Franklin Cam Wear
The front cam lobe seems to be a weak point on Franklin engines. I have been hearing more and more about Franklin engines turning up with worn down cam front lobes lately. Some with as little as 319 hours since new. I have three of them in my garage right now with the front lobes gone. I’ve had talks with both the Franklin engine Club and Charlie Hart, who was employed by Franklin when they were still in business. All agree that there is a problem, Charlie and I discussed what might be causing the front lobe wear. He thinks that when the engine sits idle for a period of time and is then installed in a taildragger like our Stinsons, the front part of the cam loses its oil coating, especially when the oil level is on the low side. Condensation occurs and forms rust on the bottom side of the cam. The rust etches the cam surface so that when the engine later is started, the area is wiped by the cam lifter and, after a few such episodes, the hard surface of the cam gets worn away. In a short time both cam and lifter are ruined.
The best thing to do to prevent such wear is to fly the bird at least thirty minutes every few weeks. The next best thing is to turn the prop through at least every three or four weeks backwards (so that the impulses on the mags won’t fire in case of a bad mag ground or switch) at least six or seven times. This will wipe at least residual oil on the cam face and lifter and remove condensation, which may have accumulated. But you really need to run the engine and get the oil distributed throughout.
Oil additives can be help. Lycoming was having cam wear problems in their engines (Ed. Notes: See may 1, 1990, edition of Aviation Consumer) is all sorts of models. They now recommend a special additive to the oil for engines that are not run often. My I. A. has told me that it really works. It works so well, he says, that it has doubled the overhaul times of the Piper Braves he takes care of. The additive is called simply Engine Oil Additive and is Part No. LW-16702. It is available at parts supply houses (Sacramento Sky Ranch) or by mail from Chief Aircraft Inc. in Oregon. Aeroshell 15W-50 has the same additive already in it and meets Lycoming’s Service Bulletin 446C requirements. If it’s doing the job for Lycoming, then it ought to help the Franklin too as I see it. (Ed. Note: The Aviation Consumer investigation came to the same conclusion, as did Charlie Hart. Lack of use was the culprit. Remember the Lycoming has its camshaft at the top of the engine. When the oil dripped off the cam after long periods of inactivity, the entire cam became exposed, not just the front lobe as with the Franklin. Don’t let your engine just set idle for weeks at a time. If you can’t or won’t fly it, get a friend to do it)