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 Post subject: Which thickness head gasket?
PostPosted: Mon Oct 15, 2018 10:45 pm 
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Is there a way to tell which thickness head gasket the engine came with, without having the previous head gasket? Or could one just use the thickest gasket for replacement with no negative effects?

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 Post subject: Re: Which thickness head gasket?
PostPosted: Tue Oct 16, 2018 9:32 am 
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c_salsaman wrote:
Is there a way to tell which thickness head gasket the engine came with, without having the previous head gasket? Or could one just use the thickest gasket for replacement with no negative effects?Thanks

Should always just reuse the same thickness head gasket (1,2,or 3 hole) that came off the engine from the factory unless the head was machined which is not recommended due to it having a very thin nickel coating on the mating surface. Using the wrong thickness head gasket
Going thicker does nothing for improving clamping force as these are steel shim gaskets and they are NOT compressible!

These are highly technical diesel engines and there are engineering design considerations and reasons why these engines came from the factory with different thickness head gaskets. They are not at all like the old school overhead valve gas engines that just get it close is good enough!
If "one size fits all" as some proponents encourage, these engines would have all came from the factory with the same thickness head gaskets and the factory service manual would not have went into all the explanations and instructions of precise measurement details to establish the correct thickness gasket when servicing the engine. And the factory would have only supplied a single thickness gasket.

When you change the head to top of piston relationship by altering the thickness of the required head gasket, you are also changing the compression ratio of the cylinders and the valve to piston clearance relationship and the very important and critical injector protrusion to top of piston relationship which can affect combustion timing, exhaust gas temperatures (EGT's), cold engine starting, and engine power curves.
Not following factory recommendations can have consequences.... :juggle:

In your case where you don't have the original gasket to know what thickness the engine came from the factory with,
Only correct way is to take measurements of piston protrusion for each piston at TDC with the head off as outlined in detail the FSM, average the measurements and use the table in the FSM to determine which is the correct thickness head gasket to use.

FSM> 2005JeepKJServiceManual.pdf
http://www.colorado4wheel.com/manuals/Jeep/KJ/
Starts on page 9-194 - 2.8L COMMON RAIL DIESEL ENGINE,
"STANDARD PROCEDURE - MEASURING PISTON PROTRUSION"

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 Post subject: Re: Which thickness head gasket?
PostPosted: Tue Oct 16, 2018 12:49 pm 
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First and foremost:
If you do not have the previous gasket, then measuring the piston protrusion is the only official way to confirm what thickness is required. This sets the distance and clearance between the piston and the valves at TDC and it is critically important to preventing severe engine damage from valve contact with the pistons.

Now, about the selection of gaskets:
Yes, this is a multi-layer steel gasket. Under 19,000 PSI of compressive force however, there may indeed be some compression of the gasket. The point of always using the two-hole (there is no 'three hole' option) gasket is to prevent the LINER from contacting the bottom of the head. There is a raised ring on the inside lip of the liner, this is a "fire ring" and in the proper installation of a high pressure design, there should be a matching groove in the head with a copper seal. This particular design does not have that groove. Using a thinner gasket does not change the height of this ring or of the liner, but may allow the head to actually contact the liner and this will prevent proper compression or clamping of the gasket and can cause warping of the head. It also reduces the force on the gasket itself and transfers it to the liner / head interface, allowing leaks.

Contrary to opinion, the compression ratio and the starting performance of the engine are NOT altered by using the thickest gasket in all cases. This has been measured and proven on several dozen engines now by me personally, and far more than that as a community. The selection at the factory of different sizes also does not take into account wear that occurs over the life of an engine, so that pistons that did not protrude previously may have developed additional bearing clearance over time and now DO protrude further at TDC, which can lead to valve contact and potential engine damage. The additional clearance offered by the extra 20 thousands of thickness are valuable and cost nothing in terms of performance.

I do not have any information to confirm or deny this "nickel coating" on the head, however I DO have information directly from VM Motori that says the head surface is too thin to be milled and that any alteration by milling is NOT authorized. The valve seats are pressed in and directly at the surface, so any milling will likely also impact the valve seats - and this is also not suggested or advisable.

Somewhere north of 50 engines are operating now with the two-hole gasket, and I have personally built over 30 of them each with the two-hole and not one has come back with problems after the fact.

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 Post subject: Re: Which thickness head gasket?
PostPosted: Tue Oct 16, 2018 1:43 pm 
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Excellent post WW. For 2 years now, I've read, and re-read that FSM. The part about 'finding the average' seemed really, well, 'weird'. I've always 'found the worst (tightest) clearance, and adjusted around THAT. Never the 'average'.

It's not about valve clearance, or even piston to head clearance. On a unaltered block or head, there is no way the piston will get into the 'danger zone' for interference. regardless of which HG is used.
Pistons are valve- relieved.. Even if the piston comes totally UP and just touches the head, the valves will be 'safe' in those pockets. (as long as there isn't GOBS of carbon on them..
Jumped timing belt is another story.

What this is all about, is the compression pressure/temp and DISTANCE OF THE END OF THE INJECTOR, to the top of that 'point' on top of the piston.
I found out just how important keeping this distance is for how well the engine runs;
4 yrs ago, I rebuilt a perkins 354. This engine was right on the 'line' for design changes, and the rebuild kit came with both versions of copper washers that fit under the injectors. I believe they were .040 inch and .020 thick respectively.
I mistakenly put in the thicker washers. .020 'difference' may seem totally insignificant.. Boy, I was wrong!
The engine WOULD NOT cold start. Period. I played with injection timing, which seemed to help a little, but I was WAY over spec. Totally inappropriate for a lugging continuous duty engine.
After pulling my hair out, it hit me where I messed up.. I put the correct washers in, and re timed it to spec. Viola'. Perfect.

Our ECM's carry all the inputs the engine needs to perform under any possible condition.
'Timing' is based on some 'SET' (can't change) and some wildly variable inputs.
The ecm will 'know' that air intake temps of 'x' with a boost of 20 psi, and should be (wild swing here, 600f) resulting in a 'light off' in X milliseconds.
The distance of the injector will already be factored in, since it cannot change.
mess with the compression ratio, (light off temps) and distance of injector to piston... and the ecm will still 'think' it's stock, when in fact it's different. The ECM can't measure the exact temp of compression pressure, but it sure can CALCULATE it based on intake air temp, boost, engine coolant, RPM and the constant variable it was assigned with (compression ratio)
How much? I've yet to read a post saying someone was seeing poor(er) performance or 'problems' with running a thicker gasket.. It's probably miniscule in the difference. The point is; While it may not really effect our 'butt dyno'.. it certainly can be a limiting factor because we've altered what the ecm has taken for granted.

I'd bet emissions are probably the first thing that is effected. These things were built to meet specs, 'tier 2, Euro 3'... or whatever. Sending these engines out the door with a 'one size fits all' gasket probably would've FAILED a large percentage of them..

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 Post subject: Re: Which thickness head gasket?
PostPosted: Tue Oct 16, 2018 8:46 pm 
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Thanks so much for the detailed responses. Unfortunately the technicality and opposing views hasn't really solved it for me. Haha.

Ww. Thanks for the link to the service manual.
Will I be able to find the warpage allowance for the head in there?

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 Post subject: Re: Which thickness head gasket?
PostPosted: Tue Oct 16, 2018 8:58 pm 
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c_salsaman wrote:
Thanks so much for the detailed responses. Unfortunately the technicality and opposing views hasn't really solved it for me. Haha.

Ww. Thanks for the link to the service manual.
Will I be able to find the warpage allowance for the head in there?

I doubt it! :ROTFL:
but
Just because some have gotten away with using the "one size fits all" theory, it certainly does not mean it is the best decision/gasket to use as Rancherman and I have tried to explain.
I still stand by original statement; if VM did not think it was important to use the correct head gasket they would have never went into all the detailed instructions in the FSM as to how to determine the correct thickness for the head gasket when servicing. They would have simply stated to use and supplied a single thickness gasket for all engines regardless of dimensional clearances and piston protrusions.
Some may think they know more than the engineers at VM who designed, tested, and wrote the FSM for this engine, and they can do whatever they want to.
I would follow the instructions in the manual....

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 Post subject: Re: Which thickness head gasket?
PostPosted: Wed Oct 17, 2018 10:26 am 
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WWDiesel wrote:
c_salsaman wrote:
Thanks so much for the detailed responses. Unfortunately the technicality and opposing views hasn't really solved it for me. Haha.

Ww. Thanks for the link to the service manual.
Will I be able to find the warpage allowance for the head in there?

I doubt it! :ROTFL:
but
Just because some have gotten away with using the "one size fits all" theory, it certainly does not mean it is the best decision/gasket to use as Rancherman and I have tried to explain.
I still stand by original statement; if VM did not think it was important to use the correct head gasket they would have never went into all the detailed instructions in the FSM as to how to determine the correct thickness for the head gasket when servicing. They would have simply stated to use and supplied a single thickness gasket for all engines regardless of dimensional clearances and piston protrusions.
Some may think they know more than the engineers at VM who designed, tested, and wrote the FSM for this engine, and they can do whatever they want to.
I would follow the instructions in the manual....



For the cost of milling the head, doing the valves, and worrying if too much has been taken 'off'.. and further thinning out the casting.. or messing up the specific Ra surface spec, Then you should test for cracks, consider new exhaust valves...

You may want to consider a 'good take off head' from VMspecialist. They are heads off of low hour test engines, developmental engines, or warrantee (where an engine came in under warrantee, and was dismantled, and 'good' parts were salvaged).
They are all checked for flatness, cracks, guides, seats and valves are checked. Mine ran me less than 500 bucks, shipping included from England. you could have them (vmspeciaist) install new exhaust valves about as cheap as anyone Stateside. You'd be done and done. Surprisingly, mine showed up in just 1 week from ordering.

For a 'short' head (4 cylinder) that is fairly wide, I'd say .005 Inch on the longitude, and .002 inch on the lateral would be the max.
Another way would be to bolt the cam cover back on the uninstalled head (no rockers installed) or cover gasket. Torque to spec, and in order. See if the cams can still turn freely. If not, I'd pass on that head.
I don't have any proof, but if a head is warped that much, cracks are probably knocking on the door.

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80,500 miles, engine is disassembled, awaiting parts 3/18
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 Post subject: Re: Which thickness head gasket?
PostPosted: Wed Oct 17, 2018 2:29 pm 
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If a head is warped enough to cause the cams to bind... I think you'd be able to see that from orbit!

Officially there is no allowable warpage, and I agree with that. You don't want any warping at all.
Officially there is also no allowable milling specification. Whether any can be milled without cutting a seat or a water jacket is a different story. I don't know because I have not tried, and I'm not a machinist with the skill to see through metal to know where the casting ports are.

Also officially the thickness allowances for the head gasket are based on the PISTON MOVEMENT and nothing else. VM designed an engine with 17-to-1 compression and an interference design, such that there is virtually no clearance when the piston is at TDC. ANY slop in the bearings under high RPM can change that measurement as the piston will have inertia and keep "moving up" past the measured TDC. If you bring a piston to TDC and then "pull up" on the crown while it is sitting there... Does it move? That is bearing slop. Maybe there will be enough clearance to not kiss the valves. Maybe not.

The service manual has procedures based on earlier designs of this engine (it clearly shows a turbo with a wastegate rather than the VNT we have) and there have been design changes that we can see physically that do not match the book. The measurements are also based on a NEW engine, not one that is worn-in and may or may not have everything else in the system in-specification (bearing wear on the rods). Measure precisely each piston on the longitudinal axis (front to back) and at both the front and back of each piston, and decide from there.

I may be "doing it my own way" but that is with the knowledge imparted by smarter people than I claim to be, and I have backed that up with actual testing of compression (which WOULD change if there was a difference) and the results speak for themselves. The engines I have built with the two-hole are all running great and starting easy. We are arguing over a potential difference of 20 thousands here, barely more than a few sheets of paper stacked.

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