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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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  #1  
Old 04-15-2013
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Failing Cutless Bearing- What are Symptoms?

I think my cutless bearing has failed. It did have about 1/8 inch play but had been performing ok. Some vibration when turning prop at idle speed, but I could avoid that RPM. At full RPM no problems until a few days ago.

I cleaned the boat bottom and also barnacles from prop and shaft, then took the boat out. Whenever I hit 2000 rpm, boat speed above 4 knots) or more (on yanmar 3gmd) the prop shaft would get a really bad vibration and griding sound. Anything below 200 rpm everything was ok. In neutral the engine revs to 0 to full rpm with no vibration or noise.

I had been planning to replace cutless in a few months but now that might not be possible. I would have thought the cutless would slowly get bad.

Does this sound like the cutless? I plan to dive the prop in a few days to inspect. Maybe I forgot to clean on one side of a prop fluke and I got a bad imbalance.

Regards
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Old 04-15-2013
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Re: Failing Cutless Bearing- What are Symptoms?

1/8th inch play is too much! Its bad.
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Old 04-16-2013
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Re: Failing Cutless Bearing- What are Symptoms?

Hey,

When my cutless was bad I got a knocking sound and bad vibration. Sounds like it's time for a change.

Barry
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Old 04-16-2013
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Re: Failing Cutless Bearing- What are Symptoms?

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Originally Posted by BarryL View Post
Hey,

When my cutless was bad I got a knocking sound and bad vibration. Sounds like it's time for a change.

Barry
Does the knocking and vibration manifest itself when using reverse, then as the bearing gets worse it starts knocking and vibrating when in forward? When I give it high throttle in reverse I have noticed the knock and vibration, now it has moved to forward gears above 2000 rpm.

Plan to dive the prop this weekend and double check for other problems, and also check engine mounts are ok. If all those check out, I am looking at pulling the boat out of water to change cutlass.
Regards
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Old 04-16-2013
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Re: Failing Cutless Bearing- What are Symptoms?

Casey,
Usually 1/16" of play in the shaft at the cutless bearing indicates it is time to replace.

I had about 1/16" of play in our shaft 2 years ago and went to replace the cutless bearing. Same knocking and vibration from the drive train you are experiencing. Turned out that our shaft was badly scored (bronze shaft).

Expect to replace the flange, shaft, shaft log hose, hose clamps, cutless bearing and stuffing box packing all at once. We did all of this ourselves (except for cutting a new shaft) and the materials cost well below $1K, or 1 boat buck. Also a good idea to have a prop shop spin your prop to find out if it is still in balance. If you do all of this I would expect your drive train to be good for another X years (40>X>=10).

If you have a bronze prop shaft I'll suggest cutting it to ease in removal as it is likely you will need a new shaft anyway and it can be quite difficult to separate the flange and prop.

Here is a long winded description of my drive train rebuild: 2011, November 30th. Begin drive train rebuild | Odalisque
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Old 04-17-2013
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Re: Failing Cutless Bearing- What are Symptoms?

Hey,

My boat is on a mooring so I rarely use reverse. I don't recall the problem being more apparent in reverse, but that doesn't mean it wasn't there first.

Good luck,
Barry


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Originally Posted by casey1999 View Post
Does the knocking and vibration manifest itself when using reverse, then as the bearing gets worse it starts knocking and vibrating when in forward? When I give it high throttle in reverse I have noticed the knock and vibration, now it has moved to forward gears above 2000 rpm.

Plan to dive the prop this weekend and double check for other problems, and also check engine mounts are ok. If all those check out, I am looking at pulling the boat out of water to change cutlass.
Regards
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Old 04-17-2013
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Re: Failing Cutless Bearing- What are Symptoms?

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Originally Posted by CalebD View Post

Expect to replace the flange, shaft, shaft log hose, hose clamps, cutless bearing and stuffing box packing all at once. 2011, November 30th. Begin drive train rebuild | Odalisque
Caleb,
Thanks for info. Yes it looks like the prop shaft is bronze and 35 years old. I was planning to go through the entire drive system and replace shaft, packing gland/hose, and cutlass bearing in 6 months to a year as everything is worn and corroded. But now that may not be possible. Tied up with some other "projects" at the moment, but might need to bite the bullet and fix boat "right" as a priority.

Read your link. Why is it that bronze is not used much for the prop shaft? Seems most go with stainless now. But the stainless seems to have more poblems with corrosion and electrolysis with the bronze prop. Seeing our bronze shafts have lasted over 30 years, bronze looks to be a good material to use.

Last edited by casey1999; 04-17-2013 at 01:52 PM.
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Old 04-17-2013
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Re: Failing Cutless Bearing- What are Symptoms?

Casey,

Bronze made a fine material for a prop shaft. It is a little softer than SS and was widely available when our boats were made. Bronze was cheap back then too.
Nowadays bronze is expensive compared to SS. Try pricing a bronze prop shaft vs SS. Formulations of SS are also much better now then they were way back when.

I will say I am not looking forward to the day (may it never come) when I have to cut our current SS shaft. The old bronze shaft took about 1 minute to cut with a fresh metal Sawzall blade.

I am not aware of increased problems of corrosion or electrolysis with the SS shaft. Talk to me in 10, 20 years and I might be singing a different tune. For now I just keep a collar zinc behind the prop and all seems fine.
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Old 04-23-2013
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Re: Failing Cutless Bearing- What are Symptoms?

I dived the prop over the weekend and found the prop had shifted forward about 3/4 inch to the point where it would rub the shaft strut. The transmission is a V-drive and the shafted could be seen at the coupling to have shifted the 3/4 inches. I think what was happening is at rpm above 2000 there was enough force to shift the prop against the strut and cause the rubbing sound and high vibration. The coupling is called a spit coupling and it has no set screw, although it is drilled and tapped for one. Not really sure what holds the prop to the coupling. Below is a pic, is it only the clamping friction?

Plan to push prop shft back where it should be and tighten everything up and maybe install set screw. If all runs without excessive vibration, I'll let here go for a few months when I will haul out and replace cutlass, packing and engine mounts. Thanks for comments.
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