1999 Sportster Oil Pump Gerotor

99sport wrote the following: One night the oil light flicked on on my 1999 XL1200S, but went off as quick as it had come. I figured it was just an electrical glitch of some kind and kept riding. Over the next week, it would periodically come back on and stay on for longer durations, but very sporadically, and if I gave the engine a rev, it would go off again. At this point I realized something else must have been culprit. I spoke with my internet motorcycle guru (Chris) and he suggested that after checking all first level problems, that I should pull the pump and gaze up inside.

So with the residual oil in the crankcase making a mess of my face as it slowly dripped down, I peered up at the drive gear, then rotated the wheel while in gear to spin the drive-gear and looked again. Spin look repeat, spin look repeat… I almost missed it, but on the last spin, I looked and one of the teeth was missing.

Though the tooth was missing, it should have only reduced the spin of the oil pump by 10%, so on the hunch of my guru, I tore pump open and found a cracked gerotor.

I then pulled the rocker boxes off to release pressure on the pushrods, and pulled the cam cover off to thankfully find the broken tooth floating in the corner (so no mystery tooth remaining to cause problems later on).

I replaced the oil pump drive gear with the upgraded Buell version (crossing fingers this never happens again) and got a new oil pump and slapped everything together. And turned the bike on, and the oil light was still on!! Thinking back on the situation, it was the return gerotor that was broken; the intake side was fine. So even at 90%, it should have still been pumping enough oil for the bike. Out with the service manual, it says that I should have 12-17 psi at idle, (or something like that), and mid 20’s at 2500 rpm at operating temp. So after a search of every auto store in town, I finally settled on a mechanically operated oil pump with a gauge capable of discerning 15 and 25 psi, (most were made for higher pressure applications.) I hooked up the gauge in place of the oil sensor, warmed the bike up observing a steady 15psi then took her out for a ride observing the stated 25+psi.

Through this, we found that the problem the entire time was a failing oil pressure sensor. I’m thankful that it failed though since it led me to find the broken oil pump/and drive gear before they could cause some serious damage.