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t is almost unfathomable to think that Harley’s Evolution engine has been out of production for 22 years. From 1985 through 1999, it powered everything from Dressers and Softails to Dyna’s and FXR’s. As one of the most successful engine offerings from Harley Davidson, it also has the distinction of being the one most often imitated. It is also the one that had the most aftermarket support. While the Panhead and the Shovelhead were in production for decades longer, the Evolution carried much of the DNA from its elder siblings forward. Even after production ceased in Milwaukee, companies like TP Engineering, S&S, Merch, and Ultima all produced the EVO engine for use in everything from West Coast Choppers to Texas Ironhorse Choppers to Big Dogs too. Some are still in production today. The more things change, the more they stay the same. Pre-Evolution engines and EVOs up until 1992
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February ‘22 - March ‘22 - CYCLE SOURCE MAGAZINE
Article And Photos By: Jason Hallman all utilized a “puke” tube or “roaddraft” to help alleviate crankcase pressure created by the up and down [stroke] of the pistons and the swing of the crankshaft flywheels. In 1992, Harley introduced cylinder heads with vent holes that allowed that pressure to be routed back into the air cleaner assembly and consumed by the engine. This created another [newer] problem that we can get into at a later date, but for now, I’d like to discuss what is called “sumping.” If you have ever started your Harley engine [big twin] and had to immediately throw a pan under the motorcycle because oil was “puking” out of it…then you have experienced sumping. This oil system vented to the atmosphere via a hole in the crankcase with a hose attached is also a great way for water to end up in your engine should you ever have to ride through water or (heaven forbid) your bike be in a flood. While sumping is common, it is
not “normal” and indicates a faulty check ball and spring assembly in your engine’s oil pump. When you park your bike and turn off the engine, the check ball in your engine’s oil pump should essentially seal off the outlet (return) side of your engine’s oil pump and prevent oil from returning to the engine crankcase through the outlet side of the pump. Let’s take a minute and look over how your Harley engine’s oil pump actually works: First off, there are two basic oil system types in combustion engines. The first is called a “wetsump,” and the second is a “drysump.” In a wet-sump engine, the engine’s oil is stored in the engine in an oil pan or bathtub type reservoir attached to the engine. The oil pump circulates the engine oil through the engine to clean, cool, and lubricate the engine bearings and other components. There is usually a filter attached somewhere in line to filter the engine oil either
