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Old 03-06-2021, 11:53 PM   #1
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Play in Stern tube bearing, what is too much

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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Old 03-07-2021, 12:13 AM   #2
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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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Old 03-07-2021, 12:21 AM   #3
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There shouldn't be enough you can feel if you try to turn or shake the shafts.
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Old 03-07-2021, 08:41 AM   #4
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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.
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Old 03-07-2021, 08:45 AM   #5
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Greetings,
Mr. B. Agree with Mr. fb. Shouldn't be able to feel any play.
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Old 03-07-2021, 09:12 AM   #6
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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.

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Old 03-07-2021, 07:21 PM   #7
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I measured today. ----.045" I can lift the shaft. How much will the bearing shrink when it is dry?
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Old 03-07-2021, 07:40 PM   #8
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I don’t know that it will shrink or not but is sounds like it needs replacement.
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Old 03-07-2021, 07:45 PM   #9
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Greetings,
Mr. B. "How much will the bearing shrink when it is dry?" I'm guessing .000". Yep, time to replace.
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Old 03-07-2021, 09:00 PM   #10
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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.
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Old 03-07-2021, 09:21 PM   #11
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Greetings,
Mr. B. Mr. Ski's answer is better (based on experience). Forget mine (based on anecdotal information).


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Old 03-07-2021, 09:34 PM   #12
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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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Old 03-07-2021, 10:53 PM   #13
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Thanks everyone. I am going to see if I can get the owner to replace.
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Old 03-07-2021, 11:26 PM   #14
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Originally Posted by Nomad Willy View Post
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.
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!
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Old 03-08-2021, 12:03 AM   #15
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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.
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Old 03-08-2021, 06:11 AM   #16
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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.

Quote:
Originally Posted by Comodave View Post
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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Old 03-08-2021, 07:19 AM   #17
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Is clearance in the centered position. So if I can jack the shaft .045" is my clearance .0225"?
Thanks
Greg
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Old 03-08-2021, 08:40 AM   #18
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Quote:
Originally Posted by Nomad Willy View Post
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.
I love your altitude!
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Old 03-08-2021, 09:51 AM   #19
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Rich,
I have other attitudes if you’d care to hear.
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Old 03-08-2021, 01:05 PM   #20
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Rich,
I have other attitudes if you’d care to hear.
I have lsel areno doubt. Why else are we all here?
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