Valve failure research thread - We need your data!

GordnadoCRD · **Posted:** Fri Jan 04, 2019 1:16 am

Quote:

VALVE REPORT IS IN!

It made me laugh when I opened the .pdf and saw they used a picture of an A428 rather than an R428. :ROTFL:

At least it gives evidence that they had no pre-conceived ideas about this engine.

layback40 · **Posted:** Fri Jan 04, 2019 1:37 am

GordnadoCRD wrote:

Quote:

VALVE REPORT IS IN!

It made me laugh when I opened the .pdf and saw they used a picture of an A428 rather than an R428. :ROTFL:

At least it gives evidence that they had no pre-conceived ideas about this engine.

The A428 (ENS) did not have this problem!
Same design from the block deck down.
Please explain anyone. dont know if they used the same exhaust valves.

GordnadoCRD · **Posted:** Fri Jan 04, 2019 2:19 am

A428 is dramatically different from R428 both top and bottom, friend.

Head is taller, different intake and common rail.

Biggest difference, is lower left side.
Notice the location of the Water pump.... Below and inboard of the HP fuel pump, which fuel pump, is approximately same as the R428.

Speaking of the HP fuel pump, notice that it is no longer driven by the timing belt, but the accessory belt. This is allowed because the pump has no relation to injection events. All it does is provide volume and pressure. On the R428, failed accessory belts, because the engine kept running, commonly got stuffed into the timing belt cavity and ultimate destruction of engine, valves, etc. With the A428, as soon as the accessory belt fails, the engine dies, before this can happen. It does make scheduled replacement of the accessory belt more important, though.

You can see that the turbo location is different. Lower and a little farther back making oil supply and return much shorter.

Oil pan sump location is different. Tapered and more centered

Look at the cam drive location in front of the head. Only the Intake is belt driven, making for a shorter belt with less stretch potential. The Exhaust cam is driven via chain from the Intake.

The Injectors are pressure fed from the top, where ours has the bleed-off (bypass) return.

The injectors are also piezo type which are fragile and shatter (fail) internally, and the small pieces recirculate back to the tank, and commonly pass through the fuel system again, damaging hp pumps, and injectors again and again until catastrophic failure. One cannot see this last bit from the outside though.

That's enough for one breath.

layback40 · **Posted:** Fri Jan 04, 2019 6:58 am

GordnadoCRD wrote:

A428 is dramatically different from R428 both top and bottom, friend.

Head is taller, different intake and common rail.

Biggest difference, is lower left side.
Notice the location of the Water pump.... Below and inboard of the HP fuel pump, which fuel pump, is approximately same as the R428.

Speaking of the HP fuel pump, notice that it is no longer driven by the timing belt, but the accessory belt. This is allowed because the pump has no relation to injection events. All it does is provide volume and pressure. On the R428, failed accessory belts, because the engine kept running, commonly got stuffed into the timing belt cavity and ultimate destruction of engine, valves, etc. With the A428, as soon as the accessory belt fails, the engine dies, before this can happen. It does make scheduled replacement of the accessory belt more important, though.

You can see that the turbo location is different. Lower and a little farther back making oil supply and return much shorter.

Oil pan sump location is different. Tapered and more centered

Look at the cam drive location in front of the head. Only the Intake is belt driven, making for a shorter belt with less stretch potential. The Exhaust cam is driven via chain from the Intake.

The Injectors are pressure fed from the top, where ours has the bleed-off (bypass) return.

The injectors are also piezo type which are fragile and shatter (fail) internally, and the small pieces recirculate back to the tank, and commonly pass through the fuel system again, damaging hp pumps, and injectors again and again until catastrophic failure. One cannot see this last bit from the outside though.

That's enough for one breath.

Great description!
Now the $64 question ~ What causes the A series not to kill valves?

GordnadoCRD · **Posted:** Fri Jan 04, 2019 11:23 pm

Quote:

Now the $64 question ~ What causes the A series not to kill valves?

We don't really know that it doesn't.

Our CRD's seem to start exhibiting this character flaw in the 8-12 year range, from what I've observed, and as it seems most tied to cyclic events, it's going to vary a great deal, depending on who is driving, how they drive, whether they tow, etc. For example someone who is rock crawling, or camping with family will demand far fewer cyclic events, and much more gentle cyclic closings, than someone who is mud bogging or sand duning.

At any rate, the A428 hasn't really been around long enough for their valves to get to this point. It's currently approaching 5 years in service, so we likely won't see any significant occurrence of this before 2022 at least; and not get to this volume of failure until 2024-5. That's based on the numbers and dates reported here in the states where miles tend to rack up much faster than other countries.

layback40 · **Posted:** Sat Jan 05, 2019 2:41 am

GordnadoCRD wrote:

Quote:

Now the $64 question ~ What causes the A series not to kill valves?

We don't really know that it doesn't.

Our CRD's seem to start exhibiting this character flaw in the 8-12 year range, from what I've observed, and as it seems most tied to cyclic events, it's going to vary a great deal, depending on who is driving, how they drive, whether they tow, etc. For example someone who is rock crawling, or camping with family will demand far fewer cyclic events, and much more gentle cyclic closings, than someone who is mud bogging or sand duning.

At any rate, the A428 hasn't really been around long enough for their valves to get to this point. It's currently approaching 5 years in service, so we likely won't see any significant occurrence of this before 2022 at least; and not get to this volume of failure until 2024-5. That's based on the numbers and dates reported here in the states where miles tend to rack up much faster than other countries.

I thought the A428 was the ENS engine & came out in the non USA market with the KK. That is the case here. So we are at 10 or 11 years. I believe that fuel plays a part. Here in Australia there are 2 main suppliers of fuel, either diesel out of the Exxon refinery in Singapore or a large refinery in India (Shell?). I know when I change from one to the other I see a significant change in EGT in my XJ that has a VM425. I suspect what I am seeing is the difference between EU & US spec diesel. The KJ that I have with a engine failure spent much of its life on US spec diesel.

WWDiesel · **Posted:** Sat Jan 05, 2019 12:45 pm

layback40 wrote:

I thought the A428 was the ENS engine & came out in the non USA market with the KK. That is the case here. So we are at 10 or 11 years. I believe that fuel plays a part. Here in Australia there are 2 main suppliers of fuel, either diesel out of the Exxon refinery in Singapore or a large refinery in India (Shell?). I know when I change from one to the other I see a significant change in EGT in my XJ that has a VM425. I suspect what I am seeing is the difference between EU & US spec diesel. The KJ that I have with a engine failure spent much of its life on US spec diesel.

Layback40, that's very interesting thoughts on the fuel composition effects. That gets us back to the chemical question of fuel and soot effects on the valve stem? :juggle:

layback40 · **Posted:** Sat Jan 05, 2019 5:27 pm

WWDiesel wrote:

Layback40, that's very interesting thoughts on the fuel composition effects. That gets us back to the chemical question of fuel and soot effects on the valve stem? :juggle:

Given that the grain size is not just on the surface, I doubt that some sort of chemical effect on the stem is occurring. The grain size appears to have increased right through the stem. This leads me to think that the EGT is more likely to contribute. Disabling the EGR will lead to higher EGT's under load as the engine gets more fresh air (oxygen) without the EGR & leaner burn leads to higher temperatures.
On the flip side, leaner combustion leads to less carbon (soot) build up on the valve stem & so avoids having burning carbon on the stem. As long as heat can dissipate from the stem through the guide faster than it is heated by exhaust gas the valves are fine.

Its important to remember with a turbo diesel it runs lean as there is an excess of air being blown in. A richer mixture actually reduces EGT's but you get smoke & can get soot build up.
The biggest issue is with hot exhaust from the EGR mixing with any oil from the crankcase ventilation & 1/2 burning to form a goo/soot in the inlet manifold. This then can make its way through & as it burns very slowly it is still soot when it exits & so can stick to valves. As it burns on the surface of the valve it causes excess heat. That is why you see small black pits in valves & seats, bits of soot get caught as the valve shuts & then burn little holes in the seat area.

Sorry, rant over!

Like most turbo diesels, the 428 needs no EGR, a richer mixture & high centane number fuel.

geordi · **Posted:** Sun Jan 06, 2019 2:35 am

One major issue - Diesels are a lean-burn engine. EGT is made higher by more fuel LESS air, if you want to reduce EGT the answer is either cut fueling or raise boost - Both of which lean out the mix.

It is the exact opposite of a gas engine.

When a gasser is working hard, you ADD fuel to cut the temperatures, or you risk melting a piston. You want a RICH mix.
When a diesel is running hard, if you add more fuel you WILL melt a piston - I've done it. I had an injector on a VW start overfueling while I was towing - so I was already running hard, and didn't recognize the marginally higher EGT for what it was, uncontrolled fueling. I melted the top of one piston. The engine had been idling normally prior to that, even when the injector was probably already drooling - because diesels normally idle around 250:1 - VERY lean.

One last thought: You said that disabling the EGR on a diesel will lead to higher EGT. This is provably false in two ways: The CRD programming is to CLOSE OFF the EGR when the power is above 40% demand - if making a rich mix would cool things, then why not open the EGR then? It would bleed boost and very much richen the mix... And smoke out the highway while heating up the pistons for no good reason.

My 2014 VW TDI is the other example. It has factory pre-turbo EGT, and they are VERY responsive sensors. At 40mph, with a functional EGR designed/programmed to be open 100% of the time (high pressure) and nearly 100% on the low pressure EGR... The EGT was about 1000 degrees. This was NOT a regen, that would have been closer to 1400 degrees on that sensor. Changing NOTHING about the programming, but physically removing both the EGR systems... The 40mph EGT is now about 650 degrees.

More air is COLDER. More fuel is hotter. I have suggested for a very long time that the excessive EGR usage with stock fuel levels (not tuned) makes TOO HOT of an EGT for the valves. My own pre-turbo CRD EGT sensor years ago had been showing around 900-1000 degrees at 70mph highway cruise and NOT towing, this is only 200 degrees below where the Manley Inconel valves are rated to.

GordnadoCRD · **Posted:** Sun Jan 06, 2019 5:53 am

layback40 wrote:

I thought the A428 was the ENS engine & came out in the non USA market with the KK. That is the case here. So we are at 10 or 11 years.
That is actually not the case. A428 was released in export Jeeps with the 2011 year model, but not in it's present form. Many things changed over the next 3 years, when the present form A428 entered the market in 2013

I believe that fuel plays a part. Here in Australia there are 2 main suppliers of fuel, either diesel out of the Exxon refinery in Singapore or a large refinery in India (Shell?). I know when I change from one to the other I see a significant change in EGT in my XJ that has a VM425.
I suspect what I am seeing is the difference between EU & US spec diesel. The KJ that I have with a engine failure spent much of its life on US spec diesel.

Fuel makes a difference in many things, but as Geordi pointed out, as far as exhaust temperatures go, Diesel and Petrol engines work in opposite ways. I do agree with you that different refinement recipes have a direct effect on how an engine runs.

So far I haven't seen any evidence that indicates we can pin this thing down to any one obvious cause. We do know that it continues to be a problem.
The research indicates that changing the exhaust valves at least with every other timing belt is probably a good idea.
Another option is having custom exhaust valves made, but there is a complete absence of information as to whether this will fix the problem, make no difference, or make it worse.
I feel if someone wants to try, that's good, but it would need to be someone that racks up a lot more miles than I do, and a sample size of one tells us exactly nothing, really.

layback40 · **Posted:** Sun Jan 06, 2019 7:06 am

geordi wrote:

One major issue - Diesels are a lean-burn engine. EGT is made higher by more fuel LESS air, if you want to reduce EGT the answer is either cut fueling or raise boost - Both of which lean out the mix.

It is the exact opposite of a gas engine.

When a gasser is working hard, you ADD fuel to cut the temperatures, or you risk melting a piston. You want a RICH mix.
When a diesel is running hard, if you add more fuel you WILL melt a piston - I've done it. I had an injector on a VW start overfueling while I was towing - so I was already running hard, and didn't recognize the marginally higher EGT for what it was, uncontrolled fueling. I melted the top of one piston. The engine had been idling normally prior to that, even when the injector was probably already drooling - because diesels normally idle around 250:1 - VERY lean.

One last thought: You said that disabling the EGR on a diesel will lead to higher EGT. This is provably false in two ways: The CRD programming is to CLOSE OFF the EGR when the power is above 40% demand - if making a rich mix would cool things, then why not open the EGR then? It would bleed boost and very much richen the mix... And smoke out the highway while heating up the pistons for no good reason.

My 2014 VW TDI is the other example. It has factory pre-turbo EGT, and they are VERY responsive sensors. At 40mph, with a functional EGR designed/programmed to be open 100% of the time (high pressure) and nearly 100% on the low pressure EGR... The EGT was about 1000 degrees. This was NOT a regen, that would have been closer to 1400 degrees on that sensor. Changing NOTHING about the programming, but physically removing both the EGR systems... The 40mph EGT is now about 650 degrees.

More air is COLDER. More fuel is hotter. I have suggested for a very long time that the excessive EGR usage with stock fuel levels (not tuned) makes TOO HOT of an EGT for the valves. My own pre-turbo CRD EGT sensor years ago had been showing around 900-1000 degrees at 70mph highway cruise and NOT towing, this is only 200 degrees below where the Manley Inconel valves are rated to.

We will agree to disagree on lean/rich & EGT's, I do not wish to give a lecture on incomplete combustion of hydrocarbons. The reason EGR's were added to engines was to reduce combustion temperatures & so reduce NOx.

GordnadoCRD · **Posted:** Sun Jan 06, 2019 12:47 pm

Combustion temperatures and exhaust gas temperatures are different things. And, as noted before, the relationship between the two with a diesel engine is very different than the same relationship of a Petrol engine. Different even yet, are engines designed to run on LPG, and it may surprise you to know that Bottled Natural Gas and LPG are very different as well.

Thank you for your consideration in not giving a lecture on this matter, as it seems would be counter-productive for all.

Quote:

The reason EGR's were added to engines was to reduce combustion temperatures & so reduce NOx.

Correct. This works, and it accomplishes it's goal through reducing available O2. However at the same time that combustion temperatures are lowered, incomplete combustion results in a higher level of still-burning oil exiting the exhaust port, which results in very measurably hotter exhaust gasses, pre-turbo.

WWDiesel · **Posted:** Sun Jan 06, 2019 1:43 pm

geordi hit on it; if EGT alone was the culprit for the valve stem failures, we would be hearing reports of piston failure or piston top damage or damage to the aluminum head long before the effects would be detrimental to the alloy metal of the valve stems. Surely the valve are designed to handle temperatures of exhaust gases. :shock:

Generally in a diesel engine, it it not recommended to run EGT above 1300 deg. F for any sustained periods to prevent piston damage.
As already said, to reduce EGT's, more boost, less fuel, and / or reducing exhaust backpressure can all lower EGT's.

Great discussion everyone with lots of great input! Still don't know the Root Cause of the valve failures but we sure know more than we did about the issue.

GordnadoCRD · **Posted:** Sun Jan 06, 2019 1:59 pm

geordi wrote:

One major issue - Diesels are a lean-burn engine. EGT is made higher by more fuel LESS air, if you want to reduce EGT the answer is either cut fueling or raise boost - Both of which lean out the mix.

It is the exact opposite of a gas engine.

When a gasser is working hard, you ADD fuel to cut the temperatures, or you risk melting a piston. You want a RICH mix.

There is another more effective fix that many manufacturers have been turning to since the early 1990s. That is multi-profile cam technology.
As RPM rise and temperatures approach detonation/destruction, they switch the cam from a torque profile to a high rev high HP profile. A characteristic of typical gas engine high rpm camshafts, is a narrowing of the lobe separation. (~108deg) This causes an increase in open-time-overlap, and allows, amongst other things, an increase of incoming fuel-air to be scavenged through the cylinder, and out into the exhaust port, cooling the piston top, and exhaust valve.
Diesels, and most supercharged engines, don't work this way. There is no solvent in the incoming air, and a high overlap wastes much of the benefits of supercharging until very high RPM. Torque engines benefit more with a wide lobe separation, (112-114deg). seen more commonly with diesels and RV engines.
That said, CRD diesels with their multi-injection/event capability, have the ability to use their post-combustion injections to function similarly, but oil doesn't have the capacity to cool that gasoline has, so the effect is much less.

When a diesel is running hard, if you add more fuel you WILL melt a piston - I've done it. I had an injector on a VW start overfueling while I was towing - so I was already running hard, and didn't recognize the marginally higher EGT for what it was, uncontrolled fueling. I melted the top of one piston. The engine had been idling normally prior to that, even when the injector was probably already drooling - because diesels normally idle around 250:1 - VERY lean.

One last thought: You said that disabling the EGR on a diesel will lead to higher EGT. This is provably false in two ways: The CRD programming is to CLOSE OFF the EGR when the power is above 40% demand - if making a rich mix would cool things, then why not open the EGR then? It would bleed boost and very much richen the mix... And smoke out the highway while heating up the pistons for no good reason.
A diesel injects a precise amount of energy (fuel) into each combustion event. An EGR reduces the amount of O2, less of the energy potential is realized during the combustion event, and is still being extracted as the exhaust exits into the manifold. Some of that continues burning and carrying excess heat. The rest exhibits as smoke/carbon particulates. The more O2 there is available for each combustion event, the more thermal energy is realized during combustion, and the less there is into the exhaust as either heat or smoke. Complete combustion pushes harder on the piston, and cools more quickly as the piston descends.

My 2014 VW TDI is the other example. It has factory pre-turbo EGT, and they are VERY responsive sensors. At 40mph, with a functional EGR designed/programmed to be open 100% of the time (high pressure) and nearly 100% on the low pressure EGR... The EGT was about 1000 degrees. This was NOT a regen, that would have been closer to 1400 degrees on that sensor. Changing NOTHING about the programming, but physically removing both the EGR systems... The 40mph EGT is now about 650 degrees.

More air is COLDER. More fuel is hotter. I have suggested for a very long time that the excessive EGR usage with stock fuel levels (not tuned) makes TOO HOT of an EGT for the valves. My own pre-turbo CRD EGT sensor years ago had been showing around 900-1000 degrees at 70mph highway cruise and NOT towing, this is only 200 degrees below where the Manley Inconel valves are rated to.

geordi · **Posted:** Sun Jan 06, 2019 2:40 pm

WWDiesel wrote:

Surely the valve are designed to handle temperatures of exhaust gases. :shock:

This is hardly a foregone conclusion... And don't call me Shirley. :lol:

WWDiesel wrote:

Generally in a diesel engine, it it not recommended to run EGT above 1300 deg. F for any sustained periods to prevent piston damage.
As already said, to reduce EGT's, more boost, less fuel, and / or reducing exhaust backpressure can all lower EGT's.

Here's the thing about the pistons and the head though - there are cooling passages in the head that are RIGHT NEXT TO the combustion chamber, and the pistons have a continuous oil jet spraying up into the underside of the piston crown. So while there is an active explosion happening for 1/4 of every cycle and 500 times every minute (at 2000 rpm)... That heat is a very brief temperature rise against continually-cooled surfaces with rather large surface areas and immense thermal inertia to overcome.

I am going to change a term here for clarity - the bottom of a valve is called the "head" which is confusing when thinking about the entire assembly - Head contacts valve seat which is also contacting the head it is pressed into. So for clarity - the bottom of the valve shall be called the "coin" since it looks like a coin after they break.

Thinking about the valves, they only contact the head in two places: The coin contacting the valve seat, and the spring / keeper / rocker arm at the top. I do not know for certain if the valves are also oil-cooled, but I suspect they are. Every one that I have disassembled comes out coated in oil along the entire length of the stem. In other designs, the valves can ONLY cool themselves by contact with the valve seat - so there is a high potential for heat-soak and the valves actually being hotter than the surrounding metal of the head and piston which are continuously cooled.

Where the piston and the head surface also only have 1/4 of the cycle under explosive heat, the exhaust valves actually have 1/2 of the cycle - because the coin gets blasted by the explosion, then the stem gets blasted by the same heat during the exhaust stroke AND there is the potential for even more added heat with afterburn fuel injection events! So if the combustion hasn't finished before the valve opens... That isn't just the measured EGT (pre-turbo) that the alloy might be seeing... That is FULL ON combustion temps and the coin is also absorbing that heat without the benefit of being closed against the valve seat and water-cooled-head to draw off that heat.

Maybe there are after-burn events programmed in the tune, I don't know for certain. I do know that multiple injection events have been used to "quiet that diesel sound" and control the noise / vibration / handling as cars are being designed. Maybe there's something to this, I don't know.

geordi · **Posted:** Sun Jan 06, 2019 2:49 pm

These temperature exchanges are a study in opposites - hot explosion touches cooled piston and head, too much thermal mass and the heat energy can't melt the piston or the head in the time it has to work. The cooling oil jets (at 200 degrees must feel like a blast of ice water compared to combustion!) under the piston and the passages in the head are always flowing - but the hot blast is only there 1/4 of the time against the piston... But 1/2 of the time against the valve.

The valves have less cooling capability and 25% less cooling time, but twice as much hot time... I think maybe the EGT is far more important than maybe we are really considering. Thoughts?

WWDiesel · **Posted:** Sun Jan 06, 2019 3:24 pm

geordi wrote:

These temperature exchanges are a study in opposites - hot explosion touches cooled piston and head, too much thermal mass and the heat energy can't melt the piston or the head in the time it has to work. The cooling oil jets (at 200 degrees must feel like a blast of ice water compared to combustion!) under the piston and the passages in the head are always flowing - but the hot blast is only there 1/4 of the time against the piston... But 1/2 of the time against the valve.
The valves have less cooling capability and 25% less cooling time, but twice as much hot time... I think maybe the EGT is far more important than maybe we are really considering. Thoughts?

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 silicon 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.

Mountainman · **Posted:** Sun Jan 06, 2019 3:40 pm

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 · **Posted:** Sun Jan 06, 2019 4:08 pm

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?

That is a very good question! In theory a higher operating temperature should promote more complete spontaneous combustion and thus less carryover of fuel still in the process of burning into the exhaust valve stem and exit area???
Guess we need a thermal dynamics engineer? :dizzy:

geordi · **Posted:** Sun Jan 06, 2019 4:14 pm

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.

Valve failure research thread - We need your data!

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