Hi,

I have a 120 NC I bought 2nd hand with what the previous owner stated was around 30 or so runs on it. After running it for around 10 flights myself with great success I noticed that the top end had begun to sag after about 10 seconds from around 8800 RPM (16x8 prop) to 6500 or so. I assumed that the engine was probably running to lean and it was the end of the day so I just packed up without doing to much to it on the ground. When I got it home, I did a tappet adjustment for the first time using standard .04 and .1 feeler gauges. One tappet was definitely below .04 so I loosend it up a bit to get back to spec. After reassembling the engine, I noticed that turning the prop through was not as smooth as it used to be. So when I started it up today with my Sullivan Starter (I know prob a bad idea) the engine seized. Prior to that I had turned the prop over around 4 times to pressurize the tank but never saw any fuel moving into the carb...sure enough, after releasing the vent plug, nothing came out.

I put it on my work table tonight and removed the carb housing to expose the backplate and the engine seize was gone! My only guess would be vapor lock but I doubt it since I was able to rotate the prop 359 degrees. I want to get in there further but I can't figure out how to remove the second backplate. At this point I'm guessing a bearing must have popped out or something.

Any ideas?

Thanks

John

Managed to get the backplate off...looks like I blew a couple bearings somehow! There's a gap where it looks like one just disintegrated and a bunch of metal filings mostly located around the center hole of the cam. [:@] Oh well...there's a guy at my field that can replace these things in his sleep after I give it a good flush. The odd thing is, the other bearings look pristine?

The bearing cage came apart. Not unheard of in the older engines.

Yep, that looks to be the size of it Dave. Spoke with someone at YS Performance and he indicated that the case should be sanded smooth. I'm just worried the case is scored too much. Will be putting the engine in the mail tomorrow

Is it appropriate to assume that the newer cages don't do this and that they are interchangeable with the older ones? The amazing thing is is that the engine actually ran (for how long?) in this state...long enough for the bearings to completely disintegrate. Gotta love YS

Oh well, have an extra Saito 120 I can put in its place until my beloved YS returns...not quite the same but adequate for now.

Cheers!

John

The newer bearings are of better quality and interchange with the old ones.

Sorry about your toy.