Tho'ts on the VM 2.8L naturally-aspirated CRD

gmctd · **Posted:** Fri Dec 19, 2014 3:49 pm

I had been ignoring geordi's thread, thinking it was the traditional bolts vs studs (ARP) argument seen on every forum - after reading thru, I think I may have some input that may be of some interest on this naturally-aspirated Diesel engine with tacked-on turbocharger
This epiphany resulted from only recently seeing a removed cylinder head (cylinder-side view) and gasket

For your consideration -

Most Diesel engines with cast-iron heads\blocks get composite gaskets with copper or steel edging around the cylinders, water passages, and bolt-holes -
this construction is very stable with cast-iron head and block assemblies - modern composite gaskets are OE-coated with appropriate sealer to meet spec'ed application
Hi-performance hi-output engines can get all copper gaskets, way better but very expensive

They also usually have 6-bolt pattern around the cylinders, with adjacent cylinders sharing one or two bolts between them, pattern-dependent
Some, usually indirect injection type, have 5-bolt pattern, adjacent cylinders sharing one bolt - the pre-cups can eliminate one bolt per cylinder

These patterns are very stable thermally and are suitable for n\a and turbocharger service with little change in assembly components, usually
only bolt tension and head gasket change for the resultant turbocharged higher cylinder pressures and temperatures

The VM 2.8L engine was obviously designed for normally-aspirated service, having only a 4-bolt pattern without between-cylinder bolts
This is not even suitable for turbocharged service, and is further aggravated by having an aluminum head - aluminum absorbs heat and gives
up that heat easier than cast iron, with result of being much less stable than cast-iron in high heat service, as in turbocharged

A look at the head gasket reveals large areas of cylinder circumference not directly clamped by head bolt tension
- likely they calculated that the small-diameter cylinder could be effectively clamped with only four bolts for n\a service
- maybe they assumed thermal stability for turbocharging by increasing coolant flow thru the block and head
- likely the ECM was programmed specifically to limit turbocharged power output
- the layered\sandwiched steel gasket construction stabilizes installation between aluminum head\block
assemblies, preventing head movement in the horizontal plane
- the steel further allows thermal conduction head to block

The head cylinder-surfaces are evenly exposed to combustion chamber temperatures - some heat is evenly removed by engine coolant in the water
jacket across the cylinder area and surrounding the intake and exhaust valves

The aluminum head on the intake side is further cooled by intake air-flow, with less expansion\contraction than the exhaust side, and the bolts are
exposed to heat at normal engine coolant levels

The aluminum head on the exhaust side is further exposed to turbocharged exhaust temperatures up to 1800*F and higher, resulting in extreme
expansion\contraction of the aluminum across the exhaust ports, with conduction of that higher heat into the head bolts on that side
- exhaust-gas temperature is much higher at the exhaust-valve inside the port than at the exh manifold outlet to the turbocharger, which is higher
than exh gasses entering the turbine, even considering fully-combusted exhaust gasses which quickly lose combustion heat
- black smoke results in even higher temperatures thru-out resulted by increased mass of the unburned fuel, which is soot, which retains
combustion temperature far longer than fully-combusted exhaust gas

This should result in some loosening of the exhaust-side bolts directly adjacent the cylinders, not so much in the outer exhaust-side bolts,
being further from combustion-chamber heat conduction

I would suspect the head gaskets would be oem-coated with a hi-temp sealer with a heat-activated adhesive cement component because of the
aluminum material with only a 4-bolt pattern, but whadoIkno, eh
- or, maybe gasket-coating is to be done at assemby-level with an oem-supplied sealer

I would think that ARP studs, rather than bolts, with non-oem gasket(if oem is not cement-stabilized)would be one preventive solution at tear-down
- a composite gasket would likely be unsuitable because of some insulative quality, limiting additional thermal conduction into cylinder
block surface, with it's larger coolant-jacket

When studs are fully seated to specs in the block, stud and block threads are fully engaged, resulting in reduced upper-cylinder deformation under tension
- spec'ed head-compression tension is fully achieved by torquing the nut on the unmoving stud threads at the top end, rather than twisting the entire
bolt\threads into the block to spec'ed tension while torquing
- this becomes highly critical in this engine with only four (count'em: 4) bolts surrounding the cylinder

- a precision deck girdle is machined for racing engines, which is bolted to the block deck and all head bolts torqued to spec - only then
will the cylinders be final bored, honed, and fitted to the pistons and rings, thus guaranteeing perfect-circle seal and reduced blow-by for maximum
power output

IMO this is one turbocharged engine where BOOST pressures, EGT's and ECT's should be critically monitored when towing, also when enhancing
performance levels for whatever purpose

The OE ECM programming and TCM shift-patterns serve to protect the engine from critical abuse -

I further suspect that pilot-injection is a major factor that has improved this normally-aspirated but turbocharged Diesel engine's survivability quotient

truckbouy2 · **Posted:** Fri Dec 19, 2014 4:49 pm

With your evaluations GM through the years, these Jeeps really were a poor experiment in diesel acceptance. A bolt-on speed parts, ginned up London Taxi motor.
It had failure all over it before it got off the line. The Princess will never tow or stress her Jeep, so I guess it should last as long as a London Taxi.

gmctd · **Posted:** Fri Dec 19, 2014 6:40 pm

Yeah, I'm kinda the resident harbinger of doom and destruction :grim:

........ or......... now we know why there were only two (count'em: 2) production runs of the li'l 2.8L puffer - also why DCJ put their primo swat team for EPA certification, GDE, out to pasture early-on :dead:

Too bad.....................

WWDiesel · **Posted:** Fri Dec 19, 2014 9:20 pm

Very interesting dissertation on the design and possibly poor application of perennials on this engine!!!! :shock:

So, after what you have stated; are you saying one should not tow or increase power levels with modified tunes on this engine as it could possibly self destruct in time if you do so?? :grim:

Many on this forum have done one or the other, or both.... :roll:

A thought, I know on my Dodge Cummins when I blew a boost connector off while towing in the mountains, the EGT went through the roof when there was no boost available. Boost does seem to help keep the EGT's below the 1300 magic number?? :?:

geordi · **Posted:** Fri Dec 19, 2014 9:47 pm

The typical bolts-versus-studs arguments on other forums usually don't contain much science, but are powered by the cold fire of emotion and butt-dyno results and evangelism about studs.

Not so, with the work that LMWatbullrun and RacerTracer did in researching the studs and their potential application to the CRD, working with ARP and figuring out the factory clamping forces and what was needed to be achieved by the studs and the torque to get there.

I disagree that this motor may have been a NA design that had a turbo slapped on it with little other changes, and there are plenty of aluminum headed engines that have hairdryers mounted on the side stuffing cubic feet of air down them, and not blowing gaskets like the CRD does. Something else must be at play, right?

You may be on to something about the number of head bolts, but then again - The VW TDI only has 10 head bolts for a 4 cylinder motor, and I don't believe any are actively 'between' the cylinders like they are on the CRD. But my research fully agrees with your suggestion about the exhaust temperatures, as the exhaust side bolt between cylinders #2 and #3 (IIRC, bolt #3 on the factory chart) is the prime candidate to be loose in comparison to all other bolts. That is also the closest bolt to the manifold outlet, so it isn't just getting the heat of cylinder #3 once per revolution, but it is getting the heat from ALL the cylinders, ALL THE TIME. Heat-soak is certainly a potential reason for a torque-to-yield bolt with questionable metallurgy to weaken over time and heat cycles!

Thankfully, ARP studs are not subject to that questionable metallurgy, their performance is predictable and strong.

I do not know enough about the head gaskets and any potential coatings to say with any confidence one way or another about its performance, other than this: If the clamping is not even all the way around the cylinders, then microscopic gaps between the layers WILL BE EXPLOITED by the impressive cylinder pressures, and this will eventually allow burn-through and pressure escaping into the water jackets. This is gasket failure. Is there a better option for gasket? I don't know. Would solid be the best? I don't know that either. What I would do or suggest, would be a thin pasting of super-high-temp or copper gasket sealant around the cylinder boundaries to attempt to enhance the seal directly adjacent to the cylinder pressures. On the next head gasket I do, this will be investigated more.

gmctd · **Posted:** Fri Dec 19, 2014 11:08 pm

I was hoping you'd comment geordi, and good stuff, but more to the relationship of the gasket to the 360* groove around the combustion chamber and the corresponding ridge on the cylinder liner - not having seen one aparted, it is not clear from available pictures

In the 8000hp nitro-methane top-fuel engines, the head or block is cut to accept a copper o'ring, compressed by head-bolt torque to provide absolutely perfect sealing required by the insanely high cylinder pressures achieved because nitro-methane brings it's own oxygen to the fracas

The VM engine would benefit from this sealing method, but the wide-spacing of the clamping bolts would be better suited to a cast-iron head

Dunno about the VW engines, or if they got aluminum heads, but seems like the 4-cyls are around 2.0 liters?

If it were me, knowing that I would not sue myself over a mistake, I would get a complete set of ARP studs for the li'l puffer, then install one-at-a-time, starting with the one between cyl#2 and#3, then #3,#4, then#1,#2, then rear #4, then front #1, pulling each down to factory spec +/- ARP spec'ed torque - this could maybe save the oem assembly with no further action - if I was still feeling frisky, I might then replace the rest of the bolts, one at a time, in order, torquing to spec B4 proceeding to the next - this would not seriously disturb the head or gasket-seal

Or, I had cohones of steel, I might just slowly re-torque the original exhaust-side cylinder-adjacent head bolts down to factory spec, providing no other head-repair was necessary at the time - might be better than leaving them loose while hoping for the best

FYI, I "enhanced" mine to impress my s-o-t-p dyno, and any totally unaware non-Diesel familiar passenger(s) :frankie:

- "holy fnork, are you sure this is a Diesel?!?!?!?!?!?!"

gmctd · **Posted:** Fri Dec 19, 2014 11:32 pm

WWDiesel wrote:

Very interesting dissertation on the design and possibly poor application of perennials on this engine!!!! :shock:

So, after what you have stated; are you saying one should not tow or increase power levels with modified tunes on this engine as it could possibly self destruct in time if you do so?? :grim:

BOOST and EGT gages should be mandatory for power upgrades - I also like trans temp and rail pressure gages - all four allows me to compensate, as necessary
Many on this forum have done one or the other, or both.... :roll:

Me, too, but I got gages - and a on-board biological computer, eh................
A thought, I know on my Dodge Cummins when I blew a boost connector off while towing in the mountains, the EGT went through the roof when there was no boost available. Boost does seem to help keep the EGT's below the 1300 magic number?? :?:

If your ECM kept dumping fuel as if BOOST was normal, then the black smoke would produce higher EGT's due to the soot content - upgraded ECM can produce high EGT's with correct BOOST by dumping as much fuel as BOOST allows - more fuel makes more BOOST - more BOOST allows more fuel - more fue...........well, you get my drift, right?

CATCRD · **Posted:** Sat Dec 20, 2014 12:21 am

Wait, so is it 4 only, or 6 / 2 shared? Just eyeballing the head in my basement it seems to be full circle 6 / 2 shared. I recall you being pretty impressed with the head bolt configuration of this engine back in the day. One of the things that gave me some confidence in power adders.

viewtopic.php?f=5&t=24878&p=247606#p247606

gmctd · **Posted:** Sat Dec 20, 2014 1:05 am

CATCRD wrote:

Wait, so is it 4 only, or 6 / 2 shared? Just eyeballing the head in my basement it seems to be full circle 6 / 2 shared. I recall you being pretty impressed with the head bolt configuration of this engine back in the day. One of the things that gave me some confidence in power adders.

viewtopic.php?f=5&t=24878&p=247606#p247606

Yep, it has 6, which was good, just not evenly distributed adjacent the cylinder, which is bad - that's why I mentioned o'ringing the head - however, having just seen the head for the first time the other day and after reading geordi's post for the first time last nite, I likely shouldn't have been quite so exuberant, tho I did also mention parts amongst the clouds :roll:

- only four bolts directly clamp the head to each cylinder, two shared

Hmmmm....we need an explosion or blown-up emojies

Also, is the head grooved around the combustion chamber periphery, or is that optical illusion in the posted pic

racertracer · **Posted:** Sat Dec 20, 2014 8:59 am

GM, I have experienced 2 Hg failures back to back one at 110,000mi and the other soon after at 113,000mi on a previous CRD that I owned.

I am now experiencing another HG failure on a newer CRD with 82,000 and plan to repair it soon. I'd like to point out that they all run the Hot Tune and I may be in agreement with you regarding your observations as stated above.

On my previous HG failures, I noticed that the head gasket leaks occured nearest the Turbo area, which lead me to believe that the excessive turbo heat is in fact one of the causes for the failure.

My question is this, in regards to the excessive turbo heat and if in fact the super heat generated by the Turbo is one of the causes for the failure, would a heat separator/gasket/ heat shield or whatever kind of detachment device that would allow the super heated turbo air or heat transfer to dissipate or lessen just before coming in contact with the aluminum head be of value.

I am visualizing some gasket or composite device made of material similar to asbestos but not, that would keep those super heated turbo temps away from the vulnerable aluminum head be of benefit?

????

What do you think?

WWDiesel · **Posted:** Sat Dec 20, 2014 10:38 am

racertracer, did you have the ARP studs installed on any of the engines prior to the HG failure? Just curious.
As to the heat sinking issue, am I thinking wrong? I would think the highest temperature the engine is ever exposed to would be in the combustion chamber and the exhaust ports in the head leading to the turbo... :?:

The turbo temperatures could never be higher than the upstream temperatures in the head and therefore the heat would always conduct toward the turbo from the head...

95Z28A4 · **Joined:** Sun Mar 30, 2014 9:53 am **Posts:** 297

So...........If I understand correctly:
The 2.8L VM N/A has 10 head bolts
The 2.8L VM turbo has 18 head bolts

In my opinion that is a significant upgrade.

Another example of more is better:
The 7.3L Powerstroke has 17 head bolts per bank
The 6.0L Powerstroke has only 10 head bolts per bank
The 6.4L Powerstroke has only 10 head bolts per bank, but the diameter of the bolts were increased
The 6.7L Powerstrokes has 18 head bolts per bank

I have never heard of a stock or mildly modified 7.3L losing a head gasket. It is very common for stock 6.0L powerstrokes blowing head gaskets...........even without EGR cooler failure. Ford upped the head bolt count with the 6.7L probably to ensure gasket retention after their bad experiences with the 6.0L and 6.4L engines.

I do agree with GMCTDs opinion on aluminum vs cast iron cylinder heads for diesels. I believe that this engine would be more reliable with a cast iron cylinder head. My 1998 12 valve Dodge has a cast iron head. I have no concerns about losing a the head gasket on this engine. Do you think World Products would be interested in casting a cast iron cylinder head for the 2.8L VM turbo? Anyone have a cracked 2.8L VM turbo cylinder head they can send to World Products for evaluation/consideration?

Being a gearhead and a hotrodder (in my younger days) I am very familiar with World Products. They make both performance and stock (improved) cylinder head replacements. They have been business for quite sometime and their products are made in USA.

http://www.worldcastings.com/products/cylinder-heads

flman · **Posted:** Sat Dec 20, 2014 11:17 am

WWdiesel

X2 on that, combustion creates the heat, the turbo is just the pump. Hheat sheild would not do a thing. Heat sheilds only protect combustable parts.

95Z28A4

Maybe we can get Sasquatch to make us a cast iron head?

geordi · **Posted:** Sat Dec 20, 2014 12:59 pm

95Z28A4: The engine with 10 head bolts is the Volkswagen 1.9L TDI powerplant in either the older ALH or newer BEW (Pumpe-Deuce) engines. I don't know for the really-new 2008+ models.

RacerTracer's engines (To my knowledge) have NOT had ARP studs installed when the gaskets have failed on any engine.

My knowledge of these engines and board members is that NOBODY that has installed the ARP studs has then experienced a head gasket failure.

However, GMCTD, you may want to note this: A couple members have attempted re-torquing the factory bolts, and this has NOT been successful - Even though I was unable to cause a failure while attempting destructive testing of one of those TTY bolts, a couple other members have had the bolts either shear off in the hole, or round out while attempting removal, or just refuse to gain further torque - which suggests metal failure and eventual shearing.

TTY BOLTS ARE NOT TO BE TRUSTED.

The extreme heat within the interior of the exhaust manifold cannot be directly controlled with shielding on the outside, this will have no effect other than potential insulation and retention of the heat that you want to remove. Oops! Besides that, heat expansion from the combustion chamber is precisely what drives the turbo in the first place. It ain't the raw airflow pushing that wheel to 100k RPM!

The exhaust manifold is iron. It bolts directly to the side of the cylinder head, so obviously the aluminum is perfectly capable of handling the heat.
Aluminum's ability to draw heat away and transfer it into other things (like water jackets) is a big benefit in why the head doesn't melt under normal usage. The whole point of the water cooling system is creating heat-inertia. Objects at rest like to stay at rest, and all that. If the "object" in this case is a temperature reading, then the larger the 'temperature inertia' that you can create, the more input energy will be required to move that temperature reading.

With me so far?

Obviously the combustion chamber is a source for amazing temperatures. But it is also fairly small, and the duration of those high temps is VERY short before a blast of (relatively) arctic air that is hundreds of degrees colder comes rushing in. So the temperature-inertia effect is limited, within the combustion chamber and the aluminum directly above it. Oil jets under the pistons and water right behind the cylinder wall both create that "temperature inertia" to keep the metal temps well within reasonable ranges.

But what about that passage toward the exhaust manifold? Right outside the exhaust valve, would be *the hottest point* of the entire system. I don't know if there is a water jacket right there - I suspect there is, but here is the kicker: Is that bolt hole between the exhaust passage and a water jacket (so there would be SOME cooling right next to it) or is it just between two exhaust passages???

I suspect that the rest of the bolts have a water jacket nearby, but this bolt shared between #2 and #3, right at the midpoint of the head, might be lacking that cooling passage... And there's the source of our problems. Can this be fixed with an iron head? Not that I know of, it would require the redesign of the cooling passages. Perhaps a stronger gasket... But I'd be ALL ABOUT putting in a copper o-ring fire ring on this engine - In an instant, I would do that! But that again, is a major re-design of the system. The laminated gasket is part of the problem, the weak bolts are the other part. If the bolts are heat-soaking and stretching / losing torque because of the heat, then they are TOO SOFT for this application and shouldn't have been selected.

Thankfully, ARP bolts are much stronger hardened steel, and shouldn't be bothered by these temps that obviously aren't hot enough to soften the aluminum, so they will remain well within their "elastic" range.

GMCTD: Replacing the bolts one-at-a-time with the ARP studs is a time-tested method of upgrading the engine without removing or disturbing the head gasket. If you don't have a leak, then this is a good way for anyone to ensure that you won't GET a leak. I would strongly suggest replacing all of the bolts with studs, not just the center rows, and set the torque as follows: for the center rows that border the cylinders, 130 lb-ft. For the outer rows, either 120 or 125, buyer's choice.

However, this is my observation on the gaskets that I have seen thus far: Where the #3 bolt between 2 and 3 on the exhaust side is weaker than the others (and PLEASE record the breaking torques for that research thread) the gasket has shown signs of combustion blow-through between the layers of gasket right at that point. The cylinder pressures are intense. Any gaps in the armor trying to keep those explosions contained, WILL be exploited. If the bolt is loose... It may be a good idea to lift the head and start with a fresh gasket.

ArmyChief · **Posted:** Sat Dec 20, 2014 1:07 pm

Has anyone who used ARP studs had a head gasket failure?

geordi · **Posted:** Sat Dec 20, 2014 1:09 pm

To my knowledge, the answer is no.

ArmyChief · **Posted:** Sat Dec 20, 2014 1:13 pm

geordi wrote:

To my knowledge, the answer is no.

Would that include someone swapping the studs out from the TTY bolts on a currently good head without removing and replacing the gasket?

flash7210 · **Posted:** Sat Dec 20, 2014 1:30 pm

Sure, combustion is HOT, but every time the intake valve opens and every time an injector sprays, the combustion chamber cools.
Fuel is still burning when the exhaust valve opens. Most of the heat from combustion goes out through the exhaust.

The turbo and downpipe could benefit from some sort of thermal insulative blanket or wrap. That would help direct heat further downstream and keep heat from accumulating under the hood.

geordi · **Posted:** Sat Dec 20, 2014 3:43 pm

ArmyChief wrote:

geordi wrote:

To my knowledge, the answer is no.

Would that include someone swapping the studs out from the TTY bolts on a currently good head without removing and replacing the gasket?

Yes, I have not heard of a single head gasket leak that has happened after ARP stud installation when there was not a leak prior on that gasket. Some have installed the ARP on their existing gasket without removing anything other than one bolt at a time, others have done the full job with a fresh gasket. I have done both styles for about 10 different people as well.

geordi · **Posted:** Sat Dec 20, 2014 3:55 pm

flash7210 wrote:

The turbo and downpipe could benefit from some sort of thermal insulative blanket or wrap. That would help direct heat further downstream and keep heat from accumulating under the hood.

I've worked on engines that were driven directly to the timing job, within 15-20 minutes of them shutting the motor off. These engines don't have a problem with heat retention under the hood. Far from it, I think that the diesel in general and these in specific are fantastic motors at running cool, sometimes to the detriment of their own fuel economy!

If the heat problem is happening as we are discussing here, and it is weakening the bolts... That has to be the only place within the engine that IS getting hot. The rest of these things are cool as a cucumber, especially when not towing.

Tho'ts on the VM 2.8L naturally-aspirated CRD

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