Help! Vibrating engine - air in the lines?

[Hartlebury lad]

Hello all- I have a problem with my recently acquired boat and it's engine vibration.

 

It's a Beta and the whole boat shudders on lower revs ie: tickover or up to 1100 rpm in or out of drive hot or cold.. It is nowhere near so bad when giving more throttle.but it is becoming a major issue. As a result, a fuel pipe sheared off recently, depositing 40 odd litres of fuel into the bilge.. It has done it for ages- even with the previous owner.

 

Apparently, the engine mountings were replaced recently, (although a liberal coating of diesel won't help) An engineer I respect suggested another mounting change to different ones but recent events suggest otherwise. After having some work done on the boat, I took it out and forgot to check the fuel supply was turned on. The boat spluttered to a halt after a couple of hundred metres, The boat would re-start, but conked out. The engineer came out and helped, and and bled a lot of air out of the system to get me going. Bingo- hardly any vibration!.

 

I saw the engineer later and said thanks for tightening the mountings on the original work and he said he hadn't touched them, leading me to believe this could be an air in the system issue. Other engineers had noticed there was no "return"? on the fuel lines and that this needed modifying.

 

This need sorting and I was going to get the mountings replaced, but is this a symptom of not having the "fuel return" in place? Sadly, everything is shuddering again following a grounding and a hefty throttle exercise, so I could do with some informed advice here.

 

Thanks in advance..........

[Kieron G]

Hi, where does the excess fuel from diesel injectors leak off to at the moment, if it's free to run then it shouldn't cause a problem. Your diesel tank breather could be partly blocked restricting fuel flow. I'm not familiar with your engine but I guess it must have a hand primer pump which the fitter used to bleed the system. maybe by disturbing this he made a temporary repair to a worn seal and air is entering there. Just a few suggestions.

[Bobbybass]

I would have thought that you would spot any leaks where air could get in.

If not 'visibly' then get some kitchen towel....and push it around every single junction ...all around the threads...and then hold it up against the light and see if there are light patches.

Having said that...many years ago I had a diesel taxi...and every few hundred miles it would build up air in the system.

It drove me mad looking for leaks at pipe joins and there were none that I could see...however..I eventually replaced the metal pipe from the fuel tank and it was fine that lead me to beleive that there was a very tiny hole in it.

 

A very important thing to check...and a regular failure on the Beta 43...(although beta will not tell you...I had this fault and RCR contacted me to say they were finding it commonly...I told my neighbour I had this problem..and he said he had also had it and he forced Beta to supply a new base engine because it destroyed his engine !! .)...

Me..?...well it was impossible to replace my damaged parts with the Beta parts..so I ended up modifying an aluminium pulley...and designing and making up a complete new type of Travelpower mounting.

It worked better than the original ( big head here !)

 

Get hold of the pulley assembly that drives the alternator and water pump...and 'waggle' it .....

Does it move slightly or rock..?..maybe put a screwdriver behind it.

The large 46mm nut that holds the pulley to the crank starts to come loose and the pulley rocks and wears. and the engine shakes about. It goes on for thousands of hours before it becomes obvious.

It is made worse if you have a Travelpower drive pulley attached as the whole assembly is too heavy...and puts immense strain on the nut.

I obtained a new iron alternator pulley and compared its taper with the crankshaft..finding they were different. That means that even after you torque the 46mm nut to 110 pound-oolicks...the pulley does not grip the crank evenly..but sits on one edge..rocking minutely and cutting itself loose.

 

If you find this problem...could you let me know so that I can get 'complaints' together about the scale of it.

 

Another thing.....is the engine sitting 'high' on the mounts ?

Its best to have the engine low on the mounts when aligned...not sitting on the full length of the mount.

If its near the top it gives it a lot of scope to move about.

If it is high..it may be best to have some thick steel plates made up to go under the mounts....so that the mount is raised and the engine has less thread to swing about on.

 

Good luck !

Edited July 5, 2013 by Bobbybass

[trackman]

If there is no diesel return pipe system, where does excess fuel go? If it can't get away from the injectors, I can't believe the engine runs! That being so I'm not surprised the engine runs badly, especially at low revs.

[RLWP]

I'm not familiar with the details of your engine. Has it got a little low pressure pump on the side of the engine. The pump is round with a ring of screws and a tiny lever. That's a rubbish description, I'll find a picture

 

I have come across these pumps on other engines, and removed one where one of the valves had broken in half, so the pump wasn't working. That gave poor idling and starting

 

Richard

 

MORE: This pump:

 

Edited July 5, 2013 by RLWP

[Henhouse]

If there is no diesel return pipe system, where does excess fuel go?

 

That is the bit I don't understand at the moment, and where you really need to start.

 

Check that the fuel system is correctly installed with all the right components.

 

From tank; Tap, Water separator, Lift pump, Fuel filter, to Injector pump. 4 pipes off to injectors. Return pipe to fuel tank.

 

You can then start to work through the system for blockages / weak joints which are allowing air in.

 

( without wishing to state the obvious, I take it that you do have diesel in the tank, and not running on empty.)

[KenK]

 

 

Another thing.....is the engine sitting 'high' on the mounts ?

Its best to have the engine low on the mounts when aligned...not sitting on the full length of the mount.

If its near the top it gives it a lot of scope to move about.

If it is high..it may be best to have some thick steel plates made up to go under the mounts....so that the mount is raised and the engine has less thread to swing about on.

 

Good luck !

Certainly agree about the engine sitting too high. My Beta 38 would never idle evenly below 1000rpm even from new. I was advised to change the engine mounts but also advised to try shimming the mounts so the engine sat lower on the mount. I fitted blocks underneath the original mounts and now the engine idles at 700rmp without any vibration.

 

Ken

[Guest]

I recall when my engine got water in it started to "lose" a cylinder at a time and vibrated a lot. If the OP's engine needed bleeding, could it have simply been running on (say) three pots, hence the bleeding was a miracle cure for the vibration? Or is that too simple? Just a thought.

Edited July 5, 2013 by Guest

[Hartlebury lad]

Thank you all for your input. If you can take the trouble to reply, I can certainly take the trouble to do the same!

 

Kieron- I will talk to my engine man about your interesting suggestion.

Bobbybass- comprehensive reply- will look at the pulley assembly and get back to you if untoward! Ditto the mounts.

Trackman- the lack of a return system is my chief suspect. Picked up by a couple of engineers. Needs addressing prior to an renewal of mountings?

RLWP- i don't recall seeing such a pump. (ta for doing the pic) Will check next week when back to the boat.

Henhouse - simple methodical advice will be followed

KenK - my engine man is keen on the mount issue. Shimming the mounts, but then fitting blocks underneath?

Catweaeal- my neighbour suspects a dodgy pot too. The engine was repaired two years ago after immersion due to a leaking stern gland and faulty bilge pump, but this problem has been with the boat prior to the rebuild

 

Will print all replies and take to my engine man!

[Chop!]

Are you sure you have not been smitten by the dreaded diesel bug? Blocks your filters and lift pump and makes the engine run very erratically