jb86

My Feedback: (8)

i have a fs 40 surpass, i put in new bearings - main and cam, ring and sleeve, valve springs. everything was cleaned, went together well, adjusted valves w/the os kit thick gauge, 1.0, turns as it should. i bench ran it, 12x4, os type f plug, wildcat 18% totally synthetic oil, 15% nitro, rich, full throttle, about 6500-7k, lots of oil came out, two 8 oz. tanks. then i started leaning. air bleed was closed to about 1 1/2 turns out. adjusted the airbleed to a smooth idle, transition. i start to lean the engine, great til about 9k, then it starts to knock. it sounds like it's coming form the top end. peaks at about 10,300, knock gets worse. i think it sounds like a ping. there is a gasket under the head as it should. i thought too high nitro, but was told 15% is fine.
any ideas of where to start? i was real proud, it's my first four stroke rebuild, i figured it would be a good practice. hope i can get it right.
jon b

Bax

My Feedback: (11)

If the engine is "knocking", that means you have it set too lean for the propeller size you're trying to use. The FS-40 Surpass should easily be able to turn over 10,000 RPM with an 11 x 8 APC prop. Your engine may have the compression fit of the piston, ring, and cylinder liner worn enough that it can't develop its proper power, or the fit of the valves may be such that the engine's losing compression.

It's not possible to say via emails, since we can't examine the engine.