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I just received new cutless bearings from Italy for the Riva B25. Unusual dimensions, so I had to get them from the Riva parts distributor. However, they are very tight and must be forced onto the shaft - leaving no play whatsoever. I believe there should be a minor clearance even when new, but the Riva guy claims bearings are good. He supplied both shafts and bearings.

This makes the shafts very hard to install and align. I'm new to shaft installations and need tips. Is it harmful to install tight cutless bearings? Any tricks to open up the bearings a fraction?

Whats their diameter? Metric or inches?

Yes there should be some clearance between shaft and bearing.

Some as in a sheet of papers worth or so.

Where bearings tight prior to installing in strut? If so, are you sure you have correct bearings. Some metric and inch sizes are close...but not close enough to be compatible.

If bearing slid nice on shaft prior to install...could set screws be too tight? Was bore of strut round. Did they collapse bearing on install.

Was shaft ok going in strut at first then as you got into the shaft log it got tighter...alignment could be off...bent/twisted strut.


Next...was any petroleum product used on the rubber cutless. Rubber in the cutlass can swell and turn hard if contaminated with oil products.

Cutlass bearings are tight in the strut but should slide on the shaft with very little effort.

Thanks, you are confirming what I expected.

Both shafts and bearings were supplied by the Riva parts dealer, and he insists that they will be fine if forced on with some silicon spray or similar. They have not been damaged or contaminated. I’d try alternatives but they are hard to find. 1 1/8 inside and unusual dimension outside.

Is there anything I can do to make a bit of tolerance? Do you think it is damaging to install them tight, or will they naturally loosen within short?

Odd Outer dimension? Hmm...maybe a metric bearing and not 1-1/8"


1-1/8" Cutless bearings come in 3 standard Outside Diameters (OD).

shaft x OD x length
1-1/8 x 1-1/2" x 4-1/2" (1.125 x 1.500 x 4.500")
1-1/8 x 1-5/8" x 4-1/2" (1.125 x 1.625 x 4.500")
1-1/8 x 1-3/4" x 4-1/2" (1.125 x 1.750 x 4.500")

What is the OD of your Bearing, what is the length?

If OD and length do not match one of the above standard sizes you may have a Metric
Bearing, most likely for a 28mm shaft.

Standard Metric is 28 x 42 x 112mm long
(1.102 x 1.653 x 4.409")


28mm is 1.102" plus a few thousandths normal clearance would be around 1.108 or so....
1-1/8" shaft is 1.125...that would make for a snug fit for sure.


If 28mm, will it wear in...yeah, I guess so...bearing wear especially quick when rubbing hard.


Regardless, I'd refrain from silicone or petroleum based lubricants to slide shaft in...I recommend when needed to use dish soap and some water.

Thanks Carl - very helpful!

Sounds like you do this for a living? Quite possible that the dimensions are mm. Lengths are 50 and 101 mm, but unsure about outside. I don’t have them available right now, but will check.

Lars wrote:
Sounds like you do this for a living? Quite possible that the dimensions are mm. Lengths are 50 and 101 mm, but unsure about outside. I don’t have them available right now, but will check.

Underwater hardware used to be our bread and butter.

50 and 100mm, is that the Strut and Intermediate strut length? They are not set as they can often accept various size bearings with different lengths. I was referring to stock size bearing length.

You are right, those are the two struts. Looks like you are onto the issue with the mm dimensions, because the outside is 40mm; likely that the inside is 28. Still, that makes for a pretty odd dimension of 28 x 40 x 101 mm. (Or 50 long for the short strut)

OD 1 5/8 would be about 41mm I guess - wouldn’t be a good idea to force that into a 40mm strut opening.

Not sure I can think of anything but soaping them on and let wear happen.. At least that is what Riva-guy says.

Lars wrote:You are right, those are the two struts. Looks like you are onto the issue with the mm dimensions, because the outside is 40mm; likely that the inside is 28. Still, that makes for a pretty odd dimension of 28 x 40 x 101 mm. (Or 50 long for the short strut)

OD 1 5/8 would be about 41mm I guess - wouldn’t be a good idea to force that into a 40mm strut opening.

Not sure I can think of anything but soaping them on and let wear happen.. At least that is what Riva-guy says.

I'm guessing in your neck of the woods Inch Bearings are not as easily accessible as they are here and they rather not stock the oddball size. They may be turning bearing OD to fit bore giving that odd size...then its force shaft in place calling it a day.

Thanks for the insights. You - and the forum - rock!

Didn’t feel good about forcing the shafts in, so ended up buying new 1 1/8 bearings, and machining down the outer diameter to fit the 40mm struts. Bit cumbersome, but they fit beautifully now, and feels good to have done it “right”.

Big thanks to Carl for insights!

You can't beat doing it the right way!

Glad the info offered some help to you,

Carl