On Thursday, September 18, 2014 3:54:36 AM UTC-4, Alexey Sharadkin wrote:
Hello



new user of O-540 here.



O-540 engine, 25 hours after OH

New spark plugs. oil - 20w50.

Fuel - 92



The problem in the following:

The temperature on the ground about 20C, cylinder temp on tow 205 C, all towing in max mode.

Towing to the release - ok.

While descending cylinder temperature drops to 130-140 C degrees.

Landing, move throttle to 2000 rpm to fire the spark plugs, all is ok.



At take-off after about 20 seconds of max.rpm start very loud claps.

Also goes vibration - unwind the screws that secure the hood.



They disappear after 30-40 seconds of towing, when the temperature of the cylinder goes up to 200 degrees.



Through trial and error found a way - after landing I change mixture to LOW to raise the exhaust temperature to the maximum, heated cylinders

to 180-190, then claps less and they will disappear faster.

But this takes time, and am not sure that this is good for the rapid heating of the engine.



Can you recommend something?



Some other considerations?

Higher density altitudes in the summer - the higher the density altitude, the lower the octane required to suppress detonation (that's why Colorado has 85 octane as regular, lower is 87...). You were probably on the edge.
Again, have you tried 100LL to see if that cures the problem?