How to check your propeller shaft runout for $35

[tugnnaweigh]

This is (hopefully) pictures of a tool I bought at Harbor Freight for $35. I use it each time I remove my propeller, I'm told the new spec. is two thousands runout and good running is five thousands. Ok, I'm going to try to post the pictures, if that fails, its a Pittsburgh Tool, part number 93051.

 

[walldog]

Good information and good pictures. Thanks for posting.

 

[Hydraulicjump]

I learn so much from this site. Sometimes I learn too much (meaning I start worrying about stuff that I shouldn't worry too much about). This may be one of them.

I have removed my prop once because I dinged it. I am hopeful I will never remove it again, but I have the gear puller and wrench to do it. Should I be checking propellor shaft runout frequently? I presume that runout should be checked if you think you might have bent the shaft. Right? Or is this something that changes without hitting something?

Thanks. I am dreading adding one more thing to my "stuff to worry about" list, which is approaching Avogadro's number (inside joke for science and engineering geeks).

Jeff

 

[SGIDAVE]

I learn so much from this site. Sometimes I learn too much (meaning I start worrying about stuff that I shouldn't worry too much about). This may be one of them.

I have removed my prop once because I dinged it. I am hopeful I will never remove it again, but I have the gear puller and wrench to do it. Should I be checking propellor shaft runout frequently? I presume that runout should be checked if you think you might have bent the shaft. Right? Or is this something that changes without hitting something?

Thanks. I am dreading adding one more thing to my "stuff to worry about" list, which is approaching Avogadro's number (inside joke for science and engineering geeks).

Jeff

Hello Jeff,

You DO NOT need to check prop shaft run out routinely.

You are correct that you might want to check for runout IF you think the shaft might be bent.

Shaft runout will not change in the absence of a LARGE causative factor....like you had a prop strike of heroic proportion.

Forum members familiar with principles of machining metal will recognize the dial indicator as a standard shop measurement tool. I use such tools to calibrate my own machinery which is for woodworking so getting things with 1/1000 inch is usually not critical. Nonetheless, I would GUESS that if you weren't careful how you rotated your prop shaft once you set up the gauge, you could INDUCE 5-10 thousandths movement which could lead one to the WRONG conclusion about the "trueness" of the prop. What I'm saying, if you take your prop in for a "check" to see how much runout, the shop will place the prop in a very particular fixture that holds it very tightly then rotates it very precisely. The rotation of our tug's prop shaft IN THE BOAT is a much less precise affair. By that I mean that the bearing in which the prop rotates probably allows a few thousandths "slop" which means it is slightly loose so that the prop can rotate as it should. Those few thou of slop (maybe 10-20 +/-) will likely increase as the boat is used and the bearing is worn. Remember that bearing is rubber or some other synthetic material subject to wear so may be misled trying to measure runout in this manner.

If your drivetrain vibrates, fix the prop. If the vibration persists, check the propshaft ALIGNMENT (with the boat IN THE WATER). Forget about prop shaft runout unless you have had a MAJOR PROP STRIKE of Avogadro's proportion :lol: ...like so bad it SHREADED the prop.

Now, I need to pick up one of those dial indicators for my woodworking shop. It DOES look useful.

Fair winds and straight prop shafts,

/dave

 

[NorthernFocus]

Hello Jeff,

You DO NOT need to check prop shaft run out routinely.

You are correct that you might want to check for runout IF you think the shaft might be bent.

Shaft runout will not change in the absence of a LARGE causative factor....like you had a prop strike of heroic proportion....

...If your drivetrain vibrates, fix the prop. If the vibration persists, check the propshaft ALIGNMENT (with the boat IN THE WATER). Forget about prop shaft runout unless you have had a MAJOR PROP STRIKE of Avogadro's proportion :lol: ...like so bad it SHREADED the prop...

All true if by "runout" you mean as in shop runout, i.e. bent shaft. However, with the boat on a trailer, using a dial indicator to check functional runout and bearing clearance is a way of checking the overall health of the shaft/bearing/coupling assembly. Worn shaft bearings can be the root cause of presistent packing leaks and/or perceived coupling issues. But worn bearings usually indicate something else is wrong(unless they are really old).

All that said.... setting up a dial indicator per the OP can indicate that something is wrong. But it doesn't tell you what is wrong. Plus as Dave points out, if it isn't done properly it can be very misleading. When you start measuring things in 1/1000 in. increments you better know what you're doing or you can lead yourself down all sorts of rabbit holes. An "out of spec" reading could be:

- bent shaft
- shaft out of round
- excessive bearing clearance
- drivetrain misaligned
- coupling problems
- lateral force applied to shaft during measurement

And there are probably a couple more that don't come immediately to mind.

So as with most things, if there isn't a suspected problem, why go there?