Knocking Diesel

Boz

Boz

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Using my Bukh DV7 after the launch of my Galion a couple of weeks ago, since last use in October, it is making a loud knocking noise...

a sneaky look in a handbook in a chandlers suggested that one cause might be the fuel quality. The fuel has been left all winter...

Being slightly nieve when it comes to diesels, is it usual to drain down the fuel tank over the winter, and if I remove the fuel and clean out the fuel filter etc, will I need to bleed the injectors after refilling with new diesel. Should I try the super diesel that some forecourts sell?

Grateful for any advice
Regards
Boz
 
I've never heard that. Top the tank up before leaving it over the winter and that prevents condensation forming which encourages diesel bug but diesel doesn't go off like petrol.

Its more likely to be a mechanical problem. Are you sure the noise is comimng from the engine and not the propshaft and propellor? Is the exhaust loose? You might be hearing the bang as it fires.
 
It coincides with the firing stroke as far as I can tell. Single cylinder diesels tend to be noisy any way. I'm going to change the fuel as a start as the engine has ony just over a hundred hours on the clock.

There is no vibration or judder as I might expect if there were problems with the shaft or prop.
 
Anything similar to

These:









Yes! ... I know these are 10's .... but I can't find any 7's. :rolleyes:
 
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chec that tappet clearence is correct. old fuel shoule be not a problem, been in the ground for a few million years so 6 months in a nice tank is ok.!!!!
 
If you run the engine up to its rated speed and then swing the fuel stop lever to the off position, the engine should come to rest with no knocking noises on the run down. If there are, then you might have a mechanical problem. Otherwise think fuel, timing or whatever.
 
I don't think it is a bad fuel issue.

When the engine is running at highish revs crack the nut on top of the injector to let fuel/air out. The engine will stall of course but tighten up before it stops completely.

If the noise stops whilst the injector is 'open' then it is probably (a) a sticking injector or (b) some air in the pipe to the injector causing a reduction in pressure to the injector hence a poor combustion.

May not work but worth a try.
 
Might be an injector dribbling

SAMYL said:
I don't think it is a bad fuel issue.

When the engine is running at highish revs crack the nut on top of the injector to let fuel/air out. The engine will stall of course but tighten up before it stops completely.

If the noise stops whilst the injector is 'open' then it is probably (a) a sticking injector or (b) some air in the pipe to the injector causing a reduction in pressure to the injector hence a poor combustion.

May not work but worth a try.
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I would agree with SAMYL regarding the injector.

I had a similar problem with my 4 cylinder Ford Diesel. It developed the most alarming noise akin to big end knocking but I eventually traced it to a dribbling injector. Basically after it had "fired" it did not completely seal so fuel dribbled into the cylinder and was prematurely ignited on the next power stroke. The cause was a bit of rust from the injection pipe.

The test is to take off the injection pipe at the injector and crank the engine. If the injector is leaking, you will see air and bubbles coming out of the fuel connection on the top of the injector.

One word of caution is to make sure the injection pump stop lever is engaged or the fuel solenoid disconnected so you don’t spray out fuel from the open fuel pipe and keep your eyes away from the injector connection.
 
Diesel knock

Just as you say fuel quality, I had my mini cooper D in for a service a couple of weeks ago and had mentioned to the mechanic that it was a particularly noisy engine to which he replied where are you buying your diesel from, the Tesco’s Asda’s sell an inferior quality fuel compared to BP, SHELL etc they have more additives that helps to reduce diesel knock. That may be the cheaper solution to your problem a different brand of diesel.
 
I've started buying diesel from company outlets rather than supermarkets. Although it's a couple of P dearer I seem to have improved from 34mpg to 36 mpg. It also doesn't seem to have that fuel knock under load when cold.
 
Not sure about fuel quality

Sneaky Pete said:
Just as you say fuel quality, I had my mini cooper D in for a service a couple of weeks ago and had mentioned to the mechanic that it was a particularly noisy engine to which he replied where are you buying your diesel from, the Tesco’s Asda’s sell an inferior quality fuel compared to BP, SHELL etc they have more additives that helps to reduce diesel knock. That may be the cheaper solution to your problem a different brand of diesel.
Click to expand...

I have had the same advice from our local Peugeot dealer regarding problems we have had with the fuel pressure regulating valves on both our 407 car and our Boxer Motorhome both of which have HDi engines.

However there is a world of difference between a modern computer driven automotive engine where the injectors are electronically driven by signals from the engine management system and the purely mechanical plunger type injection pumps and mechanical injectors found in engines such as the Bukh.

I would have thought that the Bukh would run on just about anything that will burn without too many problems.

But it could be that you have a bug in the fuel causing problems. I would open the fuel filter and have a look first.

Best of luck in your investigation.
 
Jcorstorphine said:
I have had the same advice from our local Peugeot dealer regarding problems we have had with the fuel pressure regulating valves on both our 407 car and our Boxer Motorhome both of which have HDi engines.

However there is a world of difference between a modern computer driven automotive engine where the injectors are electronically driven by signals from the engine management system and the purely mechanical plunger type injection pumps and mechanical injectors found in engines such as the Bukh.

I would have thought that the Bukh would run on just about anything that will burn without too many problems.

But it could be that you have a bug in the fuel causing problems. I would open the fuel filter and have a look first.

Best of luck in your investigation.
Click to expand...

Yes I totally agree with you modern diesel engines deliver the fuel at very high pressure I believe about 30,000 psi compared to the Buhk which may be about 3000 however the principle of compression ignitiion remains the same irrespective of how it is delivered, it is just a starting point and thought rather than paying for more elaborate service work to be done. I would be tempted to change to a different brand of fuel as a starting point.
 
Thanks

Thanks to all who responded.

I drained out ther diesel from the tank (red Diesel) and refilled with BP ultimate, with an injector cleaner added (Wynns) and it is now running better than ever....
Thanks again
Regards
Boz
 
Boz said:
Thanks to all who responded.

I drained out ther diesel from the tank (red Diesel) and refilled with BP ultimate, with an injector cleaner added (Wynns) and it is now running better than ever....
Thanks again
Regards
Boz
Click to expand...

So it could have been a sticky injector as I suggested?
 
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