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Old 16-10-2011, 12:55   #1
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Big Vibration with New Engine ?

A friend of mine has just repowered his Beneteau 34.5 with a new 30 hp Volvo engine, done by the Volvo agent at Lake Macquarie. The engine is the same size as the previous Volvo and is of the model recommended by the agent. He has paid for the engine but not the labour for the fitting of it. The driveline has a massive vibration and is jumping all over the place when it is in neutral but when he selects forward or reverse it settles down and is quite normal. The agent has suggested he take it (& pay for it) because it should settle down after about 20 hours. He and I think not. It has had new mounts and the agent can't find the problem.

Does anyone have any ideas what might be the problem?

Greg
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Old 16-10-2011, 13:04   #2
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Re: Big Vibration with new engine?

Misalignment? Also, was it aligned on the hard and then launched with no further adjustment? I've heard that can be a problem.
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Old 16-10-2011, 13:19   #3
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Re: Big Vibration with new engine?

I assume that you have checked the bedding and tightness of the motor mounts. I once had a motor mount loosen and allowed the engine to sit on the bottom of the hull, underway smooth as glass, idling at the dock a noticeable vibration that I didn't have before. I discovered the source of vibration accidently when I stood on the valve cover getting out of the engine compartment while the engine was idling at the dock.
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Old 16-10-2011, 13:28   #4
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Re: Big Vibration with new engine?

Can't help with the source but do not pay for it!

I think you knew that but just in case you were wavering.

With money, comes power to get it fixed
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Old 16-10-2011, 13:42   #5
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Re: Big Vibration with new engine?

Have you checked the idle speed, might be a bit low as its a new engine.
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Old 16-10-2011, 13:46   #6
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Re: Big Vibration with new engine?

motor mounts and alignment....... mounts should be changed with engine change, as far as i can see......
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Old 16-10-2011, 13:52   #7
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Re: Big Vibration with new engine?

Is it a 3 cylinder? They are not as smooth as the 4. Since it is fine in gear --- make sure it really is -- then it is a cylinder not working as well as the others or the motor mounts are bad. I had a Volvo that did something similar. when I finally figured it out it was a cracked motor mount.
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Old 16-10-2011, 13:53   #8
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Re: Big Vibration with new engine?

OP posted-
New mounts fitted.

And the fact it settles down when put in gear, rather than gets worse suggests alignment isn't the problem.
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Old 16-10-2011, 14:14   #9
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Re: Big Vibration with new engine?

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OP posted-
New mounts fitted.
...
But are the mounts installed properly and were they any good - probably, but who knows with out inspecting.
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Old 16-10-2011, 15:34   #10
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Re: Big Vibration with New Engine ?

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It has had new mounts and the agent can't find the problem.



Greg
I would of hoped the agent checked the mounts if they have looked into the problem.

I'm not suggesting not to check these things, but it seems like the problem may lie elsewhere, like low idle speed, due to "tight" engine or misfiring cylinder.
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Old 16-10-2011, 15:46   #11
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Re: Big Vibration with New Engine ?

Misallignment issue, tranny to shaft coupling needs to be within .005 thousands of an inch and can be a very painstaking process that requires considerable time and patience to get right. Motor mounts should be changed out as GP as part of the repower. Run the motor at in gear at the slip and grab the shaft with your hand and you will feel distinct wobble if there is a problem with adjustment. I don't understand the term agent but who ever did the work should not be paid until the job is made right. The other issue is you don't want to run the motor like this to long as you can damage the tranny.
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Old 16-10-2011, 17:03   #12
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Mis fire on one of the cylinders at low rpm.
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Old 16-10-2011, 17:16   #13
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Re: Big Vibration with New Engine ?

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Mis fire on one of the cylinders at low rpm.
But when in gear would it still not shake from same misfire?
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Old 16-10-2011, 17:29   #14
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I should dodge this cause I'm not sure. At low rpm this is exaggerated. there is torque which needs to be balanced. the torque is counterpoised by the cylinders firing in the correct sequence and time.. At low rpm the frequency and compensation are slow at higher rpm the frequency increases and the wave is shorter. As the motor lurches over the counter comes faster at higher rpm. hope that helps
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Old 16-10-2011, 17:33   #15
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[QUOTE="sabray"]I should dodge this cause I'm not sure. At low rpm this is exaggerated. there is torque which needs to be balanced. the torque is counterpoised by the cylinders firing in the correct sequence and time.. At low rpm the frequency and compensation are slow at higher rpm the frequency increases and the wave is shorter. As the motor lurches over the counter comes faster at higher rpm. Compensation of lurching i s increased. hope that helps[/QUOTE
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