Vibration isolation - Feeling the Motor

[ejnichol]

New owner of used boat. Veteran runabout skipper.

Boat is a 1995 20 ft, 5.7L w Bravo 1 with 345 hrs.. The u joint and gimble bearings appear to be fine according to mechanic and my own experience. It smooths out nicely above 4000 and goes 51mph on the gps.

Engine runs well just had it serviced and everything checks out OK. SS prop was reworked and polished. Did this before prop work anyway. Very well cared for by previous owner.

Problem is that running between 2000 and 4000 rpm as well as accelerating, (particularly under heavy application) from idle speed. There is bothersome amount of vibration present in boat hull that you feel through hands, feet and ears. I've driven other v-8 powered boats in this size and this one seems to have more than others.

I have an old 1980 Century 170 with 140 Mercruiser, aka the HMS rotbox, that feels smoother under all modes. Maybe its all the rotton wood serves as its on vibration isolator.

Do these powerplants have rubber motor mounts that wear out? Wondering maybe motor not rig properly. Really is irritating and disappointing as it is a well cared for boat in good condition.

Thanks for your opinions.

 

[HT32BSX115]

Re: Vibration isolation - Feeling the Motor

Howdy,


These kind of vibrations are sometimes hard to diagnose.......


Does it do it driving straight, turning left/right, trim- in/out and in between, etc?

If it changes left/right in/out it *could* still be gimbal bearing and/or U-joints.

When the was alignment (u-joints/gimbal bearing etc) checked last?


Regards,


Rick

 

[ejnichol]

Re: Vibration isolation - Feeling the Motor

It happens straight on. When we wet tested boat, I did it in turns and got some vibration but Mercruiser dealer states they check alignement as part of service they do. They were telling use what a nice boat we had, but that doesn't mean much as it still is buzzy.

The sterndrive was removed as I can see excess sealant from where it was remated. I asked before hand to make sure it was removed and inspected as I'm suspicious of all things mechanical new or used. Particularly suspicous of dealership expertise at least in this market.

Are the motors mounted directly to the boat frame or are there rubber motor mounts?

 

[Fishermark]

Re: Vibration isolation - Feeling the Motor

The sterndrive was removed as I can see excess sealant from where it was remated.

What sealant? There shouldn't be any sealant between the outdrive and the housing.

 

[littlebookworm]

Re: Vibration isolation - Feeling the Motor

The rear mounts are double coil lock washers with fiber washers. The front mounts are rubber, similar to automotbile engine mounts. You could try running the boat with someone else driving while you look at the front mounts for movement. It is possible the mounts are loose or worm, but, realistically, not probable. I tend to agree with the others: It sounds like your universals might be bad. Hy

 

[ejnichol]

Re: Vibration isolation - Feeling the Motor

What sealant? There shouldn't be any sealant between the outdrive and the housing.

Some type of nondrying white material. maybe it was lithium grease though didn't feel like it when i touched and wiped off.

 

[ejnichol]

Re: Vibration isolation - Feeling the Motor

They are on isolation mounts but a bad vibration is still going to be felt. One way to know for sure, pull the outdrive, fire up the engine and see if it's still there. If not (and I bet it's not) it's time to re-think the u-joints. (Pulling the outdrive is a 10 or 15 minute task if you have someone to help lift it.)

I know when I had it on the water muffs running on the trailer it had no vibration in neutral when the rpms where run up.

How many universal joints are there?

When running on the water trimming it out from full down would lessen it but thats normal based on my other boat.

 

[ejnichol]

Re: Vibration isolation - Feeling the Motor

Rick, It was just in shop for 100 hr service which included checking alignement and condition of bearings. Its a Mercruiser shop but so are most. I was suprised they didn't say we needed a gimble or ujoint.

The feeling lessens when you trim the outdrive away from full down/contact. Its more of general vibration in the boat coming from engine/drive.

Howdy,


These kind of vibrations are sometimes hard to diagnose.......


Does it do it driving straight, turning left/right, trim- in/out and in between, etc?

If it changes left/right in/out it *could* still be gimbal bearing and/or U-joints.

When the was alignment (u-joints/gimbal bearing etc) checked last?


Regards,


Rick

 

[ejnichol]

Re: Vibration isolation - Feeling the Motor

Unless yu told them of the issue the mechanic probably gave it a quick look and put the drive back in.

I'm going to see if someone from that shop can go out to lake for in water test. I think it may prove difficult to correct.

If I run in on water muffs out of the water put it in gear and run up to 3000 would that damage it or prove anything?

They didn't catch a problem with shifter on boat as its real touchy as it goes into/outof neutral to forward and stiff throughout the range, they said no problem was noted. The one on my century is more predictable/smoother but its aluminum whereas the 3000 on this boat seems to be all plastic. Loosy goosy shifter in my book. Forward gear engagement seems to be set too close neutral gate dentent. Sometimes it stumbles into forward gear.

Not that this means there no good but not a great start. The cobalt dealer who did gimble and ujoint replacement on my century several years back didn't put it back together correctly and it took and in the water test to show him/them the need to correct.

Thanks

 

[ejnichol]

Re: Vibration isolation - Feeling the Motor

Before taking it to dealer tomorrow I checked the front motor mount bolts. Both on starboard side will not tighten down. Ones on the port at least one is snugging up.

I think this is what maybe causing the strange vibration. I'm going to pull the bolts and see what the hole feels like, wet etcc..

How is this normally fixed. 15 yr old boat very dry no signs of floor rot. Thanks Eric

 

[Bondo]

Re: Vibration isolation - Feeling the Motor

How is this normally fixed. 15 yr old boat very dry no signs of floor rot.

Ayuh,... Fill the holes with epoxy putty, 'n redrill 'em...

 

[ejnichol]

Re: Vibration isolation - Feeling the Motor

Thanks for the reply. The dealer wants to pull motor and work on fiberglass. Said motor and sterndrive lined up perfectly when it was in for service.

Edit: --- In case you stumble upon this thread. On this SeaRay and pobably others motor mounts are attached to flanges built bottom of engine compartment. Even though the motor mount bolts are not fully tightened there are backing nuts so snugging them down should be accomplished once I get a wrench back there. Relieved I may avoid fiberglass work on this job.

I have no idea how tight they should be though. Any ideas?

Attached are a couple of pictures.