Bent shaft

[mtadamek]

Any opinions on what to do with a slightly bent shaft on a 41' convertible? Port shaft is bent just enough to be able to see it when running. No vibration, alignment is within specs, just a little wobble. I was just wondering if I should haul it and fix it now, or wait till next summer, or leave it alone. Any suggestions appreciated.


Thank you

 

[LENZ]

Any opinions on what to do with a slightly bent shaft on a 41' convertible? Port shaft is bent just enough to be able to see it when running. No vibration, alignment is within specs, just a little wobble. I was just wondering if I should haul it and fix it now, or wait till next summer, or leave it alone. Any suggestions appreciated.


Thank you

Where is the bend? by the motor coupling or down by the strut? If it's bad enough you might wear out you strut brg (cutless brg) a little quicker then normal. What is the spec for run-out on the shaft? .002-.005? Did you check the shaft with a dial indicator? or just visual?

Thanks Lenz

 

[Will]

Are you sure it's bent? Often a dinged prop will make a shaft wobble while in gear. To make sure, try turning shaft slowly by hand using a dial indicator to see if it's really out or not.
Will

 

[Fanfare]

Pull the shaft, send it and the prop to a prop shop. Amazingly, they can straighten the things. They can also spatter metal into the worn places where the cutless bearings are. A "Prop Scan" shop can really clean up any vibration you have picked up over the years.

 

[yachtsmanbill]

Double check the engine mounts too. A worn or loose mount in gear will show a wobble even with a true shaft. 8-71s? BOSS LADY had the rubber mounts that failed. It could also be a bad tube cutlass bearing. Break the coupling and check up and down with a dial indicator. Lifting by hand you should have
>.015" ws

 

[Boss Lady]

I have to agree with Wild Bill on this. You may have a sagging/broken motor mounts putting the shaft in a bind. I would pull the shaft to see if it is straight and you need to check shaft alignment at the transmission. I had new cutlass bearings put in at Fort Lauderdale (also known as Fort Robberdale, for the pirates that run boat yards down there) and they were pretty worn by the time I got back to North Carolina. Both engines had broken mounts and shafts were in a bind. Of course the yard in Florida didn't catch the real problem, even though the boat was on the hard for months.

 

[yachtsmanbill]

Ft Liquordale? Hey Chris, since youve got Allisons, why didnt you go with the OEM 12-71 rear mounts? I know you had those big $$$ units made. I was never a fan of those rubber jobs for 4000lbs! ws

 

[Boss Lady]

I traded the 8v71s with Allisons for 8v92s with Twin discs, also new motor mounts, since the cheapest motor mounts for the 8v71s were $900 each ($3600 per engine) which 3 per engine were actually broken. So the trade ins complete with old props, and and $35,000 got me two remanufactured, 8v92s with Twin Disc, installed, new 10" exhaust, new mounts, new 24 volt altenators, and two sets of props. I think it was the deal of the century. The guy who I got the engines from did the install. He made out since he got the engines for a song after installing some MAN grenades in the Bertram. I caught him at the right time (he needed the cash for a land deal). The best part is instead of spending money for the mounts, I got to spend it on new stuff. Not as good as a Yachtsman Willy deal, but pretty close. LOL

 

[captddis]

Chris,
Just curious, but the pics of your new engines installed in the boat, clearly show Allison "M" gears attached to the engines. It looks like the old gears were reused. Those engines would need the TD gears or the MH allisons.
Were the TD gears installed later?

 

[Boss Lady]

No, they are Allisons, the twin discs that were on the engines would not fit between the rails, so I had to go back with a different set of Allisons. I had forgotten about the fit problem. I really wanted the Twin Discs. One of the original Allisons had some problems. These are completely different gears.

 

[mtadamek]

The vessel has been completely refurbished. The props were balanced and the engines and gears completely rebuilt. 8v53's with tdmg506's. We aligned within tolerance. The only thing that could be wrong would be a bent shaft or a cutlass bearing. Bearings felt tight. We never did check the runout on the shaft, just the tolerance on the coupling with feeler gauges. It is very minor, I was kind of wanted to get an opinion on how fast to fix it. We just put her in a month ago and would like to put some hours on her. I was thinking on hauling out next year, pulling the shaft, and having it straightened.

 

[mtadamek]

It is possible that the engine alignment changed when we splashed. I figured it could be an issue, but actually went to the bottom of the to-do list. I will check it and update you on the status. Thank you.

 

[Boatsb]

Engine alignment needs to be checked and done after the boat is in the water for a few days to a week. never do it on land as the boats do flex a bit and will cause bad readings.

 

[Brian Degulis]

Put a dial indicator on it if it's 10 thousands or less it's not a problem that needs to be fixed right away. Up to 6 thousands is considered OK if your just seeing a slight wobble in the stuffing box you may not have a problem. The trans flange has a tolerance of a few thousands so does the shaft coupling if they ar lined up opossing each other that will cause you to see a wobble. You can try re indexing the couplings try breaking it and turning the shaft 180 degrees then bolt it up. Sometimes playing around with the indexing can get it down to near 0.

Brian