Question about 2003 Harley Davidson FLSTF Fat boy

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On my 2003 fat boy all oil from tank is in engine and won't return whats the cause ? runs real rough

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  • A Miller May 30, 2010

    I dont understand ... oil from what tank.

  • joygeo May 30, 2010

    all engine oil from horseshoe oil tank is in crankcase and won't return to tank. runs but shakes like mad



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Ok, I'm not exactly sure what the problem is on your Twin Cam but I can assure you that it is oil pump related. One the earlier models with the external pump, you had two pumps in one body. One pump was a "feed" pump that pumped oil into the engine. The other pump was a "scavenger" pump that pumped oil out of the engine back to the tank.

When Harley designed the Twin Cam engine, they employed a better design of pump inside the engine. It's located in the gear case along with the cams. I do not know too much about the Twin Cam engine as I specialize on the older Evolution, Shovelhead, and Panhead engnes. The older engines had a breather gear that used the crankcase pressure built up inside the engne to blow the oil from the crankcase into the gear case. I don't know if the Twin Cam still uses that method of getting the oil out of the crankcase and into the gear case.

So, with my limited knowledge of the oil pump on the Twin Cam, I'd say that this is the problem. You need to find someone that is familiar with the construction of the pump. It may be that the entire pump is bad or something as simple as a sheared pin.

Good Luck

Posted on May 30, 2010

  • wd4ity
    wd4ity May 30, 2010

    The scavenge portion of your oil pump is not working for some reason. The old Ironhead Sportsters were notorious for this. But, the gears in the oil pump were driven by these small pins. Any bit of trash that got into the pump would shear the pin of the scavenge gears and the feed gears would pump all the oil into the engine but the scavenge gears could not pump it out and back to the tank.

    The Big Twins would do it as well but they used small keys to drive the gear. The ' Evo models were bad about breaking a tooth off the plastic breather gear. The tooth would wind up in the scavenge gears of the pump and then the main drive key would shear stopping the pump altogether.

    I wish I could tell you more about your pump but due to my limited knowledge of the Twin Cam oil pump, the only thing I can tell you to do is to take it someone who know what he is doing in that area.

    Good Luck


  • Lucky Houghton May 11, 2011

    A seldom talked about Twin Cam engine problem is crankshaft shifting. Unlike the Evolution and Shovelhead cranks, the TC crank is a press-together unit where the crankpin is a "hard" press fit into the two flywheels halves. Under most circumstances, this design works well. However, in some cases, under hard deceleration and acceleration or ground-pounding tire burnouts, the three-piece pressed-together crankshaft can twist out of true, sometimes as much as .030-inch, or even more in the worst situations. Ideally, the crankshaft should be trued during assembly to within .001-inch. Under high power and torque conditions, a TC's flywheels can shift on the crankpin, causing the crank assembly to become severely out of true. This results in a severe wobbling of the right-side pinion shaft, which is located in the camshaft's gearcase. A wobbling pinion shaft often causes catastrophic damage to the engine's oil pump and cam support plate along with a loss of oil pressure and oil scavenging. Early warning signs include loud noises from the engine's gearcase area, ticking lifters, and oil dumping out of the cylinder head breathers.



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