The oiling system on overhead valve (OHV) big twin engines from 1936 through 1999 depends on an externally mounted, gear driven oil pump. The oil pump is located in the same spot on the rear, vertical face of the right-hand engine crankcase and as long as it is given a diet of clean motor oil, it will last forever. The oil pump is what provides all the moving parts in the engine with a pressurized feed of oil. The oil pump also removes oil from the engine and sends it back to the oil tank where it is cooled and stays until it is time for the oil to come back down the feed line into the pump.
The oil pump also prevents the contents of the oil tank from flooding into the engine crankcases when the engine is not running.
The pressure check valve in the oil pump prevents the oil from the tank entering the oil pump until it is needed. When looking at the oil pump from the top, you’ll see two round caps with a slot on each surface–the slot is for a screwdriver blade. The inside cap, that is the lowest of the two caps is where the check valve is housed and is the mechanism that prevents the oil from the tank entering the oil pump until the engine has started and has reached three pounds of operating pressure. The pressure check valve is a ball held against a machined seat in the body of the pump, which is held in place by a coiled spring and the coiled spring is held in place by the round cap threaded into the pump body. Over time and miles traveled, there’s a chance that the check ball will not fully seat in the pump body for any number of reasons. The main reason is usually due to some type of debris in the oil that gets caught up on the seat and prevents the check ball from sealing the feed oil passage into the pump. This in turn allows oil to seep past the check ball and flood the lower end of the engine. The term for the lower end of the engine filling up with oil is called “sumping”. Sometimes when sumping occurs the engine will start, but it will pump oil out of the breather fitting.
When an engine sumps and you try to start it, the pressure of the pistons, on their downward stroke, compresses air in the crankcases. The breather gear in the engine’s timing chest is timed to provide an open passageway to the breather oil line, which goes back to the oil tank and allows the compressed air in the cases an escape route. If there is too much oil in the timing chest of the engine it too will be compressed. Air and liquids always seek the path of least resistance; some of the oil in the timing chest will flow with the compressed air out of the breather hose and back to the oil tank. Another portion of the oil will return to the oil tank by way of the scavenge gears in the oil pump body, but not enough. Some of the oil will look for another path of escape, such as a gasket or o-ring.
Many times sumping will occur when the engine has not been started for long periods of time and will clear up by itself after the engine has run for awhile. Any debris that was caught between the check ball and seat will be swept away by the incoming oil as the engine runs. When the engine dose start, the combination of the breather gear and the oil pump returning the oil to the tank will usually clear the sumped oil out of the engine in a few minutes. If sumping continues to occur, you will need to address the check ball and seat in the oil pump. Sometimes just replacing the check ball (H-D pn 8873) will do the trick and solve the problem. Worst-case scenario is that you will have to re-cut or resurface the check ball seat in the oil pump body. The task of resurfacing the check ball seat in the pump body can be accomplished a number of different ways with either the pump bolted to the engine or the pump removed from the engine. Of course, resurfacing the seat and cleaning the pump of any cuttings or abrasive material is easier with the pump removed from the engine.
There are several seat cutters available to accurately cut the check ball seat and even though these cutters are a little on the pricey side, they do the job if the seat has to be cut. Sometimes you just need to adjust the seat, which can be done with a couple of shopmade tools. In the following photos, we’ll show you what method has worked for us in the past.
The engine check valve is accessed through the top of the oil pump body. To get to the check ball, remove the screw cap (A) then carefully remove the spring and check ball (a thin pencil magnet is useful for removing the check ball). Depending on what type of oil line you’re running on your bike, you may have to remove your breather hose and fitting (B) for the screw cap to clear. While you’re in the area, it wouldn’t hurt to check and clean your tappet screen, located under the screw cap (C).
We’re using this sectioned oil pump body so you can see more easily how the pump check valve is fixed. In the photo we are looking at the crankcase side of the pump. Just under half of the top part of the pump is cut away to show the relationship and components of the pressure valve (A) and the check valve (B). The cavity (C) houses the oil return side or scavenge gears.
We loosely assembled the valves and springs into our cutaway oil pump body to give you an idea of what they look like when fitted. Again, the engine pressure valve is the tall tower (A) and the engine check valve (B) is the lower.
Here are the tools we have either bought or made for smoothing out the oil pump check valve: check valve seat cutter (A) from Custom Chrome, check valve seat cutter (B) from Aerosharp, an aftermarket pushrod for a panhead with solid lifters (C), and a check valve ball welded to a piece of welding rod (D).
This is a close up of the engine check valve seat (arrow). The body of the oil pump is made of aluminum, which is a somewhat soft material in this condition, so it wouldn’t take much for a small particle to hold the check valve off its seat. Remember fluids will follow the path of least resistance, so oil will seep through the smallest opening.
The first tool we are showing is the cutter from Aerosharp Company. The seat cutter has a small pilot shaft that fits into the oil passageway below the seat. The body of the cutter is slightly smaller in diameter than the passage way in the pump body; both of these features align the cutter while in use. When using the seat cutter you want to use a light touch–you don’t want to remove a lot of metal from the seat area, just enough to clean it up. The cutter “cuts” when twisted in a clockwise motion between the finger tips, try not to reverse twist the cutter, as it can dull the cutter.
The two shop made tools are pictured here inserted into the pump body. The pushrod end on the left and the check ball welded to a piece of rod on the right. The check valve ball is 3/8-inch diameter which is the same size as the end of the pushrod. When using these tools you will need to use a small amount of “fine” valve lapping compound on the ball to clean up the valve seat. The lapping compound is needed because there are no cutting teeth on the balls and the compound provides the cutting action–when doing this, to lap the seat simply rotate the ball between your fingers a few turns, raise the ball off the seat and rotate and continue lapping, use a light touch and check your progress often. When you can look down the check valve opening in the pump body and see a uniform seat, you’re done. Clean thoroughly before reassembly.
The last cutter we bought is from the Custom Chrome catalog and has several nice features. The cutter has a pilot (A) a threaded guide (B) that screws into the pump body and a knurled handle (C) for turning the cutter. Not shown is a second threaded guide that allows the tool to service all aluminum pump bodies from 1968 to 1999. The knurled handle is locked to the cutter shaft with a setscrew. When using a cutter on a pump that has not been removed from the engine, smear some grease on the cutters teeth, the grease will trap the shavings preventing them from entering the oil supply.
Aerosharp Tool Corp., Inc
P.O. Box 69, 122 South Street
Wales, WI 53183
414/968-3128
Custom Chrome Inc.
16100 Jacqueline Court
Morgan Hill, CA 95037
800-729-3332
http://www.customchrome.com
Oil Pump Check Valve Reseater PN 20467 $139.99
Look for the sister article to this “Oil Line Routing”, also from Frank Kaisler. To be featured in an up-coming issue or Hot Rod Bikes.
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