ys 63 pre-ignition?
 

Dave ;

I've got a 63 (less than a year old, probably more like 6 mo., but have only 2 gall. through it) that has a rat-tat-tat sound to it when full (or close to full) throttle. I posted a ? a while back on the fun-fly forum, and heard that it might be lifter noise. A guy at the field said over the weekend, it sounds like pre-ignition! I tried a couple tanks of 15% instead of the 30% wildcat heli fuel I normally use. This seemed to quiet it a bit, but did not eliminate it. I'm nervous to run it anymore so as not damage it (if damage hasn't already been done). I know 30% fuel has been recomended on this site, and have not run it too lean. With this particular engine, though, I tried following proper break-in procedures, but to be totally honest, on the first few attempts, I bumped the starter to the prop, and BAM!!!!!, it seemed to backfire, bigtime. On closer examination, The plastic spinner, which had about 1/6" clearance (or slightly less, but was not touching sitting idle; don't read idling) from the fuse (funfly/ profile), during windup, made contact with the fuse, causing (or what I believed caused) resistance to the starter motor. (Now people reading this may say "why did you just admit that?" ; here's why > I TRY to be honest, and LOVE this motor and want to get to the bottom of this unnerving sound so I feel comfortable flying it again SOON!) I know it resisted, because the spinner backplate spun, popping the cone off, and fused to the propeller.

So............do I fool around ordering shims for the head (which I've never read to be neccesary), or do I send the motor in to get looked at, to see if the "backfire" caused some slight issues with conn. rod/timming/lifter/I don't know, problems. It seems to run great otherwise! And if so, would the warranty cover it, how long would it take, and where would I send it. I bought it from central hobbies (hope I can find the reciept!)

Please help, I need to get back to practicing prop hangin', Something this engine is real good at!

ys 63 pre-ignition?
 

Check the valves gap. Should be .003" on both. Then go fly it and don't worry. Also don't listen to everyone's opinion, as most are wrong.

ys 63 pre-ignition?
 

I adjusted the gap after about 1 gall., I'll check it again.


I don't mean to second guess you, and I will go fly it, it just seems to ME that that rat-a-tat sound, kinda like an A.K. 47 (above the cool 4-stroke sound) seems abnormal, I don't hear this with other 4's at the field (comparing to saito, I haven't heard another YS run). But if your telling me this is a normal sound for a ys engine to make, and isn't harming it, I'll try getting used to it and keep flying. My long story above was motivated by wondering (an idea I formulated, after hearing the spark knock scenario) if a slight bend in the conn. rod (or lifters) could have messed with timming, causing pre-igniton.


Like I said, I'll quit worrying about it, unles you tell me otherwise......again.