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Q-talk 120 - Report on Onan Heads Cracking

I spent a couple hours flying around IA and IL one summer evening and then returned back to DVN. I decided to practice my landings. I did 3 take offs and landings. As I was climbing out after take off number 3, I had a loss of power, a bad vibration and strange noise all at once. I made a 180 and landed down wind with out incident.

After allowing the engine to cool, an inspection revealed a failure (no compression) of the left cylinder head. I have been inspecting these heads for many years after another Q pilot told me his developed cracks. These heads were inspected 20 hours before the failure of the left head. I found cracks in the right head as well. Total time on my engine was 639 hours. I replaced these heads with new ones and have flown another 30 hours this fall. In the future I will replace these heads at 400 hours for piece of mind.

I used the following part numbers: Part # 110-3214 right and # 110-3213 left, and head gasket part # 110-3181. I believe all these numbers have been superceded to new ones. Some time ago, Q1 builders figured out that the 20 hp Onan heads and gaskets were more reliable and the engines ran cooler. Everyone has been using them ever since.

You can order a printed copy of Q-talk #120 by using the Q-talk Back Issue Order Page.