The cutlass bearing on my N30 was replaced July 2022. A couple of weeks ago I heard an unfamiliar knocking sound when the engine was in gear, and after a diver inspection it transpired that the cutlass bearing was completely gone.
Is this 2 years a reasonable lifespan for a cutlass bearing? Or are the other issues at play?
A few thoughts/facts
A new folding 2 bladed Gori prop was installed at the same time 2 years ago, could it be causing more vibration? There is a little bit of play in the blades see video here.
Engine axle looks aligned according to the yard foreman, but perhaps it’s a little misaligned?
Could the axle itself not be perfectly straight?
Or is this just normal and I need to accept that every couple of years I need a new bearing?
Robin
How much does the shaft move when pushed up and down. I have heard that 1/8 to 3/16 inch is the time to replace. In fact I just did that this spring. I was surprised to find the new bearing allowed.020in movement.
Robin,
2 years seems to be a short life. When I first got La Reina the cutlass bearings were not lasting very long and it was a combination of high silt levels in the water and an alignment issue. The Frazer river pumps a lot of silt into my sailing area, nothing I can do about that. The improved alignment has extended the life of the bearings.
Once the bearing wears and the shaft develops excessive movement the wear accelerates.
The rubber is all gone. In terms of engine alignment, the important thing is that the axel is in the middle of the hanger cylinder when the prop is off. Correct?
You mention two years but neglected to mention how many hours of motoring. In any case, to justify a worn cutlass, you must have motored a lot! So, I would say that it’s not normal and that it should last for at least 8 years.
The problem could be caused by a bent shaft, misalignment, prop out of balance, or rough surface of the shaft. Perhaps one could think of more reasons for a bearing to wear excessively.
Then you asked if the shaft should be in the center of the struts hole. No, the weight of the shaft will make it drop. If the shaft is in the middle of the hole, it is misaligned, for sure. The same goes for the other side. The shaft will not be in the middle of the shaft tube or dripless seal once it is disconnected from the gearbox.
Another fun fact about cutlass bearings is that they tend to be nice and tight when you just hauled out, and that they have a little play after being a winter season on shore. This is normal. When permanently underwater, the rubber of the cutlass (as does any plastic) swells a little as it takes on water. It shrinks when the water evaporates.
You can check the alignment of the engine by unbolting the gearbox flange (coupling). Then secure the shaft in the middle of the strut and the shaft tube. After that, take a feeler gauge and check for any space between the flanges. Don’t forget that the flanges also need to be absolutely in line with each other. The procedure is described in the manual for the Hurth v-drive gearbox.
Robin: You should have had some very bad vibrations long before that rubber material wore away. Also, the shaft may now be worn since it’s metal on metal now. In addition, you have to replace that cutless bearing before you can check the shaft alignment.
Thanks everyone, this is really helpful. I’ve relayed the information to the yard and hoping they will do the right things.
Mark H, can you point me to the right transmission manual with the alignment procedure? I’ve been looking online through a bunch of PDFs but can’t seem to find anything about alignment procedure. I’d like to share this with the yard.
Triggered an alarm here. If you have concerns that you have to give your mechanics guidance on doing prop shaft alignment I’d suggest getting recommendations for other yards. Not every mechanic does it, or should, because it can require care and patience that not all have. But any decent yard has a mechanic that can do it, and knows which mechanic that is.
Seconding multiple others, two years for a cutlass bearing is absolutely not normal or acceptable. Over seven boats in 40 years of boat ownership, I’ve needed to replace one only a few times.
I don’t understand how you could wear out the rubber in two years without hearing or feeling noise and vibration earlier, prior to sudden onset of symptoms and a total failure of the bearing. I’m wondering about defective manufacture of the cutlass bearing you installed two years ago.
I’d suggest making sure that your boatyard gives you that old bearing for inspection when you have it removed and replaced. If you’re using the same boatyard, try to find out what brand they installed two years ago, and try to make sure that this time they use a name brand like Johnson, Vetus or Morse.
There’s a lot of useful information in https://marinehowto.com/replacing-a-cutlass-bearing-sleeve-bearing/ that’s worth reviewing. (There’s long, entertaining, but not essential rant first that explains the history of “cutlass” vs. “cutless”. If you want to get to the meat, scroll down from the heading, “Rant on,” until you get to the heading, “Do Quality Bearings Matter?” Then read the rest from there.)
The work 2 years ago was done by the old owner in a different yard (Gran Marina in Alameda, watch out folks!), and the work this time around is done by Spaulding Boatworks, my local yard in Sausalito. It’s clear that the old yard made a ton of mistakes, pretty shocking actually:
The folding prop blade pins were installed inverted
There was no key in the coupling!!! and the set screws were holding the shaft in place!!!
The shaft ended up slowly riding up the coupling about 1 in and rubbing against the engine room door
And the list goes on…
Pretty shocking really. Anyway, the new yard seems great, they’ve been super thorough and I am hoping that the long list of mistakes done last time around were the root cause of the cutless wearing out.
"There was no key in the coupling!!! and the set screws were holding the shaft in place!!!
The shaft ended up slowly riding up the coupling about 1 in"
I have seen this before (not on my boat). We found the chewed up key in the bilge. The shaft spat the key out when it was put in reverse one day but the shaft/coupling must have been loose for a long time before that. A zink on the shaft just before the cutlass bearing prevented the shaft from leaving the boat. Have a look around your bilge.
If this happens away from the marina, a substitute 1/4 inch key can be found holding your steering wheel from spinning on its shaft. It will fit if the keyway has not been damaged too much.