Reporting back on my MVVS 26, the axial play became worse and I could hear slapping sound when toggling the prop back and forth. This was after 1.5 gallons. The engine continued to operate but I started loosing the top end. By the end of the 2nd gallon, the axial play was very severe.

I pulled the back plate and found that the crank pin has worn down to 2/3 of its original OD. There was quite a bit of metal particles in the crankcase. I contacted MVVS and sent the engine back for repair. I followed their shipping instruction to a T and sent it off for about $16 USPS.

I got the engine back in about 2.5 weeks. The factory replaced all internal components: piston, cylinder, crank. They did not touch the outside.

I have installed it on my new Balsa Nova 120 and flown 5 times. The engine no longer shows axial play as it did the first time around by about this time. It runs very strong - better than 8,600 on 18X6W APC. The BN 120 is so easy to hover compared to the F90, Aeroworks 80" profile Extra, Mayhem 90, DP Ulti 120, etc. that I have. It accelerates out of the hover. My BN 120 weighs in at 11lbs 2oz. Flies like a pattern plane w/3D thrown in.

I believe the original crank was not heat treated by accident at the factory. If it does not seem right, it probably isn't.