is a dry-sump lubrication system. The difference between a dry-sump lubrication system and a crankcase storage system is that the oil is stored in an oil tank, not the crankcase. The difference between these oiling systems is exactly what can cause wet sumping.
Wet Sumping Is Dangerous... and also very messy! Not only for the engine, but for the rider as well. Having engine oil blow out of the crankcase breather onto your rear tire while riding, will make for a very slippery situation!
Below we have listed some possible causes of wet sumping, that can help you cure this problem, should it occur with your engine.
Wet sumping occurs... when oil does not return to the oil tank properly. Too much oil remains in the gearcase and crankcase. The engine doesn’t like this and will remove this over supply by blowing it out of the crankcase breather.
The crankcase breather will blow it out on the ground, on earlier models, or out of the air breather on newer models. Where it makes a nasty mess on your floor or on your engine.
1. Umbrella valves in rocker boxes are stuck or worn out.
2. Pinched o-rings.
3. Scavenge port hole not aligned with the seal on the oil pump.
4. Return oil passages in heads and cylinders plugged.
5. Excessive run out of pinion shaft.
6. Geo-rotors out of tolerance.
( .004” max.)
7. Scavenge gears or oil pump body damaged from debris going thru the pump.
8. Piston rings not seated, possible by over revving engine.
The main cause of wet sumping with this style of oil pump is that the check valve doesn’t close. The valve includes a ball bearing and spring. It is sealed with a slotted cap screw on the top left of the oil pump. With this style of oil pump, it is common to blow some amount of oil out of the breather after sitting for long periods of time. (Winter storage)
However, if this problem continues, it will need to be addressed! Since the check valve is the main cause for wet sumping, we will go into greater detail with it . Before doing this, we will list other possible causes. They are as follows:
1. Umbrella valves in rocker boxes are stuck or worn out. ( Evo’s only )
2. Debris in check valve not allowing it to close.
3. Pitted ball bearing or pitted seat in check valve.
4. Bad spring in check valve.
5. Check valve cap bore depth incorrect.
( Depth should be .500” )
6. Plugged drains from Heads, Cylinders, etc.
7. Damaged gears or oil pump body damaged from debris going thru the pump.
8. Broken keys in oil pump.
9. Breather gear out of time.
10. Out of tolerance condition between O.D. of breather gear and I.D. of case
11. Piston rings not seated.
Check valve assembly, cap, spring and ball bearing.
The bottom seat, make sure the seat is a complete circle, unlike the picture. Make sure it is also debris free, clean & not pitted. If it is, the oil pump will have to be removed.
The seat with a small amount of lapping compound and a welded new ball bearing. Completely clean & reinstall oil pump.
Everything you need to rebuild your check valve. Complete check valve kit includes (1 each) ball bearing, spring and RC-1 Stainless cap.
Upgrade to our RC-1 stainless steel hexed head cap. Replaces the stock tappet screen cap ( '73 & up), the check valve cap & the oil pressure relief cap ( '80 & up).