Rocker Arm Shafts & Bushings
By Stephen Kassis
Rocker Arm Shafts & Bushings are a very common wear item on 1929-1933 Chevrolet engines. These early engines did not have a good oiling system for the top end. Consequently, the shafts, bushings and the tips of the rocker arms tended to wear out. There are no longer reproduction rocker arm kits available. However, hunting around on Ebay or at swap meets, there is still a chance to find aftermarket rocker arm repair kits to help with this kind of repair.
After 1931, Chevrolet did not offer separate bushings for rocker arms. The reason for this was that the bushings for 1932 were so thin that they must be installed in the rocker arm BEFORE the oil groove was cut into the bushing. Some NORS shaft & bushing sets have oil grooves, however, the old reproduction rocker arm bushings did not come with grooves. As part of the installation of 1932-1933 bushings, a groove must be cut into the center of the bushing for good oil flow to the weep hole at the top of the rocker arm.
One alternate method that we have seen for 1932-1933 was to cut a shallow groove right into the rocker arm shaft itself. In the few that we saw done in this manner, it provided an amazing increase in oil flow to the top of the rocker arm weep hole. Whether the bushing is grooved or the rocker arm shaft, it is vital to help improve oil flow. Failure to do this will cause a lack of oil at the valve stem or pushrod tip.
After removing the original bushings, press in the new bushings into the rocker arms. Bushings that have oil grooves will also have holes for oil passage. It is important that the oil passage holes are lined up with the holes in the rocker arm when installing the bushings. On bushings without holes, drill a hole through the bushing, using the weep hole as a guide. Use a drill that is the same size as the weep hole. Note: 1929-31 models use an oil wick to feed oil to the pushrod tip (FS-75). Be sure the oil hole is lined up in the bushing when installing them. Replace these wicks when rebuilding the rocker arm assemblies.
For bushings without grooves, cut a shallow groove in the bushing, all around the center of the bushing. One method to do this is using a Dremel tool with a flat cutting disk. Cut most of the way through the bushing but try not to go all the way through. A lathe or milling machine would be the preferred method if you have access to one. The groove needs to be at least the width of the oil weep hole (about .040″ or 3/64″), but slightly wider won’t hurt.
If it is decided to cut the groove into the rocker shaft, a depth of around .019″ (1/64″) should be used. This must be done at each oil hole opening on the shaft. Again a width of about .040″ (3/64″) should be used.
Once the groove is cut, use emery cloth to remove any rough edges and fit the rocker arms to the shafts. Be sure to oil all bushing surfaces prior to assembly.
1932-1934 rocker shafts should have original shouldered bolts holding the rocker shafts to the rocker stands. There are four of these bolts. The bolts are shouldered to insure that the rocker arm shafts are installed properly, with oil holes to the bottom. Some reproduction shaft kits will not allow for a shouldered bolt, so these must be changed. These are not a hardened bolt, so they should be available at an auto parts or hardware store. Purchase bolts with no shoulder that match in length and size to your originals.
CAUTION: When installing 1932-1934 rocker arm shafts, INSURE THAT THE OIL HOLES ARE ON THE BOTTOM. Failure to do this will cause poor oiling to the bushings and therefore, premature failure of the bushings. 1929-1931 rocker shafts have oil holes at the top and bottom and can be installed either way.
Check the rocker arm adjusting screws when rebuilding the rocker arms. Important: Actually remove each adjusting stud completely from the rocker arm. Check the threads carefully as these can break off and cause the adjuster stud to lock or move after being adjusted. Replace any adjusters with broken threads. (FS-68)
Last, but not least, check the tip of the rocker arm where it meets the top of the valve. This is a common wear area as lack of oil usually causes severe wear. If there is “cupping” at the rocker arm tip, it must be resurfaced until it is smooth. If this is not repaired a proper adjustment of the rocker arms will not be possible. Feeler gauge readings will be inaccurate. Distortion to the feeler gauge will be noted with impressions of the worn area transferred to the flat metal of the gauge. In these cases it will be necessary to build up the tip of the rocker by welding with a hard material like Stellite welding rod. A machine shop can then grind the tip smooth while keeping it slightly rounded.
A properly rebuilt rocker arm assembly will have snug fitting bushings on a smooth shaft. It will also have good oil flow to the rocker arm bushings, pushrod tips and the ends of the rocker arms that push on the valve ends. Lack of oil at these spots will eventually cause problems. Always check the oil line and oil distributor valve and clean or replace as needed.
If a proper shaft & bushing rebuilding kit cannot be sourced, an alternative is to have the rocker arm shafts industrial chromed and machined back to standard size. This still leaves the problem of bushings, which may have to be custom made.
If all else fails, we offer a rebuilding service for rocker arms for 1929-1962 6-cylinder engines. (Rebuild Service)
