Anyone had problems with Mercruiser motor mounts ?

[barkerrd]

(1991)25' Renken with 4.3 mercruiser alpha 1 .Has a new gimbal bearing , u-joints, and coupler . The ignition timing is dead on . Engine runs excellent but has an annoying vibration . A friend of mine , who is an auto mechanic said it feels like the engine is bolted directly to the boat .
Anyone else had a vibration problem like this ? In neutral ? These are "liquid filled" motor mounts.

 

[Bondo]

Re: Anyone had problems with Mercruiser motor mounts ?

Ayuh,........

Was everything realigned after the repairs,..??..??.....

 

[ziggy]

Re: Anyone had problems with Mercruiser motor mounts ?

Has a new gimbal bearing , u-joints, and coupler .

and an alignment to go along with these? with a alignment bar?

does it only vibrate at idle or is it thru the rpm range too......any worse with more rpm....

 

[barkerrd]

Re: Anyone had problems with Mercruiser motor mounts ?

Yes , it was alined at a mercruiser dealership , Dover Marine

 

[barkerrd]

Re: Anyone had problems with Mercruiser motor mounts ?

vibration is worse at low rpms ... don't notice it at high rpms

 

[JCF350]

Re: Anyone had problems with Mercruiser motor mounts ?

Only the front mounts are fluid. Did you replace the fiber and "spring" washers at the rear mounts?

While somebody is operating the throttle observe movement at the rear mounts to see if there is metal to metal contact.

 

[Don S]

Re: Anyone had problems with Mercruiser motor mounts ?

It may be the new coupler was defective. I have seen many brand new couplers both Mercruiser and Volvo have the center hub installed slightly off center. That is why it's always recommended to align the engine turn the engine 90?, 180?, and 270? and recheck the alignment to make sure it's still dead on. Many mechanics never do that test.
If they are just slightly off, they will vibrate at low speeds.

 

[wncrjb]

Re: Anyone had problems with Mercruiser motor mounts ?

It may be the new coupler was defective. I have seen many brand new couplers both Mercruiser and Volvo have the center hub installed slightly off center. That is why it's always recommended to align the engine turn the engine 90?, 180?, and 270? and recheck the alignment to make sure it's still dead on. Many mechanics never do that test.
If they are just slightly off, they will vibrate at low speeds.

I have heard that every now and then you might come across a coupler that is not perfect, but, my question is..... if it is off enough to cause a vibration at idle, will it do any drive line damage and should it be replaced ASAP, or, can you just run it and not worry about it?

wncrjb

 

[JCF350]

Re: Anyone had problems with Mercruiser motor mounts ?

I have heard that every now and then you might come across a coupler that is not perfect, but, my question is..... if it is off enough to cause a vibration at idle, will it do any drive line damage and should it be replaced ASAP, or, can you just run it and not worry about it?

wncrjb

ASAP, or it will eat the splines out of the coupler.

 

[thunder219]

Re: Anyone had problems with Mercruiser motor mounts ?

My GW Invader done the same thing yours is. When I bought the boat the guy said it done it from the time it was new. Had several people look at it and no one could ever find a problem. I watched the dealer turn it during alighning it like Don S. said, I dont know about the other guys that worked on it because I was not there when they done it. I dont know if yours just started doing this or always has just thought I would share it. Also, I dont remember if it was on here or where but someone said something about the hull being thin could let the vibration travel more. I cant remember how they worded it but it was something about the hull thickness.

 

[180shabah]

Re: Anyone had problems with Mercruiser motor mounts ?

vibration is worse at low rpms ... don't notice it at high rpms

can you define low RPM's?

idle (650)
fast idle (1200-1500)

Do you know if your engine has a balance shaft? 4.3's do vibrate when you get just over 1k, but it goes away as the revs climb.

 

[barkerrd]

Re: Anyone had problems with Mercruiser motor mounts ?

First , thank you for all the responses . I first noticed the vibration in Nov. 2005 on a short cruise with the previous owner . At the time I didn't think it was a big deal . Since then the new bearings , a new prop , spark plugs ... the vibration is always the same . I guess it is something I have to live with .
But I still think it is the motor mounts

 

[barkerrd]

Re: Anyone had problems with Mercruiser motor mounts ?

What is a balance shaft ?

 

[oops!]

Re: Anyone had problems with Mercruiser motor mounts ?

harmonic balance???

what are the mounts bolted to?

oops

 

[barkerrd]

Re: Anyone had problems with Mercruiser motor mounts ?

The mounts are bolted to these two large stringers on the bottom of the boat .Aren't everybody's ? and yes, the bolts are tight
As far as the harmonic balance , I have whatever a stock 4.3 mercruiser has

 

[JCF350]

Re: Anyone had problems with Mercruiser motor mounts ?

What is a balance shaft ?

This shaft is located under the intake manifold and is intended to reduce harmonic vibrations.

Check the pics at this site (scroll down the page a bit for the V6).

rapidoauto.com/default.aspx?p=/engines.aspx

 

[barkerrd]

Re: Anyone had problems with Mercruiser motor mounts ?

Hey jcf350 ,
Thanks for the help , Is this shaft an aftermarket product they came up with because the 4.3 V6 is prone to vibration ?

 

[180shabah]

Re: Anyone had problems with Mercruiser motor mounts ?

Hey jcf350 ,
Thanks for the help , Is this shaft an aftermarket product they came up with because the 4.3 V6 is prone to vibration ?

All 90 degree(or any angle other than 60) V6's are prone to vibration. The balance shaft was added by GM in 1991, so you may or may not have one. It is a weighted shaft that was "inserted" in the dead space between the camshaft and intake manifold. It spins in the opposite direction of the crankshaft, and kills the nasty shake between 1000 and 1500 RPM. It also kills about 30hp. Extra rotating mass, friction etc.....

 

[Hashi]

Re: Anyone had problems with Mercruiser motor mounts ?

Man...I'd take the boat back to Dover Marine and have them check it out. Repairs or replacement parts are usually under warranty for a limited time.

 

[flabum]

Re: Anyone had problems with Mercruiser motor mounts ?

That engine is a non-balance shaft engine. Mercruiser started using the balance shaft engine in 1993.

What does this mean?

The pre-1993 GM 4.3 litre engine has an inherant imbalance that is very noticable at low to mid range speed. GM rectified this problem by introducing a balance shaft to the engine to offset the vibration. In doing so, they had to change the design of the block to fit the balance shaft. You cannot add a balance shaft to the engine and there is nothing you can do to eliminate the vibration.

If you ever need to rebuild that engine, you can purchase a rebuilt balance shaft long block as an upgrade.