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Due to the mass of call volume & inquires with requests for the M-Eight oil pump back cover O-ring groove, we’ve added the groove. Although Feulings in house testing on healthy engines did not show a benefit. The O-ring may have potential benefits in certain circumstances such as engines with higher cylinder leak down, poor subseal O-ring seal, raised sump hole and or sump plug (see tech tips below) and looser lifter to lifter bore clearances.

If desired, install O-ring from factory pump. Remove O-ring from OE cover and install into Feuling cover


1.) The oil pump scavenge port O-ring must be installed into the engine case, well lubed & the oil pump must properly fit & seal at the scavenge port. Any sacrifice of this seal will result in scavenging and wet sumping issues.

2.) Install new O-rings into engine case, use assembly lube on O-rings to aid in installation. Install the camplate & oil pump as a complete assembly. We advise to rotate crankshaft flats & oil pump gear flats vertical for easier install


The main sump port on the inside of the engine case is in a slightly different location & height in each case. This port is created when the bottom plug hole is machined and tapped. This breaks through the casting wall creating the sump port.

NOTE: the further the bottom plug installs into the case, the more of the scavenge port hole is blocked off. For optimum oil scavenging and lower sump levels, verify that your plug doesn’t block this port. It is advisable to trim the plug and or use thread tape to change the position of the plug if it blocks the port.

– Easy work when the cases are split, as it’s visable.

– With the engine in the motorcycle, the threads can be counted from the bottom of the engine case using a mirror & a 90 degree pick, count the threads up to the side scavenge hole.


It is important to get the correct hot oil level in your bike. Feuling recommends running the oil level 90%-99% full when hot.

Note: The oil pick up port is on the right side of the engine. Letting the bike idle or warm up on the kickstand will naturally fill the engine case and skew the oil level in the tank.

We recommend the following steps to achieve proper oil level:

  1. Check cold oil level.
  2. Ride the bike until operating temperature is reached.
  3. Shut the bike off while still in the upright position. (This insures an accurate reading)
  4. Once the bike is on the kickstand check oil level.
  5. Add or remove oil as needed


  1. Oil level too high – see above
  2. To verify if engine is wet sumping, ride motorcycle under normal riding conditions up to operating temperature, shut off engine before sitting down on kick stand. With bike straight up pull the ¼ allen head plug from bottom of engine case. Measure oil, a healthy engine with a Feuling oiling system should see between 3-6oz. If more oil is present address oil level and all other steps below.
  3. Detonation, check tune, fuel, exhaust/intake leaks
  4. Blow by through rings and cylinders, perform a leakdown test
  5. 1/4 NPT sump plug screwed in too deep on bottom of engine case blocking pick up port
  6. Leaky piston cooling jet valves and or leaky cooling jet gaskets
  7. Oil type: If running synthetic try running conventional, we highly recommend the use of conventional oil in the M-Eight engine
  8. Oil pump sub seal O-ring damaged and or incorrect installation, install oil pump/camplate per our instructions
  9. Loctite was used on oil pump and camplate bolts, interfering with oil pump side clearances and camplate sealing to case
  10. Oil pump housing, cover or camplate face scored from debris running through it and or dry start up etc., excessive crank end play/runout
  11. Breather valves in rocker boxes not working correctly and or issue with O-ring seal inside head. Note the valves do not sit squarely on cylinder head thus cocking the valve and compromising the seal. The O-ring groove on the valve is too large for the O-ring, we recommend running an additional smaller O-ring on the top of the OE O-ring which can help hold the OE O-ring in position and assist in sealing. Use HD drain plug O-ring #11105 or a -012 to -013 O-ring.


  1. Low oil level
  2. Pressure relief valve in oil pump not seating and sealing
  3. Scoring in oil pump housing and or camplate face surface, possible dry start up, debris in oil and or excessive crankshaft end play and or crankshaft runout
  4. Leaky piston cooling jet valves and or leaky cooling jet gaskets
  5. Loose camplate pinionshaft bore ID to crank pinionshaft OD clearance, we recommend 0.0005″ – 0.003″
  6. Loose lifter to lifter bore clearance, we recommend 0.001″ -0.0015″ lifter to lifter bore clearance – See Feuling tool #9004
  7. Loose rockershaft to bushing clearance and or excessive side end play
  8. Out of spec pressure side of oil pump due to scoring
  9. Loctite was used on oil pump and camplate bolts interfering with oil pump side clearance stack up and or camplate sealing to case
  10. Broken oil pump gears, inspect for debris in oil, excessive end play and or crankshaft runout
  11. Stripped or loose camplate/oil pump bolts causing camplate or oil pump to leak


  1. Low oil pressure
  2. Thrusting wear from rocker arms on rocker arm stand offs in cylinder heads
  3. Quick install pushrods flexing and creating valvetrain harmonics, possible pushrods contacting tubes
  4. Under performing lifters: Scored lifter internals, valvetrain harmonics, loose lifter to lifter bore clearance, we recommend 0.001″ -0.0015″ lifter to lifter bore clearance – See Feuling tool #9004
  5. Excessive crankshaft runout and or excessive crankshaft end play
  6. Valvetrain harmonics, bad valvespring to camshaft combination
  7. Flexing crankshaft
  8. Compensating assembly worn, compensating bolt not installed all the way

This Info Supplied Courtesy of FEULING PARTS –

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