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Old 06-03-2013, 00:47   #1
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Engine mounts; engine vibration on gear

Hello,

I have some engine vibration which in my opinion is excessive when I have the engine running and switch from neutral to gear. On neutral its ok. Starts when I shift to gear. Add more revs, get more vibration. I believe this is due to old and tired engine mounts and I took one out today and on the pic and video you can see how it looks; it sits lower than the new one on the left (rubber compressed or worn), and it is no more rigid; the bolt has quite a lot of free play available to it (see video). The new one is completely rigid.

I haven't taken the other three out yet, but what say you, based on the condition of this one it is already enough to say these engine mounts are the cause for the vibration? The old ones like this definitely need to be changed?

The engine is a Perkins Prima M50, 4 cyl, 50HP.

-Erik
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Old 06-03-2013, 00:55   #2
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Re: Engine mounts; engine vibration on gear

I would also be checking the alignment with the shaft. The "in gear" vibration sounds like there is an alignment issue. Replacing the mounts may get it all in line again, if the old ones have dropped as shown. The cutlass bearing may also need attention.
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Old 06-03-2013, 01:02   #3
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Re: Engine mounts; engine vibration on gear

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Originally Posted by 40 South View Post
I would also be checking the alignment with the shaft. The "in gear" vibration sounds like there is an alignment issue. Replacing the mounts may get it all in line again, if the old ones have dropped as shown. The cutlass bearing may also need attention.

Thanks Craig, yes, that unfortunately I would need to do as well if I replace the engine mounts, and I believe it can be a very tidious job.. I have a few books explaining the technique but is does look like a lot of measuring and adjusting.
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Old 06-03-2013, 02:10   #4
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Re: Engine mounts; engine vibration on gear

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Originally Posted by ErikFinn View Post
Thanks Craig, yes, that unfortunately I would need to do as well if I replace the engine mounts, and I believe it can be a very tidious job.. I have a few books explaining the technique but is does look like a lot of measuring and adjusting.
I'm just saying... it would be quite silly... to replaces the Rubbers...no I mean cutlass bearings.

Without also changing the the isolation mounts...I mean the rubbers that mount the engine.

now wouldn't really.

Lloyd
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Old 06-03-2013, 03:38   #5
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Re: Engine mounts; engine vibration on gear

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Originally Posted by FlyingCloud1937 View Post
I'm just saying... it would be quite silly... to replaces the Rubbers...no I mean cutlass bearings.

Without also changing the the isolation mounts...I mean the rubbers that mount the engine.

now wouldn't really.

Lloyd
Hmmm, not sure if I understood correctly...
But for now I plan to start by changing those engine mounts...

And by "that unfortunately I would need to do as well" I was referring to the engine alignment with the prop shaft. The cutlass bearing is the last on my list at this stage... Hopefully its not too worn...
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Old 06-03-2013, 06:16   #6
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Re: Engine mounts; engine vibration on gear

I am guessing poor alignment is what caused the failure of your mounts. Although tedious getting the alignment correct is very important to the overall health of the rest of you shaft system. If you do not feel you can get the alignment within 5 thousandths then I would suggest a flexible coupling. Although flexible couplings have their own problems and I think the best way to go is to get the alignment as close as possible. Good luck
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Old 06-03-2013, 06:27   #7
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Re: Engine mounts; engine vibration on gear

The mounts are what fixed vibration for me. They just get old from age and carrying the engine weight.
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Old 06-03-2013, 06:46   #8
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Re: Engine mounts; engine vibration on gear

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The mounts are what fixed vibration for me. They just get old from age and carrying the engine weight.
Wouldn't one thing lead to another? I mean, if you remove the old mounts, even one at at time, with bracing, etc. the engine must be realigned, no?
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Old 06-03-2013, 06:54   #9
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Re: Engine mounts; engine vibration on gear

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Wouldn't one thing lead to another? I mean, if you remove the old mounts, even one at at time, with bracing, etc. the engine must be realigned, no?
Yes of-course. But if you re-align the engine with the old mounts, you still have the problem.
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Old 06-03-2013, 12:42   #10
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Re: Engine mounts; engine vibration on gear

The engine mounts need replacing. Do that first, then realign the engine/trans to shaft once that's done. Realignment is a necessary step after engine mount replacement. Once that's done you should have gotten rid of the vibration. If not, the next thing to do is check your cutlass bearing. If you replace that and it still vibrates badly then the next thing to check is the straightness of the shaft.
Old engine mounts that have been soaked in diesel for a few years will degenerate.
With flexible mounts such as yours you should also have a flex coupling between trans and shaft.
Good luck.
kind regards,
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Old 06-03-2013, 20:11   #11
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Re: Engine mounts; engine vibration on gear

Thanks for all your posts guys,
I'm thinking the way to go forward now is to replace the mounts and align, and see what the situation is then. I'm currently in Penang, Malaysia and support here does not exist but fortunately I have instructions on a few good books which I hope to be helpful when it comes to the alignment. I expect the alignment job not to be easy though, never done it, and it seems to involve a LOT of measuring and adjusting.
For a starting point I'll measure the gap as pointed out on the picture with a feeler gauge, and adjust the nut on the new mount accordingly, and hopefully this will be close to the original adjustment, hopefully giving me a starting point not too far from the correct adjustment. On the bolt there is about one inch room for adjustment. That times four for each corner. Oh sheesh, I hope my method works or I'll be spending weeks trying to get the adjustment correct! Should mention too that the top nut, the locking nut, is not visible on the pic, the engine bracket attaches above the larger nut you can see on the pic. See the video for the complete mount.
The prop shaft does not have a flex coupling, I believe this is the original setting how it came out from the factory.
To check the cutlass bearing the boat must be on the hard, correct? I'm currently in the slip.
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Old 06-03-2013, 21:07   #12
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Re: Engine mounts; engine vibration on gear

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Originally Posted by ErikFinn View Post
Thanks for all your posts guys,
I'm thinking the way to go forward now is to replace the mounts and align, and see what the situation is then. I'm currently in Penang, Malaysia and support here does not exist but fortunately I have instructions on a few good books which I hope to be helpful when it comes to the alignment. I expect the alignment job not to be easy though, never done it, and it seems to involve a LOT of measuring and adjusting.
For a starting point I'll measure the gap as pointed out on the picture with a feeler gauge, and adjust the nut on the new mount accordingly, and hopefully this will be close to the original adjustment, hopefully giving me a starting point not too far from the correct adjustment. On the bolt there is about one inch room for adjustment. That times four for each corner. Oh sheesh, I hope my method works or I'll be spending weeks trying to get the adjustment correct! Should mention too that the top nut, the locking nut, is not visible on the pic, the engine bracket attaches above the larger nut you can see on the pic. See the video for the complete mount.
The prop shaft does not have a flex coupling, I believe this is the original setting how it came out from the factory.
To check the cutlass bearing the boat must be on the hard, correct? I'm currently in the slip.
If the boat has been running out of alignment for any length of time, the cutlass bearing will be toast. Most CB's will last about ten years barring any electrolysis. Most rubber isolation mounts will last about ten years, barring any leaking fluids.

If you're going to do running gear then it makes $CENTS$ to do it all at one time. Props tuned, shaft's tuned, CB's, and Mounts changed.

Other wise you will be chasing bearings and seals on the drive, as well as packing glands.

Lloyd
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Old 07-03-2013, 11:23   #13
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Re: Engine mounts; engine vibration on gear

You can check your cutlass bearing in the water with fins and snorkle. Just dive down, grab the prop and try to shake it up and down and then side to side. If it clunks and rattles when you shake it then you'll need a new cutlass bearing. Make certain no one is near the starter button when you're doing this!

Your alignment will be tedious but not hard. Yes on the feeler gauge. Measure at top and on each side and the bottom. You'll be able to adjust a little then measure again, adjust some more and then measure again until you get within proper tolerances. If you have a book that explains it then you are miles ahead.

Your final engine alignment should be done while the boat is in the water.

kind regards,
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Old 07-03-2013, 11:32   #14
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Re: Engine mounts; engine vibration on gear

What am I missing here ? The OP said the vibration only happens in gear and increases with throttle. That could be as simple as barnacles on the shaft or propeller, a plastic bag on the prop or a very worn cutless. I'd take a look at the other end (prop,shaft, bearing) first.
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Old 07-03-2013, 18:34   #15
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Re: Engine mounts; engine vibration on gear

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What am I missing here ? The OP said the vibration only happens in gear and increases with throttle. That could be as simple as barnacles on the shaft or propeller, a plastic bag on the prop or a very worn cutless. I'd take a look at the other end (prop,shaft, bearing) first.
Thanks, boatpoker that's a good tip!
I actually did dive with a mask and snorker, (no scuba gear) under the boat to see the prop, but unfortunately the water wasn't clear enough to see the condition of the prop. By feel, it didn't appear to have barnacles, but on the other hand I couldn't stay under water long enough to be really confident..

As it appears that the engine mounts are not satisfactory anymore, and because I've started to remove them now, I will replace them and try to get the prop shaft alignment good. If I get that done but the issue still prevails, well I suppose then I must check anything that I have in between the gearbox and the prop zinc...
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