bad motor mounts

[prowlersfish]

I was doing some maintenance and noticed a broken mount . On further inspection I found 2 sheered mount studs one pull out stud . and one good mount the only easy to see one was ok .All on the starboard engine The engine had moved about 1.5 inchs forward . None of the bolts had pulled ou of the stringers

Moving a 1400 lb gorilla around in a tight beige was no fun for sure , But I had to get it done

[gettaway]

Wow, was this on your boat? good thin y!ou found it

[Stripermann2]

Paul, you...are not 1400 pounds!

[prowlersfish]

Not yet

Yes they are my mounts . Not much fun to replace .

[k9th]

So when it moved 1 1/2" forward did it move the prop shaft with it?

[prowlersfish]

Sure did Tim

[gitchisum]

That must have made for some thin clearance of prop tip and bottom paint.
Good thing you found it visually and not auditory!!

[prowlersfish]

You would have thought I would have heard or felt something when the engine was trying to pass the boat


Looing at the mounts I believe 1.5"many be incorrect .It probably was closer to 1 inch .

BTW the mount studs were 3/4"

[RWS]

I suppose the question to be answered is

What is the CAUSE of failure...

in my own repower, we tied full length, 1/2" thick aluminum brackets fwd/aft, the full length of the engines. through bolted to the top of the stringers.

The idea was to spread the torque over a greater area and not to rely on the existing gas motor mount configuration.

Is this a realistic approach and could tying both fwd and rear mounts together make for a stronger installation?

Is this an issue of mounts that were not quite up to the task applied?

Overstressed?

RWS

[prowlersfish]

I suppose the question to be answered is

What is the CAUSE of failure...

in my own repower, we tied full length, 1/2" thick aluminum brackets fwd/aft, the full length of the engines. through bolted to the top of the stringers.

The idea was to spread the torque over a greater area and not to rely on the existing gas motor mount configuration.

Is this a realistic approach and could tying both fwd and rear mounts together make for a stronger installation?

Is this an issue of mounts that were not quite up to the task applied?

Overstressed?

RWS

If the issue was the lag bolts pulling out then the brackets Would be the fix. The mounts where rated for the job .FWIW same mounts on the port side are perfect . The right rear mount stud was pulled out of the rubber poss due to rust . The Left rear and right front sheared off the studs left front was fine . My theory is the RR mount failed and caused undue strain in the RF and LR mounts causing them to fail . Uneven loading could also have been a factor . One other factor could be that was the engine I always used for trolling so it was in and out of gear for hours on end . Most likely a combo of all .

[prowlersfish]

I suppose the question to be answered is

What is the CAUSE of failure...

in my own repower, we tied full length, 1/2" thick aluminum brackets fwd/aft, the full length of the engines. through bolted to the top of the stringers.

The idea was to spread the torque over a greater area and not to rely on the existing gas motor mount configuration.

Is this a realistic approach and could tying both fwd and rear mounts together make for a stronger installation?

Is this an issue of mounts that were not quite up to the task applied?

Overstressed?

RWS

If the issue was the lag bolts pulling out then the brackets Would be the fix. The mounts where rated for the job .FWIW same mounts on the port side are perfect . The right rear mount stud was pulled out of the rubber poss due to rust . The Left rear and right front sheared off the studs left front was fine . My theory is the RR mount failed and caused undue strain in the RF and LR mounts causing them to fail . Uneven loading could also have been a factor . One other factor could be that was the engine I always used for trolling so it was in and out of gear for hours on end . Most likely a combo of all .

[RWS]

two engines of equal horsepower, but different torque - the gas vs the diesel.

the diesel provides more torque which must be managed, however your mounts were rated for this engine.

another consideration:

in FWD one side of the engine wants to LIFT, the other side wants to COMPRESS.

in reverse, it's the exact opposite effect.

RWS

[prowlersfish]

THe mount were (are) much larger then what would have been used for gas . Also remember the mount take a lot of force pushing forward (and reverse) from prop thrust .

[gitchisum]

Paul-

Do you change out the the other side now? or wait for them to fail?

I tend to lean towards proactive replacement / maintenance. Motor mounts wouldn't even be on my radar though.

Makes me wonder what else I should be thinking about to prevent failure while away from the dock.

[RWS]

THe mount were (are) much larger then what would have been used for gas . Also remember the mount take a lot of force pushing forward (and reverse) from prop thrust .

WOW

I never considered the push/pull of prop thrust !

That is a HUGE issue.

Its funny, the outboard factory 454 mounts on mine were attached to wooden (oak I think) blocks, and everything was simply lag bolted to the top of the stringers, no thru bolts whatsoever.

The starboard front wood block was cracked, and the PO had put a piece of fiberglass mat over the crack - like that would have made a difference.

All of the 8 mounts were solidly rusted - no adjustment was available.

This was one of the many factors that played into the decision to replace the 454's

By the way, that 1/2" thick aluminum plate is bonded to the top of the hollow International stringers with 5200 PLUS thrubolted - we had to add deck plates to the sides of the hollow stringers for access to put nuts/washers on the bottom side.

Its funny that I never even considered the thrust issue and that everything is tied to the boat at those four points !

Now I am even happier that I did what I thought at the time to be way too much overkill....

Anyone considering a diesel repower to an International (non mid cabin based) should consider this kind of upgrade.

RWS