There are many ways to upgrade the Parallel Twin engine. One of them is realizing an external oil feed as Arthur van Til did. He didn’t weld small manifolds to the top of the cylinder head like Mototrans did but he used the left hand cam bearing cover. To make sure the oil reaches both camshafts he made a connecting piece as well. With this “easy” way you don’t have to weld directly to your cylinder head. The options are to either open the engine cases and block the oil passageway at the bottom of the studs, or block the oil orifice on the left hand side of the cases just below the cylinder bank.
Blocking the oil passage in the orifice
The oil orifice/restrictor bolt in the top left case can be blanked off.
I did this by tapping M4 into the crossover hole and putting a threaded plug in here with thread sealant. Peen the edges so the threaded plug cannot get loose.
The theory is: the oil goes through the 1mm orifice and into the crossover hole. It cant cant go past the o-ring so it must go through the orifice. Since drilling and tapping a threaded hole into the 1mm orifice leaves you with an o-ring stuck on your drill/tap, the crossover hole is large enough to fit a grub screw. The added advantage is that if it were to get loose the grub screw cannot fall into the channel and into the main bearing.
grub screw in the orifice with thread sealant. I am not advertising the brand as shown, there are other alternatives.
Connecting the camshafts together:
Using an Aluminium bushing with 2 orings and a passageway provides the oil form the lefthand camshaft to the righthand camshaft. You will need to removes the Aluminium blanks from inside the camshafts, and drill/grind a hole in the lefthand camshaft, diameter 4~5mm. Note: the camshaft is hardened, I grinded the first 3mm with a pencil stone bit in the die-grinder and then with a normal HSS drill. Wash and blow out the camshafts!
Similarly, instead of using a pencil stone bit, a solid Carbide drill can be used in one go to make the hole.