Prop Shaft: A: New Cutlass Bearing Loose on the Shaft

[Roger Rathbun]

1988 C34 Mk1 #647, Universal M25XP

My boat is on the hard now for bottom paint, hull polish etc.
Decided to do maintenance on the PSS Dripless Shaft Seal ie replace bellows, hose clamps,O-rings, set screws.
I had several areas of difficulty but can deal only with one in each post.
   
A: Cutlass Bearing
My yard had the same tool for cutlass bearing removal shown in Mainsheet's article 'A New Prop Shaft' on his website:
http://www.pbase.com/mainecruising/new_shaft
It's a beauty and really beefy (will handle shafts up to two inches). Mine came out easily. With the cutlass out, and the shaft coupling off, the shaft slid out easily clearing the rudder by 1/4 inch.
My problem is this:
I clean the shaft with an abrasive bristle cone in a cordless drill. Works great and leaves the shaft nice and shiny. With the shaft out, when I slide the new cutlass on it seems much looser than I expected. If I stand the shaft upright, the cutlass will slide easily down the shaft (gravity). I can feel the play between the bearing and shaft. The old bearing (quite worn) will not do this.

Pic 1807 shows the shaft section which sits in the cutlass. The grooves are caused (I think) by small critters (barnicles) which grow between the ribs of the cutlass all winter. When I run the motor and turn the shaft, the tiny calcium shell cuts a groove. I can see the hard bits in the old cutlass at the right places. The grooves are not caused by the two set screws securing the cutlass (not in the right places). I don't think these grooves affect the operation of the cutlass.
(NOTE my first attempt at posting this was rejected because I could not shrink the pic's enough. This second attempt has only the first pic but the following description of the remaining three gives the general idea.)

Pic1816 is a shaft measurement (caliper reading) off the cutlass site. I get 998 or 999 (thousandths) over most of the length of the shaft.

Pic 1824 shows 999 at the cutlass site.

Pic1821 shows 997 in one of the grooves. Another showed 996 but they are only grooves, not lengthwise disturbances.

I have taken the shaft and cutlass back to the chandlers and tried another bearing they had in stock: same thing! These are the same bearings you all use:
Johnson Cutless Bearings 1" x 1&1/4" x 4". Manufactured by DURAMAX MARINE.

Question A1: Is this a problem? Does the cutlass rubber swell or expand a bit when submerged (like nylon) to become a tighter fit? I'm worried this situation might cause a lot of vibration.
Thanks

[Ron Hill]

Roger : The cutlass rubber is not going to swell!  Is there any chance of you trying the new cutlass bearing on another 1" shaft (stainless or bronze)?

The new cutlass bearing should fit snug on the shaft.

[Roger Rathbun]

Thanks Ron. I'll look around, see if I can find another shaft.
I called tech support at Duramax (440-834-5400). Very helpful. Says there should be clearance 3-8 thousandths between top of the nitrile rubber ribs and the shaft for water film. If you hold the bearing on the shaft between thumb and forefinger, and push with thumb (at 6'oclock), you should clearly see space at 12 o'clock. I'm relieved.

[Stu Jackson]

Roger, you can post more pictures in subsequent "Replies".

[Roger Rathbun]

Thanks Stu. This is pic 1824 referenced above.

[Roland Gendreau]

I wonder if the fit to the shaft will improve once it is pressed into place? 

[patrice]

Hi,

As Roland said, this is exactly what I was going to answer you.
You are trying the bearing loose on your shaft, but remember that when you will put it in the support, being press fit, will 'squweeze' it.
The ID of the bearing won't be the same, and fit between the bearing and shaft will become good.

[lazybone]

Hi,

As Roland said, this is exactly what I was going to answer you.
You are trying the bearing loose on your shaft, but remember that when you will put it in the support, being press fit, will 'squweeze' it.
The ID of the bearing won't be the same, and fit between the bearing and shaft will become good.

I hate to disagree Patrice, but I don't see any way that the metal bearing sleeve will signinificatly compress in radius after fitting.
Press fit tolerances are very, very small.

[Roland Gendreau]

Here is a thread on the subject that agrees with my hypotheses that the bearing ID will be reduced when it is pressed into the housing:

http://www.cruisersforum.com/forums/f55/cutlass-bearing-1830.html

[patrice]

Just to give you a rough idea,
Take your caliper and measure the OD of the bearing, and measure the ID hole where you will install the bearing.  Say this will give you the compression you will end up on the bearing.
Measure the OD of the shaft and the ID of the bearing.  This will give you the play dimension.
Now take your play measure minus the compression value = this will give you the final play you will get.
Again, this is not accurate procedure, but will give you a ROUGH estimate.

[lazybone]

From my machinists handbook under press fit for no rotational forces.
0005/.0010

I would be curios what the actual inside\outside measurements for the parts are?

[Ron Hill]

Guys : Reread the post as Roger's cutlass bearing is NOT pressed in, it is held in place by set screws!!!

What I asked Roger to do was to find out if the cutlass is the fit problem? and then to see if the shaft is the fit problem?!

A thought

[Roger Rathbun]

Thanks everyone for all the input.
Some of the dimensions requested:
Old cutlass bearing:       OD 1.248 to 1.250 (a few 1.247 and 1.253 spots!) Could have been distorted during push out.
New cutlass bearing:      OD 1.250 everywhere
                                  ID  1.007 to 1.008
Note this inside dimension is hard to measure (rib to rib) and it is only the first 1/2 inch into the bearing.
The shaft is 0.998 to 0.999"
The strut is very difficult to measure (at least for me). It is definitely not perfectly round. Think about it. Been in the water for 26 yrs, several bearing replacements - I can see the cut marks inside from the hack saws, who knows what pounding might have been applied.
Strut:            ID lots of 1.248 to 1.250, a few 1.246 and even 1.253" Again the caliper only measures in the first 1/2 inch.

Patrice: I had thought about this earlier and expected (hoped) that the compressed bearing would be a little tighter on the shaft, BUT NOT MUCH. It does seem that it might be pretty hard to compress a tube.

Ron: I have not found another 1" shaft. FYI this bearing will definitely be a press fit. The yard want me to sand the inside of the strut with emery cloth. They think their big pusher might still have trouble. Even after about one hour's working on it, I can only get the bearing in about 3/4 inch (by hand). I don't expect I should ever be able to get it in very far by hand but it is still pretty tight. The set screws are insurance I think.
The old bearing can be pushed in by hand about 1 to 1&1/2 inches. I plan to keep working on the strut and when happy, install the shaft and use their tool to push in the bearing from the aft. I hope it all goes in tomorrow, maybe launch Sat. Will report on how it goes.

[Solstice]

Hi Roger,
FWIW, after my 2nd season with the new boat I found a bit of play in my CB also. Although I do a realignment check every spring, I suspected that the Dealer didn't align properly and created some wear. Being a bit OCD, I decided to do what you did--I removed the old CB then ordered a Johnson Duramax. Found the same amount of play, so I called them and talked with an engineer. They provided the same info you posted: OD Tolerance is +/- .001, .002 Interferernce, .003-.008 ID tolerance. They also said there is tolerance for a water film. Since this didn't match my experience or what most will say about CB ID fit, I set about calling Morse (the other major manufacturer and the vendor Catalina uses) and ordering one of theirs. Same tolerances and same conversation. I then called the following: Buck Algonquin and Spartan in Maine. Finally I talked with Gerry Douglas. After all this, I installed the new Bearing and after a season found no play even though when I first installed it seemed to have the same play as the old one which based on my caliper readings were within spec of both CB vendors. Part of the reason for all my additional research and concern is because my shaft is fed through a Fiberglass skeg, not a strut and it is NOT press fit--this goes against all conventional wisdom. However after speaking with all of the above and in particular Gerry I had no choice but to trust that the slip fit plus set screws is by design. I have indeed found this to be the case. Sorry to provide all the extra info., but if your shaft is true and not scored where the Cutless should go, you should be fine per the CB engineers. Good luck and I apologize in advance if I confused the situation.

[Ron Hill]

Roger : As far as I know there are only two types of struts:
1. A pressed in cutlass bearing held in by compression
2. A bearing that is held in by two set screws (usually the starboard side)

The pressed in bearing can not be inserted more than about 1/8"
while the setscrew bearing might be inserted up to a couple of inches and then pressed or tapped into position until seated.

I know of no pressed in bearing strut that also uses set screws - as the set screws are completely unnecessary!
 
If your shaft shows set screw impressions, someone (a dunce) turned the set screws in completely thru the cutlass casing and violated the rubber into the shaft!!

If your yard did this work, I'd recommend that you not have even have them do minor surgery unless you Life Insurance is paid up!  

Don't know what else to tell you!!  A few thoughts