Prop Install with a stop?

[SirMichael]

Last fall, I had to remove the prop off my '88 Hunter 28.5. It has a Yanmar 18hp diesel and a 14" 2 blade prop with a 1" tapered shaft.

I tried everything that I could think of to remove the prop, all kinds of pullers, and finally had to hire someone to come and remove the prop. He had a removal tool something like this, and it finally popped off (with a BANG!)... The nut was still in place to keep the prop from dropping.

So, I want to try to keep this problem from happening again. When I removed the nuts from the prop shaft last fall, they were about 1/8" away from the edge of the prop, indicating that the prop had walked up the tapered shaft (under power) and thus made removal difficult.

Do I dare put something on the shaft to keep the prop from walking up shaft? Something like drilling a 1/8" hole through the shaft just above the prop and inserting a stainless steel pin, or putting a clamp on the shaft (but that would seem to want to walk too!).

Sir Michael

 

[jssailem]

Simply stating it... NO!
Michael. You want the prop to be fitted to the shaft. The prop should be gripping the shaft tightly so that the shaft and prop are one. The conjecture that the prop walked up the shaft is unlikely (unless you did not have the prop firmly on the shaft. If that is the case you are fortunate that the prop was still attached. It could have just as easily fallen off the shaft or worse wobbled and damaged the shaft and hull.

Here is a recommended method of fitting the shaft and prop. Honing the fit so that it is tight and solid. It may pop/bang again next year. It will be unlikely to slip off leaving you propless.

Lap-Fitting a Propeller to a Shaft - Marine How To

Slide The Prop On The Taper Step 1 - The first step is to slide the prop, or prop hub, onto the shaft without the key. Be sure the shaft & prop hub are clean.

marinehowto.com

 

[Ralph Johnstone]

The prop was improperly fitted last time. Even worse, the prop pitch may not be the correct match for the shaft pitch.

When I removed the nuts from the prop shaft last fall, they were about 1/8" away from the edge of the prop,

Unfortunately, the fit is so poor that the prop axis will very likely wind up misaligned with the shaft axis if you try to grind them back into some kind of fit.

At this stage your best bet is to call in a qualified fitter to assess the problem and make recommendations. Close fitting of mechanical parts does not seem to be your strong point.

Watch the fitter when he's working on your boat because if he's good, he'll want to show off his skills and you'll have a better appreciation of how the prop and shaft pitches match each other to behave as a solid unit.

 

[Tally Ho]

The prop and nuts may not have been installed properly or there is something wrong with one or the other…(the nuts should have been in contact with the prop and the prop should not be able to “walk” up on the shaft), but they will come off with a BANG ! That is just the nature of the tapered shaft and prop.

Fo not put anything (lubrication, grease, etc) on the shaft. It is intended that they “stick“ together.

Here is when I took mine off to replace it with a 3-blade feathering prop (Maxprop).

I used a home-made prop puller….works pretty well…

Greg

 

[SirMichael]

“At this stage your best bet is to call in a qualified fitter to assess the problem and make recommendations. Close fitting of mechanical parts does not seem to be your strong point.”

I did not install the prop, I’ve had the boat for eight years and sometime prior to that the prop was put on. Believe it or not, I am pretty decent mechanic!

I’ll try the Prussian blueing and the valve grinding compound…
Sir Michael

 

[capta]

You could have saved yourself a lot of hassle by just heating the prop's hub with a torch. Bronze heats up much faster than the SS shaft, so the prop will always come off easily, with a simple puller.

 

[SirMichael]

I tried heating (map gas) the prop, for a LONG time too! I bent a couple of pullers in the process. Like I said, it took a very big puller (with a lot of leverage) to get it off.

Sir Michael

 

[Ralph Johnstone]

Believe it or not, I am pretty decent mechanic!

Sorry about that but it was you solutions for securing the loose prop which had me a little worried :

Do I dare put something on the shaft to keep the prop from walking up shaft?

Something like drilling a 1/8" hole through the shaft just above the prop and inserting a stainless steel pin,

or putting a clamp on the shaft (but that would seem to want to walk too!).

These thoughts gave me the impression you were not too familiar with how a tapered shaft and prop mated together to create their amazing strength as if the two parts were a single piece.

I tried heating (map gas) the prop, for a LONG time too!

If I could mention, the basic idea in any heat shrink or heat expansion operation is to do it "as quickly as possible." In the above example, you want that prop hub heated as fast as possible so it gets hot (expands) yet the prop shaft remains cool (doesn't expand) due to the lag in the heat movement to the shaft. It's the difference in temperature between the hot prop hub and the cooler shaft which releases the prop due to the "relative" thermal expansion of the prop. After a several minutes of heating, the shaft will be the same temperature as the hub and if it hasn't parted yet, it ain't going nowhere. Never. The answer to this problem is a larger, hotter torch, while the prop is under great stress from the gear/prop puller.

 

[Ralph Johnstone]

I’ll try the Prussian blueing and the valve grinding compound…

One further suggestion is to measure the pitch of the shaft and compare it to the pitch of the prop hub before destroying both. Really quite easy to do.

 

[SirMichael]

Well, it cost me about $15 for the blueing agent & grind compound, but I got it done. The valve grinding compound that I found (wasn’t a lot of choice yesterday) wasn’t what I would’ve liked, as it grooved the shaft more than it should have. The blueing agent showed that most of the pressure was at the smaller end of the taper, and it was some pressure at the very top, the middle was almost untouched.

I did check for being key bound, and mark the shaft. But when I put on the nut too fasten the prop, it pushed the prop up past where the line was. I’m sure I’ll have a very difficult time getting it off next time as well. at least I know who to call to get it off.

I just had the prop checked & rebalanced professionally, hopefully I got rid of the vibration.

Sir Michael