Things were just a little too cozy...

[JeepSJ]

Pulled the heads from my old engine this weekend and found a disturbing sight -



This was a low-miles stock engine when I purchased it. I pulled the heads at that time to inspect the cylinders and all looked good. I reinstalled heads with FelPro gaskets and ARP studs. The only other modification to the engine was a DSG gear drive.

This wasn't the only cylinder. Several others showed imprints of the intake valve in the carbon on top of this piston. This one is the worst though as there is an actual indentation in the top of the piston from the exhaust valve.

I think I found the reason this engine always sounded mechanically noisy.

[JeepSJ]

The more I look at things, the more I come to the conclusion that there must be a problem with the cam timing from the gear drive. Has anyone taken the time to degree a cam after installing a gear drive to verify that these things are accurate?

[Robyn]

How far out of the cylinder is the piston protruding ???

You bought this engine used ??

Was it a rebuild ???

If so, by who, and were the decks cut ???

Almost looks like that piston is above the deck some ???

When you had the heads off did you use a standard head gasket ???

Specs say the piston should be even with the deck to NO more than .005 above the deck at TDC
The decks can be machined .010" butttttttttttttt I have taken them to .015" in a pinch to get a good clean surface.
The thicker (.010") gasket must be used when the decks have been cut.

These engines are really really tight inside even from the factory.
I am thinking that the gear drive would need to be waaaaaaaaaaaaaaaaaaaaaay off to cause this type of issue.

The stock timing chains can and do get pretty loose over time (Causing some valve timing changes) and there are no issues with valves smacking the pistons.

The cam profile on these engines is pretty mundane and should not even be an issue.

How many pistons show valve contact??



More info please

[JeepSJ]

How far out of the cylinder is the piston protruding ???

Haven't measured yet but they appear flush. This was just a rough check using a straightedge across the deck.

You bought this engine used ??

Yes

Was it a rebuild ???

No, it was supposed to be a low mileage used engine. When I pulled the heads and main caps the lack of wear supported this assumption.

If so, by who, and were the decks cut ???

N/A

Almost looks like that piston is above the deck some ???

Actually that picture the piston is down in the hole.

When you had the heads off did you use a standard head gasket ???

Yes, Felpro standard thickness.

Specs say the piston should be even with the deck to NO more than .005 above the deck at TDC
The decks can be machined .010" butttttttttttttt I have taken them to .015" in a pinch to get a good clean surface.
The thicker (.010") gasket must be used when the decks have been cut.

These engines are really really tight inside even from the factory.
I am thinking that the gear drive would need to be waaaaaaaaaaaaaaaaaaaaaay off to cause this type of issue.

I'm going to do some measuring before I take it the rest of the way apart. I know what the factory lobe center should be with a stock chain so I can compare to that.

The stock timing chains can and do get pretty loose over time (Causing some valve timing changes) and there are no issues with valves smacking the pistons.

Yes, but that retards the cam. There may be an issue with advanced cam timing.

The cam profile on these engines is pretty mundane and should not even be an issue.

It is mundane but these are an interference engine. There isn't enough room for the valve to be all the way open and the piston to be at the top of the stroke.

How many pistons show valve contact??

I only have the passenger head off so far and it only looks like 1 exhaust had firm contact hard enough to cause an indentation in the piston. 3 of the intakes have left impressions in the carbon but don't look like they actually made metal to metal contact.

More info please

I will share more as I continue to investigate. I wish I could find the notes I made about what holes I pulled the bent pushrods out of when I took the top end apart a couple years ago.

[arveetek]

I wish I could find the notes I made about what holes I pulled the bent pushrods out of when I took the top end apart a couple years ago.

Sounds like this engine has had this problem for a while then. Valves hitting a piston will definitely cause bent pushrods.

Casey

[JeepSJ]

Got the engine pulled and got the other head off. Amazingly none of those pistons showed any signs of valve contact. Next need to finish disassembly so I can send the rods over to the machine shop for resize and the crank so everything can get balanced. While it is apart I'm going to match-port the intake and exhaust. I'm putting in a new set of valves and I'll have the machine shop cut the minimum go get the heads flat.

But before I pull it apart, I'm going to do some measuring to see if I can find that side had the issue.

[JeepSJ]

Sounds like this engine has had this problem for a while then. Valves hitting a piston will definitely cause bent pushrods.

Casey

Yeah, it was noisy when I first installed it. I pulled it apart about 5 years ago to have the injection pump rebuilt and was going to swap out the lifters because I thought I had a bad lifter. It has been sitting ever since.

[JeepSJ]

Just noticed something also over the weekend. All of the pistons are marked with their location. You can see the "2" in the center of that piston. Is that normal on a factory engine?

[john8662]

That engine has been rebuilt. Those are Mahle pistons and look to be .040" oversize by the 100 marking.

This will require a dial gauge and bridge to see what the piston height is at TDC.

Maybe it had .010 thicker gaskets on it previously.

Since both valves are hitting, it's either a piston protrusion problem or incorrect valve depth and install height (machine shop can verify this), also uses dial gauge and bridge.

[Robyn]

Will certainly be interesting to see wasssssup on that one side.

My bet is the deck was cut.

Check along the ledge at the top of the block to see if anything was stamped there to indicate that a cut was done on the deck.

To step back some ... If the cam timing was off then both sides would have had valve to piston interference issues ????


Very interesting situation... Very curious to see what you find.

Robyn

[JeepSJ]

Other side showed no signs of hitting at all.

Is there something I can measure on the head to see how much the heads have been shaved?

No markings on the block or deck at all.

I'm seriously pissed at the company that sold me the engine. Now I have to question the integrity of the rest of the internals. Questions such as did they do something stupid like grind the crank?

[Robyn]

The main concern is the piston top to deck dimension with piston at TDC.

If the head/s have been cut they are not as tough ($$$$) to replace.

You can use a depth mic and check the distance between the face of the valve/s and the face of the head. (Use a ground bar to span the chamber and place the mic on the bar)

My bet is still that the deck on the one side was cut.

These can be cut .010" and I have personally gone to .015 to save a block, but any cut of substance requires the use of the thicker gasket.

Very common to see the area around the front two cylinders gasket fire ring eroded into the block.
Without cutting the deck the gasket will fail again.

If after a thorough cleaning there is any indent into the deck where the fire ring sits the deck must be machined.



Felpro makes the new gaskets with a stainless block off for the front two water passages.
This stops the coolant from laying against the bare block and causing corrosion that results in the gasket failure.

Using premixed coolant (green) is much better than the concentrate as the "local" water can be all over the map as far as it's PH and mineral content.

Keeping the coolant readings proper helps a lot to stop issues.
(Use the little dip sticks with color chart)


May well be a combination of a head that's been cut as well as the block.


Check your piston protrusion as well as the valve face to surface on both sides.

Get all the numbers and it should ferret out what happened.

Good luck and keep us in the loop

[JeepSJ]

Well the info on the oversize pistons confirming this was a rebuild made me go back out to the garage and really search the block for any markings. Sure enough, on the back of the block on that side (had to remove the layers of paint to read it) I found "SUR007". There was so much paint over it that you could not make out that it was a stamping - I only saw it when I put a light across it sideways. Once the paint was off it was very clear. Assuming that means they took 007 off that side. No markings on the other side. No markings on either head indicating that they had been machined but I would still like to know what the spec is for how deep the valve should be in relation to the deck. I just ordered a bridge for my dial indicator.

Interesting looking at the bores again...nice crosshatch still but you can really tell that it wasn't bored with a torque plate.

[JeepSJ]

Using premixed coolant (green) is much better than the concentrate as the "local" water can be all over the map as far as it's PH and mineral content.

My dad taught me at a very early age that the only 2 things you ever put into a radiator are coolant and distilled water. I still follow that rule. I always keep a couple gallons of distilled on hand for radiators and batteries.

[Robyn]

Daddy was spot on.

Getting reliable info on the valve depth may be difficult at best.

Check your other side and see what the differences are between the two.

IF they scalped .007 off the deck and the head was cut too, that would explain the issue.

Likely a .010 thicker gasket would fix the interference issue, but things need to be right.

Years ago I had a 6.5 that cracked the #3 main web in the oil squirt hole and it went up into a cylinder until it hit water

I bought a "Guaranteed" CRACK FREE block from a rebuilder's service company.

Block was bare.

Cleaned it, magged it and then bored it for .020" pistons.

The decks were a bit sketchy so decided to surface them.


All good ..... Ahhhhhhhhh, noooooooooooooooo.

Started assembly and discovered the #2 piston hanging out of the hole .030"


LEFT SIDE had been hit before, so ended up with big issues.

No marks on anything.

Ended up using a custom made MLS gasket BY Cometic (Bad jump)
These are nice gaskets, but not for the 6.5 (not enough head bolts)

The engine ran great for a year until the gasket failed.
These engines need the composition gaskets to live.

Ended up digging up a NEW AMG block.

Long convoluted story of some very interesting happenings at AMG, Navistar and it's employess.

But I ended up with a great engine in the end.

So many things go on out there in the re building game that it can drive ya nuts.

As far as Torque plates go, not many floating about in the hands of most shops for these engines.

With .004" PISTON clearance they seem to do OK

There may be plates made now, but in years past it would have had to have been custom made inhouse.

Sounds like you are gaining on it

Robyn

[JeepSJ]

As far as Torque plates go, not many floating about in the hands of most shops for these engines.

I own one.

[DmaxMaverick]

I own one.

I remember that post, and pics. Very useful tool, especially with what you have now. Very accurate for measuring absolute piston decking and valve recess. More accurate than a bridge and dial.

[Robyn]

Sweeeeeet

Getting the cylinders nice and round is dependent on using a plate.

The final torque on the deck can and does change the shape of the bores.

[JeepSJ]

Finally getting back to my project here...too many house projects keeping me away from mechanical stuff.

Got the block completely stripped last night so I could get the rods and crank over to the machine shop today. My how 15 years of knowledge makes you notice things that you haven't seen before.

I purchased the engine back in 2003 or 2004 and pulled the pan and installed a set of DSG girdles. When I pulled it apart I realized that I had smaller outer bolts on the mains. That didn't make sense since this was supposed to be a 1997 block, which should have the bigger bolts. I must have just thought I scored a later block when I installed the girdles. Remember this was supposed to be a "low mileage stock engine" that was sourced from a diesel engine supplier.

After I removed the girdles, I noticed that the outer bolt holes in the caps were large. Hmm... I pulled the main caps and what do you know, inserts in each of the outer holes. Well, why would they have gone through all that trouble with the rebuild? Yep, because the block was cracked. Web between 1 & 3. Extended about 2" up the front of the web and a little shorter on the back of the web.

Hindsight being 20/20, buying a rebuildable core would have put me far ahead in terms of cost and reliability. A "great deal" on a "low mileage" engine sounded good at the time.

I already had plans to scrap the block, so really nothing more lost by finding the crack. Just makes me want to punch the idiot that sold it to me.

[richp]

Hi,

Years ago I dropped a valve on my 6.2 non turbo Jimmy Blazer.

Shut it down almost at once, and got away with nothing more than a nice circular imprint in the carbon on the piston. No further damage evident, and it ran well for years afterward.

FWIW.