Prop swap question

[Swampwrench]

Just replaced my slightly dinged up acme 2561 with a Johnson wakepro. Putting the new prop on, it didn’t seat nearly as far up the shaft as the one I took off. I had to tighten almost as hard as I could (hand wrench) just to get the nut on far enough to get a cotter pin back through. With the original prop, the nit was seated about 2-3 threads above the pin.

Is this normal? Unfortunately, OJ props is closed for the weekend. I’m a little leery to put the boat back in the water with this concern... any advice would be greatly appreciated!

2016 G25, acme 2561 replaces with Johnson wakepro 970, 1.25 shaft

Thanks y’all.
Brent


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[charlesml3]

Since you got the cotter pin through you should be fine. Keep in mind that the only thing the prop nut does is hold the prop on when you go into reverse...

-Charles

[Swampwrench]

Thanks!


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[XBIGPUN66]

You may need to lap the prop so it fits correctly to the taper of the shaft.

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[charlesml3]

You may need to lap the prop so it fits correctly to the taper of the shaft.

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I've heard people talk about this and I've seen the video. I still can't figure out what the real benefit is. What does this do?

-Charles

[XBIGPUN66]

It makes it so that the taper of the shaft and the hole or tunnel in the prop match up exactly. This would make for a more exact metal to metal fit and contact. The end of the shaft where the prop goes on has a taper and if supposed to have an exact metal to metal fit. If you can imagine trying to fit an ice cream cone (the pointy kind) in to a cup holder in your car or in to a cardboard toilet paper tube that illustrates the concept. It fits very loosely and would be hard to "seat in" to the hole (the cupholder).

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[charlesml3]

It makes it so that the taper of the shaft and the hole or tunnel in the prop match up exactly. This would make for a more exact metal to metal fit and contact. The end of the shaft where the prop goes on has a taper and if supposed to have an exact metal to metal fit. If you can imagine trying to fit an ice cream cone (the pointy kind) in to a cup holder in your car or in to a cardboard toilet paper tube that illustrates the concept. It fits very loosely and would be hard to "seat in" to the hole (the cupholder).

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I understand the mechanics of lapping them. I have yet to hear someone post a reasonable explanation as to what benefit it provides.

Normally, lapping a tapered shaft is done to provide either an air-tight or fluid-tight seal between the two. Clearly this doesn't apply to a prop on a propshaft.

-Charles

[gary s]

Charles look up the definition of machine taper . Also check this out,same principle - cheap to produce,reliable and fast to make a change

[shag]

I know it should be common sense and I am sure you've already checked, but be sure the keyway hasn't slid a little when you put the prop on... I have seen a time or two where someone slid the prop on and the key pushed up a little in the slot preventing the prop from goin go n all the way..

[charlesml3]

Charles look up the definition of machine taper . Also check this out,same principle - cheap to produce,reliable and fast to make a change

You keep answering a different question. You're answering "How do I lap a tapered shaft?" I'm asking: "What is the benefit of doing this on a tow boat?"

[Quinner]

You keep answering a different question. You're answering "How do I lap a tapered shaft?" I'm asking: "What is the benefit of doing this on a tow boat?"

He made 1 reply, "you keep answering...." ????

Google it, you will get the answer. Proper fit, to ensure tight fit/no vibration, so prop will not loosen, so prop slides all the way on the shaft to were it should be, etc. etc.

[gary s]

I'm asking: "What is the benefit of doing this on a tow boat?"

If you read the link I provided you would have seen this-" This precision fit makes the crank and flywheel a permanently matched pair" Same applies to machining a shaft and propeller. You have two different operations,machining a taper onto a shaft and reaming a propeller taper. They are done in different locations,by different people and companies, tolerances can build up, lapping them makes them fit exactly together as a pair. It is the taper not the key or nut that holds the prop on. It's just like blueprinting an engine,just making sure all factory tolerances are what the manufacturer specified. It takes so little time and effort why wouldn't you do it?

[charlesml3]

It takes so little time and effort why wouldn't you do it?

Well, a couple of reasons. The biggest being: The factory does not do this. Neither do the mechanics at my dealer.

Now if you want to do it because it just makes you feel better or sleep better at night, then fine. Totally cool. I do all kinds of maintenance on my boat simply because it makes me feel better about it.

The problem I'm having with this whole thing is: "What problem are you trying to solve?" I get your explanation about what it does. I understand that it's about mating a prop and a prop shaft that weren't made at the same place. I get that doing this makes them mate better. But this whole thing seems like a solution in search of a problem. If the prop mates with the shaft, the key fits, and the prop nut goes down far enough for the cotter pin to go through (older boats) or the Nylock to grab properly (newer boats) then why does this need to be any more than that?

It's not going to make anything last longer. It's not going to make the boat run any better or smoother. Again, "it just makes me feel better about it" is a perfectly good answer. Please understand, I'm not trying to be difficult or start an argument. I'm honestly looking for a reasonable explanation as to what benefit this provides with regards to a prop on a tow boat. I understand your explanation about blueprinting an engine, but that analogy doesn't seem to really apply here. There are tolerances there that must be within thousandths or really bad things can happen.

-Charles

[desertskier]

The driveshafts in our boats have been known to break off. I know I have heard of a few. Here is an explanation I found on the internet (so it must be true). Personally, I experienced a loose prop several years after the dealer installed it so I started lapping after that but not being an expert it just makes me feel better. Also, it is my understanding that the taper holds the prop to the shaft not the nut. That is why you need a puller to get the prop off and the nut is only torqued to about 35ft lbs.

"There are occasional reports of propeller shafts mysteriously breaking, usually just aft of the prop shaft bracket. Although many of these reports involve high-powered planing-hull boats, trawlers and sailboats are occasionally involved. This type of shaft breakage usually results in loss of the prop. Upon investigation it is usually found that the prop shaft was the correct diameter for the torque being transmitted, that it was true and properly supported and was made of well-finished, quality material. Yet, it failed. Numerous theories are advanced for the cause of the failure. The shaft and prop are replaced and in many instances the replacement functions without problem for many years. The cause of the failure remains obscure. One major cause of this type of prop-shaft failure isn't a mystery. It results from the manner in which the prop is mounted on the prop shaft.

The section of the propeller shaft onto which the propeller is fixed is tapered, with a matching taper bored into the hub of the propeller. It is generally assumed that the taper of the shaft matches that of the prop bore. Unfortunately, the match between these tapered surfaces is often not as precise as we assume it to be. The prop slides onto the shaft easily, and when the securing nut is tightened it appears to be securely seated on the shaft. In reality, the contact area between the shaft and the prop bore may be less than total, with a minute amount of space between the shaft and prop over sections of the mating surfaces. On many boats, especially those powered with modest-size engines, the fit of the prop to the shaft is sufficiently close and allows trouble-free transfer of energy from the shaft to the prop. In more highly powered boats the slight looseness of the prop on the shaft allows a small amount of rocking movement between the prop and the shaft. This movement imparts a cyclic stress on the shaft that adds to the cyclic loading always present as a consequence of the presence of underwater hardware ahead of the rotating prop.

Cyclic-loading failure

The cyclic loading created by what we may call prop rocking accumulates rapidly, at the rate of one cycle per revolution of the shaft. At typical shaft speeds of 1,200 rpm, 72,000 cycles occur in one hour of operation, more than seven million in 100 hours. While the prop shaft is designed to deal with the normal-magnitude cyclic loading, it may be unable to withstand the combined effect of the normal and prop fit-induced loads. The shaft fails, usually just aft of the shaft support bracket, with loss of the propeller. In many instances, the prop cannot be recovered, and it is assumed that the failure was caused by impact with an underwater object. Prop shaft failure can be prevented by grinding or lapping the bore in the prop so that it precisely matches the taper of the prop shaft. "

[scottb7]

wow. interesting info. i love a good argument about lapping or not lapping like over maintaining or not over-maintaining, neither of which has a moral high ground.

i could not follow the above " marks to determine when you were quoting someone else and when you were stating your own opinion. you did not cite your reference. nor do you have to, but it did span like 3 paragraphs.

but if nautique thought that lapping props would keep g boats from busting shafts i would think they would have said so by now. and to my knowledge it is only g boats that have had this problem. so you might be right in that it might help or actually prevent the problem, but i kind of doubt it. if i had to guess it would be that a 17 x 17 is too much flipping prop for the shaft...

i always - on principle alone, just kidding, well kind of (but if you aren't smiling at this point you won't get the reference) - hate to agree with charles, but literally almost no one laps a prop, so i sure as heck ain't gonna start now...so if you want to do so, like he said do it for the "it makes me feel better", and enjoy the heck out it making you feel better. i think i will start changing my oil, every 10 hours to make me feel better - just kidding...

and while the cause of the "failure remains obscure" (note the quotes used in combination with eachother in nearby proximity) we don't know if it is "obscure" because nautique won't admit the actual reason or not...but there - is to my knowledge - chime in if possible - no other boat mfgr "donating" (note the incorrect use of " because i am quoting myself) propellers to the bottom of lakes.