tight gear box?

[mr bill]

Recently bought a used 912ULS that had a prop strike (cracked but not broken off blades). Flange checked ok with a dial indicator. Having read a thread that there should be some internal clearances that allow the prop flange to move in/out and rotationally a little. With some effort the prop flange can be rotated, but there is no free play at all. The engine has the newer case, so I cannot just sent the gearbox in for an inspection. Any ideas?

[Av8r3400]

LEAF is right there in your neighborhood. Why not take it over to them and have it inspected?

[HighWing]

I think the in out movement is an illusion. My experience with several engines is that there is a little gear lash in the direction of rotation and if you are not paying strict attention to the direction of force applied to the prop, it can appear that there is forward / aft play. I get it a lot from friends that come into the hanger and move the prop and it will usually feel to them that it is the latter.

[Dave S]

Bill,

Lowell is precisely correct. The 912 has no "in and out" play on the prop shaft.

There is a small amount of gear lash (relief between the gears) which is measured in 1/1000's of an inch at the prop hub in rotation and barely noticeable to the eye - measure it with a dial gauge.

The gear lash is noticeable out at the end of the prop blade if the prop is bolted up - should be able to rock the blade back and forth and notice a very slight amount of movement at the blade tip - like about the amount of a spark plug gap - helps if you have a stick fastened to the floor aligned with the prop tip to see the rather small amount of motion. The only resistance to the gear lash is seals and bearings which isn't much so it should show up with little effort.

As Lowell indicated - the gear lash at the prop tip may be percieved as "in and out" movement if a person holds the blade in such a manner as it flexes. Careful observation should sort that out.

The drive gears are straight cut and they cannot operate without a little lash.

Direct drive continental and lycoming engines have a little in and out play because it is needed for oil flow for the engine main bearings - the rotax setup is a ball bearing mounted countershaft for the prop so it does not need or have any in and out play.

Sincerely,

Dave S

[Monocock]

(cracked but not broken off blades)

Out of interest, what were the blades made from? Wood, composite or metal? I'm not going to suggest for one minute that the answer will be able to give you a sound assessment of the state of the engine, but a cracked composite or wood prop doesn't sound like much of an impact to me at all...

[Av8r3400]

A friend of mine slid into a snowbank doing no damage to his two blade warp but cracking the case on his gearbox...

[Monocock]

That's another good reason for not having a Warp Drive then!! I was meaning the more normal lighter weight high performance composite types such as Ivo, Ecoprop and Kiev

[mr bill]

The blades were made of wood. I called Leading Edge Airfoils and they told me that the output shaft is mounted on ball bearings, so there should be no longitudinal movement and the gears have only a few thousands clearance in the gear mesh, the only way you can feel any backlash is with a prop mounted. So having heard much the same from all of you and Leading Edge, I feel more gooder and I can look for other things to worry about. Wings are ready for cover, but waiting for the composite leading edge. In the meantime, working on the tail feathers.

[Monocock]

Best of luck. The "S" is a stonking engine and you won't be short of power!!!!!!!!