Reprinted with permission from Donny Petersen, Heavy Duty Cycles, toronto, Ontario

HEAVY DUTY CYCLES Technical Article Section

Please read disclaimer at the end of this article, thank you.

Summer 2004

Oiling + Oil Filtration

1999-2004

Part II of III

Last month we delved into the feed side oiling of the Twin Cam engine. We also began to examine Harley Davidson’s assertion that any timing case component engine breakdowns and related debris does not affect other parts of the engine as outlined in Service Bulletin M-1097 titled “Cam Bearing Repair Kits”:

“After careful inspection, Harley Davidson has determined that complete engine disassembly is unnecessary. All contamination is confined to the cam department and the return oiling system.”

I opined that the fine metal particles transfer from the timing compartment of the engine through the pinion bearing that separates this compartment with the bottom end compartment. I felt this occurred via suspended particulate in the oilified mist that is transferred back and forth with violent pressure differentials caused by rapidly ascending and descending pistons. Then an AIM Techline reader Mike Goshert with extensive mechanical knowledge emailed that ” (your) explanation that metallic debris would not be circulated through the entire engine would only be accurate if all the oil passed through the oil filter! The filter has an internal bypass so element restriction does not reduce flow and create a pressure drop. It would probably scare us to death if we knew how little oil was filtered. Think about it…20-50 is relatively high viscosity oil and 10 micron is a relatively fine filter element. A high percentage of the oil bypasses the filter element; there is no other logical conclusion. The pressure across the filter element is established by a fairly light bypass spring inside the filter-not by the oil pump. Odds are that a metal particle could make a number of passes through the system before it was finally caught by the filter element.” Well, after a few minutes of contemplation, I realized that there are now two sources of impure oil traveling from the timing compartment throughout the motor. In fact, Mike’s comments take this even further in that debris created anywhere in the engine can travel most times unimpeded throughout the engine without being immediately and totally filtered. We will begin by reviewing the Twin Cam return side oiling system, breather functions, oil pressure problems, oil cooling, correct oil levels and checking procedures and then we will be in excellent shape to learn all about oil filtration next month.

Oil Return from the Engine

Scavenge means “return” or “pick up and return”. Evos have to scavenge oil from the crankcase via a breather gear and return the oil to the timing chest. The return side of the oil pump scavenges this and other oil in the timing chest to return it to the oil tank. This involves two separate steps. On the TC88 this is reduced to one step as the oil pump scavenges oil from the crank and the timing chest at the same time thus dual scavenging. There is less oil to scavenge in the crank and more in the timing area because returning oil from the top end is directed right into the timing chest. In the Evo, this top-end returning oil goes into the crank to slosh around on the flywheels causing inertial drag. We also get a minor speed advantage with the new system since this drag is reduced considerably. Oil is sucked up by the return gerotors in the pump and is fed through a return line in the cam support plate. The oil exits the support plate on the inboard side near the rear and into a passageway in the rear pinion side crankcase flange. The oil is directed to the return fitting located above the feed fitting and below the vent fitting and returned to the oil tank on the Softails. Dyna and FLT model oil is returned to the oil pan