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Cutless Bearing Replacement


Look familiar? First a riddle: What's dry and cracked and green all over? A 30-something year old cutless bearing on a classic cruiser. Early this spring I wanted to find the source of an annoying vibration coming from the starboard side aft of the boat. I knew the boat needed cutless bearings after the surveyor identified them as worn but serviceable 2 years prior.

I knew I didn't want to pull the shafts and monkey with the dripless shaft seals. Not to mention the boat was not blocked high enough in the rear to get the shafts out anyway.

I decided I wanted to do them with the shafts in place. While many people have crafted their own tools for this very job, I decided to leave the engineering to a professional. I must first disclose that I am not a paid spokesperson. I am one who likes to give credit where credit is due. I ended up buying a tool from a company called StrutPro (https://strutpro.com ). For my 1.5" shafts with struts that accept Flatfish style bearings, I purchased the tool capable of pressing a 6" long bearing.

At $450, the price of admission is not insignificant for one of these tools. However, I was chatting with a dock mate who said he got his 2 bearings replaced at $1000 each from a local service outfit. My washed-up engineering brain quickly computed a prospective $4000 repair bill was not out of the realm of possibility with two struts per shaft on my 41 Commander. I figured with the purchase of the tool and doing it myself, I could keep the repair bill under $1000. That leaves $3000 to make future bad investments in the boat :)

Shipping was really quick from StrutPro. I think the tool arrived in less than a week.


I ordered 4 replacement bearings (and a bunch of thruhulls - another blog about those to come) from Defender, which also arrived quickly.

One an unseasonably warm stretch in February I decided to try and knock out this project ahead of the spring launch rush.

First order of business to was remove the set screws. I had this sinking feeling that they were going to be difficult to remove but I was met with a pleasant surprise when they all snapped loose and backed out with ease.

Because of the dual strut per shaft arrangement, removing the forward bearing requires pressing it aft out of the forward strut, then pressed again through the rear strut and out.


I opted to use a ratchet with a long handle rather than an impact gun so I could get a better feel for the force being applied and any binding that may occur. I'll warn you that once you start cranking it feels like nothing is going to happen even while continuously applying torque to the tool. Until something happens. It will surprise you if you aren't expecting it. A loud pop. Loud enough where I gasped, thinking I broke the strut or the tool. Luckily it was neither. The cutless bearing moved! From that point on its a game of tightening one side of the tool, then the other, then repeat. The tool is very forgiving to minor lateral misalignment but the job goes a lot faster if the tool is kept square against the bearing and strut.

First press done!

Now lets get the aft bearing out and get the forward one out through the aft strut!


I repeated the process for the other shaft. The first press took about 30 minutes with a moderately steep learning curve getting the hang of setting up the tool. The remaining presses took less than 10 minutes each. Pro tip: it helps to gently tap the strut with pressure applied to the tool to encourage the first *POP* for stubborn bearings.

Installation is opposite removal. Another pro tip: place the new bearings in the freezer overnight before installing. This shrinks the outside diameter of the bearing temporarily which makes pressing much easier. As an added measure, I applied a little dishsoap on the OD of the bearing.


After all the new bearings are installed, I very carefully fitted a 1/4" drill bit to my cordless drill, carefully passed the bit through each set screw hole and created shallow craters on the surface of the OD of the bearings. This creates an anti-rotation feature on the bearings. Based on my experience, I doubt rotation would ever occur with the tightness of the press fit, but I agreed with the physics of it so I went ahead and did it anyway.

Add a little blue Locktite to each set screw and cinch them down. Job done!

As you can see, this is a very doable job for the DIYer and is both satisfying and cost effective. If you'd like to recoup some of your money, you could always sell the tool for a few bucks.

On my first trip out this year the vibration was gone and the running gear was totally quiet. This was a fun little job that made a huge impact!


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