Play in Stern tube bearing, what is too much

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Beekeepergreg

Beekeepergreg

Senior Member
Joined
Nov 28, 2017
Messages
150
Location
United States
Vessel Name
Mayrose
Vessel Make
Mainship 34 pilot
Pre-purchase a 34 Mainship Pilot, the shaft has about 1/16" play.
My 30 Mainship Pilot has no play.
What is acceptable?
Thanks
Greg
 

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The ABYC guide for my 2” shafts says from a minimum of .005” to a maximum of .010”. It depends on what size shaft you are referring to but 1/16” is out of specs for most of our shaft sizes. The surveyor used a plastic set of feeler gauges that would bend to match the shaft OD to measure the clearance.

A 1.5” shaft goes from .004 to .009”.
A 2.5” shaft goes from .005 to .011.
Per the chart the surveyor included on my boats survey.
 
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There shouldn't be enough you can feel if you try to turn or shake the shafts.
 
It's a 2" shaft, I am going to take a dial indicator down with me and measure. Look closer at the groves.
I really appreciate the feedback.
Greg
 
There really shouldn't be any. Take a close look at the bearing, you may have to remove the prop for the best view point. If the bearing has worn even a tiny bit lopsided it's time to replace.

It is not a huge job but bear in mind that there are thousands of bearings replaced every year. It may seem impossible to get the old one out but it can be done. I had to split mine with a sawzall and get it to cave in on itself.

pete
 
I measured today. ----.045" I can lift the shaft. How much will the bearing shrink when it is dry?
 
I don’t know that it will shrink or not but is sounds like it needs replacement.
 
Greetings,
Mr. B. "How much will the bearing shrink when it is dry?" I'm guessing .000". Yep, time to replace.
 
0.045", yes a bit worn, but in my experience that is not putting one in panic mode. Rubber bearings tend to swell in the water. And usually the bearing is loaded either up or down in running conditions, so the play does not matter. I have been around boats with much more play that had zero symptoms as far as vibes, noise, etc. I would plan on replacing it at your convenience, maybe next scheduled haul.
 
Greetings,
Mr. B. Mr. Ski's answer is better (based on experience). Forget mine (based on anecdotal information).


iu
 
On my last haul-out the yard guy recommended I change mine. I could feel it and guessed it was under 1/16”. I’ve seen some that were over 1/8”.

When I was in the Navy I rode the ferry back and forth to North Island in SD. When he pulled up to the float and reversed to a stop there was much noise and vibration. Wouldn’t be surprised if that 40’ boat had 1/4” slop in the aft bearing.

It could be true that there’s no need for concern unless there’s so much vibration things may come apart. Most or nearly all the vibration may be an imbalanced prop, drive shaft or something bent. It would be a plus if you knew your shaft was straight and the rest balanced. I’d say if things are smooth standing in the cockpit above the prop all’s well.
 
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Thanks everyone. I am going to see if I can get the owner to replace.
Greg
 
Nomad Willy said:
On my last haul-out the yard guy recommended I change mine. I could feel it and guessed it was under 1/16”. I’ve seen some that were over 1/8”.

When I was in the Navy I rode the ferry back and forth to North Island in SD. When he pulled up to the float and reversed to a stop there was much noise and vibration. Wouldn’t be surprised if that 40’ boat had 1/4” slop in the aft bearing.

It could be true that there’s no need for concern unless there’s so much vibration things may come apart. Most or nearly all the vibration may be an imbalanced prop, drive shaft or something bent. It would be a plus if you knew your shaft was straight and the rest balanced. I’d say if things are smooth standing in the cockpit above the prop all’s well.
Click to expand...

Wow, you rode the ferry in SD? It had been history a good while when I first attended ASW school there in 1970. Crikey, you must be older than me! :)
 
Rich,
The ferrys were known as the nickel snatchers. I was there in the early 60’s. The boats called ferries were about 50’ long, wood planked, much like an old rowboat. Powered by a very loud 6-71. Yea I’m old but that means I’ve been young longer than you.
 
The specs below are for a new installation. Buships Technical Manual advises 2" shafts should have minimum clearance of .017, maximum of .091. The maximum clearance is very generous.

In many cases misalignment is evident if you check the clearances around the bearing ends. If/when you decide to change it be prepared to realign the engine, strut or both. Also, the prop shaft may be worn where it rides in the bearing. It may still have a little clearance with a new bearing.

Comodave said:
The ABYC guide for my 2” shafts says from a minimum of .005” to a maximum of .010”. It depends on what size shaft you are referring to but 1/16” is out of specs for most of our shaft sizes. The surveyor used a plastic set of feeler gauges that would bend to match the shaft OD to measure the clearance.

A 1.5” shaft goes from .004 to .009”.
A 2.5” shaft goes from .005 to .011.
Per the chart the surveyor included on my boats survey.
Click to expand...
 
Is clearance in the centered position. So if I can jack the shaft .045" is my clearance .0225"?
Thanks
Greg
 
Nomad Willy said:
Rich,
The ferrys were known as the nickel snatchers. I was there in the early 60’s. The boats called ferries were about 50’ long, wood planked, much like an old rowboat. Powered by a very loud 6-71. Yea I’m old but that means I’ve been young longer than you.
Click to expand...

:flowers: I love your altitude!
 
Rich,
I have other attitudes if you’d care to hear.
 
I put my dial indicator on the top of the strut with the stem on the propeller shaft, then push the shaft up. In your case it sounds like .045 is the clearance. I agree with what Ski said. If it is already out of the water change it. If not, catch it next bottom job unless it is causing some type of operational issue.

If there is an alignment issue that will add to the expense. A new bearing may bind if the shaft is not aligned well in the strut. If that is the case the engine, strut or both may need to be realigned.

Beekeepergreg said:
Is clearance in the centered position. So if I can jack the shaft .045" is my clearance .0225"?
Thanks
Greg
Click to expand...
 
rgano said:
I have lsel areno doubt. Why else are we all here? :)
Click to expand...

I wonder what state (or continent) I was in when I proofread THAT?
 
Bill,
The seller had replaced a engine mount last fall, I don't think he had it aligned.
My guess is the failing engine mount misaligned the shaft and caused bearing wear.
BTW, I checked my current 30 pilot. No play whatsoever.
Greg
 
Maximum allowable clearance for a propeller shaft bearing is 2% of the shaft diameter.
E.g. for a shaft with a diameter of 50 mm; the maximum clearance allowed is 1 mm.
This is a general rule of thumb which works for most bearing types.
Different tolerances might be used for specialized bearings.
Easy to measure with a dial gauge on top of the shaft, zero it out with the shaft in the bottom position and then move it up and take a reading.
Sorry for the metric measurements, I'm from Europe. :)
 
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