What is the best thing to do when you run into an obstacle on a restoration project, and you don’t know exactly how to proceed? Do nothing, as this is the time to step back and figure out a way to take the pieces apart without causing more damage. Disassembling mechanical components or any parts of a car that have been subject to 100-years of corrosion and are locked together is one of the toughest parts of the job. The 1914 Simplex 50 h.p. Model “F” Long-Stoke Speed Car engine being rebuilt here at The Old Motor for The Collier Collection turned out to contain a very big “what do I do now” problem.
To start at the beginning of the story, in 1913 Simplex changed the design of its T-head cylinders from using one spark plug over each valve (two) in a cylinder to one plug centrally located directly over the piston. The reason for the change was the low octane fuel of the time became even less potent starting in the early teens when more kerosene was added to gasoline to make it go farther due to shortages. At one point in time, much of it was a fifty-fifty mix.
- The lead photo (above) shows one of the T-head blocks with a spark plug well removal tool.
- Simplex T-head blocks with the centrally located spark plug wells at the top. 1912 and earlier engines used two spark plugs in each cylinder located in a large port plug that threads into each of the large openings seen on either side of the casting.
In these engines even with two plugs per cylinder, the poor fuel was causing a spark knock problem. Simplex found that with one central plug, combustion occurred faster, eliminating the problem. The plug well being surrounded by water also resulted in better cooling for the spark plug that further helped to eliminate another preignition problem, an overheated spark plug.
The casting was redesigned to take a single upside down hat-shaped spark plug well that was machined from alloy steel seen (below). During the normal service life of the engine, the well remained removable but with long use and exposure to coolant it can cause a major problem for restorers.
The bottom of this well is threaded into a tapped hole in the middle of a boss on top of the cylinder head. It is sealed by a copper washer between the two parts that can withstand combustion pressure, and at the same time keep coolant out of the cylinder. At the top, the well passes through a machined hole in the water jacket in the casting where is was originally sealed by Oakite to prevent external coolant leaks.
In time as you will see, this well with a wall thickness of only 3/16-inch, will rust through causing a leak. Two of the four wells had a leak through this sidewall and a third one was leaking from the seal on the top. Past experience with other Simplex engines has shown that many of these wells are close to rusting through or are leaking.
- This illustration of a T-head engine clearly shows two large port plugs located above each valve.
The problem we faced in removing them is caused at the top of the spark plug well where it passes through the outer water jacket. Coolant gets between the two components and both rust in time with the corrosion continuing to expand and lock the two parts together. Rust that forms between two parts that are saturated in water, in time grows in thickness and exerts extreme pressure between the two parts. This pressure is what locks the two parts together and makes it impossible to separate them.
The usual remedies to soak the offending area in penetrating oil will not work because there is a seal at the top of the well to keep coolant from leaking out. The rusted area is just below this seal and the oil will not seep through it. Even if you were able to get it in there it would not help because the problem due is due the expanded rust.
This leaves four other methods to try: moderate heating and rapid cooling of the inside of the well to try to break the bond, shock from the fabricated spark plug well tool with an impact wrench, heating the casting around the well, which would likely cause it to crack, and finally brute force. The last two are not an option as the odds are either will cause damage to the cylinder castings.
This leaves only two options neither of which will work for any great length of time: patch the areas that are rusted through and continue to do so in the future, or insert a sleeve that in use has been found to continue leaking at the bottom. The long-term fix is to machine the wells away on a milling machine and make new ones that will eliminate the problem.
Rather than risk damaging the castings the last option was chosen. The first step (above) is to center the well precisely to within two thousands of an inch with the spindle of the milling machine by using a dial indicator. This center location was then entered into the machine’s digital readout to record it for later reference. Step two (below) involved machining the top of the flanged well off with a milling cutter.
This milling machine is twice the size of the normal Bridgeport mill and was chosen because it is often used to machine new replacement parts. In the past, it has been used to machine new: engine block castings, crankcases, chain-drive transmission and differential cases and other large parts.
These cylinder castings are quite large (it’s a 600 c.i. engine) and measure 16.5-inches tall. The mill has twenty plus inches of room under its spindle, but, in this case does not leave enough room for a conventional boring head and boring bar.
A little more innovation was in order, and the short fly cutter (above) was quickly converted into an adjustable boring bar. This was done by clamping a square steel block with a set screw in its center into the back end of the tool slot. After loosening set screws holding the cutter bit, this allows the set screw to advance the cutter bit for successively larger cuts.
Next the spark plug well was moved back to the center position recorded earlier, and a light cut of .010-inch (three times the thickness of writing paper) was bored down to the flange at the bottom with the cutter. This first small cut on all four of the wells broke through to the heavily rusted outside diameter, demonstrating just how thin they were.
After all four of the wells were bored out, all that remained was the bottom flanges seen (above right and below). Two 3/8-inch counterbored holes were then cut into this flange, and the tool on the left was machined and two corresponding pins are pressed into the bottom of it that fit into the holes in the flange. With a 30-inch long wrench, the flanges then came out fairly easily.
After removing all four of the flanges, and cleaning up all of the associated areas in the blocks, the new spark plug wells (below) were machined. A high strength and temperature resistant stainless steel alloy was chosen for the new pieces. A soft copper washer will again seal the bottom of the well to the cylinder head, and a temperature resistant (400 degrees) viton rubber O-ring will seal the top.