flygilmore

Wanted to put this out there since my nephew and I just started breaking in his new 1.20AX. Anyway, after 4 tanks through the motor (which ran perfect by the way) we noticed a loud clicking when back flipping the prop to compression. To me, it sounds like the connecting rod where it has some play (and the fact that the prop is turned clockwise looking from the front) and perhaps it is something that will go away with more run time. Anyone experience this loud click when turning the motor reverse and hitting the compression stroke???

Thanks!!!

liquid_TR

Yes, I have.. I noticed it while I was playing with the prop back and forth at home, when the engine was at rest on the plane.
It went away after I put some oil thru the glow plug hole to wet the cylinder wall and ring.
I didnt made that noise when flipped forward, it did it when flipped backwards only.
I assumed the cylinder wall got too dry, so I oiled it. I never heard that sound again.

flygilmore

Yes, that is how his does-only makes the loud click when flipped backwards. I think it is something with the connecting rod and where it is at teh top/bottom of its cycle and there is a bit of play in it. When turning the motor in the correct position, it doesn't make any noises and is a smooth as can be which leads me to believe that there is nothing wrong along with the fact that it is one fine running engine!!!!

Thanks for your input-any one else have this experience??

XJet

Check the crankshaft for any radial (side to side) and axial (back and forth) movement.

It's possible that your engine shipped with faulty bearings (it happens sometimes) and I've seen some very weird symptoms produced by such bad bearings.

There should be no perceptible movement in the crankshaft if you hold the prop tips and rock them back and forth or push/pull on the prop hub.

N1EDM

My Feedback: (2)

I had a Magnum 91 that did that (consider it a OS clone). I tore the engine down and everything was perfect. My conclusion is that this is the ABC piston sticking to the top of the cylinder sleeve because the engine is brand new.

I'm not sure if I'm right or not, but I'm pretty confident in my analysis. Can't explain why this does it for you when backflipping, but not when running in the correct rotation.

Bob

Bax

My Feedback: (11)

With many larger-bore two-stroke engines, you'll hear such a clicking sound. It's usually the ring striking the upper lip of one of the ports. This happens when flipping backwards because the loads are placed in a different direction than when the engine is flipped forward or is running forward. This is not a thing to be concerned about, it's very, very common.