Prop re-installation tips.

[Whiskymac]

After spending four days over the last three weeks on my cutlass bearing project, interspersed with redesign and rebuild of my boat yard friend's homemade bearing "pusher", we finally completed the project bar the final re-installation of the prop.
I have made a couple of searches but haven't managed to answer my questions regarding torque/tightening of the castellated nut and whether any type of grease/ lube can be used which would make future removals (of the prop) easier.

Thanks,

Jeremy.

[KWKloeber]

Look at mainesail's website - he shows how to lap a prop.
YBYC but you should use the lapping process.  It IS NOT the keyway you depend on, it's the precise fit between shaft ad prop hub.

kk

[Whiskymac]

Thanks KK, I did read Maine Sail's article before I started but I ran into the following issues:

1. I had trouble sourcing Prussian Blue. I went to 4 different auto stores and no one had heard of it. I'm sure this isn't terminal as I'm sure I could find it online, I just wasn't certain whether this was for re-install or only for fitting a new prop.

2. He refers to tightening to the "proper" torque but does not specify an actual torque. I'm assuming this is because it is different for different shaft/nut sizes?

3. His photos show the use of two nuts, one thinner and one thicker and castellated, my boat has only the thicker one. Are our boats set up differently or could it be that mine is not configured correctly?

Thanks,

Jeremy.

[KWKloeber]

I'm surprised NAPA didn't stock it. Lapping should be done both on new installs and refitting.  Who says it was lapped properly when it was first installed, anyway?

The most secure is to use a lock (jam) nut but yes, it's probably the exception especially on Catalina's.  I have an article about locking on the prop - I will post it as soon as I get back to my pc on wed.

ken

[lazybone]

Look at mainesail's website - he shows how to lap a prop.
YBYC but you should use the lapping process.  It IS NOT the keyway you depend on, it's the precise fit between shaft ad prop hub.

kk

On my 34 the opposite end of the shaft at the trans coupling relies almost entirely on the keyway to deal with the radial loads.  The set screws there are for axial loads.  The shaft twist some to dampen the shock load but they pretty much mirror the forces at the prop.

Bigger shafts and props have larger stresses But... anyway,  proper practice is to lap the prop.   

[Bill Shreeves]

Whiskeymac.  Found Permatex 80038 Prussian Blue Fitting Compound from amazon dot com for less than $6.  I'll be ordering it today since my new prop should be shipping to me soon.

[lazybone]

You can use any Sharpie marker as a wear indicator.

[Bill Shreeves]

Whiskeymac - I re-read mainsails post and I'm wondering if he might be using the term 'torque' as a description to tighten it until the "thin" sharpie marker line disappears rather than to a specific ft lbs.

[KWKloeber]

Here's the article I promised about using a locking nut.....

http://www.boltscience.com/pages/twonuts.htm

Prop nut torque depends of course on the shaft/nut size, but for our 1-inch shafts somewhere around 40-50 ft-lbs is good.  I believe I used 45 ft-lbs 20 years ago, and it's still on there (I think)

kk

I'm surprised NAPA didn't stock it. Lapping should be done both on new installs and refitting.  Who says it was lapped properly when it was first installed, anyway?

The most secure is to use a lock (jam) nut but yes, it's probably the exception especially on Catalina's.  I have an article about locking on the prop - I will post it as soon as I get back to my pc on wed.

ken

[Bill Shreeves]

KK - Great info but, thats torque to put on the second nut to lock the two nuts, or the one furthest aft, not the torque on the first nut "pressing" the prop on the tapered shaft which is what I thought the question was.  The more I think about it, the prop manufacturer has to have a spec for the torque to hold the prop on the shaft.  That crap isn't left to "tighten her good and firm my man and a wee bit more".  I hope to be getting my new prop shipped to me next week and if there's no info with it regarding the torque, I'll call the mfg and share what I find out.

[KWKloeber]

Why not simply call the factory!?!? 
CTY installs props every day of the week (or used to every day).

kk

[Whiskymac]

Good idea KK. I have a calll in to CTY and will report back when I get a response.

[Whiskymac]

Ok, here's the scoop.

I followed KKs advice and called the factory.

I spoke with Warren who told me no one had ever asked about the torque to be applied to the prop nut and that most experienced yards just knew roughly how much force to apply (which I found a little odd considering the tendency of many owners to want to do as much maintenance work themselves as they can). He also felt that I should definitely have a "two nut" system rather than the single castle nut I found on my boat. He suggested I follow up with General Propeller in Florida and/or with Michigan Wheel Propellers.

I called General Propeller first and cleared things up quickly. Either the 2 nut system or the single castle nut are OK and he said ( as Bill suggested) that there is no torque value to apply but just tighten until "tight" and adjust enough to be able to insert the pin. I forgot to ask the process for the 2 nut system.

I also managed to source the Prusssian Blue from another Napa store so I think I'm now set up to lap fit the prop back to the shaft this weekend.

Thanks to all for the advice.

[KWKloeber]

Jeremy,

unbelievable that no one "in the know", has a clue!   

The MAXIMUM torque value for a 3/4" brass bolt/nut is around 100 ft-lbs (depending on whose chart you use.)  I figure the controlling factor is the brass nut, not the stainless shaft.  So I used about half the MAX value -- 50-ish -- as a working value.  Someone poo-pooed that, but that's my story and i'm stickin'toit.   

Ken

[lazybone]

Its a 1" shaft turned by a small toy like engine. Maybe we're over thinking this.  I mean really, the whole "a keyway is not enough", "you have to lap the prop", "what's the exact torque value on each nut".  Please stop.