Broken strut, another question?????

[Ken Cross]

With my Hunter 30G I've motored at least 15 miles with the strut broken off. It was run up to 2900 rpm. We only noticed a knocking sound during turns and never felt much vibration. In hindsight I know that the noise was caused by the propshaft contacting the Stern tube. The shaft is bronze with a PSS dripless shaft seal.

My question: do I need to replace the shaft? Can I just assemble with the old shaft and measure run-out near the prop and know if it's bent? Is I can measure it with a dial indicator, how much run-out is acceptable?

I know someone on this forum can answer this.

Ken

 

[DayDreamer41]

@Ken Cross have a look
http://www.pacificmarine.net/engine...er-shaft/propeller-shaft-tolerance-tables.htm

 

[LeslieTroyer]

Ken I would be very very surprised if your shaft isn’t bent beyond repair.

Les

 

[Ken Cross]

Ken I would be very very surprised if your shaft isn’t bent beyond repair.

Les

That's not what I wanted to hear. I may have my son check it. (He's a machinist). Now that I have some specs. I see I can also get a new shaft right here on SBO. For anyone who hasn't ordered from them, they do a great job.

Ken

 

[kloudie1]

While on the hard, with the strut broken off, the shaft can be removed without pulling the rudder.. (if you can get the coupling off) so it can/should be checked.. If a shop knows what they are doing, they can straighten the shaft like new.. but not many machine shops take the time/are skilled enough to do that.. Replace it with new if there is any doubt. Because the shaft is in compression when pushing the boat, a little out of straight will get bigger with higher RPM.. The alignment of the new Cutless is critical; the strut is not easy to get back exactly where the old one was.. Not an easy job., and ya must have some machine savvy.

 

[LeslieTroyer]

Ken go to Cabelas and pick up a laser sight “shell”.(~$20). Have your son turn some aluminum rod the diameter (minus a few thousandths) of the strut with a hole in the center for the shell. Now you have a great tool for getting the strut into position.

Les

 

[DayDreamer41]

Ken go to Cabelas and pick up a laser sight “shell”.(~$20). Have your son turn some aluminum rod the diameter (minus a few thousandths) of the strut with a hole in the center for the shell. Now you have a great tool for getting the strut into position.

Les

@LeslieTroyer, would the objective be to align the laser dot with the the center mark on the output shaft of the trans?

 

[LeslieTroyer]

That could be an aim point if the engine was properly aligned in the first place. Otherwise shoot for center of the stern tube.

Les

 

[DayDreamer41]

@LeslieTroyer , I wonder if one could build a wood wedge with the shaft size bored through the center of it and the OD of at the mid-point of the wedge be sized to the stern tube ID, with enough flat on the midpoint to hold it securely, lightly drive the wedge into the stern tube with the shaft already through the wedge. This would have alignment and holding qualities to secure the shaft in position while one was mounting the strut. Wonder if that would work?

 

[Charles Erwin]

Laser pointer is good as far as it goes but there are two alignments involved - offset and angular. The strut bore needs to be as parallel to the stern tube bore as is possible. The transmission output coupler position is adjustable vertical and horizontal so it can be aligned with the stern tube in both offset and angularity but neither the strut nor the stern tube is adjustable - hence the need to make the bores collinear to start with. Here is better explanation.

https://stevedmarineconsulting.com/the-ins-and-outs-of-engine-and-shaft-alignment/.

And

https://stevedmarineconsulting.com/the-ins-and-outs-of-shaft-alignment-part-ii/?upm_export=print

Charles

 

[Charles Erwin]

PS. Les’ arrangement works if the transmission output is left in place and the laser holder is dead square in the strut bore. If you use a new strut casting it most likely will not be the exactly the same dimensions as the old so the strut base gets faired to the hull

 

[ggrizzard]

Ken, what is a "30G"? A later model Hunter 30?

 

[Ken Cross]

Ken, what is a "30G"? A later model Hunter 30?

A 30 G is a tall rig (50 foot mast clearance) Hunter 30 with a walk through transom. There are 30 G and 30 T models that I understand are similar. Ours is a 1989 model although I've seen one from 1988 and newer that looked the same.

Ken

 

[Ken Cross]

Interesting fact: I spoke with a dock mate with the same make model year boat and his strut broke last year. He motored it back from the San Juan Islands (40 plus miles) with the broken strut and said his shaft did not bend. He simply replaced the strut during an overnight hang. He did state that all the mounting bolts were bent when he disassembled it so he replaced them.

My question has been and still is: Why did it break?
Ken

 

[Mark Maulden]

What is the strut design and where did it break?

 

[All U Get]

Did the bronze look off color.

 

[chuckwayne]

Escape's strut was cracked when delivered by hunter, and the dealer painted overe the strut, crack and all. It took heavy seas and 10 years before the strut broke in heavy seas and I sailed/motored for the rest of a 2 week flotilla (25-40 hours motoring) without knowing something was wrong. At the end, returning to home, we noticed an occasional knockin noise. Once back on our mooring, Escape was hauled for a hurricane warning and we saw the broken strut; reomeved the base of the old one and installed the replacement using the shaft and stern tube to align and center. Used a laser and dial indicator to check for runout and all was OK. Once Escape was back afloat, checked the alignment at the flange.

 

[JimInPB]

Does anybody have a specification for maximum allowable runout (bend) on the shaft? Same question for bearing clearance.

 

[ggrizzard]

Thanks Ken.

 

[Ken Cross]

Does anybody have a specification for maximum allowable runout (bend) on the shaft? Same question for bearing clearance.

DayDreamer41 provided this:
http://www.pacificmarine.net/engine...er-shaft/propeller-shaft-tolerance-tables.htm

Ken