Have a .46 evolution, that the rear end of the muffler would come loose after a short run even after torquing the long screw and double nutting the end. Found that the long screw gong thru the muffler was expanding when hot. I ran the engine 'till hot then retightened the screw and problem solved. Good luck, red

Tighten the pass through bolt when hot (at max expansion), add lock nuts and torque them when hot.  That should hold the parts together.  As you have already noticed, tightening up while cold allows the heat to expand everything leading to loose parts.  You mght find some success by also using Loctite on the threads  but every thing has to be oil free for best results.

Good luck,

Chip

I've also use JB Weld in the threads, or peened the nut/ass end of the muffler, and the bolt and the nut..using a real sharp scratch awl.

I use high temp gray silicone to seal the rear pieces and also use it on the bolt, nut and on the surface where it attaches to the crankcase.

It holds everything in place and stops any oil leakage

On several planes I had problems with the pass-through screw the muffler on a Evolution 46 NT. I found the screws were stretching, primarily when the engine was run hard or high rpms such as on a quickie 500. Two bullet proof solutions are the Macs black muffler for lighter than stock with stock like performance or a Jett tuned muffler for a power boost. It looks like Evolution has contracted with Jett to supply (blue) tuned mufflers to their product line as well. http://evolutionengines.com/Products...x?ProdID=EVOM1

Why do the replacement mufflers solve the problem? From your analysis the screws for them must be different and stretch less? Do they come with new screws, and can the screws be bought separately for use with the stock muffler? I have the 36 46 and 61 NT engines. The 61 NX engine differs from the 61 NT engine by only the head. I have tried to buy the NX head to upgrade my NT, but they are always backordered. Wonder why?

Thanks,

Sincerely,

Richard