Bukh DV20 idling rough

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Stoker1538
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Bukh DV20 idling rough

Post by Stoker1538 » Mon Jun 11, 2018 9:58 am

The engine in my centaur is running very rough at idle, by this I mean it’s shaking all over the place.
I’ve put new engine mounts on, but I also had the flywheel off to access under the engine. Could it be the flywheel out of balance? As I did notice some drilling’s in the back of it presumably where it’s been balanced.

When it’s revved up it smooths out

Or could it be idling too slow? I don’t have a rev counter so don’t know how I can tell the revs

Any suggestions greatly appreciated
Alex

BrightStar
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Re: Bukh DV20 idling rough

Post by BrightStar » Mon Jun 11, 2018 1:41 pm

Hi,

Make sure the flywheel is fully on and tight!

If you changed the mountts is the alignment correct

How much do you need to rev up to have the engine running smooth, if it only a bit, then you might be too slow, try adjusting the slow run stop

Could be a dicky injector.

If after you have revved up and throttled back its smooth could be a slight fuel leak at the injector.

Restricted exhaust - needing a de-coke

If its smooth in neutral but rougher in gear could be something on the prop

Lots of possibilities but probably easy to fix once you find it
Brightstar
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Stoker1538
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Re: Bukh DV20 idling rough

Post by Stoker1538 » Mon Jun 11, 2018 2:49 pm

Boats out of water at the moment so nothing on the prop.
Smoothes our at about half revs either in or out of gear.

I replaced mounts one at a time, how can I check alignment, I’m confident it’s still good.

After revving up and returning back to idle it goes back to shaking again

Fuel is unknown age, how could I test this to see if it has MBG in it? I’ve put a new fuel filter on before I ran it. It’s all bled through.

Flywheel is on tight and torqued up also

Exhaust is clear has had a new elbow fitted as old one had cracked.

Don’t know when it was last serviced, probably a good place to start. Although I don’t know what oil it should take I’ve seen lots of different suggestions

Thanks

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Re: Bukh DV20 idling rough

Post by BrightStar » Mon Jun 11, 2018 3:29 pm

Regarding oil I use the cheap Halfords diesel engine straight mineral oil in my MD7 of similiar era to your Buk, they dont need fancy high dispercency oils that modern engines need. 10/30 or 15/30 is fine.

If the vibration is the same in and out of gear alignment probably not an issue.

Does the engine start easily and does it smoke.

When it is running in tick over, slacken off the fuel pipe to each injector, one at a time, if the engine stops its running on one cylinder, if it smooth’s down one cylinder is causing your problem.
Brightstar
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Jolly Roger
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Re: Bukh DV20 idling rough

Post by Jolly Roger » Mon Jun 11, 2018 5:23 pm

Running the engine out of the water means your hull is not supported the same as when in the water. Also the water will also help dampen any within hull vibrations.

If there is any alignment problem, this will only be able to be checked once in the water.

The rough slow running is possibly be running too slow at idle, but the flywheel should smooth it out. The other thing I would certainly arrange is to get the injector checked for spray pattern. If it is slightly blocked then you will be suffering fuel starvation at slow speeds.
Roger
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Stoker1538
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Re: Bukh DV20 idling rough

Post by Stoker1538 » Mon Jun 11, 2018 5:51 pm

Thanks guys, will check the injectors and let you know how I get on

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