Cutless bearing
 

Posting about shaft packing got me thinkin about cutless bearings and
when it is time to replace them. My shaft wiggles just a little bit
(almost no play) in the bearing and it is 24 yrs old. Last time I was
in a boat yard, I went around wiggling shafts in cutless bearings and
found a huge variation in bearing "play". Some were tighter than mine
but most were looser. One was so loose it would THUNK from side to
side. What is normal and what is bad?

I replaced mine, when it would make a noticable jump (not quite a "thunk")
when I wiggled it side by side). I would guess it was at least 1/32" of
play. It did smooth out the prop vibration a bit. Different boats respond
differently to cutless bearing play it seems.

David

wrote in message
oups.com...
Posting about shaft packing got me thinkin about cutless bearings and
when it is time to replace them. My shaft wiggles just a little bit
(almost no play) in the bearing and it is 24 yrs old. Last time I was
in a boat yard, I went around wiggling shafts in cutless bearings and
found a huge variation in bearing "play". Some were tighter than mine
but most were looser. One was so loose it would THUNK from side to
side. What is normal and what is bad?

Normal *installed* clearance is 0.003-0.005" per inch of shaft diameter.
The *installed* requirement includes the 'press fit' in the housing
...... which means that the bearing inside diameter gets smaller when
you *press* it into the housing.

So when ordering a new bearing you must measure (with micrometer) the
housing journal inside diameter to ± 0.001 AND the shaft diameter.
to±0.001

A perfectly sized cutless installed to a shaft/engine that is perfectly
aligned will last many many years.


article .com,
wrote:

Posting about shaft packing got me thinkin about cutless bearings and
when it is time to replace them. My shaft wiggles just a little bit
(almost no play) in the bearing and it is 24 yrs old. Last time I was
in a boat yard, I went around wiggling shafts in cutless bearings and
found a huge variation in bearing "play". Some were tighter than mine
but most were looser. One was so loose it would THUNK from side to
side. What is normal and what is bad?

Is wear in the cutless bearing determined by how well the engine and
shaft are aligned?

No. besides misalignment, wear can occur by abrasion of the
undissolved contaminants in the water ... silica particles, etc.

How to measu after you perfectly align the engine, put a dial
indicator on the shaft at the cutless bearing and 'move' it then
relocate the dial indicator 90 degrees on the shft and move the shaft.

Each manufacturer of cutless bearings (the good ones) will have a
specified 'installed' clearance. What I mean by installed clearance
is that the bearings inside diameter will become smaller when you
press/push it into the housing journal.

When you replace to a new cutless, accurately measure the shaft to
0.001", remove the bearing from the housing and measure the inner
diameter of the housing to 0.001". Simply give these dimensions to
the bearing supplier. Obviously the shaft must be fairly free of
defects such a galling, pits, etc. or the shaft should be
remachined/polished back to 'true'. Surface roughness on the shaft
will promote bearing wear (during 'start-up', when the shaft is no
supported by the water film and the bearing material is actually
touching the shaft. Otherwise when running the shaft will be prevented
from touching the shaft by a thin film of water - a hydrodynamic
bearing. Thats why the sizing is fairly critical as the clearance is
VERY important. .


In article .com,
wrote:

Is wear in the cutless bearing determined by how well the engine and
shaft are aligned?

Rich,
Interesting topic. I can't help but wonder how many people can measure to
..001. Shaft measurement (OD) is fairly straight forward, but inside measurments
(ID) of the housing require a device ...the name of which I don't recall.
And if they can, what are the odds that the center axis of the housing is
that of the shaft. What are the odds that the shaft is straight..even if new?
I.e., the run-out.
To complicate things further, when the engine is spun up to 2,500 rpm,
isn't the torgue of the engine going to cause misalignment by at least a
few .001's? Maybe a good arguement for U-joints and pillow blocks?

I wonder what the maximum clearance is that would still provide a
"water bearing"..any idea?

As I say..interesting..:)
Norm B
On Tue, 14 Jun 2005 20:11:50 GMT, Rich Hampel wrote:

No. besides misalignment, wear can occur by abrasion of the
undissolved contaminants in the water ... silica particles, etc.

How to measu after you perfectly align the engine, put a dial
indicator on the shaft at the cutless bearing and 'move' it then
relocate the dial indicator 90 degrees on the shft and move the shaft.

Each manufacturer of cutless bearings (the good ones) will have a
specified 'installed' clearance. What I mean by installed clearance
is that the bearings inside diameter will become smaller when you
press/push it into the housing journal.

When you replace to a new cutless, accurately measure the shaft to
0.001", remove the bearing from the housing and measure the inner
diameter of the housing to 0.001". Simply give these dimensions to
the bearing supplier. Obviously the shaft must be fairly free of
defects such a galling, pits, etc. or the shaft should be
remachined/polished back to 'true'. Surface roughness on the shaft
will promote bearing wear (during 'start-up', when the shaft is no
supported by the water film and the bearing material is actually
touching the shaft. Otherwise when running the shaft will be prevented
from touching the shaft by a thin film of water - a hydrodynamic
bearing. Thats why the sizing is fairly critical as the clearance is
VERY important. .


In article .com,
wrote:

Is wear in the cutless bearing determined by how well the engine and
shaft are aligned?

engsol wrote in
:

Rich,
Interesting topic. I can't help but wonder how many people can measure to
.001.

Are y'all talkin' 'bout the same ones I see all covered in gook and
wigglers and barnacles or those ones in the magazines that look like a
trophy for someone's game room?

Do you measure .001" before or after you scrape off the barnacles and green
slime?...(c; I wonder how many hours those shrimp boat cutless bearings
have on them and who measured their clearances. Seem to put a lot of tough
hours on them around the leaky packing glands.

--
Larry

You know you've had a rough night when you wake up and your outlined in
chalk.