The muffler was designed to silence the otherwise loud report of the exploding charge of gas, which is released from the cylinders by the sudden opening of the exhaust valves.

While these devices are differently shaped and formed, the functional purpose and action is practically the same in all designs.

The burnt or inert gases are forced from the cylinders on the exhaust stroke. It passes into the exhaust manifold which absorbs some of the heat before it reaches the muffler.

Fig. 48 shows a three compartment muffler. The burnt gases enter compartment No. 1 from the exhaust pipe. This compartment is sufficiently large to spread the volume which lessens the pressure and force. It then enters the rear compartment No. 3, through the center pipe; it expands again and passes through the perforated spacer plate, enters compartment No. 2, and escapes through the nozzle in an even silent flow.

The muffler at all times produces a certain amount of back-pressure on the engine which results in a slight loss of power. The back pressure exerted by the majority of mufflers, however, is very slight and has a tendency to counter balance or equalize the sudden shock delivered to the bearings by the explosion over the piston head.

The muffler may also become fouled by the use of too much or too heavy a grade of lubricating oil, which will cause the expansion space and the small holes in the spacer plates to become clogged with carbon and soot. This carbon and soot soon bakes into a hard crust causing much back pressure which results in a considerable loss of power. This condition will become noticeable first by a loss of considerable power caused by an overheated motor. If this condition is not remedied, the exhaust manifold and pipe leading to the muffler will soon become red-hot, causing much danger of a serious damage loss to the car from fire.

Muffler.—To eliminate or remedy this condition, disconnect manifold pipe from the muffler, remove the muffler from hangers, and disassemble it by removing the nuts from the tie rods which release the end plates. This will allow the compartment walls and spacer plates to be drawn from the sleeve. Each compartment and spacer plate should be removed sectionally, and its position carefully noted, in order that it may be replaced correctly in re-assembling. The walls of the sleeve, and the compartment end plates are scraped and rubbed with a piece of sandpaper. A small round file may be used in cleaning the center pipe. The spacer plates are scraped and sandpapered. The small holes in the spacer plates may be opened by using the tapered end of a small file. Fig. 49 shows a muffler of another design. The burnt gas enters a compartment containing three saucer shaped spacers which retard and break up the volume. It then passes through an open compartment and enters reversed spacers through small holes near the sleeve wall. It centers or forms slightly in volume and escapes to the next compartment through a small hole in the center of the second spacer. This action of forming and breaking is kept up until the outlet is reached.