MAN D 2840 LXE 401

[mat]

Dear all,

I am looking at a boat (Sunseeker) with twin MAN D 2840 LXE diesels rated at 820 HP each. They have about 500 hours each.

The engines seem to be operating perfectly over the whole RPM range above idle (no smoking, no vibration, no knocking, etc.)

However, when they are idling, about 500 RPM, there is excessive vibration that propagates over the whole boat. The local MAN service people attribute the vibration to the fact that at idle the motors are operating on half cylinders. On the other hand, it seems to me that so much vibration is not normal.

Any ideas? Has anybody faced a similar problem?

Thanks in advance,
MAT

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[tcm]

Hi, I have MAN engines, V12's and yes there used to be monster vibration around this crossover period - when half the bank are switched out to all switched in.

However , following a rebuild just finsihed (today!) the crosover vibration is a tiny fraction of what it used to be. Now, post rebuild, it might be a bit rough at that rev range, but not hammering the whole boat at all - as it used to do.

You may find one engine distinctly smoother than the other - try one up to reasonable revs - the boat may only just plane - and then the other. If one is smooth, the other not, this lends the lie that it's "normal"

Oh, and shortly after my engine being really rather boat-shakingly rough - the fuel pump camshaft drive gear broke and the damage will cost bout £16k in total to sort out. The expert MAN enginerrs had not the slightest clue why it happened and still don't, so they ain't all-knowing. Bout 500 hours too.

Incidentally, i think the crossover should be nearer 1000-1200 rpm - when the roughness is the transition between a six cylinder and a 12 (or 4 to eight or whatever).

Otherwise, at tickover it's a it's a six (or four) cylinder motor innit? So they should be smoothish at tickover, really?

I wd say that a rattly boat at tickover will be an utter, utter pain. The crossover to which the MAN enbeineer refers is higher up the rev range, imho - about 1000 rpm where you hardly ever crusise - you always go faster to plane the boat, or slower, to bumble about in the marina. Imagine if the boat ws shaking at that point. Ugh.

i wd stop looking at the boat, and find another. sorry.

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[PhilF]

are you talking to yourself here, bit of a coincidence all these mats

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