Discussion in 'Props, Shafts & Seals' started by Beau, Jul 6, 2015.
I agree.... I am not defending my situations - I'm looking for the solution after 16 years?
Get that taper and hub inspected. Lap them in.
What I think we have been saying.
I had occasion to pull props for re-pitching on a Bertram 31, and was puzzled to see dis-coloration at the forward end of the shaft taper, and when I cleaned up the keys, there was a groove worn on both sides exactly at the height of the shaft key way depth. I decided to lap the props to the shaft and found that while the prop slid forward with a definite stop( no key in place), the forward end of the taper would never make contact with the bluing. Took the props to the local machinist who also makes shafts and fits couplings to shaft, etc. he immediately set his taper reamer up on a vise and turned the prop by hand, which revealed that the prop taper bore was not straight, but convex and not making contact the entire length at all. We got such a pile of Nibral shavings that I had to make sure the prop hub was not now sliding so far forward that the nuts couldn't tighten. Thankfully, there were still threads for the nuts to turn onto. I also made new keys that fit properly in width and height. Result was the boat has never run so smooth and quiet.
I was shocked that such a poorly machined taper could be sent out by the Manufacturer, these props had always been tuned to Class 1, but still the boat was not happy and completely smooth before this last work.
My SOP now will to always check the prop tapers on a reamer, not the mandrel the prop shops typically use.
If they come loose again, and I have every reason to expect they will, I will suggest your method to my prop tech.
I've been bit bad by bore cleaned up a few times thru the years.
Once, the tool chattered and near ruined the prop.
Another time it was a worn or damaged tool. Odd surface like your example above.
Months ago, they cleaned up the bore after the blades were repaired. Sharpie test looked good. Should have checked out the blade spacing to the strut. (shook my teeth out).
Yes, having the bore cleaned up is a good idea, always check the fit with a rule and marker/dye before final assembly.
I am sure, that the many, many wheels I have sent in thru the years have had a bore tool in them and no problems. Just some lessons from the crappy vault.
A dye and rub should-of shown up the need to re-ream your wheels.
Isn't it time to consider a new/different prop tech?
I've have one of the best on the Island, Johnson and Johnson.... They KNOW props. But you are correct, someone is not doing something correctly. Though both props will come loose at different times.
Insanity. Doing the same thing over and over again and expecting a different result.
Something is not right. I'm almost willing to put money that the keyways are too long.
Key ways or the keys?
Well my doctor confirms I am not insane,so. We've done the dye , we've done the lapping. neither prop is "riding" the key, everything is balanced and straight. I'm still of the mind that my torque in reverse may be at least part of the issue. Happens again, I'm having everything machined., am even going to change the nuts, on the theory that perhaps they've lost some metal
Are they stainless nuts or bronze? Crowned?
If not crown or castle, can you mark them (scribe or punch)?
If they are loose again, determine if the nuts are moving any.
You should take the time to see what the keyway actually does, if properly matched and lapped the keyway is not needed - look at many engine gears these days that have no keyways just a lapped surface and tightened by bolt.
Northern Lights raw water pump drive gear mount is a fine example I'm sure many have seen.
I'm aware of the fact a keyway is not needed. I have seen on a handful of boats were the key was just a touch too long, as you tightened the nut, it pushed the key up the taper and didn't allow the prop to seat all of the way against the shaft, yet the nut would tighten, etc. Then you'd haul the boat and the nuts were loose because the use allowed the props to slide up a little further. Aside from improperly lapped props, the key being a touch too long is the only other reason I've seen the prop nuts being loose.
Loose prop nuts can cause the shaft to crack, usually at the keyway area, I've seen that a few times also.
Also if you're props are Michigan/Federals they had some back in that era where the hubs weren't cut 100% properly, but close.
So I am neither insane nor stupid. Those kinds of posts go into my JUNK mail and reflect negatively on the poster - drinking? Anyway, I've done everything suggested 2-3 times over. I am going to try a different noted prop tech if it happens again.
You need to make sure the key slides all the way through the hub. When they come back from the prop shop they usually have a slight burr on the large side of the bore. All it takes is a couple of passes with a file. The torque is not causing the problem. If that wheel is properly on the taper it will stay tight. Do you know who did the machine work on the taper? I would check the key first, then the hub for cracks, then blue the shaft.