Hi All,

During a bit of routine airframe servicing yesterday I noticed that my YS160 had a very small amount of end-float in the crankshaft i.e., it was possible to push/pull the shaft in/out rather than any side to side movement. Very small amount, but enough I could feel and hear it. It needed a fairly firm push/pull to make it move. This prompted me to put the tacho on it which I hadn't done for ages and it's down at about 7600rpm on a 17x12 APC, 30% OptiFuel YS, sea-level, hattori rigid header and long pipe. Everything else is fine, ticks over/runs/transitions well, also replaced plug and checked for leaks and checked valve gaps.

Given that it has a disc valve in the back, I'm thinking this is not good. Is it normal?

Cheers,

A

Sounds like the bearings may be worn, when's the last time they were replaced? It's probably not hurting the disc valve, since the pull of the engine will pull the crankshaft to it's furthest forward position, but it's still an issue that seems to be robbing your engine of power. Bearings would be my first guess... of course if you've spun a bearing you could have damage to the case as well so when you replace the bearings check the case for wear.

A worn, or out of adjustment disc valve will also rob you of power,
I agree, a bit of end play is nothing to worry about, but only if the rear bearing is good.

YS SERVICE AUST

OK, thanks guys.

No other sign of bearing wear - no side play, wowing noises, greying of exhaust eflux, blowing plugs etc.

Two other suggestions have been:

: split tapered collet not quite "home" once compressed b the prop driver - haven't checked yet.
: a small amount of end-play to be expected/desired since the ali crankcase will expand more than the steel shaft. I must admit I haven't checked it directly after stopping at the end of a run whilst it's still hot.

I need it this weekend for a comp (lack of power is irrelevant compared to the rest of my flying ) but will then strip it to investigate the slightly low output.

HS

Hi Guys,

Finally got it stripped. Rear bearing was shot - hadn't spun in the case or anything or come to pieces, but was definitely a bit rough when rotated. Replaced it - no more end float.

Thanks for the help.

A

Sweet, I got one right!