Got the shaft out, what to look for? - SailNet Community

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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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Old 04-09-2010
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Got the shaft out, what to look for?

I'm replacing the cutlass bearing and have the shaft out. What exactly should I look for to determine that it is still good? The shaft is 7/8 bronze, around 26 inches in length and could be 45 years old for all I know.

I don't see scoring that I can actually measure with my tools, there is some very slight scoring here and there, very little where the shaft passes through the stuffing box. What is considered significant?

Straightness. I put the shaft on a machinists granite alignment table and can measure gaps between the shaft and table of less than 4 thousandths of an inch in a couple of spots. These areas appear to be slightly oval rather than bent along the length. I do have a slight bend in the threaded portion right at the last half-inch likely from the prop puller getting the stuck propeller off.

Another issue is the zinc leeching from the bronze, correct? Although I have no way to measure that.
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Old 04-09-2010
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Its one of the issues i am decideing on right now in my restore

The shaft was running good BUT there is a bit of wear in the stuffing box and cutlass area and i found places like this

Prices New Shafts ~ Proper Pitch - Marine Propeller, sales and service, marine boat propellers, shafting and drive train sales and reconditioning services, Selbyville, Delaware, Mid Atlantic USA

That seem to do a nice job a a fair price
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Do all marine diesels have gear reductions? If my engine is turning at 2700 rpm, how fast is my shaft turning?
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Old 04-09-2010
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redness, swelling, discharge...
Uh, nebbermind.
I gotta stop answering by just reading the titles of threads.


Seriously, 4 thou sounds like it is within spec. Run a die over the threads and see if the appearance of bend on the tail end of the shaft disappears.

Last edited by bljones; 04-09-2010 at 07:48 AM.
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I did run a die over the threads to clean them up and it did nothing to straighten the tip. I didn't put any lateral pressure on the die though. I'm hoping that since the bend at the tip is past the prop it won't effect anything.
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Old 04-09-2010
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Originally Posted by preservedkillick View Post
Do all marine diesels have gear reductions? If my engine is turning at 2700 rpm, how fast is my shaft turning?
What is your transmission gear ratio???
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Sailingdog,

Just looked through the manual. Specs on all sorts of things, nothing about gear ratio. The manual does elude to the fact that it is a Hurth Gearbox though. I'll see if I can find out more when I go to the boat tomorrow.
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Look for a stamped metal label on the engine or transmission. It will usually have the gear ratio printed on it.
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Sailingdog,

Just looked through the manual. Specs on all sorts of things, nothing about gear ratio. The manual does elude to the fact that it is a Hurth Gearbox though. I'll see if I can find out more when I go to the boat tomorrow.
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Quote:
Originally Posted by preservedkillick View Post
Do all marine diesels have gear reductions? If my engine is turning at 2700 rpm, how fast is my shaft turning?
Your HURTH is probably 1.5:1, or 2:1, or 2.5:1. As sailingdog says - check the nameplate. It should be on top of the gearbox, usually on the STBD side of center. I'm guessing that yours is 2:1, so the prop is turning half the speed of the engine. Dezincification (yeah, spell THAT three times fast) is often indicated by pitting in the surface or splotchy discoloration in the surface. I wouldn't worry about a slight bend in the shaft as long as it is AFT of the prop and the prop nuts. If in doubt, have a (reputable) marine machinist check it. Good luck!
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