How To: Rocker Arm Rebuild
Now that the Cannonball is over, Occhiolungo can get back to more workshop stuff and How To articles… Click on the How To link on the right side of this page to see older articles.
When I bought the boxes of bits that were to be assembled as the 1916 Excelsior motor, there were a few sets of worn out rockers in one box. In the photo below you can see the pivot holes have been worn oval and the hemispherical surface that receives the pushrod is worn. Lubrication for both of these wear surfaces was lacking, and over the last 80-odd years the parts were run and run with occasional drops of oil and continuous exposure to dirt, dust and other grit…
The rockers on the right have been cut with a hacksaw. By moving the socket/pushrod closer to the rocker pivot, the leverage ratio changes and the valves lift slightly further. It is an old tuning trick that I thought I would try with one set of worn out rockers. The additional valve lift feeds just a bit more air/fuel mix into the motor for a bit of more power. The modification is fairly simple; much easier than re-profiling the camshaft to get the same effect.
This view shows two of the rockers after welding. The socket is now full of new metal (half of the ball & socket joint with the pushrod).
The two rockers on the left have been machined and polished. A carbide ball end mill was used to cut the spherical socket to the correct size to fit the pushrod end. At the center there is a very small little hole that is used to drip oil onto the ball/socket joint. This oil probably goes away within a few minutes of riding, but that is the way that the Excelsior factory made the parts.
On the bottom left rocker there is a new flip top oiler to lubricate the rocker pivot. These will be used on all the rockers, and judiciously filled with oil before each ride. I don’t want to be like the previous riders and wear these parts out! Reproduction oilers come from Restoration Supply Company, just a few bucks each. Size 1/4-32.
The next step was to make and install bearing bronze sleeves into the pivot holes. The rockers had been hardened when new, so I had to cut them using a carbide end mill to take out the oval shape. Once the holes were round, I made round plugs of bronze, pressed them into the rockers, then machined them to the correct width to fit the rocker pivots on the motor.
Once the bushings were the correct width, it was pretty simple to drill and ream them to fit the new pivot screws that I had made previously. Here is a photo showing two of the rockers, plus one new pushrod end. The old pushrod is below.