Oiling System

Standard System
Two basic modifications are necessary to the oiling system on 50 and 70cc motors if you expect to use them for racing or they are highly tuned street motors. Number one is making sure your motor has the large size oil pump. Number two is increasing the size of the oil restriction orifice to the cylinderhead. Both are explained below.

In this photo you see a side by side comparison of a 50cc and a 70cc oil pump rotor. The 70cc rotor is obviously thicker, the thicker the rotor the more oil it will pump. If you have a highly tuned 50cc motor make sure you replace the oil pump with the complete pump unit from a 70cc motor. You must replace the entire pump because the body of the pump that holds the inner and outer rotor is deeper on a 70cc to accommodate the thicker rotors. No need to buy an expensive pump from Takegawa or Kitaco etc. The 70cc pump will do the job.

70cc pump rotor thickness 3.76mm (.148")
50cc pump rotor thickness 3.26mm (.128")
This means at least 15% more oil flow from the 70cc pump

This orifice (photo coming soon) is next to the lower right cylinder stud. It controls how much oil flows to the camshaft and rockers. The standard size seems to be about 0.75mm, for racing applications I open it up to about 1.0mm. DO NOT ENLARGE THIS ORIFICE TOO MUCH. If you make this orifice too large the main bearings and connecting rod bearings may not get enough oil. I would only recommend this modification for motors with a 70cc oil pump. A 50cc pump may not be able to supply enough oil to keep both the cam and the main bearings happy if you enlarge this orifice. If you do have a 50cc oil pump you should make sure this orifice is very clean and that no dirt is in the oil passages right behind it.

More help for top end oiling (Thanks to Richard at Ardjuna Racing for this tuning tip)

This is what an oil pressure enhancing washer looks like. I made this one from a description given to me by Richard at Ardjuna racing, he has since sent me a factory made washer but as you can see here it can be done at home. This washer is made from thin brass shim stock. I used a spare camshaft sprocket as a guide for the bolt holes. The center hole is for the cam cover bolt to pass through and is about 1mm larger in diameter than the bolt.

Here is the washer mounted on the camshaft. As you can see it fits on the outside of the camshaft sprocket. Normally oil flows in the far end (right side when installed in the motor) of the camshaft where centrifugal force throws some oil through the oil holes in the bearing surfaces and the lobes, however on a stock motor most of the oil will flow right through the camshaft and out the sprocket end without doing anything. Without this washer the hole for the bolt to pass through is much larger than necessary and leaves too much room for oil flow out of the camshaft. With the washer installed more oil is held inside the camshaft and forced out through the holes in the bearings and lobes where it can do the most good. Since the flow is restricted where it flows out of the camshaft you will now have some oil pressure forcing oil into the bearings and lobes.

Here you can see the washer mounted in the cylinder head. The hole in the center of the washer where the bolt goes through is slightly larger than the bolt so some oil will have a place to escape and lubricate the camshaft chain. So far this modification seems to be very successful and caused no bad side effects during testing and during the first race of 2000. Soon I will be disassembling the cylinder head for inspection and I will update this page if necessary to include what I discover from inspecting the parts.

Note: If you make this washer at home be sure it is not so large in diameter that it interferes with sprocket thrust stop on the inside of the cam sprocket cover. When you look at the sprocket you will see a shiny area where it touches the thrust stop, DO NOT MAKE THE WASHER BIG ENOUGH TO ENTER THE SHINY AREA OR IT WILL BIND THE CAMSHAFT !