Ask Paul: What to do about oil-fouled plugs?

Q: My partner, Lou, and I just had our Piper PA 28 235 overhauled and are having problems with the lower plugs getting oil fouled. The plugs have been cleaned a couple of times but she runs rough and they foul again. The mechanics are talking about putting a thin wire plug in. My concern is that we could have a leak in the valve stem seal, rings, or head or valve cover gaskets. The cylinders were rechromed and we had new rings, the valves machined, etc. One shop did the machining and cylinders, another shop assembled everything.

Where should we start?

TOM CAMP, via email

A: I think the best and easiest place to start is by referring you to a couple of my past posts, which addressed this type of situation. The first is titled “Why is my spark plug oil-fouled?” The second, “How to break-in your engine,” was printed in the Sept. 5, 2012 edition. I believe both of these articles will provide you with some important information, which will hopefully allow you to eliminate the situation you are presently struggling with.

I must caution you, though, that since you have chrome cylinders, it is important to follow the recommendations of the facility that did the chrome work on your cylinders. Most chrome plate facilities that I’m aware of always provide their own recommendations regarding which oil to use for break-in and how the engine should be operated during break-in. Comparing what I’ve written in the articles with what the chrome facility provided would be a good place to begin, but their recommendations should take precedence over my comments because they know their process and what is required to get proper break-in better than I do.

I’d suggest you review my comments regarding going to a hotter spark plug before you dash off and spend a lot of money on a set of good fine wire spark plugs. A simple check of Lycoming Service Instruction 1042 will provide you with all of the information regarding the correct spark plugs for your engine and additional information on the various heat ranges. Since you didn’t mention a specific engine model, I’ll guess since it’s a PA-28-235, you’ve got an O-540-B series engine and that’s where I would be checking in SI 1042 to see which spark plugs are approved.

As you’ll read in the Sept. 5 article, I mention the fact that I don’t want you to “baby” the engine during break-in. It is is very important that the engine be run at higher power settings during break-in, but it’s also important that all engine operating temperatures be monitored and not allowed to exceed the manufacturer’s recommendations. If you are in doubt about what those limits are, please refer to your Lycoming Operator’s Manual for your specific engine model.

Let’s hope by using the proper break-in oil and operating the engine properly for break-in, you will solve the oil fouling problem.


Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

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