Notes from Speedwell Garage...

That is not opportunity knocking...

As part of their efforts to keep up with the horsepower race, Packard increased the compression on their engines for 1953. An 8:1 compression ratio is not much for a modern car, but it is getting to the top end of what can be conveniently achieved on a flathead without incurring the problem of spark knock, also known as preignition. As a result, many '53 cars are prone to knocking, and the problem carries through into '54.

Preigniton is caused by hot spots in the combustion chamber igniting the fuel/air mixture before it is time. This usually causes an explosion in the combustion chamber, instead of a controlled burn. The sound of this explosion is like hitting the cylinder head with a hammer. You will notice it when pulling hills, or when accelerating sharply. Preigniton is destructive to the pistons and rings, and decreases the efficiency of the engine.

These hotspots in the combustion chamber come about from either a buildup of carbon, or by hindered cooling. (On the very high compression 359 engines, Packard used an aluminum cylinder head for improved heat transfer away from the combustion chamber.) Sometimes one can forestall knocking by switching to a better grade of gas, or by retarding the timing a bit. This is a bit of a pact with the devil, ^,cause either way it will cost you more--setting the timing back on these straight eights cuts the performance and the gas mileage.

I recently had in a '53, which had a horrible problem with knocking, even on premium. When I tore the engine down, I expected to see a lot of carbon in the head, but did not find it. What I did see, when looking in through the thermostat hole was a lot of calk, that is, deposits left behind from years of running hard water in the coolant. This is the same problem that you have from time to time with your coffee maker!

The solution was similar, if more drastic. While the head was off the car, I took duct tape and sealed off all of the holes on the bottom side. I then laid the head flat and filled it up through the thermostat hole with muriatic acid, such as one buys at the hardware store for cleaning a swimming pool. After about an hour, I drained the head, removed the tape, and pressure washed it through every available orifice. A surprising amount of debris came out. ONLY use this trick on cast iron cylinder heads!!

The heat transfer problem was solved: When the car was put back together, it no longer had any tendency to knock even with regular gas, and on a hard pull with the timing slightly advanced!

Ross Miller