Beta38 running rough at low revs

[dave.e]

Can any engine experts offer me some advice please? My boat has a Beta38 that is 9 years old and has run for just under 2,000hrs. It has been serviced by the previous owner and then by me, at shorter intervals than suggested in the manual, but over the past few months it has started running really rough at low revs. At revs above 1100 it runs smoothly and quietly, but below 1100rpm, the engine vibrates badly. The idle speed is now lower than the 900rpm it used to run at, but now varies anything from 850 down to around 700rpm.

 

The way the engine shakes below 1100rpm is almost as if it’s only running on 3 cylinders.

 

The fuel filter has been changed recently, but made no difference. The air filter is less than 12 months old. The water separator has no sign of water or diesel bug, and I use Fuelset additive at 25ml per 100l.

 

Does anyone have any idea what could be the cause?

 

Thanks,

Dave Edwards

[Arnot]

Can any engine experts offer me some advice please? My boat has a Beta38 that is 9 years old and has run for just under 2,000hrs. It has been serviced by the previous owner and then by me, at shorter intervals than suggested in the manual, but over the past few months it has started running really rough at low revs. At revs above 1100 it runs smoothly and quietly, but below 1100rpm, the engine vibrates badly. The idle speed is now lower than the 900rpm it used to run at, but now varies anything from 850 down to around 700rpm.

 

The way the engine shakes below 1100rpm is almost as if it’s only running on 3 cylinders.

 

The fuel filter has been changed recently, but made no difference. The air filter is less than 12 months old. The water separator has no sign of water or diesel bug, and I use Fuelset additive at 25ml per 100l.

 

Does anyone have any idea what could be the cause?

 

Thanks,

Dave Edwards

Does it actually run roughly i.e coughing and smokey exhaust?

 

or

 

Does it actually run reasonably well but leap about alarmingly?

 

If it's the latter it may be the engine mountings starting to disintegrate.

 

I have noticed that these engines do leap about as they get older.

 

Hope this helps

 

Regards

 

Arnot

[dave.e]

Does it actually run roughly i.e coughing and smokey exhaust?

 

or

 

Does it actually run reasonably well but leap about alarmingly?

 

If it's the latter it may be the engine mountings starting to disintegrate.

 

I have noticed that these engines do leap about as they get older.

 

Hope this helps

 

Regards

 

Arnot

 

Thanks for the reply Arnot.

 

It's not coughing or producing smoke. It is shaking, so it could be the engine mounts, but I'm confused about why the idle speed has dropped and become erratic.

[Keeping Up]

Can any engine experts offer me some advice please? My boat has a Beta38 that is 9 years old and has run for just under 2,000hrs. It has been serviced by the previous owner and then by me, at shorter intervals than suggested in the manual, but over the past few months it has started running really rough at low revs. At revs above 1100 it runs smoothly and quietly, but below 1100rpm, the engine vibrates badly. The idle speed is now lower than the 900rpm it used to run at, but now varies anything from 850 down to around 700rpm.

 

The way the engine shakes below 1100rpm is almost as if it’s only running on 3 cylinders.

 

The fuel filter has been changed recently, but made no difference. The air filter is less than 12 months old. The water separator has no sign of water or diesel bug, and I use Fuelset additive at 25ml per 100l.

 

Does anyone have any idea what could be the cause?

 

Thanks,

Dave Edwards

Maybe it IS running on 3 cylinders (or three and a half). Could be a blocked injector, or a bit of coke on one of the valves.

[david and julie]

The way the engine shakes below 1100rpm is almost as if it’s only running on 3 cylinders.

Valve clearances too tight? drawing air from a loose union? both would show up more at tick-over and are relatively easy to check.

 

Next would probably be a compression test and have the injectors checked whilst they're out.

[David Schweizer]

I am not very familiar with the Beta engine, but if the throttle is controlled by a cable, it may have stretched a bit or the stop screw may have worked loose. Probably worth checking the simple things first before dismantling the engine.

Edited March 14, 2009 by David Schweizer

[steelaway]

Can any engine experts offer me some advice please? My boat has a Beta38 that is 9 years old and has run for just under 2,000hrs. It has been serviced by the previous owner and then by me, at shorter intervals than suggested in the manual, but over the past few months it has started running really rough at low revs. At revs above 1100 it runs smoothly and quietly, but below 1100rpm, the engine vibrates badly. The idle speed is now lower than the 900rpm it used to run at, but now varies anything from 850 down to around 700rpm.

 

The way the engine shakes below 1100rpm is almost as if it’s only running on 3 cylinders.

 

The fuel filter has been changed recently, but made no difference. The air filter is less than 12 months old. The water separator has no sign of water or diesel bug, and I use Fuelset additive at 25ml per 100l.

 

Does anyone have any idea what could be the cause?

 

Thanks,

Dave Edwards

 

 

Hi Dave

 

I think that the tick over speed simply needs adjusting back to 900/950 rpm

As you say the engine wants to leap of the mountings when it is to slow.

 

Alex

[Yoda]

I think one of the injectors is partially blocked. Take them all out and clean them. Don't adjust anything until you have established what is wrong.

[dave.e]

Thanks to everyone for your replies.

 

My gut feeling was that it may be a blocked injector. If it were a valve not closing due to a flake of coke, I assume that there would be more exhaust smoke. I asked our local boatyard to check the injectors a few weeks ago, but nothing happens very quickly - I think their engine expert is abroad at the moment.

 

I think I would benefit from going on an engine training course.

 

Thanks again for your help.

 

Dave

[Ex- Member]

You've probably checked this, but if you have an air filter fitted, check it isn't clogged up that could also cause a slower idle.

Edited March 15, 2009 by Julynian

[Tony Brooks]

Thanks to everyone for your replies.

 

My gut feeling was that it may be a blocked injector. If it were a valve not closing due to a flake of coke, I assume that there would be more exhaust smoke. I asked our local boatyard to check the injectors a few weeks ago, but nothing happens very quickly - I think their engine expert is abroad at the moment.

 

I think I would benefit from going on an engine training course.

 

Thanks again for your help.

 

Dave

 

 

Let it idle and slacken each injector union in turn. halt a turn is plenty. Its just like checking an old car for misfires. If on injector makes no difference to the idle or makes far less deference than the rest then thats the cylinder that has problems. Make sure both valves on that cylinder have a small gap between the rocker and the valve stem. If one has none at all give the engine a "flick over" on the starter and recheck. If it still has no small gap adjust that clearance.

 

I expect they will both have clearance and if so the only way to tell if its a valve or injector without taking the head off or having the injector tested is a compression test.

 

Personally I think its a faulty injector that would cause smoke, not a stuck valve. A stuck valve would produce clouds of vaporised fuel (white fumes) but an injector is most likely to fail either by dribbling all the time of by producing jets rather than a mist and that would tend to make black smoke.