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cutless bearing play - measures 0.010

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bobct

Advanced Contributor
I got the strut reinstalled yesterday and checked a couple of things. I measured the area where the bearing wears on the shaft and then did the same in a few other spots on the shaft. The measurements were essentially the same.

I don't have any play (maybe "play" is too strong a word) side to side but measure 0.010 moving up and down. I have an 1.25" shaft. In looking at the chart the Mark posted, it shows 1" and then jumps to 1.5". What's interesting is the "Minimum operating clearances" are 0.015 and 0.016 respectively.

If I'm reading that chart correctly, I'm actually below that range so if anything, the clearance is a little tight. I'm less worried about that, the shaft spins easily dry. I should be ok. Do you guys agree?


Bob
 
Bob: what you are describing is radial "play" or clearance. You need a minimum for the water film to exist. The maximum is when the gap is too large to support that same film.

If you look at the names on what I posted, it does have a little age (BuShips was done at the peak of the vietnam war). Modern materials and techniques have improved. I used it as a guide, more for the worn (too big) end. I think you are fine, especially with the easy spinning shaft. heck, I think you are ready to come down here and change my strut bearings!
 
Thanks Mark. With that, I'm off to install the my prop! Sure, I'd be happy to make a trip down there. If you really get stuck, just post your questions here, I'm sure we can help :)
 
bobct said:
I don't have any play (maybe "play" is too strong a word) side to side but measure 0.010 moving up and down. I have an 1.25" shaft. In looking at the chart the Mark posted, it shows 1" and then jumps to 1.5". What's interesting is the "Minimum operating clearances" are 0.015 and 0.016 respectively.

If I'm reading that chart correctly, I'm actually below that range so if anything, the clearance is a little tight. I'm less worried about that, the shaft spins easily dry. I should be ok. Do you guys agree?


Bob
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no paint on the shaft, I presume. Anyway, you will be good to go!!
 
yes, shaft is clean. I reinstalled everything yesterday and moving on to the rest of my punch list. You guys have convinced me it'll be ok, I know where to find everyone if not :)
 
Ooooh! I'd better start looking for a new identity!

It'll work just fine. Trust me.

Jeff--I mean, ah, Fred
 
FWIW, I got a call back from one of my associates. Turns out the AB&YC standards do address the shaft -bearing clearance, but not in totality. As best as i can tell, for most gasoline powered setups, for NEW installations, you will find the range from 0.003 - 0.009" of clearance. as far as a maximum (time to replace) clearance, the standards are silent.

With most things, when in doubt, check with the bearing maker for details.
 
ok, so I'm in the ballpark, albeit on the high end. My feeler gauges had a thin film of rust in spots so that bumped up the # a little. The reason I was making an issue out of this is because I've never felt play on either side until now. I looked at my Stb engine and while it spins fairly easily, I can tell it's off a hair. I guess that creates enough tension so that you can't feel any movement.
 
I would just run it and see what happens. If no vibration use it and forget about it. Is the bearing from a reputable company? I wonder if it isnt just a little out of spec.
 
sammi said:
I would just run it and see what happens. If no vibration use it and forget about it. Is the bearing from a reputable company? I wonder if it isnt just a little out of spec.
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At a pre-purchase survey last spring a surveyor noted 1/8"-5/32" of radial play in the port cutlass beaing on my Albin trawler. He said it might be "serviceable" but should be replaced if any vibration was noted during sea trail. If it ran O.K. (which it did) he said repair could wait for the next haul out given the low hours it would see up here in the Northeast. It caused no apparent trouble or vibrations during last season and I replaced it this spring (2" shaft/Cummins 6BTM diesel).

The new bearing fits tightly around the shaft with zero clearence or radial play. I assume it was desgined that way. So it would appear that either your shaft is slightly undersized or the ID of the bearing is slightly oversized. But I agree with the others that it is not likely to cause any trouble given the small amount of radial play you noted.

Best wishes,

Tom
 
I'll have to disagree with the clearance chart details or at least update things, that chart generalises over all water lubricated shaft bearings without giving specific details as to the type of material used in the bearing and its wall thickness or thermal conditions.

I can quote accurate figures for one of the more recent materials used in marine shaft bearings (commercial, military and some leisure boats)
For a 1" shaft in a 1.5" carrier you are looking at only 0.0047" as min radial displacement MRD.
Change it when it gets to 0.025"
This is current data where I can give you the break down of how this figure is arrived at. This includes unscheduled thermal expansion and some moisture swell of material for running temp to 40deg C.
The actual MRD for a 1" shaft is 0.0012"
You can check the clearances for instal and running on this calculator, just enter shaft OD and bearing Carrier/strut ID
http://www.h4marine.com/Downloads/Maritex AQUARIUS General Calculator REV 20100519.xls
 
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