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Old 13-05-2021, 13:43   #1
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Laptop 3 blade classic lapping hub/shaft while in water

I just took off my max prop 3 blade classic 1.5" shaft, 83mm hub. In-water job. Wasnt that bad. I shipped it to PYI for a rebuild. Last year I got a new shaft and I never lapped the hub to the new shaft. I just tightened the nut and put the safety pins and assembled the blades.
It turns out hub was not super tight on the shaft and nut was only hand tight as I was able to pull it off by hand. Least is still very usable there is no play in there whatsoever.
I'm in the water and don't plan to haul out.
Is it feasible to lap the hub while under water when I receive the rebuilt prop?
Also how much torque should I apply to the nut for 1.5" shaft 83mm hub?
How does one lock the shaft to prevent it from spinning while tightening the nut if I'm in the water and have no means to disconnect the coupling.
I have 72c borg Warner transmission.
On the classic, blades are not in yet so I cannot prop wooden block against the hull and blade.
Thanks
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Old 13-05-2021, 14:11   #2
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Re: Laptop 3 blade classic lapping hub/shaft while in water

I know the answer only concerning blocking the shaft. Take a piece of 2 by 4 long of something like 8” or 10”. When the prop starts to turn with the nut tightening put the block of wood between the hull and the blade of the prop going up. Shaft and prop are now blocked, that’s it
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Old 14-05-2021, 06:30   #3
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Originally Posted by sailormed View Post
I know the answer only concerning blocking the shaft. Take a piece of 2 by 4 long of something like 8” or 10”. When the prop starts to turn with the nut tightening put the block of wood between the hull and the blade of the prop going up. Shaft and prop are now blocked, that’s it
max prop classic does not have the blades installed when you tighten the nut
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Old 14-05-2021, 10:13   #4
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Re: Laptop 3 blade classic lapping hub/shaft while in water

Quote:
Originally Posted by phorvati View Post
Is it feasible to lap the hub while under water when I receive the rebuilt prop?
No.

Quote:
Originally Posted by phorvati View Post
Also how much torque should I apply to the nut for 1.5" shaft 83mm hub?
Torque the nut as much as you can with a long breaker bar, remembering not to rotate the nut past the pin alignment holes.

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Originally Posted by phorvati View Post
How does one lock the shaft to prevent it from spinning while tightening the nut if I'm in the water and have no means to disconnect the coupling.
Use a pipe wrench on a non-bearing surface of the prop hub. Start watching at 5:10 into this video:

https://youtu.be/vZyanqMUkGs
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Old 14-05-2021, 11:17   #5
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Originally Posted by fstbttms View Post
No.



Torque the nut as much as you can with a long breaker bar, remembering not to rotate the nut past the pin alignment holes.



Use a pipe wrench on a non-bearing surface of the prop hub. Start watching at 5:10 into this video:

https://youtu.be/vZyanqMUkGs
Thank you. Why cant I lap the hub and shaft taper? If i put lapping compound on the shaft and slide the new hub and rotate.
My issue was the hub and nut were only hand tight after 1 year. It might be due to me not tightening as much as I should have or it might be due to never lapping the cone taper.
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Old 14-05-2021, 12:00   #6
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Why cant I lap the hub and shaft taper?
Because you cant apply Prussian blue underwater and that being the case and even if you were able to use the lapping compound underwater, you would be shooting blind.
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Old 14-05-2021, 13:04   #7
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Originally Posted by phorvati View Post
Thank you. Why cant I lap the hub and shaft taper? If i put lapping compound on the shaft and slide the new hub and rotate.
My issue was the hub and nut were only hand tight after 1 year. It might be due to me not tightening as much as I should have or it might be due to never lapping the cone taper.
If you are sure it can be done, just go ahead and do it. Why ask the question if you are going to doubt the advice of a professional giving you free advice? (and fstbttms is a pro...) If Matt says you can't do it underwater, I'd take his word for it. He spends more time under boats than you do...

The process of properly lapping to a good endpoint is a lot more complex than just putting some grinding compound on and spinning it back and forth.
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Old 14-05-2021, 13:08   #8
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Because you cant apply Prussian blue underwater and that being the case and even if you were able to use the lapping compound underwater, you would be shooting blind.
Oil is needed for lubrication to ensure smooth lapping and proper fit and to avoid scratches. That would be a better explanation instead of just can't do it.
So I will be running a risk of shearing the key and shaft keyway if interference fit is not good.
I will assemble everything and within a month of use go back to inspect. Because my hub and nut were only hand tight and I had extra vibration after about 1 year after installing new shaft
Might need a haul out after all, if this nut turns loose again.
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Old 14-05-2021, 13:22   #9
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Re: Laptop 3 blade classic lapping hub/shaft while in water

I've said this before in here- props of all kinds are installed on unlapped shafts both in and out of the water every day with zero issues. Probably thousands every year in this country alone. While lapping the shaft may technically be the best way to go about installing a prop, it is by no means necessary. If it were, I would find loose props on almost every boat my little dive service cleans. But we don't. In fact it is quite rare.
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Old 14-05-2021, 19:46   #10
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Originally Posted by fstbttms View Post
Because you cant apply Prussian blue underwater and that being the case and even if you were able to use the lapping compound underwater, you would be shooting blind.
When lapping you don't need prussian blue to check your work, you visually inspect both surfaces for an even and consistent finish on both surfaces. I have built engines in many shops and lapped many valves. You might use prussian blue initially to see how bad the fit is, but you can do that just by lapping for a spell too.

I don't see why you couldn't lapp underwater, but it sure would be awkward.
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Old 14-05-2021, 20:08   #11
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Originally Posted by phorvati View Post
Thank you. Why cant I lap the hub and shaft taper? If i put lapping compound on the shaft and slide the new hub and rotate.
My issue was the hub and nut were only hand tight after 1 year. It might be due to me not tightening as much as I should have or it might be due to never lapping the cone taper.
I'm glad you asked why it couldn't be done and got the explanation, rather than worry why someone else ridiculed you for asking. I too like to learn.
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Old 14-05-2021, 21:10   #12
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Originally Posted by fourlyons View Post
When lapping you don't need prussian blue to check your work, you visually inspect both surfaces for an even and consistent finish on both surfaces. I have built engines in many shops and lapped many valves. You might use prussian blue initially to see how bad the fit is, but you can do that just by lapping for a spell too.

I don't see why you couldn't lapp underwater, but it sure would be awkward.
+1.

It will probably be a pretty lousy lap job, but how can it possibly make the fit worse? Maybe mix some waterproof grease in with the lapping compound to keep it from washing away too easy.

It’s your own boat, the worst that can happen is you waste some time underwater.
Or you drop the hub and lose it, and then have to
buy a whole new prop.
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Old 14-05-2021, 21:41   #13
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Re: Laptop 3 blade classic lapping hub/shaft while in water

As for blocking the shaft - do it inside the boat at the coupling. A second person holding the block while you torque the nut, so it doesn’t wiggle free would be nice.

Another possibility just came to mind - a strap wrench around the prop body....

Matt
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Old 16-05-2021, 19:20   #14
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Re: Laptop 3 blade classic lapping hub/shaft while in water

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Originally Posted by mlydon View Post
As for blocking the shaft - do it inside the boat at the coupling. A second person holding the block while you torque the nut, so it doesn’t wiggle free would be nice.

Another possibility just came to mind - a strap wrench around the prop body....

Matt
Thanks, yes the helper will be good. I'd rather not bite into the hub or shaft with the pipe wrench.

The reason i asked is because my hub was lose(actually I was able to get it out by hand without a puller), 1 year and about 1000NM worth of motoring after I installed brand new shaft with existent hub/maxprop classic 3 blade. I was out of water at the time, but did not bother lapping. And here i am now a year later and don't want to pay another 1K for haul out to lap the prop. I'd rather go swimming. I have the setup for it and don't mind spending hours if needed under water.

Its either lack of lapping or I did not torque it as much. More likely did not torque it as much as I should have.

I might not lap, but just torque it harder. then I will just keep en eye on it. This is important and I cant be ignorant. Have to own it and that's why im trying to understand.



Prop is on the way to PYI for a rebuild. i will see what they say in terms of wear, especially because I had extra vibrations and I was attributing them to worn max prop. I pretty much replaced everything else.
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Old 16-05-2021, 19:47   #15
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Re: Laptop 3 blade classic lapping hub/shaft while in water

You misunderstand me - a STRAP wrench is rubber or nylon, works by the strap going around the whole hub and squeezing evenly - it’s a friction/constriction thing - no sharp teeth biting into metal.....kind of like a very flexible oil filter wrench

Matt
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