Engine Vibration

Carbon · March 31, 2025, 11:22:27 AM

I've got what I think is a bad engine vibration with my C34. I've assumed that the problem is that it needs new engine mounts. However, this weekend, I got a little more serious about the new mount project and spent some time looking it over. I'm starting to question whether the mounts are the problem.

The vibration is the same whether it's in or out of gear, so I don't see how it could be alignment. I'm starting to think that the engine may be in a bind.

If you try and move the engine, it's almost like it's bolted directly to the stringers. When the engine is running, it hardly moves at all on the mounts. It could be that the mounts are so far gone that they have not give to them. Or it could be that it's bound up on the mounts.

Any advice would be appreciated.

Jack

Ron Hill · March 31, 2025, 01:33:31 PM

Jack : You have the original engine mounts!! That port side forward mount is probably shot from oil while changing the filter. I'd change all of the mounts and you'll have a NEW engine!!

A thought

waughoo · March 31, 2025, 02:09:09 PM

New mounts would likely be a good place to start. As the rubber ages, it hardens and collapses which effectively gives you no isolation from the hull.

Carbon · March 31, 2025, 02:19:32 PM

Quote from: Ron Hill on March 31, 2025, 01:33:31 PMJack : You have the original engine mounts!! That port side forward mount is probably shot from oil while changing the filter. I'd change all of the mounts and you'll have a NEW engine!!

A thought

Sounds good.

It seems like in most of the pictures on this site, the mounts look bad when they are shot. These mounts look fine. No evidence of rust or oil, but they are quite old.

If you can believe the Hobbs meter, and I think you can, the engine only has around 500 hours on it. I can see where the mounts could be bad just from age and supporting the engine for 37 years. But again, they look just fine.

I can't see any harm in replacing the mounts, they are fully depreciated.

Thanks for the replies.

Jack

KWKloeber · April 02, 2025, 01:37:43 PM

Jack

You'd need to observe / video the mounts with the engine vibrating to get a fair picture of what's going on. If there is no movement in the mounts' rubber then the vibration is being transferred directly to the stringers.

Ron Hill · April 03, 2025, 02:09:51 PM

Jack : Those mounts are 37 years old. I change out my original mounts back in about 1997/8?. It was the BEST mod that I have ever made to my C34 - It was like I had a new engine, it ran so smoothly!!

You holding out for 50 years before you change the mounts???

A few thoughts

Carbon · April 04, 2025, 12:57:24 PM

Quote from: Ron Hill on April 03, 2025, 02:09:51 PMJack : Those mounts are 37 years old. I change out my original mounts back in about 1997/8?. It was the BEST mod that I have ever made to my C34 - It was like I had a new engine, it ran so smoothly!!

You holding out for 50 years before you change the mounts???

A few thoughts

Ron

I'm not holding out, I'm perfectly willing to replace them. I've got the receipts to show how much love I've lavished on my boat.

It just seems to me that the problem might be that the engine is bound up on the mounts, not the mounts themselves. I've found lots of posts on this forum where old mounts seem to be Ok if not great. I have not found anyone who has my symptoms; the engine does not move at all.

I could see where old mounts might become too soft or where they might become hard and not let the engine move enough. The fact that my engine won't move on the mounts at all seems like a mechanical bind. I'm fairly certain something is going on beyond the mounts being old.

Having said that, replacing the mounts and a fresh alignment will almost surely fix the problem. That's what I'm going to do.

Thanks for the replies; I'll report back.

Noah · April 04, 2025, 02:45:23 PM

To throw another perspective into the mix: my boat is a 1990 with just 750 hours on the engine and the motor mounts are working fine. So, my takeaway—-year built, while something to consider, doesn't always determine the lifecycle of boat engine parts.

Jim Hardesty · April 04, 2025, 02:51:34 PM

Quotereplacing the mounts and a fresh alignment will almost surely fix the problem. That's what I'm going to do.
QuoteThink that's sound thinking. Also consider a new cutlas bearing at this point. I don't think that a good alignment is possible without one.
Jim

Jim Hardesty · April 04, 2025, 03:02:22 PM

QuoteTo throw another perspective into the mix: my boat is a 1990 with just 750 hours on the engine and the motor mounts are working fine. So, my takeaway—-year built, while something to consider, doesn't always determine the lifecycle of boat engine parts.

It's been my experience that rubber parts can get old just sitting on a shelf. I just googled tire exploration, and the recommendation is 6 years, that's shelf life.
Just my 2 cents,
Jim

Noah · April 04, 2025, 03:50:21 PM

I get it with tires, as there are liability/safety issues involved. Engine mount/vibration, not so much. But it could be? I would be rich today if my wife didn't zealously throw away everything in our house that had reached its manufacture's "best if used by" or "expiration" dates printed on the packaging. ;-)

Carbon · April 08, 2025, 08:44:35 AM

I've decided to replace the engine mounts and I'd like to get it done before the sailing season gets into full swing.

I thought picking the mounts would be easy: Vetus K50s on the front and K75s on the back. However, now that I've done a little more research, I find that some people are not happy with that setup.

https://c34.org/bbs/index.php/topic,1344.15.html

The complaint is that some get serious vibration at low RPM.

Does anyone have any insight into what's considered the "best" setup? A lot of the comments about problems with the Vetus mounts are old. Perhaps there is something better out there in 2025.

Any advice would be appreciated.

Jack

Ron Hill · April 09, 2025, 02:57:47 PM

Jack : Many years ago I replaced all of my original engine mounts with Vetus K50s. I found out that the K50s were a bit too soft so I changed out the REAR mounts to K75s! That solved the problem. I didn't change out all to K75s for $$ reasons and suspected that the K50s in the rear were the problem!! Which they were!!

I'd recommend that your change to all K75s and you'll be OK!!

A few thoughts

Carbon · April 10, 2025, 12:11:42 PM

Quote from: Ron Hill on April 09, 2025, 02:57:47 PMJack : Many years ago I replaced all of my original engine mounts with Vetus K50s. I found out that the K50s were a bit too soft so I changed out the REAR mounts to K75s! That solved the problem. I didn't change out all to K75s for $$ reasons and suspected that the K50s in the rear were the problem!! Which they were!!

I'd recommend that your change to all K75s and you'll be OK!!

A few thoughts

Ron

Thanks for that advice. That's what I'm probably going to do.

What do you you think of simply going back with the factory mounts? They are expensive from Catalina Direct, but if they work the best then that still makes sense.

Thanks

Jack

KWKloeber · April 10, 2025, 02:18:21 PM

Quote from: Carbon on April 10, 2025, 12:11:42 PMThey are expensive from Catalina Direct, but if they work the best then that still makes sense.

First of all, never buy DF isolators from CD. Buy them direct.

Second, where did you hear that "they work the best"??

Folks change them out FOR A REASON. It would be simple to replace same with same one.

Don't overthink this. K75s all around!