LOST JEEPS :: View topic - Valve failure research thread

Since we are looking more towards EGT, might a 190 degree stat be better idea vs the 203, or does the 203 temp keep the valves cleaner and therefore cooler?

WWDiesel wrote:

I still hold out the hope that the manufacturers of the valves designed and tested them to be able to withstand exhaust and combustion temperatures under all conditions.
But yes I know it is not a given just as not much else is a "given" except the valve failure itself.
I agree that EGT could be a factor in the failures, but so far no common denominator has surfaced unfortunately.
So many variables really muddies the water on this issue, certainly not black and white or even close to it.
A lot of conjecture indeed.

One other thought to add; a valve *normally gives up a great portion of its **heat flux or heat loading through contact with the valve seat and the valve guide. That is why a lot of guides are made of silicone infused bronze.
But I don't remember anyone reporting excessive valve guide wear on the failed valves?

*About 75% of the heat from a typical valve is conducted to the seat, and the remaining 25% goes up the stem and out through the guide. On engines with three-angle narrow seats, the amount of heat transfer that takes place through the stem is even higher because less heat can be dissipated through the narrower seat. So if the guide is worn, the valve may run hotter.

**Heat flux is defined as the amount of heat transferred per unit area per unit time from or to a surface. In a basic sense it is a derived quantity since it involves, in principle, two quantities viz. the amount of heat transfer per unit time and the area from/to which this heat transfer takes place.

As I said above, I am not certain that there are oil passages around the stems in the valve guide - BUT the guides definitely have some flexible silicone with a small spring seal at the top. This could certainly be a liquid containment system to cool the stems.
I was told by a head shop that this is a three-angle valve seat and cannot (easily) be ground, that is why lapping the new valves in is the only procedure that we can really do in the field to match up new valves with the seats. It does make a liquid-tight seal though. Any custom valves would have to obviously respect the valve grinding, what shows as the contact patch when I lap them in is VERY narrow indeed, maybe a 1/16 wide strip at the most. Certainly not much to transfer that intense heat, so I can easily see where the stem would be soaking up far more of the heat than might otherwise be in another design.
Diesels also tend to create more combustion heat than gas engines, as evidenced by the valve options from Manley for diesels - the heat ranges go a lot higher than for gas, with the alloys becoming more creative including sodium-filled to transfer the heat up the stem more effectively.
We might actually be on to something here.

One other thought to add; a valve *normally gives up a great portion of its **heat flux or heat loading through contact with the valve seat and the valve guide. That is why a lot of guides are made of silicone infused bronze.

*About 75% of the heat from a typical valve is conducted to the seat, and the remaining 25% goes up the stem and out through the guide. On engines with three-angle narrow seats, the amount of heat transfer that takes place through the stem is even higher because less heat can be dissipated through the narrower seat. So if the guide is worn, the valve may run hotter.

We don't have to reinvent the wheel with this. There are many sources that have published their findings. Mfg's R and D studies, and engineering papers from sources such as MIT are readily available and most informative.

https://www.tandfonline.com/doi/abs/10.1080/10407780590959943?journalCode=unht20

GordnadoCRD wrote:

We don't have to reinvent the wheel with this. There are many sources that have published their findings. Mfg's R and D studies, and engineering papers from sources such as MIT are readily available and most informative.
https://www.tandfonline.com/doi/abs/10.1080/10407780590959943?journalCode=unht20

US $50.00 to read.

layback40 wrote:

GordnadoCRD wrote:

We don't have to reinvent the wheel with this. There are many sources that have published their findings. Mfg's R and D studies, and engineering papers from sources such as MIT are readily available and most informative.
https://www.tandfonline.com/doi/abs/10.1080/10407780590959943?journalCode=unht20

US $50.00 to read.

Link to the paper in PDF form at no cost:> https://www.researchgate.net/publicatio ... aust_Valve
But after reading it a couple of times, it really does not answer many questions for our issue.
It is an interesting paper though.

Mountainman wrote:

Since we are looking more towards EGT, might a 190 degree stat be better idea vs the 203, or does the 203 temp keep the valves cleaner and therefore cooler?

I'm going to postulate that with about an 800 degree temperature differential between the combustion / EGT and the cooled surfaces... A 20 degree swing that far away from the EGT temps probably isn't going to affect the EGT much at all - everything else being equal.

Would it be possible, maybe by the aluminum head twisting, expanding, contracting, warping as mentioned, to cause the valves to bind in the guides enough to allow them to contact the pistons? Has anyone who has seen broken valves on one of these engines ever mentioned the valve stem being stuck/tight in the guide when disassembling? Or do they slide out easily? I was thinking that with a break there might be an edge or lip that would hang up afterward. But it has been mentioned how clean the breaks are, so it might be something that could have been observed. I know it is usually hard to break down what happened because of the catastrophic aftermath in the cylinder as evidenced by the pics posted.

I believe the valve stem itself is overheating in the exposed exhaust flow area for some reason that has not been fully determined as of yet which is causing the valve stem metal to crystalize (elongate the molecules) or exfoliate or both which weakens it over time and contributes to its eventual catastrophic failure. But that's just my opinion and is totally conjecture on my part. :banghead:

WWDiesel wrote:

After having looked down the pistons of probably 25 non-failed valve job engines now and another 5 or so that had failed... I COMPLETELY agree with your assessment.

There have been some that have been "difficult" to remove the valves, but that seems to be just the intake valves and buildups of our favorite problem - EGR sludge. Once the old valves are extracted and the guide cleaned by running old valve through a bunch of times with a healthy dose of brake cleaner... I'm not finding a reason to suspect anything other than outright temperature causing these valve issues.

Metals soften and weaken long before their melting point, so it stands to logic that if the temps are too high, problems can happen even without outright melty-failure.

I have seen NO EVIDENCE AT ALL to support any theory that the head "twists" or "warps" in any meaningful way when there is an active water pump and coolant in the engine. There is ALWAYS a substantial coolant flow through the heater loop and the EGR cooler loops which comprise nearly half the area of the primary thermostat outlet from the head. The head also has an oil cooling jacket, which further serves to balance the temperatures between it and the block below. I do not believe it is possible for "hotspots" to form without substantial failures happening elsewhere to remove all the liquid flowing through the head.

These types of failures would not be subtle or missed by even the most absent-minded operator.

geordi wrote:

WWDiesel wrote:

geordi... you are neither an engineer or even a properly trained technician. You do not have the qualifications to make this statement, despite the fact that you replace parts on damaged CRD engines.

The word you used in your post above are typical weasel words... what on earth do you mean by writing ""twists or "warps" in any meaningful way? Did you actually measure head warpage of a failed CRD engine at a machine shop or engine rebuilding shop? What are your measurements?

The results of the metallurgical testing on the valve failures are inconclusive at best. The results should not simply be studied and judged by metallurgical engineers, but also be sent to engineers at an engine manufacturer to determine the cause of these failures. A metallurgical engineer can tell you if a valve breaks or otherwise fails due to flaws or weaknesses in the metal itself, but nothing more. Only an engineer specializing in internal combustion engine design can tell you why an engine part fails for reasons other than flawed metal, as he or she will look at the specific application of the failed part and ALL circumstances surrounding that failure.

Author:	geordi [ Sun Jan 06, 2019 4:16 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
Mountainman wrote: Since we are looking more towards EGT, might a 190 degree stat be better idea vs the 203, or does the 203 temp keep the valves cleaner and therefore cooler? I'm going to postulate that with about an 800 degree temperature differential between the combustion / EGT and the cooled surfaces... A 20 degree swing that far away from the EGT temps probably isn't going to affect the EGT much at all - everything else being equal.

Author:	WWDiesel [ Sun Jan 06, 2019 4:36 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
geordi wrote: WWDiesel wrote: I still hold out the hope that the manufacturers of the valves designed and tested them to be able to withstand exhaust and combustion temperatures under all conditions. But yes I know it is not a given just as not much else is a "given" except the valve failure itself. I agree that EGT could be a factor in the failures, but so far no common denominator has surfaced unfortunately. So many variables really muddies the water on this issue, certainly not black and white or even close to it. A lot of conjecture indeed. One other thought to add; a valve normally gives up a great portion of its heat flux or heat loading through contact with the valve seat and the valve guide. That is why a lot of guides are made of silicone infused bronze. But I don't remember anyone reporting excessive valve guide wear on the failed valves? About 75% of the heat from a typical valve is conducted to the seat, and the remaining 25% goes up the stem and out through the guide. On engines with three-angle narrow seats, the amount of heat transfer that takes place through the stem is even higher because less heat can be dissipated through the narrower seat. So if the guide is worn, the valve may run hotter. **Heat flux is defined as the amount of heat transferred per unit area per unit time from or to a surface. In a basic sense it is a derived quantity since it involves, in principle, two quantities viz. the amount of heat transfer per unit time and the area from/to which this heat transfer takes place. As I said above, I am not certain that there are oil passages around the stems in the valve guide - BUT the guides definitely have some flexible silicone with a small spring seal at the top. This could certainly be a liquid containment system to cool the stems. I was told by a head shop that this is a three-angle valve seat and cannot (easily) be ground, that is why lapping the new valves in is the only procedure that we can really do in the field to match up new valves with the seats. It does make a liquid-tight seal though. Any custom valves would have to obviously respect the valve grinding, what shows as the contact patch when I lap them in is VERY narrow indeed, maybe a 1/16 wide strip at the most. Certainly not much to transfer that intense heat, so I can easily see where the stem would be soaking up far more of the heat than might otherwise be in another design. Diesels also tend to create more combustion heat than gas engines, as evidenced by the valve options from Manley for diesels - the heat ranges go a lot higher than for gas, with the alloys becoming more creative including sodium-filled to transfer the heat up the stem more effectively. We might actually be on to something here. The silicon I was referring to is infused into the valve guide material itself to lower valve to guide friction to help prevent galling of the valve to the guide. Not sure what part it plays in the heat transfer properties. I was not talking about the silicone rubber valve seal on top of the guide which is very common in many engines to reduce oil travel down the stem and into the combustion chamber as the guide wears. Valve guide seals are very important on intake guides especially in gas engines but no so much in diesel engines and on exhaust valve guides. We used to only put new seals on intake valve guides when rebuilding heads for this reason. As to the three angle valve seat grinding, it is easily done if you have the proper tools, equipment, and knowhow. But you better know what your doing when performing the grinding. I used to do them myself all the time on high performance race engine heads when I worked at a Machine and Speed Shop.

Author:	layback40 [ Sun Jan 06, 2019 5:38 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
WWDiesel wrote: One other thought to add; a valve normally gives up a great portion of its heat flux or heat loading through contact with the valve seat and the valve guide. That is why a lot of guides are made of silicone infused bronze. About 75% of the heat from a typical valve is conducted to the seat, and the remaining 25% goes up the stem and out through the guide. On engines with three-angle narrow seats, the amount of heat transfer that takes place through the stem is even higher because less heat can be dissipated through the narrower seat. So if the guide is worn, the valve may run hotter. The guides are normally made from an alloy steel/iron that is high in silicon NOT SILICONE. 3 angle seats are very common. Most modern engines have them. Having a very small contact width improves sealing. As to how most of the heat is dissipated is conjecture. The lower part of the stem gets to be about the same temperature as the base of the valve. There is no oil lubrication of the valve guides. the composition of the guide alloy & the exhaust gas provide the lubrication. These first generation CRD engines, unlike the later piezo systems dont control combustion very well & can result in high EGT's. Its a bit like throwing a can of gas on a fire compared with the same amount of gas thrown on a tea spoon at a time. Any one with an EGT gauge that has their EGR connected & then can disconnect it can give us an indication on the effect.

Author:	geordi [ Mon Jan 07, 2019 3:00 am ]
Post subject:	Re: Valve failure research thread - We need your data!
I don't have a running CRD at the moment, still building the engine that had dropped a valve on the previous owner. But my new 2014 VW TDI has a very nice EGT sensor from the factory - under the same operating conditions before / after and with the only changes of removing the DPF and blocking the EGR completely... The difference in EGT was about 350 degrees. This was at 40mph, flat land, steady cruise control, more than 5 seconds or so after engaging the cruise. Very low power demand on the engine, horsepower was reading about 14 (scangauge calculated). I cannot believe that there was such a massive restriction in the DPF to have contributed much of anything to this change in EGT, but prior to the change the temps were about 900-1000, after it is 650 and consistently repeatable. The engine had already been tuned with an EGR delete but because of the design of "high pressure" EGR, there basically is no way to close that off without removing it and blocking the port. So the high pressure EGR was definitely in play during the "before" test.

Author:	GordnadoCRD [ Mon Jan 07, 2019 3:56 am ]
Post subject:	Re: Valve failure research thread - We need your data!
We don't have to reinvent the wheel with this. There are many sources that have published their findings. Mfg's R and D studies, and engineering papers from sources such as MIT are readily available and most informative. https://www.tandfonline.com/doi/abs/10.1080/10407780590959943?journalCode=unht20

LOST JEEPS http://www.lostjeeps.com/forum/phpBB3/

Valve failure research thread - We need your data! http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=84902	Page 9 of 10

Author:	layback40 [ Mon Jan 07, 2019 10:37 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
GordnadoCRD wrote: We don't have to reinvent the wheel with this. There are many sources that have published their findings. Mfg's R and D studies, and engineering papers from sources such as MIT are readily available and most informative. https://www.tandfonline.com/doi/abs/10.1080/10407780590959943?journalCode=unht20 US $50.00 to read.

Author:	WWDiesel [ Tue Jan 08, 2019 11:02 am ]
Post subject:	Re: Valve failure research thread - We need your data!
layback40 wrote: GordnadoCRD wrote: We don't have to reinvent the wheel with this. There are many sources that have published their findings. Mfg's R and D studies, and engineering papers from sources such as MIT are readily available and most informative. https://www.tandfonline.com/doi/abs/10.1080/10407780590959943?journalCode=unht20 US $50.00 to read. Link to the paper in PDF form at no cost:> https://www.researchgate.net/publicatio ... aust_Valve But after reading it a couple of times, it really does not answer many questions for our issue. It is an interesting paper though.

Author:	GordnadoCRD [ Tue Jan 08, 2019 1:25 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
WWDiesel wrote: layback40 wrote: GordnadoCRD wrote: We don't have to reinvent the wheel with this. There are many sources that have published their findings. Mfg's R and D studies, and engineering papers from sources such as MIT are readily available and most informative. https://www.tandfonline.com/doi/abs/10.1080/10407780590959943?journalCode=unht20 US $50.00 to read. Link to the paper in PDF form at no cost:> https://www.researchgate.net/publicatio ... aust_Valve But after reading it a couple of times, it really does not answer many questions for our issue. It is an interesting paper though. It answers in detail and true accuracy, all of the heat dispersion questions being batted about above, regarding valve guides and seats in gasoline and diesel exhaust valves, and why lean and rich mixtures are so different between SI vs CI and different fuels. The even have a paper regarding how valve grinding and spring pressure effect exhaust valve cooling.

Author:	Mountainman [ Tue Jan 08, 2019 2:54 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
geordi wrote: Mountainman wrote: Since we are looking more towards EGT, might a 190 degree stat be better idea vs the 203, or does the 203 temp keep the valves cleaner and therefore cooler? I'm going to postulate that with about an 800 degree temperature differential between the combustion / EGT and the cooled surfaces... A 20 degree swing that far away from the EGT temps probably isn't going to affect the EGT much at all - everything else being equal. Makes sense. I guess even if it was a 3x equation it would still be less than 100 degrees.

Author:	kmagg [ Tue Jan 08, 2019 8:03 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
Would it be possible, maybe by the aluminum head twisting, expanding, contracting, warping as mentioned, to cause the valves to bind in the guides enough to allow them to contact the pistons? Has anyone who has seen broken valves on one of these engines ever mentioned the valve stem being stuck/tight in the guide when disassembling? Or do they slide out easily? I was thinking that with a break there might be an edge or lip that would hang up afterward. But it has been mentioned how clean the breaks are, so it might be something that could have been observed. I know it is usually hard to break down what happened because of the catastrophic aftermath in the cylinder as evidenced by the pics posted.

Author:	WWDiesel [ Tue Jan 08, 2019 11:16 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
kmagg wrote: Would it be possible, maybe by the aluminum head twisting, expanding, contracting, warping as mentioned, to cause the valves to bind in the guides enough to allow them to contact the pistons? Has anyone who has seen broken valves on one of these engines ever mentioned the valve stem being stuck/tight in the guide when disassembling? Or do they slide out easily? I was thinking that with a break there might be an edge or lip that would hang up afterward. But it has been mentioned how clean the breaks are, so it might be something that could have been observed. I know it is usually hard to break down what happened because of the catastrophic aftermath in the cylinder as evidenced by the pics posted. To my knowledge, no one has reported any indication of valve contact with the piston other than when the valve head actually breaks off and embeds itself in the top of the piston. With such catastrophic damage that occurs when a valve does fail, it may be next to impossible to ascertain for certain if the valve is actually coming in contact with the piston prior to failure. We do know many have reported broken timing belts and the valves hit the pistons hard enough to crack or break the rocker arms without valve stem failure. But I don't believe anyone has reported any valve stem to guide sizing or galling either? But those who have been unfortunate enough to experience valve stem failures certainly may have more insight on this? I personally don't believe the head or the valve guide plays into the failure. I believe the valve stem itself is overheating in the exposed exhaust flow area for some reason that has not been fully determined as of yet which is causing the valve stem metal to crystalize (elongate the molecules) or exfoliate or both which weakens it over time and contributes to its eventual catastrophic failure. But that's just my opinion and is totally conjecture on my part.

Author:	geordi [ Wed Jan 09, 2019 12:06 am ]
Post subject:	Re: Valve failure research thread - We need your data!
WWDiesel wrote: I believe the valve stem itself is overheating in the exposed exhaust flow area for some reason that has not been fully determined as of yet which is causing the valve stem metal to crystalize (elongate the molecules) or exfoliate or both which weakens it over time and contributes to its eventual catastrophic failure. But that's just my opinion and is totally conjecture on my part. After having looked down the pistons of probably 25 non-failed valve job engines now and another 5 or so that had failed... I COMPLETELY agree with your assessment. There have been some that have been "difficult" to remove the valves, but that seems to be just the intake valves and buildups of our favorite problem - EGR sludge. Once the old valves are extracted and the guide cleaned by running old valve through a bunch of times with a healthy dose of brake cleaner... I'm not finding a reason to suspect anything other than outright temperature causing these valve issues. Metals soften and weaken long before their melting point, so it stands to logic that if the temps are too high, problems can happen even without outright melty-failure. I have seen NO EVIDENCE AT ALL to support any theory that the head "twists" or "warps" in any meaningful way when there is an active water pump and coolant in the engine. There is ALWAYS a substantial coolant flow through the heater loop and the EGR cooler loops which comprise nearly half the area of the primary thermostat outlet from the head. The head also has an oil cooling jacket, which further serves to balance the temperatures between it and the block below. I do not believe it is possible for "hotspots" to form without substantial failures happening elsewhere to remove all the liquid flowing through the head. These types of failures would not be subtle or missed by even the most absent-minded operator.

Author:	Mountainman [ Wed Jan 09, 2019 2:18 am ]
Post subject:	Re: Valve failure research thread - We need your data!
X3. I've had a machine shop resurface 20+ and they haven't found one bound up valve, or worn guide. I'm looking forward to seeing more EGT numbers!

Author:	turblediesel [ Fri Jan 11, 2019 5:42 am ]
Post subject:	Re: Valve failure research thread - We need your data!
Finally installed my ARP studs and here are the release torque numbers: 3-85 2-80 1-85 10-85 9-90 8-85 7-85 6-85 5-95 4-85 11-75 12-80 13-80 14-85 15-75 16-75 17-75 18-85 I've only torqued to 110'# so I'm not finished and my #14 stud bottomed out and stands .582" above the head. That's the one in the back on the exhaust side. The rest of the studs stand .509 to .547 above the head. There was a recent thread from a gentleman who cracked his cam-carrier/intake with too-high studs... can somebody direct me to that thread? My new studs are the ARP-VW variety. I'm guessing the block didn't get tapped as deep for that stud and I'm considering pulling that stud and shortening the block end of it in order to keep the hex intact on top. Thoughts and ideas are welcome.

Author:	TKB4 [ Sat Aug 10, 2019 6:37 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
CRD year:2005 Mileage at failure: 204,000 Mileage with functional EGR: Probably 89,000 previous owner installed GDE tune at that time and had EGR delete and GDE tune after 130,000 miles Method of EGR delete: GDE tune at 89,000 mechanical delete at 130,000 Most common driving 50% city/50% Highway relatively flat areas about 10% light towing less than 2500 lbs Exhaust Temperature gauge: NONE No known issues with overheating ARP studs: yes one by one at 198,000 still had small coolant leak Redone with new head gasket and copper Kote at 200k Replacement Rockers: Yes at 200,000 with new style but old rockers were good Time /mileage between engine work and failure 4,000 miles and about 6 months after Cylinder Failure: Number 3 How many valves and which ones: One Exhaust valve No rockers failed Location of break: near the valve coin Pic link https://imgur.com/3bxHDWi https://imgur.com/EN5d1xo Here is pic of head stamp: https://imgur.com/2Pai7E0

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Author:	geordi [ Fri Jan 11, 2019 1:05 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
Where did you get the studs? IDparts will swap it out for you if you got it from them. You also may have run out of threads on the stud rather than depth in the hole... BUT here is the measurement: If your studs in positions 11-14 are showing more than two threads above the top of the nut, there will be problems with the cam cover.

Author:	turblediesel [ Mon Jan 14, 2019 10:16 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
From ID Parts a few years ago, the 2xVW with two spares kit. They all look good. Trimmed my tall stud down to 5.25" overall and it seems happy so I'm doing the same for the other three along the exhaust side. Also ground the camifold webs down a little since measurement made them seem like they might contact the ARP nuts. Probably not and now I'm sure.

Author:	GordnadoCRD [ Fri May 10, 2019 5:55 am ]
Post subject:	Re: Valve failure research thread - We need your data!
. "Camifold.." I like that! That's probably the best polite term I've heard that piece called.

Author:	TURBO-DIESEL-FREAK [ Sat May 25, 2019 3:57 am ]
Post subject:	Re: Valve failure research thread - We need your data!
geordi wrote: WWDiesel wrote: I believe the valve stem itself is overheating in the exposed exhaust flow area for some reason that has not been fully determined as of yet which is causing the valve stem metal to crystalize (elongate the molecules) or exfoliate or both which weakens it over time and contributes to its eventual catastrophic failure. But that's just my opinion and is totally conjecture on my part. After having looked down the pistons of probably 25 non-failed valve job engines now and another 5 or so that had failed... I COMPLETELY agree with your assessment. There have been some that have been "difficult" to remove the valves, but that seems to be just the intake valves and buildups of our favorite problem - EGR sludge. Once the old valves are extracted and the guide cleaned by running old valve through a bunch of times with a healthy dose of brake cleaner... I'm not finding a reason to suspect anything other than outright temperature causing these valve issues. Metals soften and weaken long before their melting point, so it stands to logic that if the temps are too high, problems can happen even without outright melty-failure. I have seen NO EVIDENCE AT ALL to support any theory that the head "twists" or "warps" in any meaningful way when there is an active water pump and coolant in the engine. There is ALWAYS a substantial coolant flow through the heater loop and the EGR cooler loops which comprise nearly half the area of the primary thermostat outlet from the head. The head also has an oil cooling jacket, which further serves to balance the temperatures between it and the block below. I do not believe it is possible for "hotspots" to form without substantial failures happening elsewhere to remove all the liquid flowing through the head. These types of failures would not be subtle or missed by even the most absent-minded operator. geordi... you are neither an engineer or even a properly trained technician. You do not have the qualifications to make this statement, despite the fact that you replace parts on damaged CRD engines. The word you used in your post above are typical weasel words... what on earth do you mean by writing ""twists or "warps" in any meaningful way? Did you actually measure head warpage of a failed CRD engine at a machine shop or engine rebuilding shop? What are your measurements? The results of the metallurgical testing on the valve failures are inconclusive at best. The results should not simply be studied and judged by metallurgical engineers, but also be sent to engineers at an engine manufacturer to determine the cause of these failures. A metallurgical engineer can tell you if a valve breaks or otherwise fails due to flaws or weaknesses in the metal itself, but nothing more. Only an engineer specializing in internal combustion engine design can tell you why an engine part fails for reasons other than flawed metal, as he or she will look at the specific application of the failed part and ALL circumstances surrounding that failure.

Author:	vwroad87 [ Sat May 25, 2019 4:31 pm ]
Post subject:	Re: Valve failure research thread - We need your data!
TURBO-DIESEL-FREAK wrote: geordi wrote: WWDiesel wrote: I believe the valve stem itself is overheating in the exposed exhaust flow area for some reason that has not been fully determined as of yet which is causing the valve stem metal to crystalize (elongate the molecules) or exfoliate or both which weakens it over time and contributes to its eventual catastrophic failure. But that's just my opinion and is totally conjecture on my part. After having looked down the pistons of probably 25 non-failed valve job engines now and another 5 or so that had failed... I COMPLETELY agree with your assessment. There have been some that have been "difficult" to remove the valves, but that seems to be just the intake valves and buildups of our favorite problem - EGR sludge. Once the old valves are extracted and the guide cleaned by running old valve through a bunch of times with a healthy dose of brake cleaner... I'm not finding a reason to suspect anything other than outright temperature causing these valve issues. Metals soften and weaken long before their melting point, so it stands to logic that if the temps are too high, problems can happen even without outright melty-failure. I have seen NO EVIDENCE AT ALL to support any theory that the head "twists" or "warps" in any meaningful way when there is an active water pump and coolant in the engine. There is ALWAYS a substantial coolant flow through the heater loop and the EGR cooler loops which comprise nearly half the area of the primary thermostat outlet from the head. The head also has an oil cooling jacket, which further serves to balance the temperatures between it and the block below. I do not believe it is possible for "hotspots" to form without substantial failures happening elsewhere to remove all the liquid flowing through the head. These types of failures would not be subtle or missed by even the most absent-minded operator. geordi... you are neither an engineer or even a properly trained technician. You do not have the qualifications to make this statement, despite the fact that you replace parts on damaged CRD engines. The word you used in your post above are typical weasel words... what on earth do you mean by writing ""twists or "warps" in any meaningful way? Did you actually measure head warpage of a failed CRD engine at a machine shop or engine rebuilding shop? What are your measurements? The results of the metallurgical testing on the valve failures are inconclusive at best. The results should not simply be studied and judged by metallurgical engineers, but also be sent to engineers at an engine manufacturer to determine the cause of these failures. A metallurgical engineer can tell you if a valve breaks or otherwise fails due to flaws or weaknesses in the metal itself, but nothing more. Only an engineer specializing in internal combustion engine design can tell you why an engine part fails for reasons other than flawed metal, as he or she will look at the specific application of the failed part and ALL circumstances surrounding that failure. He TDF, tone it down. I am an engineer and have witnessed my kind make many errors in diagnosis. And I have been given incredible insight and diagnosis from none "edumakated" people. We are a bunch of tinkerers here trying to maintain and upgrade where possible our little tractors. CHILL OUT and contribute, discuss, disagree but don't attack, ever.