What Engine and Year Do I Have?

[johncarrol]

I'm the very fortunate and proud owner of a 2005 M1123 HMMWV. I understand AMG installed GEP engines in them after 2001. The 6.5 N/A engine in mine has a casting# that ends in 506, but does not have the number 506 cast in the lifter valley. My engine has a tag on the back that says it is a GM rebuilt engine that was done in 2010. The date code (I think) in the back of the block reads: K170. I was told that the US military had a lot of GM produced and rebuilt by GM engines that were lying around and used to replace engines in HUMVEES that needed them after 2001. My question is: what year is my engine and why, if it is a GM engine, does it have a casting number ending in 506?

[DmaxMaverick]

November 17, 2000 (not a GEP/AMG block). Without some records, why or how it got there is anyone's guess. Consider the possibility the engine wasn't replaced by the military, but perhaps a seller who sourced it after it was decommissioned. Many (if not most) military CUCV's and HMMWV's were/are decommissioned and liquidated in a non-running status.

[More Power]

I a 2000 model year GM casting has survived this long - assuming it has some thousands of miles on it - it'll likely be OK for the foreseeable future. All of the AM General block casting date codes are 5 digits in length. Navistar cast all of AMG's 6.5L blocks and heads. Visit the following forum thread to learn more about casting date codes and some other good stuff.

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=24325

[Robyn]

GEP ENGINES have the<> cast into the valley Some call it the "Double diamond"

All AMG 6.5 have this and do not have any reference to GM at all.

As mentioned someone else likely swapped out the dead one and used what they could find.

[johncarrol]

So was the GM block with casting number ending in 506 was the last version produced by GM before GEP took over? What were the years the GM 506s produced? If so, is it the best GM 6.5 block out there? And what was changed from the previous castings? I'm curious that when another company-GEP took over with a whole new internal block design, why would they use a casting# ending in 506? I may never find out the complete history of my 2005 HMMWV, but it started out its life with full armour and a new GEP 6.5, then in 2010 Came back from wherever and the US military, not a third party, replaced everything that had any mechanical wear on it, so it would be ready and able to serve and protect our armed forces again if needed. Then it sat until May 2017 with about 50miles on a new odometer when the US military auctioned it to the person I purchased it from. When I purchased it, it had 130 miles on it since 2010. I'm sure since the engine has a tag that says it was a rebuild from GM it should be a quality job if GM wants to keep a good relationship with the US military.

[Robyn]

The stories on the 6.5 and it's sordid history are many.

The 6.5 came into being long ago.

Actually the design heralds from 1982 when the 6.2 was introduced in the GM light trucks.

From 1982 to late 1989 the 6.2 underwent various minor running changes, with head gasket updates, precup changes (Likely emission related) Minor additions to the engine controls (Addition of a minimal ECM )

1990 (Give or take) the block and crank were altered with the introduction of the 1 piece rear main bearing seal.

In 1992 the cylinder bore was increased (Block casting core changed to allow bigger bores) and the 6.5 came to be.

Addition of a turbo charger came in at this time as well to help the 6.5 compete with Ford and Dodge.

The 6.2 n/a engine was still available through 1993 and was simply an underbored 6.5 block casting.

(The 6.2 was never offered from the factory with a turbo although the 1990 and 91 Square body rigs had a dealer installed Banks system available)

The 1992 and 1993 GMT400 models (Except Suburbans) were equipped with the DB2 mechanical injection pump and a mechanical turbo wastegate control.

1994 saw the introduction of the DS4 electronic injection system.

NOTE
The military did not use the DS4 on the HMMWV as to put it simply...The system was not worth a damn and reliability was no where near MIL quality.

Actually the DS system was A JOKE.


The 6.5 in the early days saw a few different casting #'s the 599 block was common in 1994

With internal structural failures showing up (Center main web cracks) and also overheating of piston crowns under hard use there were other modifications.

The castings switched to the 506 which in it's early incarnations was basically the same as the 599

The block had the same large diameter main cap bolts in all positions.

The later 506 blocks saw the outer bolts on the center mains reduced to 10mm diameter with a large flange head, with the idea being that the bolt holes in the block being smaller would be less prone to cracking down the web.

Great plan but did not stop the cracking.

Then about 1996-97 (approx) the 506 was fitted with piston spray nozzles in the main webs to direct a continuous stream of cooling oil onto the underside of the piston crown to help reduce piston temperature and get the heat where the oil coolers could deal with it.

Again, a great plan with dubious results.

The tooling used to bore the holes in the main webs clipped the lower cylinder skirts which resulted in a stress riser and a point that could and did start cracks.

The early "squirt blocks" had a fairly large orifice insert diameter and the large passage that was drilled to a fit the inserts further weakened the center main webs, and failure in the webs was seen.

The next gen 506 saw the size of the squirt passages reduced.

About 1998 the 506 started seeing radial cracks in the #8 cylinder near the top rear just below the deck adjacent to the head bolt in that location.

This caused a compression leak into the cooling system and ultimately a failure of the engine.

GM did not really address any of the issues and the final castings were done by NAVISTAR

Not until AMG bought the rights to the engine did things change.

2001 and later

AMG redesigned the 6.5 all the way.

The cracking issues were addressed with better alloys in the block and heads.

The main webs were cast thicker
The cylinder deck was made thicker and the cause of the cylinder cracking was eliminated. (Likely a stress riser in the area of the water jacket near the deck.


I did not cover the issues of overheating of the two rear cylinders and cracking of the heads between the valves.

There were mods made Along the way to try and address these things.

The dual thermostat and hiflow water pump came about to increase coolant flow and help eliminate hot spots due to stagnation in certain areas of the block and heads.

A block with GM on it that's not cracked and that was rebuilt should run a long time.


I also did not mention the crankshaft breakage.

Cast iron cranks were a poor idea in a diesel and yet GM used them.

Crank failures were not rampant, but did happen.

AMG introduced a forged steel shaft in the P400 variant of the 6.5 and this piece can be retro fitted into the optimizer and should fit the older GM iron.

Minor small failures in the valve train, but not anything worth ranting on.

And there it is.

Biggest failures of the 6.5 was in the office of the bean counters trying to save 15 cents.

As far as GM's relations with the MIL goes /????????

AMG now owns the 6.5 and even the HMMWV is or will be phased out of service in favor of a different vehicle.

I would not be surprised that the rebuilt 6.5's are all contracted out anyway and not actually done by GM.

[johncarrol]

Thanks Robyn for all the great info. I was led to believe that the military contracted out all the HMMWV engines that needed rebuilt to a third party, not GM. Up until now, all the rebuilt military ones I saw had a tag on them etched and stamped showing where and when they were rebuilt and the bore and bearing journal sizes after the rebuild. Mine is the first one that has a different tag that says it is an engine that came from a GM facility, and on the tag there is a line that reads RB date and is stamped MAY 2010. I always thought GM didn't rebuild engines themselves, they just sold NOS engines. The 4L80E has the same tag on it. Does anyone have any info on these GM rebuilt engines? Also, about the statistics on the heat related problems with the GM 6.5s; I wonder what percentage of the problems came from HMMWV installations' vs GM truck ones? The HMMWV body was designed and built over and down around the engine and transmission to give it a low center of gravity, along with high ground clearance and a low overall height. The radiator and external coolers were mounted at an angle for the same reason. It used a heavy duty hydraulic fan clutch that locked up around 200+ degrees. Until the fan locked on, there was no airflow to amount to anything going through the radiator because there was no place for the air to escape unless it is forced out by the fan, unlike in a civilian truck. What is easier on an engine? one that sustains a temp of 195 degrees or one that goes from 220+ to 190 constantly throughout its lifetime. Then add a very hot turbo mounted very close to the rear of the engine where there's hardly any room left to do so and no airflow to carry away the heat to try to make up for the added weight of the extra armour to add more power. Them ship them to the most harshest conditions for an engine-the desert. I'm surprised any 6.2/6.5s lived any length of time in them. I guess I'm trying to defend the GM 6.2/6.5s because people are being led to believe that they are junk compared to the GEP ones.