June/July 2000 Tech Feature
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   Four Cylinder Lubrication
   By Rob Olsen
Most early four cylinder motorcycles had a total loss, splash feed oil lubrication system. Connecting rods dipped into the oil and flung oil around inside the case to reach bearings and cylinder walls. Mostly it whipped the oil into a heavy mist attempting to reach all areas of the motor internals. Problems arose when the oil in the crankcase flowed to the back of the pan when going up hills and the problem was the front connecting rods did not reach the oil level. In effect starved the front crank bearings, and the reverse when going down hill. If you didn't keep your engine topped up with oil the level was even lower, compounding the problem. 

Skipping ahead to 1929 and looking more closely at a pressure feed oiling system that all 4 cylinder motorcycles used by then, shows a necessary progression. Due to improved roads, faster speeds and consumer demands for more comfort, reliability and speed, a pressure fed oiling system was developed for the motorcycle. Although the photos are from the Henderson service bulletin, the principle is exactly the same for Indian 4's. They are well related due to the fact that if it wasn't for the Henderson brothers, Indian may not have had a 4 cylinder motorcycle until much later. 

Click on pictures for full size

Early Four lubrication. Henderson 1920-28 (3 main bearing crank), but Indians are much the same.

It all begins with the oil in the pan being drawn through a screen and tube to the oil pump. The oil is sucked into the pump by the rotating oil pump gears and is fed directly to the main bearings and to the oil pressure gauge. As oil comes to the main bearings it feeds through a hole in the main bearing shells that match up with a hole in the case, typically at about 50 lbs pressure. In later models the pressure was increased with the use of larger gears to 75 lbs. Oil passages are drilled through the crankshaft to reach each connecting rod bearing, but in the case of the center bearing it is up to the oil grooves to feed the passage to the connecting rod bearings via grooves cut in the bearing. This groove connects the main oil feed to the oil holes in the crankshaft to feed the rods. 2 grooves are cut in the center bearing to line up with the oil passage in the crankshaft and a short groove is cut between the grooves to connect the 2 oil grooves.

Later pressure feed lubrication, Henderson 1929-31 (5 main bearing crank), but again Indians are similar.
The two diagrams represent earlier 3 main bearing crankshafts and the later improved 5 bearing crankshaft. As oil is fed through the passages under pressure to the rod bearings, it is also aided by centrifugal force, in fact there is enough force from the rotating shaft to pull more oil out of the center bearing causing less pressure at that bearing to cause additional wear. This problem has been addressed before and I have found a way to cut the oil grooves to act as valves to equalize center main and rod bearing pressures, and continually test for the best possible pressure and lubrication. As each bearing is filled with oil and the crankshaft is rotating oil is pushed out the ends of each bearing and thrown around inside the crankcase in a heavy mist to help oil the cam bearings and the exccess oil in the rod bearings is thrown underneath the pistons and into the cylinder walls, This luricates the piston pins, cools and lubricates the cylinder walls. The exccess being scraped off by the lower ring in the piston. The back of the crank shaft has a hole drilled lenght wise to meet with the feed to the end bearing. This hole pressure feeds oil to the clutch and transmission areas and returns by gravity back to the oil pan. 
Crankshaft oil hole passages to rod bearings. Lower bearing cap with oil grooves
As oil heats up and thins a drop in oil pressure can be seen. Lower oil pressures on the gauge can also be an indication of problems due to worn oil pump gears, to worn bearings. Worn bearing clearance allows a drop in the pressure at the bearing. A large diametrical clearance will not allow the crank shaft to suspend in the oil film therefore the crankshaft begins to knock on the bearing surface and then compounding the problem. Bearings begin to go out of round and and wearing the crankshaft. Bearings can heat up partially blocking the oil grooves and starving the rod bearings. 

Although not yet readily accepted, and oil filter on the fours is one of the best ways to protect your expensive motor. Much easier to install on a Henderson than an Indian, 4 an oil filter provides some cooling as well. The worst particles come from the clutch and trans gears. The steel particles small enough to go through the pickup screen are pumped directly to the bearings causing premature wear. Without a filter, oil should be changed quite regular to lessen the problem of recirculation of metal particles. 

Gear driven oil pump
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