In The Shop: Evolution Oil Pump

We have replaced buckets of Evolution and Shovelhead oil pumps over the years. Unlike Twin Cam oil pumps that sometimes fail by design, the Evolution and earlier oil pumps were typically good until worn from tens of thousands of miles, or damaged as a result of cam or tappet bearing failure. The latter, catastrophic failure from another motor component, is the more common reason for Evolution oil pump failure.

Recently, in the shop, a customer brought us a composite Softail that he had just completed building. Overall, the bike was well built. Even meticulously wired. The bike however had an older, supposedly rebuilt, bottom breathing S&S motor with a pre-92 Harley oil pump. The bike was sumping excessive oil from it’s bottom breather hose.

After inspecting for correct oil line routing and verifying good oil return to the tank, we stretched the oil pump check ball spring and verified that the bore was clean but, like we figured; that was just wishful thinking. There was not a noticeable change after running the m/c.

Next, we removed the cam cover for an inspection of the breather gear, timing marks, and overall cam compartment. Everything there checked out. We were now confident that the oil pump, that had been reused, should have been retired prior to this rebuild.

We replaced the old pump with a tried and true S&S billet oil pump assembly. Before beginning oil pump replacement, we removed the drain plug from the bottom of the S&S crankcase so that the excess oil in the bottom end could drain while we worked.

Pump replacement is not extremely difficult but it can be tedious. It is important to work clean. The paper gaskets are very thin and need to be handled gently. Prep and clean gasket surfaces thoroughly. It is also important to practice patience while aligning the pump halves or installing the small keys and retaining clips.

After plumbing our oil lines, priming the new pump and refilling the oil tank, the job was complete. Upon starting the bike, we had strong oil return to the tank and not even a mist of oil from the bottom breather hose. That is the outcome we have grown to expect when we use quality parts from S&S Cycle.

It’s always nice to be able to do a job one time correctly and move on to the next.

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