Engine Mounts Bad?

[Gordon J]

I am trying to figure out if my engine mounts are bad. I know that they have not been set up right and I am addressing that issue, but, I might have a bad mount or two.

The mechanic who is giving me an assist claims they are not bad, but I am suspicious. The mounts are on my Cummins 6BTA5.9 producing 330 HP. They were made by Barry Engineering.

The problem I am trying to solve is that when idling in gear, I get a loud banging from the engine room. This disappears at about 800 RPM.

What are the standards for determining whether these are bad?

Thanks in advance.

Gordon

 

[bayview]

You might be hearing bad rubber bumpers in the transmission damper ir a bad harmonic damper.

 

[Gordon J]

There is no vibration coming from the inside of the engines or transmissions, as far as I can tell.

 

[Keysdisease]

15 year old mounts certainly aren't performing as designed. Try poking the rubber in each mount carefully, especially the one under the injection pump. Fuel will kill a mount pronto and make the rubber a soft gooey mess.

 

[Gordon J]

No goo here

15 year old mounts certainly aren't performing as designed. Try poking the rubber in each mount carefully, especially the one under the injection pump. Fuel will kill a mount pronto and make the rubber a soft gooey mess.

Keysdisease,

Gooey mess would be obvious, but not here. All we have is hard rubber that is mis-shapened when compared to photos of the original. I have a feeling that this is a question for folks with that particular mount. I may give the company a call on Monday.

Gordon

 

[DavidM]

This is just me. I have seen many mounts changed to correct a problem and it didn't do any good. So I would listen to your mechanic. Sure, correct any bad installation issues like poor alignment, but mounts last longer than we often think.


You say the noise comes from the engine room, but it doesn't come from the inside of the engine or transmission. Where does it come from?


David

 

[caltexflanc]

Get a second opinion. None of us are on-site to diagnose your issue.
A mechanic or yard would typically like nothing more to than to score an engine mount replacement job. Typically, but I suppose not always, bad mounts evidence themselves in constant noise and vibration.

 

[High Wire]

If the engine was banging, wouldn’t you see or feel the motion? Especially if it’s an engine mount moving around.

 

[Civilitas]

The problem I am trying to solve is that when idling in gear, I get a loud banging from the engine room.

It sounds like you are on the bridge trying to localize the sound.

Where does it sound like the banging is coming from when you are IN the engine room? I know the OA 456 doesn't have a stand-up er, but there is room to go in there with a stethoscope and look/listen around and localize it within a few minutes.

A BF screwdriver works great as a mechanical stethoscope if you don't have an acoustic one handy!

You could be right, but I think some time in the room with a 'scope would narrow it down pretty fast. From a humorous article from Dave Gerr a while back, like said above, bad mounts are typically vibration that gets worse, not noise that goes away.

 

[O C Diver]

Check the bolts holding the mounts to the boat and the bolt holding the mount to the engine and / or transmission hangars. They need to be torqued tight. Had the same problem on my charter boat. Found the 2 bolts holding one mount to the engine bed, could be tightened about a half a turrn each. That was all it took.

Ted

 

[Gordon J]

Might be on to something

Check the bolts holding the mounts to the boat and the bolt holding the mount to the engine and / or transmission hangars. They need to be torqued tight. Had the same problem on my charter boat. Found the 2 bolts holding one mount to the engine bed, could be tightened about a half a turrn each. That was all it took.

Ted

Thanks Ted. I will take a look at those bolts. I have been down in the engine room and have not been able to tie the noise to a particular engine mount. What I can tell is that the amounts are currently not set up properly. Whether that is the problem, or whether the mountains have failed and that is why they are bottoming out, is the question. My mounts are made by Barry engineering, and according to their instructions, a bottom pad should rest no closer than 1/8 inch to where they mount is installed. Some of mine bottom out which I suspect is causing the bumping noise.

My question had to do more with whether I would be able to just adjust the amounts and continue using them or replace them. The rubber looks solid on all, but I don’t know how these might fail and what a failed mount might look like.

Gordon

 

[bayview]

A piece of hose works as a stethoscope as well.

Watch the mounts as someone shifts in and out of gear to see if they move a lot.

 

[DeroDiesel]

IMO, If the sound goes away after around 800 RPM, it could very well be the torsional coupling rubber giving out... at low RPM you will hear horrible "clacking" until enough load between the engine and gear locks" the coupling together (sometimes metal-to-metal) and the sound goes away...

Do you "see" any rubber bits near the bellhousing of the engine?

Can you post pictures of your Barry mounts as well? If they are out of parallel, there could be multiple issues going on at once here...

 

[Irish Rambler]

I had a similar problem when we bought our ex hire boat. An engine mount bolt was broken and some lazy mechanic just welded it and of course the rubber melted and covered up his botch job.
You can see them in my blog 'Ireland to the Mediterranean Part 1'.
There's only one way to be sure and have peace of mind, change the mounts, they're not prohibitive but you must be super meticulous on realigning the engine/gearbox to your shaft, even if you have a flexible coupling aim for perfection, near enough is not good enough.

 

[Gordon J]

no bits of rubber

IMO, If the sound goes away after around 800 RPM, it could very well be the torsional coupling rubber giving out... at low RPM you will hear horrible "clacking" until enough load between the engine and gear locks" the coupling together (sometimes metal-to-metal) and the sound goes away...

Do you "see" any rubber bits near the bellhousing of the engine?

Can you post pictures of your Barry mounts as well? If they are out of parallel, there could be multiple issues going on at once here...

I have found no detritus around the engine. When it makes the noise I feel/hear nothing coming from the engine/transmission. I also can't see or feel where the noise is coming from. Three of eight engine mounts are bottoming out on the frame, and according to Barry, that probably means they are shot. I have four new mounts on hand and will begin the arduous process of replacing them next week.

Had the mounts on the engine been slotted instead of drilled, the process would have been easier, slide one out and the other in. But I will have to find a way to lift the engine to replace the mounts....

Unless someone knows of a painless way to do It that I have not thought of.

Gordon

 

[DeroDiesel]

Any chance of adding a few pics of the mounts and how they're attached to the engine/stringers, etc.???

 

[Irish Rambler]

Any chance of getting your hands on an old scissor jack that was used on small cars to change a spare wheel ?
Use the scissor jack to support the engine beside the mount which you wish to change until you see the tension come off the mount.
Carefully loosen the bolts where the mounting arm is attached to the engine and all the mounting bolts
Remove the mounting arm and engine mount, replace the engine mounting and secure the mounting arm, lubricate the engine mounting vertical threads with copper-slip anti seize compound.
Make sure you can access the adjusting nut on the engine mounting thread below the arm.
Repeat the process on all 4 engine/gearbox mounts.
Then with extreme caution turn the shaft by hand and check the gearbox shaft coupling for alignment in both planes so it's within 2 thou at 12, 6, 3 and 9 o'clock positions.
Be exact on this procedure
Finally check tighten all nuts and bolts and recheck the alignment. Take pride in a job well done with a cold beer

 

[Comodave]

I would also take very exact measurements at each mount so that you can more easily get the engine back into a close alignment. May save you some time if you get it in the ballpark before you start checking alignment.

 

[Rusty]

We recently changed our mounts. I removed the hatches in the salon and used a 4x4 across the opening. I used another 4x4 as a lever with a steel cable attached to the engines to lift them. Lift the front, pull the old mounts out and put the new ones in. Repeat for the rear mounts. We need to raise the engines about two inches. We changed the eight mounts in under two hours.

 

[sdowney717]

flex plate the joins engine to trans might be worn out.
When engine is idling, it ought to be smooth running, and wont be vibrating enough to cause it jump around making a banging like loose mounts.

Slow idle might hear the trans gears backlash, engine is pulsing the power with every fire of a piston. the power flow is not smooth like an electric motor. The effect is pronounced at slow engine rpm.

 

[DeroDiesel]

I have found no detritus around the engine. When it makes the noise I feel/hear nothing coming from the engine/transmission. I also can't see or feel where the noise is coming from. Three of eight engine mounts are bottoming out on the frame, and according to Barry, that probably means they are shot. I have four new mounts on hand and will begin the arduous process of replacing them next week.

Had the mounts on the engine been slotted instead of drilled, the process would have been easier, slide one out and the other in. But I will have to find a way to lift the engine to replace the mounts....

Unless someone knows of a painless way to do It that I have not thought of.

Gordon

Without pictures... we're ALL guessing...

 

[Gordon J]

OK, here's the picture

I changed this mount today. You will see that there is a pad at the bottom. According to the instructions the rubber pad is supposed to be no closer than an eighth of an inch from the bottom of the stringer and an eighth from the top of the mount.

I used the old mount to lift the engine a quarter inch or so and put a 2x4 under the front of the engine to support the weight while removing the mount. I unbolted the engine mounting bracket from the engine and took out the old mount and replaced it. I measured before putting the new one in.

Less than an hour from start to finish. Now I have three more to go. The new mount is holding the load while keeping the rubber snubber pad centered.

 

[Comodave]

Sounds pretty easy.

 

[DeroDiesel]

That mount is completely destroyed! Yes good thing you're replacing all the mounts (especially if they all look like that)... you were basically "hard mounted" to the stringers... rock n roll!

When re-installing, the most important part of the final assessment will be to ensure that all mounts are in "parallel"... if your shaking your head... type in "Isolator Mounting & Parallelism" into Google and go from there... GOOD LUCK!

 

[Gordon J]

One at a rime

That mount is completely destroyed! Yes good thing you're replacing all the mounts (especially if they all look like that)... you were basically "hard mounted" to the stringers... rock n roll!

When re-installing, the most important part of the final assessment will be to ensure that all mounts are in "parallel"... if your shaking your head... type in "Isolator Mounting & Parallelism" into Google and go from there... GOOD LUCK!

Derodiesel,

Thanks for the assist. I changed each mount one at a time. I measured each one to ensure that I got it back to a near perfect alignment. In the end I needed to change only three. The others all have the specified eighth of an inch clearance above and below the pad as shown in the picture.

I tested the boat while tied to the dock. I still got it initial shaking bumping noise when putting that in gear, but this time it stopped within a second after the propeller came up to speed. Clearly this is an issue of engine bumping on the mounts. I may have to crank up the RPMs.

 

[DeroDiesel]

What is your prop shaft flange to transmission output flange alignment tolerance? Are you within .0005 with a feeler gauge?

 

[psneeld]

0.0005"?

Like to see that done accurately.

Some pros will argue that many boats and flexible mountings make anything less than 0.001" for every inch of coupling diameter a waste of time.....especially the softer the mounts.

 

[Gordon J]

Ocean Alexander manual calls for a .007 inch tolerance.

 

[DeroDiesel]

TYPO ---- 5 thousandth's (0.005) or better is where you want to be...

My zero finger was working overtime...