NAILING - Page 2 - PeachParts Mercedes-Benz Forum

Dionysius · #16 09-28-2009, 06:58 PM

Quote:

Originally Posted by sasquatchgeoff

I would add mal-adjusted injectors to Dion's very complete list as well. Differing pop pressure between cylinders will affect timing and/or combustion. The spec on my engine is < 3 bar between cylinders.

Good point Sasq. I forgot that one.

In fact I would extend it to mal-adjusted delivery valves as well.

It seems that the list is endless once you start.

Dionysius · #17 09-29-2009, 04:10 PM

If I were to try to define 'Nailing' I would do so in terms of it being a disorganization of the explosion process.

In a normal situation a primary singular coherent combustion/explosion wave with a smooth well defined flame/pressure front occurs at the expected angle in the crankshaft rotation for each cylinder. Nailing represents a perturbation to this organized process caused by one or more of the following (with no implied order of precedence):

Assymetrical injector spray pattern
Carbon build up in the pre-chamber and other explosion space
Mechanical distortion or damage to the explosion space
Damaged or distorted atomizer
Air ingress into the hi pressure fuel lines (Many causes give rise to this including air ingress into the lo pressure side being referred into the hi pressure circuit sometimes but not always by the IP)
Incorrect IP timing relative to crankshaft/cam timing
Mal-adjusted valves
Very low temperature in the explosion space caused by GP issues, low ambient conditions, etc.
Low compression
Out of spec Injector pop pressures (both differential and absolute settings)
Out of spec IP Delivery Valve pressures (both differential and absolute settings)

Please come up with more or suggest better wording.........

jt20 · #18 09-29-2009, 04:18 PM

the term 'disorganized' may be a bit general. You can have a very well-formed flame front that simply happens too quickly or doesn't allow for a controlled burn. (ie.. allowing air to mix in at a given rate).

The difference might be like lighting a balloon filled with gas versus spraying that same gas from a flame thrower in the same amount of time.

...one explodes with a resulting shockwave due to the speed of the flame front. The other expands the the surrounding air to the same degree, but softens the impact.

jt20 · #19 09-29-2009, 04:27 PM

Quote:

Originally Posted by Dionysius

In a normal situation a primary singular coherent combustion/explosion wave with a smooth well defined flame/pressure front occurs at the expected angle in the crankshaft rotation for each cylinder.

is it safe to say that we are trying to avoid 'explosions'? And what we really want is a controlled burn that happens over a range of 'crankshaft angles'?

Ian White · #20 09-29-2009, 04:46 PM

would replaced injector nozzles still cause nailing? I had C Sean Watts pop test, and replace my nozzles with monarchs and my knock was a little less noticeable.

Dionysius · #21 09-29-2009, 05:09 PM

Quote:

Originally Posted by Ian White

would replaced injector nozzles still cause nailing? I had C Sean Watts pop test, and replace my nozzles with monarchs and my knock was a little less noticeable.

If the Nailing is being caused by more than one contributor then that could explain what you experienced.

fruitcakesa · #22 09-29-2009, 06:35 PM

I am experiencing a similar phenom in the 82. Valves were done 5k ago and clean, tested and balanced original injectors were installed and it seems like nailing is more pronounced than prior to the injector R&R
I have not timed or compression tested the engine as it starts reliably and runs strong.

Diesel911 · #23 09-29-2009, 09:29 PM

I have about a year on a Rebuilt set of Injectors with Monark Nozzles.
About 6 or so Months ago I finally got around to Drip Timing my IP and set it at aroximately 28 degrees BTDC.
I ended up with undesirable Nailing.
I had to retard the timing some to reduce the Nailing.

Up until I advanced the Timing I did not think advancing the timing could cause Nailing. I thought it was only Late Timing that did that.
I guess you have to find the "sweet spot" for each vehicle when it comes to timing.

sasquatchgeoff · #24 09-29-2009, 09:45 PM

My Monarks are still in the process of "breaking in" - no nailing, but I will give 'em about another month and take them in to be re-adjusted within 3 bar of each other.

sasquatchgeoff · #25 09-29-2009, 09:52 PM

Quote:

Originally Posted by Dionysius

In fact I would extend it to mal-adjusted delivery valves as well.

yes, from what I understand it is important NOT to move DV's when replacing seals. Just delicately remove the holders and swap bad o-rings for good ones (if present) and carefully replace the copper seals on top of the DV's. I had a couple of seals accidentally drop down the side into the "well" where the DV's were and had to perform a "Dr Kildair" to get them out (with a dental pick) without disturbing the valve itself.

Dionysius · #26 09-29-2009, 09:58 PM

Quote:

Originally Posted by Diesel911

About 6 or so Months ago I finally got around to Drip Timing my IP and set it at aroximately 28 degrees BTDC.
I ended up with undesirable Nailing.
I had to retard the timing some to reduce the Nailing.

Up until I advanced the Timing I did not think advancing the timing could cause Nailing. I thought it was only Late Timing that did that.
I guess you have to find the "sweet spot" for each vehicle when it comes to timing.

Here is my theory....only a theory.......With advanced timing you could be getting a similar effect to 'pre-ignition' in a gasoline engine which could be confused with 'Nailing'. What I mean by 'pre-ignition' here is the explosive force being presented to the piston when it is still in the up stroke. I would expect it would also be characterized by roughness, vibration, and poor MPG.

fruitcakesa · #27 09-30-2009, 11:35 AM

Could leaking injectors cause nailing. I have a weep forming around the center joint on 2 injectors. Return lines were replaced 10k ago with viton and I haven't checked them for leakage.

sasquatchgeoff · #28 09-30-2009, 01:49 PM

Return fuel is little or no pressure and not part of the combustion fuel feed.

Dionysius · #29 09-30-2009, 05:06 PM

Quote:

Originally Posted by fruitcakesa

Could leaking injectors cause nailing. I have a weep forming around the center joint on 2 injectors.

See second to last bullet in my list above: "Out of spec Injector pop pressures (both differential and absolute settings)"

Such a leak that you observe implies an uncalibrated subject. The answer to your question is 'Yes'.

240dddd · #30 10-02-2009, 02:37 AM

as a diesel noob I have also wondered about 'nailing' and what it really sounds like. My car sounds a bit like a tractor, but isn't that what all older diesels kind of sound like?

Does anyone have an audio recording or know of one on youtube that provides a clear auditory example of what nailing sounds like?

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode