Diesel knock

Suppose it was a bit misleading , but I knew what I ment , knocking is light throttle, more so around town/light load,no noise when i back off.

I filled it with diesel took it for a good run ,still the same.

just about to nick an injector out of a mates disco, a bit of trial and error,not ideal but

I'm no diesel expert, never really liked them :doh: till a while ago, but have built alot of petrol engines for motorsport over the years, so me ear is tuned in

Dent said:

Suppose it was a bit misleading , but I knew what I ment , knocking is light throttle, more so around town/light load,no noise when i back off.

I filled it with diesel took it for a good run ,still the same.

just about to nick an injector out of a mates disco, a bit of trial and error,not ideal but

I'm no diesel expert, never really liked them :doh: till a while ago, but have built alot of petrol engines for motorsport over the years, so me ear is tuned in

Click to expand...

OK .... there are two main reasons for diesel knocking.

Pre-ignition CAN NOT HAPPEN in a diesel unless the injection timing occurs too soon.

Reason 1. The timing is too far advanced, so back the pump off a TINY BIT. ONE DEGREE on the pump is TWO degrees on the crank. That might be enough to make all the difference.

Reason 2. one or more of the injectors has a lazy or broken needle-spring. Whip out the injectors and get them tested. I have and use a Hartridge POP Tester. Super tool.

Quite honestly there is almost never any other reason for diesel clattering happening.

It would be a good plan to check the belt just in case, especially if YOU don't know when it was last renewed and who did it.

CharlesY

CharlesY said:

OK .... there are two main reasons for diesel knocking.

Pre-ignition CAN NOT HAPPEN in a diesel unless the injection timing occurs too soon.

Reason 1. The timing is too far advanced, so back the pump off a TINY BIT. ONE DEGREE on the pump is TWO degrees on the crank. That might be enough to make all the difference.

Reason 2. one or more of the injectors has a lazy or broken needle-spring. Whip out the injectors and get them tested. I have and use a Hartridge POP Tester. Super tool.

Quite honestly there is almost never any other reason for diesel clattering happening.

It would be a good plan to check the belt just in case, especially if YOU don't know when it was last renewed and who did it.

CharlesY

Click to expand...

Cheers, the plan to try one of me mates injectors went the way of the pear, just got the bonnet up ,garage lit up etc, gets a phone call from his missus ,the dogs got out and run off .

A couple of months ago it seemed to loose a little power so put some injector cleaner in and went on holiday with it ,300 mile and it cleared, so
maybe it is an injector playing up again.

Dent said:

Cheers, the plan to try one of me mates injectors went the way of the pear, just got the bonnet up ,garage lit up etc, gets a phone call from his missus ,the dogs got out and run off .

A couple of months ago it seemed to loose a little power so put some injector cleaner in and went on holiday with it ,300 mile and it cleared, so
maybe it is an injector playing up again.

Click to expand...

I suggest an injector needs to be looked at.

Get the engine warm, and leave it running with the bonnet open.

If you BLIP the throttle can you hear the clatter?

If so, put on goggles (to keep diesel spray out of your eyes) and slacken the number one injection pipe by TWO FLATS at the injector and blip the throttle sharply wide open and off again .

Did it still clatter? If yes, it isn't that injector. Tighten the pipe nut, and head for number two pipe. Repeat. Repeat on #3 then #4.

If slacking ONE injector pipe STOPS it clattering when you blip the throttle, that's the injector to take out first, and swap for a known good one. There could be two or more duff injectors but that's unlikely.

If this process does not stop the clattering on a throttle blip, then either all the injectors are needing set, which is very hard to believe, or the timing is too far advanced. Suspect an injector because timing doesn't slip to advanced - it always moves to retarded if it slips.


If you don't need the car for a few days you can post the injectors up and I can set them, but there are so many easy ways to do a trial-and-error injector swap there's no point.
CharlesY

Thanks,

I think I'll try to find a second hand injector for now, then get them recond after xmas, got two kids with hd tv's and laptops on santa's list, not a good time for cash flow

Dent said:

Thanks,

I think I'll try to find a second hand injector for now, then get them recond after xmas, got two kids with hd tv's and laptops on santa's list, not a good time for cash flow

Click to expand...

Please let me know how you get on with this.
I would like to know. All good experience.

CharlesY

CharlesY said:

Please let me know how you get on with this.
I would like to know. All good experience.

CharlesY

Click to expand...

Will do, got a couple of hours spare in the morning so I'll run through them.

Think an injector might take some finding around here, scrappies won't let me take one out of a complete engine, looks like ebay .

Dent said:

Will do, got a couple of hours spare in the morning so I'll run through them.

Think an injector might take some finding around here, scrappies won't let me take one out of a complete engine, looks like ebay .

Click to expand...

ave got some gooduns spare if you want a loan

am sure we've had this conversation before ?

Sean said:

ave got some gooduns spare if you want a loan

am sure we've had this conversation before ?

Click to expand...

Had a feeling someone on here had some , want to sell one ?

One a different note, seen the fog can't see me disco.....maybe not a bad thing .

Dent said:

Had a feeling someone on here had some , want to sell one ?

One a different note, seen the fog can't see me disco.....maybe not a bad thing .

Click to expand...

don't want to sell one, or as a set, but your welcome to come over and try swapping one out

no fog ere, just snow

Sean said:

don't want to sell one, or as a set, but your welcome to come over and try swapping one out

no fog ere, just snow

Click to expand...

Cheers, I'll see what the score is in the morning.

The disco was covered in ice this morning, but started first time and sounded fine.

Just taken it for a good run, noise is still there, but when I free rev it with the bonnet up I dont seem to get the same noise, just normal ( as I call ) diesel noise. Seems as if it needs slight load to do it.

I've undone the injectors , each one seemed to have the same effect on the engine.

The one thing I did notice, is that if you put your hand on the injectors no.1 feels much more harsh.

Think I'll have a quick look at the timing, might knock it back just to try it, but cant see why it should of advanced, then it's injector swap time, will I get away with the sealing washers, just to try it or do they have to be renewed each time ?.

Dent said:

The disco was covered in ice this morning, but started first time and sounded fine.

Just taken it for a good run, noise is still there, but when I free rev it with the bonnet up I dont seem to get the same noise, just normal ( as I call ) diesel noise. Seems as if it needs slight load to do it.

I've undone the injectors , each one seemed to have the same effect on the engine.

The one thing I did notice, is that if you put your hand on the injectors no.1 feels much more harsh.

Think I'll have a quick look at the timing, might knock it back just to try it, but cant see why it should of advanced, then it's injector swap time, will I get away with the sealing washers, just to try it or do they have to be renewed each time ?.

Click to expand...

Do you have an engine stethoscope?

I reckon Injector #1 may be the culprit - possibly a broken or weak spring
Swap it at the first opportunity.

They come apart easily, but you need a Pop Tester to set them up again.

The timing sounds OK if the thing does NOT clatter when blipping the throttle off-load.

The whole situation point to a dodgy injector allowing early injection because the spring pressure is way too low.

CharlesY

CharlesY said:

Do you have an engine stethoscope?

I reckon Injector #1 may be the culprit - possibly a broken or weak spring
Swap it at the first opportunity.

They come apart easily, but you need a Pop Tester to set them up again.

The timing sounds OK if the thing does NOT clatter when blipping the throttle off-load.

The whole situation point to a dodgy injector allowing early injection because the spring pressure is way too low.

CharlesY

Click to expand...

Don't think I've got a stethoscope anymore, going to see if I can pick an
injector up later.

Cheers.

Dent said:

Don't think I've got a stethoscope anymore, going to see if I can pick an
injector up later.

Cheers.

Click to expand...

I suggest you don't touch the pump timing until you KNOW there are four good correctly set injectors in the head.

CharlesY

Spot on CharlesY , put another injector in no.1 and the noise has gone, also can't feel any harshness through the injector ,performance wise , it seems to rev cleaner in the higher gears.

How much does veg effect egt ?, I've got a better intercooler to go on it, so going to fit a thermocouple and get some temp readings before I up the boost and fuel anymore .

could anyone explain to the uninitiated, what is diesel knock and what is piston slap?

ormondstreet said:

could anyone explain to the uninitiated, what is diesel knock and what is piston slap?

Click to expand...

Right .... great question!

PISTON SLAP first ....

On the way up and down the bores, the piston is leaning on the CONROD, and on three strokes out of four, the piston is pressing down on the conrod. On the other stroke it MAY be pulling up on the conrod, depending if it has a turbo and if so how hard the turbo is blowing at the time. As a piston is RISING the BIG END of the rod is on the RIGHT SIDE of the crank, and so the piston is being pressed against the LEFT side of the bore. At top dead centre the BIG END changes sides, and goes to the LEFT side of the crank, and the piston then goes down and is pressing on the RIGHT side of the bore. At bottom dead centre the conrod and piston both change sides again, and this happens to every piston twice per revolution.

At the very top and very bottom of every stroke the PISTON STOPS momentarily as the CONROD changes sides and direction. At this moment there is no force pressing on the piston - it is loose, as it were. If there is any wear of the piston and bore, especially the piston skirt, the piston takes a short sharp kick to the other side of the bore, making a quite distinct noise called PISTON SLAP. There is no cure other than to make less clearance between piston and bore. New pistons, or a re-bore AND new pistons, is the solution.

DIESEL KNOCK or CLATTER

This is a bit like "pinking" or pre-ignition in a spark engine, but not quite.
In a spark engine the whole air-fuel charge is ignited in one go, but not so in a diesel, where the fuel is injected in a stream, NOT in one sudden dollop.

KNOCKING happens when too much of the fuel is injected too soon, and after a fair bit of fuel is in, it then ignites with a woomph, while the piston is still rising on a compression stroke a long way from top dead centre. Basically, the crankshaft is shoving the piston UP, while the fuel-ignition is trying to push it back down. The result is a short sharp series of GROSS OVER PRESSURE events rather like detonation in a spark engine, which you will hear very distinctly.

Too much of this will eventually cause damage, typically blowing a head gasket, damaging the lands between the piston rings, and the big end bearings. It also reduces power somewhat, thus also wasting fuel.

How's that?

Does that help you see the situations?

CharlesY

Dent said:

Spot on CharlesY , put another injector in no.1 and the noise has gone, also can't feel any harshness through the injector ,performance wise , it seems to rev cleaner in the higher gears.

Super!
Now try to sneak away with that injector still in the head!

Open the injector and take out the spring, I bet it's broken.

How much does veg effect egt ?,

Probably not different temperatures compared to pump fuel.

I've got a better intercooler to go on it, so going to fit a thermocouple and get some temp readings before I up the boost and fuel anymore .

Click to expand...

If you work the fuelling up carefully, I think you will find there's a lot of black smoke before it gets too hot. You won't go that far - too smokey.

Anyway, too hot is only too hot over a long period of time. Super-boost to zoom past a couple of trucks would do no harm.

CharlesY