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Old 01-10-2011, 17:25   #1
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Question About Cutlass Bearings

I have to replace the entire shaftlog and prop bearing and am about to order the pipe I need.

I looked at cutless bearings, and for my shaft size (1 1/8) I find both metallic and non metallic bearings, with an OD of 1.500.

Now if I go with 1 1/2 pipe, OD 1.900, schedule 40 will give me a slop fit of .055 per side. If I go with shedule 80, this will give me a interference fit and the bearing will have to be pressed in place. Using tools I don't have and will either have to buy or fabricate.

Which is better? I'm inclined to go with a non metallic bearing and epoxy on the sloppier fit. Easier to install, easier to remove later.

Comments?
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Old 01-10-2011, 17:30   #2
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Consider this. If you have to press it in, how will you get it out later when you need to replace it? Cutlass bearings are held in place with set screws, so a little play is no big deal.
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Old 01-10-2011, 17:32   #3
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Re: Question about cutless bearings.

sabre--is yours in the hull or in a strut
i was told had to fit perfect.
what kind of shaft log is it....
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Old 01-10-2011, 17:53   #4
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Re: Question about cutless bearings.

Have a piece of schedule 80 pipe bored to size at your friendly local machine shop and they can drill and tap for the set screws at the same time. An hour to do both.
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Old 01-10-2011, 18:09   #5
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Re: Question about cutless bearings.

my bearing is a press fit
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Old 01-10-2011, 19:05   #6
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Re: Question about cutless bearings.

Quote:
Originally Posted by perchance View Post
Have a piece of schedule 80 pipe bored to size at your friendly local machine shop and they can drill and tap for the set screws at the same time. An hour to do both.
+1 and having a heavier walled pipe just seems to be intuitively better.
A snug fit and set screws will always be better for later maintenance then a press fit or a glued sloppy fit.
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Old 01-10-2011, 19:38   #7
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Re: Question about cutless bearings.

Quote:
Originally Posted by SabreKai View Post
I have to replace the entire shaftlog and prop bearing and am about to order the pipe I need.

I looked at cutless bearings, and for my shaft size (1 1/8) I find both metallic and non metallic bearings, with an OD of 1.500.

Now if I go with 1 1/2 pipe, OD 1.900, schedule 40 will give me a slop fit of .055 per side. If I go with shedule 80, this will give me a interference fit and the bearing will have to be pressed in place. Using tools I don't have and will either have to buy or fabricate.

Which is better? I'm inclined to go with a non metallic bearing and epoxy on the sloppier fit. Easier to install, easier to remove later.

Comments?
As you talking about using PVC as a shaft log on a FRG boat? Or metal tubing on a metal boat?
- - Assuming metal tubing on a metal boat - the fit should be zero clearance. That is 1.500 cutlass bearing O.D. with a tubing that is 1.500 I.D. That would suggest the Schedule 80 - 1.500 I.D. pipe.
- - Cutlass bearings are normally press fit into place. Although the realistic tool for this purpose is normally a sledge hammer and a piece of 2x4 wood.
- - The Fiber cutlass bearings are much easier to both install and remove since they can be easier cut than metal shell bearings.
- - The thicker walled Schedule 80 will also allow you to drill and tap set screws to help hold the cutlass bearings from rotating.
- - Additionally, take special care that the tubing does not get "warped" by the welding procedures. And be sure that the tubing is really welded in place for maximum strength. Installing a new/replacement cutlass bearing in the field normally involves some significant pounding and you don't want the shaft log to break free.
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Old 02-10-2011, 17:05   #8
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Re: Question About Cutlass Bearings

@Zeehag, its a 4 inch long section of pipe on the prop struts and a 12 inch section coming through the hull. Since I'm going to be building the mounts, replacing the shaft log and the prop bearing tube all at the same time I'm going to use a 6 foot long section, which will be mounted to the bearers at the appropriate off set for the transmission, and then welded at the hull and prop struts. Once its all solid, I'll take my grinder and remove the bits in between.

@ Osirissail, the tube is steel, as is the boat. I like Wotnames idea of using the schedule 80 bored out a tad to allow the bearing to be slid in and locked with set screws.

I'll see about getting the pipe and have it bored out in the next week.

thanks everyone for the guidance.
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Old 02-10-2011, 18:38   #9
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Re: Question About Cutlass Bearings

If you bore out the pipe to make it so that the cutlass bearing slides in and out easily, then I strongly suggest that you should only use the metal type cutlass bearings, see below.
- - And drill and tap for several set screws around the shaft log and bearing. The rotational forces from the rotating propeller shaft against the non-moving rubber "bearing" are considerable especially when sea life and debris works it way up into the flukes of the rubber part of the cutlass bearing.
- - Without set screws installed so that they enter a drilled indent in the shell of the cutlass bearing, it is likely that the whole bearing, shell and all will start to rotate in the shaft log tubing. And it has the potential for the bearing to work/walk its way out of the boat's shaft log. There's a reason why the standard installation is "press fit" with zero tolerance between the I.D. and O.D.
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Old 03-10-2011, 00:53   #10
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Re: Question About Cutlass Bearings

The bearing should be a press fit. You can make an appropriate mandrel with a hole in the middle, use a length of threaded rod with a heavy washer on the inside end of the tube, and gradually pull it in as you tighten the nut on the rod, or just belt the mandrel with a heavy hammer.
A bit of anaerobic sealant smeared over it could also be useful.
To remove it, just get a hacksaw blade, tape one end to make a handle, and slit the bushing. It will collapse and be easily removed.
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Old 03-10-2011, 04:42   #11
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Re: Question About Cutlass Bearings

Buy the bearing with the 1.75 OD, and have the machine shop reduce all but the last .5 to size. Leaves you a shoulder to grip next time removed. works for me.
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Old 03-10-2011, 06:05   #12
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Re: Question About Cutlass Bearings

Quote:
Originally Posted by Blue Stocking View Post
Buy the bearing with the 1.75 OD, and have the machine shop reduce all but the last .5 to size. Leaves you a shoulder to grip next time removed. works for me.
Huh? What are you reducing in size? The shell of the cutlass bearing or the shaft log? If you are removing 1/8" of the brass shell of the cutlass bearing, that is a lot of metal. How much of the brass shell is left?
- - The cost of the machine shop time to do this would be a factor. Why not just keep it simple (KISS) and use a non-metallic with the 1.50" O.D.? And then you (or the next owner) can use stock cutlass bearings in the future.

Here is a chart of the brass shelled and the non-metallic cutlass bearings for 1-1/8" prop shaft:
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Old 03-10-2011, 07:10   #13
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Re: Question About Cutlass Bearings

Johnson Duramax make 1.125 shaft size bearings, up to 2.00 OD. Leaving the shoulder on the bearing makes later removal very simple. shrug.
15 mins on the lathe--$25
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Old 03-10-2011, 10:08   #14
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Re: Question About Cutlass Bearings

Depends on the bearing material, as press fitting a bearing will give rise to bore closure so there needs to be extra clearance on the shaft. The latest composite bearings (no rubber) can be supplied or machined to any size. There are a number of suppliers of these now.

Epoxy fit makes fitting and removal a very easy DIY job with no special tools.

Best to check with bearing manufacturer, for the ones I use they provide a calculator and recommend they are fitted as clearance bedded on epoxy (be sure to use a low temperature epoxy so that when you come to remove the bearing a small ammount of heat will soften the epoxy, we use Araldite 2011)

Here are the sizes the calculator comes up with (in mm, 1" = 25.40mm)
Clearance fit.
Shaft 28.575 carrier 38.10
ID 28.68 - 28.78
OD 37.80-37.90

Interference fit.
ID would be 28.70 - 28.80 as it would close down as it is pushed in, and the OD is only 0.03 - 0.04 bigger than the carrier.

Epoxy fit is a much better option than pressing them in.
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Old 03-10-2011, 10:42   #15
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Re: Question About Cutlass Bearings

From my experience on commercial and leisure vessels with shafts from 1" to 8"

Set srews are there as added security.
Bearings require support either as a known interference fit or as a clearance fit with a bedding of epoxy, this in most cases is enough to prevent rotation or movement. Set screws are an extra form of security. If you use them to hold the bearing you are likely to squeeze the bearing, they should only sit lightly in the bearing dimple or hole.
"bearings should only be a press fit"? only if the manufacturer has sized the ID for a press fit, it will be smaller once fitted

Several mentions of hammers, not a good idea especially on struts.

"standard installation is press fit" I wouldn't say it is standard, more historic and common. There have been freeze fit and clearance fit options for more than 20 years now using newer materials.
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