For the use by Chris-Craft dealers when speaking with prospective purchasers, the Chris-Craft Dealer Manual for 1932, provided an explanation of the difference between a Chrysler Marine engine and an automotive engine of the same make. Now, remember, we’re talking about 1932 Chrysler marine and automotive engines; there are certainly more differences between modern marine and automotive engines. But, here are the fundamental differences.
The manual explained that there was a vast difference between marine engines and automotive engines. While marine engines were built in the automobile plant, using their engineering facilities and production equipment, they were intended strictly for marine use. As a basis for marine engines, the plants used the same raw material as for their heavy-duty truck and motor coach engines, which they had been building for several years, and which were made to withstand severe service.
The manual also provided an explanation of why each of the differences between marine and automotive engines were necessary.
Greater Bearing and Piston Clearance
A marine engine operates at full throttle about 85% of its lifetime, whereas, an automotive engine operates at full throttle rarely over 10% of its lifetime. There is never any coasting for a boat. Therefore, there are greater pressure loads on the bearings and pistons, which increase the frictional resistance. This resistance generates heat and heat causes expansion. For this reason, more clearance must be allowed in the bearings and pistons to take care of this expansion.
Water-Cooled Exhaust Manifold
The use of water-cooled exhaust manifolds is necessary for two reasons – the increased temperature caused by maximum throttle operation and the location of the engine inside the hull where there is no air circulation to dissipate the heat.
The engine being located in the hull where there is no air circulation around the oil pan and the heat caused by maximum throttle operation, make it necessary for a marine engine to have an oil cooler. The oil is cooled by passing it through a tubular radiator connected to the water intake between the engine and the intake scoop on the bottom of the boat.
Larger carburetors are used to get more horsepower per cubic inch displacement.
Positive Gear Water Pump
A positive gear water pump is necessary because the cooling water must be picked up from the bottom of the hull. After the engine has been idle for some time, the water will drain back out of the pump. Therefore, the pump must be of the type that will prime itself.
Increased Oil Capacity
The oil capacity is increased because there is more oil in the circulation system of the marine engine due to the oil capacity of the oil cooler. Also due to the greater bearing clearances required and maximum horsepower developed, more oil is used than in an automotive engine.
New Oil Pan
Due to the angle at which the engine is installed in a boat, the design of the oil pan is changed to insure the proper distribution of the oil.
Reverse Gear Instead of Transmission
Gear changes are not needed in a boat; therefore, direct drive is satisfactory for all speeds. A reverse gear handles the only change in the function of the transmission.
Positive Drive Clutch
On an automobile engine, the clutch is held in by spring pressure against the plates. On a marine engine, if the spring was made strong enough to hold with the horsepower developed by these engines, it would require too much effort by the operator to disengage the clutch. On a marine engine, the clutch is held engaged by positive pressure through a toggle connection to the reverse lever.
So, having said all that, if you had your heart set on dropping the 350 small block Chevy from the old family truckster into your classic Chris-Craft runabout, you might want to think that one through a little more; there may be a few extra items you need to take into consideration. Just sayin’…
Content from the Chris-Craft Dealer Manual from 1932, courtesy of the Chris-Craft Antique Boat Club Historical Archives; photos by Stephen D. Griffitts