When is it time to replace shafts?

[whaler23]

I'm having a strut replaced on my '74 36C and an engine mount on one of the Cat engines. Both shafts have been pulled, original 1 1/2" diameter. The yard thinks I should replace both shafts. Both show some pitting and wear marks where they go through the cutlass bearings on the struts but nothing I would consider significant. So, what is acceptable wear on these shafts and is there any alternative but replacement? Engines are original 3160 Cats rated at 210HP each.

 

[MikeP]

Hmm...I'm no shaft expert (though I have received a few) but I wouldn't worry about them at all unless there was some serious issue that was plainly visible - like if it was twisted or bent. Otherwise, I don't know what else could be wrong with them. It's not like they are going to wear out by sitting there or being used. But I'd certainly defer to those who know more about it.

 

[Tim Powell]

I do not know exactley what to say but mine were cracked and the ware was where the shaft went through the strutt. we took them to a machine shop and they found the cracks they said just a matter of time befor you loose prop and al cracks are not good mine was a 1986 45c. There was no visible damage but they found some food for thought Tim

 

[Passages]

If pitting is minor and the packing gland is not excessively leaking - leave 'em alone. At 210 hp, you are not dealing with a high output senerio where things will get ugly fast.

At the cutlass, it's even less of an issue. Do you feel vibration at cruise? If no - fogetabouit.

If you want, you could use a strip of plumbers sandpaper and try to smooth the pits on the shaft. Suspect you will need much patience for this as it will be a slow go.

 

[jim rosenthal]

Get a second opinion, I think. If the shafts are true, I'd clean them up a bit and put them back in. With that relatively modest power, I don't think you ought to worry too much.

 

[saltshaker]

Have them checked out by a good reputable prop shop. If the shafts are straight and there are no cracks or signs of metal fatigue, have them fix the wear spots and put them back in. All shafts wear at the cutlass bearing and through conventional packing glands.

 

[hibanx]

How much money are we talking about for new shafts?...an ounce of prevention.

 

[whaler23]

2400 for both, plus install...

 

[ron6785]

All of the above , and you can get wear where the shaft go thru the cutless bearings but a machine shop can true up the shafts and build up the wear areas for a lot less than new shafts. If they're badly pitted where they go thru the bearings that can of course cause excessive wear on the bearings which are not inexpensive to replace .

 

[fissioneng]

We had quite an in depth presentation at Hatt school about shafts. Lots of discussion about mismatched tapers between the prop and the shaft causing cracking. The statistic was thrown out that 65-75% of shafts that this company examines show cracking in the keyways because of this.

If they're out of the boat, I would have the keyways/tapers checked by a good shaft shop.

 

[saltshaker]

2400 for both, plus install...

Is that tapered on both ends? Sounds like a good price but don't just replace them if you can get them fixed for a few hundred bucks. Make sure you are getting Aquamet 22 and not an inferior metal. Some shops will sell you Aquamet 19 or Aquamet 17 to save a few bucks.

 

[REBEL]

We had quite an in depth presentation at Hatt school about shafts. Lots of discussion about mismatched tapers between the prop and the shaft causing cracking. The statistic was thrown out that 65-75% of shafts that this company examines show cracking in the keyways because of this.

If they're out of the boat, I would have the keyways/tapers checked by a good shaft shop.

Did they discuss radiussing the keyway corners and using rounded keys as well? A sharp inside corner is the most prevalent area for a crack to start.
I lost a $4000 nibral wheel when the shaft fractured in the middle of the taper. Upon pulling the shaft, it was found to have considerable pitting in the shaft log area also.
This was identified by a metalurgist as "oxygen depletion corrosion" from sitting stagnant in salt water. The active oxide coating that occurs needs fresh water and oxygen to keep it active. This was a stainless steel shaft. Upon pulling the other shaft, the same situation was observed. It was recommended that I file and blend the corrosion out to prevent a stress fracture from occuring there as well. Incidently, that shaft was original to the boat and in fact, had a radiussed keyway. So far so good after 5 years. rebel

 

[saltshaker]

Did they discuss radiussing the keyway corners and using rounded keys as well? A sharp inside corner is the most prevalent area for a crack to start.
I lost a $4000 nibral wheel when the shaft fractured in the middle of the taper. Upon pulling the shaft, it was found to have considerable pitting in the shaft log area also.
This was identified by a metalurgist as "oxygen depletion corrosion" from sitting stagnant in salt water. The active oxide coating that occurs needs fresh water and oxygen to keep it active. This was a stainless steel shaft. Upon pulling the other shaft, the same situation was observed. It was recommended that I file and blend the corrosion out to prevent a stress fracture from occuring there as well. Incidently, that shaft was original to the boat and in fact, had a radiussed keyway. So far so good after 5 years. rebel

This brings up a very good point. A radiused key way is the way to go. You need to make sure the new shafts are a perfect fit. The taper and the key way are the weakest links if not perfectly fit for the props and couplings. When I did mine they took my couplings for a custom face and fit.

 

[jim rosenthal]

I agree that you should only get A22 if you buy new shafts. But for less than $2400 you can get a lot of reconditioning work done on the old ones.

 

[REBEL]

Thats great, but the other issue that hasnt been addressed is a torsional bend. THAT cannot be repaired. 100 horse power over a 16-20 foot shaft WILL twist. reb

 

[saltshaker]

Thats great, but the other issue that hasnt been addressed is a torsional bend. THAT cannot be repaired. 100 horse power over a 16-20 foot shaft WILL twist. reb

True. I believe most here are recommending fixing the wear spots if the shaft is otherwise OK.

 

[Kiwipushrod]

If You did'nt have any vibration before and You're replacing both cuttlass bearings, run'em again with a good engines alingment. Then use the $2400 for more cruising fuel.

Kiwi

 

[rsmith]

I'm having a strut replaced on my '74 36C and an engine mount on one of the Cat engines. Both shafts have been pulled, original 1 1/2" diameter. The yard thinks I should replace both shafts. Both show some pitting and wear marks where they go through the cutlass bearings on the struts but nothing I would consider significant. So, what is acceptable wear on these shafts and is there any alternative but replacement? Engines are original 3160 Cats rated at 210HP each.

first Ive heard of 3160's for years. We repowered our 34 with them in '71 when we saw how well they were doing in the 36. We had to bump the shaft size up to 1.5 from 1.25. dropped the struts 2in and swung a 22x22 wheel.Made a big difference how we fished the boat.speed -range etc. Allowed us to fish the offshore canyons from Montauk to oregeon inlet.
If there is scoring where the cuttlas bearing rides it will eat them up quicker same goes with the gland packing. Depends how much you use the boat. I got to the point on the 50 where I was replacing bearings every year.And I have 2 struts per side and its a PITA. Also a deep score can be a precursor for a break.( ever score something before you break it)

 

[REBrueckner]

Are these Aquamet 22 shafts?? the standard alloy....then no worry...

If 2/3 of the shafts show keyway cracks, that's evidence it doesn't matter much. The keyways barely do anything. Use the existing shafts unless, as noted, you have vibration; then they should be checked. If you can shake the shafts side to side at the struts, the cutlass bearings should be replaced.

New cutlass bearings might be a good idea if the shafts are at all loose in them. 1.5" shafts should be plenty for 210 HP engines...it's not like you are right on the edge of needing larger diameter shafts...those should handle 300 HP for example....

Any yard will advise replacement because
(a) they make some money,
(b) they will virtually guarantee no future problems when NEW shafts are used,
(c) they don't want to be bothered with you again if there is a problem and old shafts are in use...

$2,400 is awfully expensive insurance especially if you are a recreational user of maybe 100 or 200 hours run time annually.

 

[whaler23]

We're cleaning them up and re installing this week. Thanks for the replies.