LMH Vmax 7 engine
I have had two .074's and still have one and i also have two .061's one heli and one airplane .
I have had no problems with any of them .
I also have three of Norvel's .25 engine with no problems .
I followed the following procedure on all of them and they all run great.
Take the head off and the screw on back plate out and remove the carb and muffler . Clean all parts in denatured alcohol to remove the residue put on for shipping . Dry parts thourghly and use some high temp silicon sealent used for car engines and seal the bottom of carb, the draw bar that holds the carb on and the back plate. Before sealing the back plate drop a few drops of oil onto the con rod and the crank pin .
Put a few drops of oil into the cylinder and rotate allot while watching TV and it passes pretty quickly . Then put a few more drops in and rotate with an electric starter for a while .
With the airplane engines it is easy to mount a prop where the engine sits horozontal to break in so the con rod in the back gets plenty of lube but with the heli engine the motor sits normally in the verticle position with the rod to the top .
Find a bolt that will fit the crank and get a prop that fits your engine, .061=6x3, .074=7x3, and mount the engine horizontal to a board and break it in per the instructions .
I have done this to all my Norvels and have had no problems with air leaks or rod problems .
Barry