Star Re. Box 357A Detroit Lakes, Minnesota 56501
The purpose of this article is to discuss problems which often occur in the valve train of the Associated and Galloway engines that use a flat valve pushrod supported by two cast guidesone on the block and one on the cylinder head. I have encountered problems on the two engines and I imagine the same situation could exist on other engines of similar design.
What happens is that the pushrod wears on the bottom side where it passes through the guides. The guides also wear some. When this happens it allows the centerline of the pushrod roller to drop below the centerline of the cam gear. When the cam lobe contacts the pushrod roller, it tries to push the roller down rather than forward. This causes everything to bind and puts a strain on all of the parts involved. The result is excessive wear on the gear teeth. In one case, it broke teeth out of the cam gear and on another engine it broke the casting that holds the cam gear pin.
To check for this problem it is necessary to remove the crankshaft and flywheels from the block. Check for timing marks or mark the gear so the timing will be right when you put it back together. Make sure all the contact surfaces along the valve train are lubricated. Then turn the cam gear by hand in the normal direction of rotation this is opposite of flywheel rotation. The gear should turn freely through a complete rotation without binding. If it doesn't, check the pushrod and guides for wear.
The agricultural machinists of yesteryear had a simple and effective remedy for this situation: cut some strips of galvanized tin and slip these between the pushrod and guide. Leave the strips long enough so you can wrap the ends around the guide to hold them in place. This repair solves the problem, but it doesn't look real cricket on a restored show engine.
The best way I've found to repair the pushrod is to build up the worn places by welding and then grind and file the welding to the proper dimensions. In this way if the guides are worn, you can build the rod up oversize and fit it to the worn guides. If the guides are worn real badly, they can be built up with nickel rod and filed to shape. It is also a good idea to check the pushrod roller to see that it turns freely and doesn't have any flat spots. If you have your own machine tools, it is not difficult to make a new roller or any machine shop can make one at a minimal cost.
By checking for this problem and repairing it if necessary, you will probably extend the life of the gears and avoid some serious damage. I hope this information will help someone so they don't have to find out the hard way!