There are a number of Radial Engine Operation techniques that can shorten cylinder life (head failure). There are also a few mechanical problems that can cause premature cylinder head failure. The following items, hopefully, will shed some light on the subject.
- This engine is equipped with a float type carburetor that supplies more fuel to the engine during take off, and very high power output, than the engine actually needs. This extra fuel is metered to the engine through an economizer valve (actually a fuel enrichment valve). This extra fuel serves to cool the cylinder head during take off. If a pilot doesn’t use full throttle for take off, he is actually leaning the engine and possibly over heating the cylinder head and exhaust valve, increasing the potential for head failure.
- It is recommended procedure for a pilot to maintain one inch of manifold pressure for every one hundred R.P.M. he is running while on approach for landing. If a pilot ‘chops’ the throttle, prior to landing, he may ‘super cool’ or ‘shock cool’ the cylinder heads. This sets up tremendous stress in the aluminum head, and if done habitually, can lead to cylinder cracks.
- If the fuel enrichment valve mentioned above is defective (may cause unusually low fuel consumption) the results will be similar to not using full power on take off. i.e. excessively lean mixture and high E. G. T. valve, and head temps.
- Contaminated fuel (diesel mixed in gas) or gasoline with too low an octane rating, or excessive alcohol content in the fuel can all cause detonation or pre-ignition during high power output. This causes piston and ring failure as well as cylinder head failure (premature).
Cracks can often be found in the head prior to failure. Look for black staining between any two fins across the top of the cylinder, or around the exhaust side. The classic indication will look very black, not dark brown like burned oil. If the black stain shows between two fins and not their adjacent fins, look for a crack.
I hope this is of some help to you in trying to safely and economically operate the Radial Engines.