Most of the people on this forum know of the term "end play". But, a lot of people on this forum don't really know what end play is and why it is a subject at all.
Basically, aluminum and steel expand differently as the engine heats up. We are talking about a very small amount in one of our engines. But, there is a difference.
End play is there to absorb the difference as the steel crankshaft does not expand as much as the aluminum crankcase between the bearings.
If the aluminum case expands betweenn the bearings more than there is end play, the crankshaft is pulled against the big bearing and bearing housing. This can cause some drag and loss of rpm.
If the end play is greater than how much the aluminum expands, cable thrust can shove the connecting rod bushing into the rotor, causing wear on the rod, or in the case of a steel rod or steel needles, causing a wear pattern on the rotor. There is some drag and a loss of rpm as the rotor is pushed against the back plate.
If there is too much end play, the crankshaft can push against the connecting rod, perhaps keeping the connecting rod slightly past 90 degrees, causing wear and a loss of rpm.
So, how much end play do you want? As little as necessary. We are talking in terms of thousandths of an inch.
You want the crankshaft to fit firmly in the bearings. The bearings keep crankshaft in proper alignment with the connecting rod. The bearing should not easily slide on and off the crankshaft. You do not want the crankshaft to shift backwards and forwards in the bearings.
If the bearings are properly installed there will be very little endplay produced by the bearings themselves. When the engine is running, as long as the crankshaft does not drag against the large bearing housing or cause the rotor to drag against the back plate, you have good end play.
It may be hard to believe, but our crankshafts flex and stretch very tiny amounts as the engine runs. The crankcase also flexes and stretches as the engine runs and heats up. The bearings must be adequate to support the crankshaft in place so the engine can achieve optimum performance.
A great running engine is the result of a very good recipe. Where you run your boat and the boat design need you to work up the best recipe. When you have the right fuel, pipe, prop, glow plug, bearings, and end play, you have the right recipe for your engine's peak performance.
Basically, aluminum and steel expand differently as the engine heats up. We are talking about a very small amount in one of our engines. But, there is a difference.
End play is there to absorb the difference as the steel crankshaft does not expand as much as the aluminum crankcase between the bearings.
If the aluminum case expands betweenn the bearings more than there is end play, the crankshaft is pulled against the big bearing and bearing housing. This can cause some drag and loss of rpm.
If the end play is greater than how much the aluminum expands, cable thrust can shove the connecting rod bushing into the rotor, causing wear on the rod, or in the case of a steel rod or steel needles, causing a wear pattern on the rotor. There is some drag and a loss of rpm as the rotor is pushed against the back plate.
If there is too much end play, the crankshaft can push against the connecting rod, perhaps keeping the connecting rod slightly past 90 degrees, causing wear and a loss of rpm.
So, how much end play do you want? As little as necessary. We are talking in terms of thousandths of an inch.
You want the crankshaft to fit firmly in the bearings. The bearings keep crankshaft in proper alignment with the connecting rod. The bearing should not easily slide on and off the crankshaft. You do not want the crankshaft to shift backwards and forwards in the bearings.
If the bearings are properly installed there will be very little endplay produced by the bearings themselves. When the engine is running, as long as the crankshaft does not drag against the large bearing housing or cause the rotor to drag against the back plate, you have good end play.
It may be hard to believe, but our crankshafts flex and stretch very tiny amounts as the engine runs. The crankcase also flexes and stretches as the engine runs and heats up. The bearings must be adequate to support the crankshaft in place so the engine can achieve optimum performance.
A great running engine is the result of a very good recipe. Where you run your boat and the boat design need you to work up the best recipe. When you have the right fuel, pipe, prop, glow plug, bearings, and end play, you have the right recipe for your engine's peak performance.
