used if the valve is slotted, or make your own tool that can be twisted between the palms of your hands as if you were trying to start a fire with sticks.
On the right is a picture of the job half complete, on the right is the unground valve and seat, and on the left is a seat and valve after grinding. On the unground seat you can see some pitting and surface flaws that will not make for a great seal. The left side is a mostly completed valve and seat. Most, if not all, of the pits are gone, and for the few pits left there is plenty of valve seat surface around them that no compression will be lost.
To start the process, a small amount of course grit grinding compound is applied to the landing on the valve. (For clarity, the “landing” is the area of the valve that contacts the valve seat. I’m not quite sure that is the proper term- and I’m too lazy to look it up- so you can comment freely and let me know what the proper term is.) A spring is placed over the valve stem and the valve is inserted into the guide so that the spring keeps the valve off of the seat. Using the valve grinding tool, apply light force to the top of the valve to bring it in contact with the seat while grinding. This force to use could be compared to an average-sized school textbook, 2-3 lbs at most. If using a screwdriver or manually grinding, the valve should rotate about half a turn one way, then slightly more than half a turn the other, a few times a second. The valve should turn back and forth, but rotate slowly overall so that all parts of the valve landing grind all parts of the valve seat. When properly ground it should look like this.
Click here for the valve grinding gallery.
Once the valves were ground and reinstalled in the head, the head bolts and studs were cleaned up with a tap and die, and the head was torqued down on to the block. I didn’t use a torque wrench, but I probably put between 40-60 ft-lbs on them. With the head installed, the rocker arm could be installed next- but it had to be repaired first.
The rocker arm is a lever with a yoke on one side that attaches with a pin to the push rod, and the other side has an adjustment screw that depresses the exhaust valve. The intake valve is actuated by the vacuum created by the piston and held closed with a light weight spring. The problem with the rocker arm was that one side of the yoke was broken off and missing completely. In that picture I already ground down the broken portion in order to braze a new piece on.
I chose a piece of steel bar (no idea what alloy or composition) from my grandpa’s abundant stock piles of old random rusty pieces and cleaned it up. I ground it to be about the same profile as the lower yoke piece and drilled a hole in it. Luckily my grandpa had a second engine that I was able to measure for the proper yoke spacing, and I used a bolt and stack of washers to hold down the new yoke end in the proper position.
With the new piece held in place I brazed it with an oxy-acetylene torch. I checked the brazed part for fitment before finishing it with a grinder. I left enough material that I was able to grind away to leave a small boss on the top to mimic the boss on the bottom of the yoke. After finishing and painting it, it is almost indiscernible from the original. Only a trained eye could tell that it was repaired and not a completely cast piece. I don’t have a close up picture, you’ll just have to take my word for it!
After finishing the rocker arm, I was able to install the ignitor, ignitor trip assembly, and push rod. The ignitor was luckily functioning quite well, and didn’t require disassembly or repair. I say this is lucky, because this is not a part that I would have been able to easily repair. I cleaned it in mineral spirits and painted and installed it. The ignitor is an interesting piece of equipment in that it was used to create the spark inside the head prior to the invention of spark plugs. It functions by having a set of points inside the head that are sprung closed. The ignitor trip assembly preloads a second rotating mechanism on the outside of the head, and at a timed point, releases this rotating mechanism. It snaps to rest, impacting a rod connected through the head to the points causing them to open for a split second. This is timed to coincide with the magneto’s ignition point. The magneto is a small permanent magnet generator with a hefty coil assembly. During ignition, the magneto is “generating” the maximum current through the points in the ignitor. By snapping these points open the magnetic flux in the coil collapses, causing a voltage increase within the coil. This increase is on the order of tens of thousands of volts, easily sparking across the points of the ignitor and igniting the compressed gas mixture in the head. This is a very simple design because there is only a single coil, not a primary/secondary coil as in today’s ignition systems. If you are interested in different ignition methods, I highly recommend researching antique engines. There are quite a number of ingenious designs prior to battery powered ignition systems. Most of these systems (spark plug based) are still used in small engines powering lawn mowers, weed-whackers, and other small battery-less engines.
The magneto I left to more capable hands. I removed it in the beginning and sent it to a guy that my grandpa knows who overhauled it for $100. Well worth the money for a properly functioning mag. I installed it with the timing marks on the cam gears and it functioned beautifully.
The final piece of the “upper assembly” is the crank case cover. There is not much to it, other than a rather intricate gasket and a breather. The breather was nothing more than the bottom half of a grease cup. My grandpa had a new grease cup top that I was able to use. I drilled holes around the side of the top without drilling into the thread. I then put brass screen on the inside to keep large particles out of the breather. I also put a large ball bearing in the bottom of the cup to act as a one-way valve. This ensures that the crank case is negatively pressurized while the engine is running. Without this valve the engine would alternate blowing and sucking outside air in through the breather. This is more effecient, however there is a large chance that dirt and debries can make it past the breather filter and into the crank case. By negatively pressurizing the crank case, oil is also less likely to seep out of any gaskets. The downside is that there is a chance that a loose piece of gasket gets sucked loose into the crank case. I’ll have to monitor it over time and see if my fears are warranted. I can easily remove the ball bearing and pack the breather with filter material.
That’s it for this episode. Last up is the carborator rebuild and first run! Hopefully it won’t take me another year to write those!