[Cougar429]

Some castor helps, but is not exclusively required here. Duke used to recommend it since early tests on synth tended to see them flash and not protect the engines very well.

Mike, what nitro content? Can you post a pic of the head button, specifically the combustion chamber?

The reason is older Fox engines were built for low to no nitro, (FAI) fuel and tended to detonate if over 10% was used. There were mods you could do to open up the head button to allow for it and I have done that with a button head end mill, (no pun intended). The first pic is a before and after on a 50BB which, depending on the version should be close to your 45.

I also fabbed several different head buttons for a pair of Eagle IV 60's. Tested them and the best of the lot looked almost identical to the new version they sent me with the repaired 60 when the piston burned out during break in. Those are seen in the next 2 pics.

Although the stock muffler did not work very well, the basic engines were nearly bulletproof. Worth making the effort to make them behave. The last pic is of the same 50 bolted to my Seamaster. Resurrected that plane a decade ago and fabbed adapters for OS carb and exhaust. Carb was just an experiment since the original tended to rich mid range, (mods for that, as well) but the OS muffler worked fine, quieting the exhaust with no power loss.

Over the years have had to replace rings on some 3 times, while the sleeves survived with almost no wear. That hardened sleeve required longer break in and I used to find a lot of low time Fox engines at swap meets since most did not put in the effort to get there.

Unfortunately a quick search shows the Fayetteville site that had the mods listed down and out.