Is the O-435 a tough engine?

Q: And when you think they are almost forgotten…I have a good O-435 Lycoming in my 108-3 Stinson, but it is new to me. Is the bottom end a weak point at all? Crank, block rods, bearings?

Or is it tough engine? Power to weight ratio is low, but that is fine.

What do I watch for on this engine? Or is it just treat it good and it will treat you good?

A: Almost forgotten may be a stretch, but you should consider yourself lucky to have one of these dinosaurs! The best advice I can suggest not knowing the history of your aircraft and engine is to recommend using some common sense.

Now that I stop and think about that, maybe that’s as uncommon these days as your O-435.

Anyway, I’d suggest you review the history of this engine and see what you can learn with regard to past maintenance and operation.

As I’ve said many times in the past, my concern with an engine this old is the extended periods of inactivity. When you couple that with infrequent oil changes, I get a little nervous about the internal condition of the engine with regard to corrosion. Typically, the cylinders, camshaft and tappet areas are the most vulnerable.

A good borescope inspection can quickly tell you the condition of the cylinders, assuming your engine is still equipped with plain steel bore cylinders. Of course with the age of this engine, it may have had chrome cylinders installed many years ago, eliminating the concern for corrosion in the cylinders.

Since it’s a more extensive challenge to learn what condition the cam and tappets may be in, I’d prefer, in your case, to try to determine if there is a developing situation in that area by doing an oil analysis.

However, approaching it from this angle requires that certain very important things be done.

First, at the next scheduled oil change it’s important to get the engine up to normal operating temperature before draining the oil. Follow closely the instructions of the oil analysis firm on how to take a proper oil sample.

At this point you’re ready to send the sample off to the lab for analysis. Also at this time you’ll want to do a good visual inspection of the oil pressure and suction screens for any possible particles that may have been trapped.

Assuming nothing is found, you should be good to continue your normal servicing of the engine.

Now here’s the hard part. You should never base any decisions as to the condition of the engine on only one oil analysis unless the report comes back saying to ground the aircraft because of metal contamination.

You should fly the aircraft so that you can get at least one or two more good oil samples with about the same number of operating hours as when the previous sample was taken.

Note: The key to oil analysis is to compare several sample findings over the same operating hours, so we’re comparing apples to apples, so to speak.

With regard to the overall reliability of any engine, it’s simply a matter of operating and maintaining it in accordance with Lycoming’s manuals using the old philosophy — you take care of it and it’ll take care of you!