Prechamber Ball - Page 3 - PeachParts Mercedes-Benz Forum

OM617YOTA · #31 05-07-2015, 03:52 PM

Quote:

Originally Posted by spock505

I think we have to agree to disagree on this one.

'Pinking' is basically pre-detonation during to up-stroke of the piston causing a premature 'knock'of the small end. It is of course predominately gasoline engines but given the right circumstances can happen with diesel too.

Anyway, back to the topic in hand - still think they were removed for whatever reason.

Shirley if the temps got high enough to melt the ball it would melt the alloy head first? not sure on temps for either metals melting point but sounds plausible.

Two points.

1. Pre-ignition and detonation are two different things. Pre-ignition is where a fuel/air mixture is ignited by a source other than the spark plug, and out of correct time. Detonation is where the entire fuel charge combusts at once resulting in a huge pressure spike, instead of a steady flame propagation from a single point that spreads across the fuel charge in an even manner. I do agree that these could happen in a diesel, were another fuel present. Leaky turbo seals?

2. The cylinder head has a nice constant stream of cooling water flowing through it. If the ball got loose and was just rattling around in the prechamber with both no cooling and what is essentially a huge flow of fresh air(oxygen) flowing past it, it could very easily disintigrate into nothing. Ever use a cutting torch? Same idea, fast oxidation.

mytmousemalibu · #32 05-07-2015, 05:40 PM

Quote:

Originally Posted by spock505

Shirley if the temps got high enough to melt the ball it would melt the alloy head first? not sure on temps for either metals melting point but sounds plausible.

Not necessarily. Its all about heat rejection. The prechambers have a tight fit to the cylinder head not only for mechanical sealing but that tight fit allows heat to wick off into the cylinder head casting and thus the coolant to be taken away. A tight fit is necessary for that to work. If the ball-pin became loose in its mounting bore, like finger loose or worse, like vibrating around loose, then the thermal transfer to the prechamber body & cylinder head becomes very poor. It can't easily reject heat and it can build up till it fails or melts. That ball is red hot in normal operation anyway.

This is the same reason that processors in computers have that thermal compound paste on the mounting surfaces of the chip to reject heat into the cooling system. Its also the same properties that could keep anything else from being damaged like the cylinder head, which in this case is cast iron. Not saying that the head can't be damaged by this heat but it's unlikely. Cast iron is pretty tough and also the head material is an excellent heat sink and is liquid cooled. There is exposed cylinder head material on these engines where the glow plug protrudes into the PC and we don't see or hear of it being damaged, even on our alloy headed diesels.

Kinda like how you can take a plastic bottle or cup of water and boil it over a campfire in the plastic. By itself the bottle would melt and burn but the thermal rejection into the water keeps that from happening.

spock505 · #33 05-07-2015, 06:16 PM

Quote:

Originally Posted by mytmousemalibu

Not necessarily. Its all about heat rejection. The prechambers have a tight fit to the cylinder head not only for mechanical sealing but that tight fit allows heat to wick off into the cylinder head casting and thus the coolant to be taken away. A tight fit is necessary for that to work. If the ball-pin became loose in its mounting bore, like finger loose or worse, like vibrating around loose, then the thermal transfer to the prechamber body & cylinder head becomes very poor. It can't easily reject heat and it can build up till it fails or melts. That ball is red hot in normal operation anyway.

This is the same reason that processors in computers have that thermal compound paste on the mounting surfaces of the chip to reject heat into the cooling system. Its also the same properties that could keep anything else from being damaged like the cylinder head, which in this case is cast iron. Not saying that the head can't be damaged by this heat but it's unlikely. Cast iron is pretty tough and also the head material is an excellent heat sink and is liquid cooled. There is exposed cylinder head material on these engines where the glow plug protrudes into the PC and we don't see or hear of it being damaged, even on our alloy headed diesels.

Kinda like how you can take a plastic bottle or cup of water and boil it over a campfire in the plastic. By itself the bottle would melt and burn but the thermal rejection into the water keeps that from happening.

Let me ask you a straightforward question, how many melted pre-chamber balls have you come across during your involvement with Mercedes engines?

HappyHappy · #34 05-07-2015, 06:55 PM

Quote:

Originally Posted by spock505

Let me ask you a straightforward question, how many melted pre-chamber balls have you come across during your involvement with Mercedes engines?

Quote:

Originally Posted by spock505

Let me ask you a straightforward question, how many melted pre-chamber balls have you come across during your involvement with Mercedes engines?

I realize you're not asking me but based on the facts concerning the materials and forces involved I suspect no has, ever!

The circumstances within the engine even in the most concentrated and localized area's will not allow the temperature to exist necessary to "melt"(change a mass's state from solid to liquid) the materials involved.

Generally speaking the average "steel" has a melting point of around 2500 degrees F, steel heated to that temperature would be "white hot", steel heated to even the high shades of "red hot" are going to be much less, as much as 600F less than the 2500 F needed to melt steel.

As I've stated in earlier posts it is in my opinion that it is perfectly plausible that the failure of the prechamber ball's design integrity under the circumstances of high heating and severe pressures could over time pretty effectively contribute to the physical disintegration of the ball including it's eventual complete destruction. I would simply offer the evidence of the prechambers in question that clearly evidence missing steel material from area immediately adjacent to where any ball would have originally existed. The missing material around the machined hole in the prechamber could logically have only occurred if they had been installed in place in a running engine.

It seem almost inconceivable that such an occurrence would take place in more than one prechamber unless there was some shared causative factor.

heating steel will result in scale forming on it's outside surface and eventually being shed, I'm banking that this is the mechanism which is occurring inside the prechamber that reduces the ball to particulate mater which is eventually is reduced down to a size that is capable of fitting through the holes in the prechamber tip. From the photos the holes in the prechambers (now without balls) appear to have the holes in their tips enlarged by some erosive force, my guess is high velocity combustion jets destructively enhanced by carrying disintegrated ball material.

Prechambers with intact balls sometimes have holes with slightly altered dimensions but I've never seen any with this very significant degree of alteration.

mach4 · #35 05-07-2015, 10:31 PM

Loving all this discussion. Can't wait to get back and pull the rest of the prechambers and inspect the pistons to see what's going on.

mytmousemalibu · #36 05-08-2015, 01:08 AM

Quote:

Originally Posted by spock505

Let me ask you a straightforward question, how many melted pre-chamber balls have you come across during your involvement with Mercedes engines?

Had a junk/parts engine that had a couple that were eroded pretty bad and the ball was a bit loose. I have been into other diesels that had some erosion/gas cutting issues in prechamber components. I have live around, owned, and worked on diesels all my life. My family has had quite a few. I myself have had about 10-12 Mercedes diesel pass through my hands. Not counting all that have been through my family, our used car lot or owned by my equally diesel crazy best friend. My veins have diesel and jet fuel running through them

mytmousemalibu · #37 05-08-2015, 01:28 AM

I think all you need to do is think of the operation of an Oxy/Ace cutting torch and its principals. The combustion process could create a condition that produced cutting torch like results. The high temperature and gas velocity is there already. Could the balls have been loose and allowed excessive heat to build up? Could the timing have been off and contributed to higher temperatures? Could worn out and out of spec injectors contributed? Could someone have added to or been burning something other than diesel? Perhaps someone tried to correct poor running and put too much additives in? Could someone have monkeyed with the injection pump or timing? Tried propane or nitrous? Long wide open throttle stretch on a poor running engine? Overheated engine? Point is there are a lot of variables that could be at play/cause it. I think its entirely possible the engine could burn them out in the right circumstances. Could certainly have been removed by someone too. By the pictures posted, it sure seems that the conditions are there to erode the metal of the prechamber body itself where the ball-bar was, is it not so crazy to think it burned up the ball too?

HappyHappy · #38 05-08-2015, 02:42 AM

Quote:

Originally Posted by mytmousemalibu

I think all you need to do is think of the operation of an Oxy/Ace cutting torch and its principals. The combustion process could create a condition that produced cutting torch like results. The high temperature and gas velocity is there already. Could the balls have been loose and allowed excessive heat to build up? Could the timing have been off and contributed to higher temperatures? Could worn out and out of spec injectors contributed? Could someone have added to or been burning something other than diesel? Perhaps someone tried to correct poor running and put too much additives in? Could someone have monkeyed with the injection pump or timing? Tried propane or nitrous? Long wide open throttle stretch on a poor running engine? Overheated engine? Point is there are a lot of variables that could be at play/cause it. I think its entirely possible the engine could burn them out in the right circumstances. Could certainly have been removed by someone too. By the pictures posted, it sure seems that the conditions are there to erode the metal of the prechamber body itself where the ball-bar was, is it not so crazy to think it burned up the ball too?

The O2 Acetylene is essentially a chemical reaction of super oxidation. The O2 is added to iron/steel after being heated to temp, the addition of the pure O2 actually oxidizes through the steel melting what is not consumed in the process. The heating part just makes use of the greater susceptibility of steel to oxidize at elevated temps. You heat the spot on the steel to allow the O2 to start its cutting action. When giant steel objects are cut a regular cutting torch is used to start the cut and then a second man comes in with an O2 lance and picks up the cut and carries it out without any mixed gas added heat, the O2 alone cutting develops the heat necessary to sustain the cut. I've seen them cut 60" in diameter propeller shafts like that.

The temperatures and the conditions never get nearly that hot in the prechamber, there is never going to exist enough O2 in the prechamber to do that. O2 is limited to about 18% in the ambient atmosphere, way less than needed to burn, melt, liquefy steel or iron. Concievably could someone make use of some sort of a liquid fuel/oxidiser pumped through the IP and injectors, possible but hard to imagine something like that happening.

OM617YOTA · #39 05-08-2015, 09:48 AM

I've done something similar, start a cut with the torch and then turn off the gas and let the oxy do the work. Even if it was just air going past the prechamber balls and going waaaaaaay slower than an oxy/acet torch, it would have plenty of time to work.

spock505 · #40 05-08-2015, 11:26 AM

These engines have been to Pluto and back in how many decades? yet here we are with the first (to my knowledge) of melted pre-chamber ball.

Nope, if you were to add up the total number of miles covered by these engines it would have shown up before now and more than once.

Come on guys, that's only reasonable.

If you don't know the history or previous owner its far more likely they were removed. Is there no way you can trace the owner?

Shortsguy1 · #41 05-08-2015, 12:14 PM

Quote:

Originally Posted by spock505

...yet here we are with the first (to my knowledge) of melted pre-chamber ball.

Several previous cases are documented:
prechamber ball fell off
Prechamber Ball Sound?
IP Destroying Injectors, GP, and Prechamber? [long]
240D Missing prechamber ball and compression results.
Ball Bearing in Pre-Chamber ?
Broken Pre-Chamber tip and ball
etc.etc.etc.

spock505 · #42 05-08-2015, 02:58 PM

Quote:

Originally Posted by Shortsguy1

Several previous cases are documented:
prechamber ball fell off
Prechamber Ball Sound?
IP Destroying Injectors, GP, and Prechamber? [long]
240D Missing prechamber ball and compression results.
Ball Bearing in Pre-Chamber ?
Broken Pre-Chamber tip and ball
etc.etc.etc.

Thanks bud, however the first two mention a ball coming loose causing a lot of noise and damage, something I pointed out above.

The third mentions the same damaging the pintle, again this is something I referred to above.

I haven't looked at the others.

Please note, I am not trying to be right for the sake of it and more than happy to be proved wrong, it's that imo the most likely option is owner intervention.

BillGrissom · #43 05-08-2015, 03:22 PM

Quote:

Originally Posted by HappyHappy

...
The circumstances within the engine even in the most concentrated and localized area's will not allow the temperature to exist necessary to "melt"(change a mass's state from solid to liquid) the materials involved.

Generally speaking the average "steel" has a melting point of around 2500 degrees F, steel heated to that temperature would be "white hot", steel heated to even the high shades of "red hot" are going to be much less, as much as 600F less than the 2500 F needed to melt steel.
...

I disagree with what I think you are trying to suggest. Flame temperature of a stoichiometric air-hydrocarbon flame is typically close to 2500F. I did combustion research in my Phd thesis and measured flame temperatures w/ thermocouples and laser scattering. Welding flames (and liquid rockets) have much higher flame temperatures because they don't use air with its 70% nitrogen that robs heat energy (without significantly reacting). Many have melted (or "eroded") a hole in a thin steel pan by leaving it on a gas stove without water.

Everyone is correct that conduction to the head protects metal normally. A loose pin would not have that. While the bulk sees the time-averaged temperature (below melting), a thin layer at the surface could melt at each combustion event. Even without melting, it reacts much faster with O2 at high temperatures (i.e. erode via oxidation). Ex. tungsten has a melting pt >5000 F, but doesn't last long at 800 F in the presence of O2.

Thus, the missing ball pin could have disappeared thru the small pre-chamber outlet ports as vapors or small drops and perhaps not even damaged the piston.

Re the "straightforward question" about melted ball pins observed in practice, that is hardly straightforward. Good luck compiling that data or performing such research. But this site is one of the best to relate experiences, and some have already answered.

Shortsguy1 · #44 05-08-2015, 03:36 PM

Quote:

Originally Posted by spock505

Thanks bud...

You are very welcome.

mytmousemalibu · #45 05-08-2015, 05:14 PM

Quote:

Originally Posted by HappyHappy

The O2 Acetylene is essentially a chemical reaction of super oxidation. The O2 is added to iron/steel after being heated to temp, the addition of the pure O2 actually oxidizes through the steel melting what is not consumed in the process. The heating part just makes use of the greater susceptibility of steel to oxidize at elevated temps. You heat the spot on the steel to allow the O2 to start its cutting action. When giant steel objects are cut a regular cutting torch is used to start the cut and then a second man comes in with an O2 lance and picks up the cut and carries it out without any mixed gas added heat, the O2 alone cutting develops the heat necessary to sustain the cut. I've seen them cut 60" in diameter propeller shafts like that.

The temperatures and the conditions never get nearly that hot in the prechamber, there is never going to exist enough O2 in the prechamber to do that. O2 is limited to about 18% in the ambient atmosphere, way less than needed to burn, melt, liquefy steel or iron. Concievably could someone make use of some sort of a liquid fuel/oxidiser pumped through the IP and injectors, possible but hard to imagine something like that happening.

I understand the principals behind oxy torches and lances perfectly. I've used oxy/ace torches quite a bit myself. I referenced the oxy/ace simply as the cutting action and damage done. High velocity hot gases can indeed cut metal including combustion gases. If fact our former race car a number of times has torched right through the solid copper cylinder head gasket. This was a pushrod hemi engine that had the pushrods running right next to the upper end of the cylinder/combustion chamber where it goes into the head. That area is a weak spot and I still have a couple of pushrods that were torched and cut when it blew through the copper head gasket, the steel cylinder liner, and the stainless fire ring and into the pushrod bore. Also repaired the cylinder head where it cut through the aluminum. All of the damage done looks identical to what a cutting torch can do. If i can find one, I will post a picture. Mind you those burn't up pushrods were 7/16 diameter 4135 steel, melted in a fraction of a second. Heck, look up pictures of burn't exhaust valves. I have personally seen burned/torched exhaust valves made of inconel of all things! Also consider, while its nothing like the oxygen of a cutting torch, in a forced induction engine, you are effectively increasing the the amount of available oxygen by cramming more atmospheres into the cylinders. You don't need high oxygen content to cut metals, high gas velocity, and high pressure under high temperature will do it. It doesn't have to be in one violent blast, it can be erosion over time. Like I said, look at the picture Mach4 posted of the hole in the body of the prechamber severely eroded and enlarged.