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Discussion Starter · #1 ·
I'm about to purchase a boat, haven't made the final decision yet. I was just telling the owner I want a diesel mechanic on board for the sea trial, that the mechanic would mostly be listening to the rhythm, noting any discordant beats.

At which point the owner informed me that when the engine RPM hits 1100-1200 there's a distinct engine vibration which has been a function of the engine since he owned the boat. He just quickly moves beyond that to 1500 to avoid the vibration.

The engine is a Volvo Penta 2002 on a 1986 CS30.

Is this a cause for concern?
 

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Usually normal engine 'harmonic imbalance'. Check the vibration with and without the boat in gear (forward AND reverse).

The usual cause of such harmonics are 'shaft whip' due to poor engine alignment, poorly set/aligned or worn-out cutless bearing, and improper stuffing box packing (unequal circumferential loading of the packing by the packing gland).

Suggest that if you're concerned that you deduct the cost of an engine, etc. realignment in the negotiated price. What's the 'clearance' status of the cutless bearing?
 

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Gypsy Rover II, our last boat (had a Yanmar 2GM20F - brand new engine) vibrated at 1400 and 2800.

Mystery (our current boat - Yanmar 2QM20H) vibrates at about 1500. I would guess she also vibrates at 3000, but never had it up to that.

Just my very limited experience with diesels.

Rik
 

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Discussion Starter · #5 ·
What's the 'clearance' status of the cutless bearing?
I gave the prop and shaft a good tug and turn and there was no play at all with the shaft in the cutlass bearing, the prop turns fine - didn't seem to be unbalanced.

Regarding your suggestion of going to this RPM range in forward and reverse, what's your thinking behind this? If the vibration continues then it's probably a misaligned shaft?
 

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Discussion Starter · #6 ·
Check this site on the Volvo 2000 series engines. I had one once!!
Volvo-Penta engine overlook
Yep, I'm well aware of bad reputation of the Penta. *sigh* I'd better learn to sail without an engine, right?

Here's why I'm risking it:

  • The owner could afford to have the boat professionally maintained, the engine looked like it too.
  • The owner was a daysailer, the sort who probably went out once or twice a year. I figure the hours on the engine are very low.
  • The owner hasn't used the boat at all in the past 7 years, it's just been sitting on the cradle - but still maintained each year. I figure even better, though I worry whether the diesel in the tanks will have turned sludgy.
  • It seems to me from that link that many of the problems with the Penta are due to salt water. This boat has only known freshwater, and on a lake (Lake Ontario) that doesn't have a lot of weed, nets, lobster pots, mud/silt, etc. - things that foul the prop or get sucked into the intake.

Nevertheless, if I buy this boat I'm going to be super paranoid about this engine. I'd better take some diesel mechanics courses.
 

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I gave the prop and shaft a good tug and turn and there was no play at all with the shaft in the cutlass bearing, the prop turns fine - didn't seem to be unbalanced.

Regarding your suggestion of going to this RPM range in forward and reverse, what's your thinking behind this? If the vibration continues then it's probably a misaligned shaft?
Eliminates the transmission (thrust bearing, clutch / flex plate etc.) anomalies.
 
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