Here are the necropsy photos. We'll start with the rod bearings. Looks like the oil analysis was spot on based on the flaking of the outer bearing material and the wear in the second layer.

and next, the mains:

The oil pan was pristine. nothing whatsoever in the sump area. You are looking at an empty pan - not one full of oil - it's that clean!

And now for the bad news...these block were notorious for developing cracks in the main web area emanating from the main bearing cap bolt holes and the sharp transition where it was machined for the mating surface with the main cap. A lot of guys consider this normal and rebuild the blocks using some type of main web girdle.

So it looks like my gamble paid off of buying a new AM/GEP engine off the assembly line instead of waiting to see if my engine was rebuildable. You can't buy the AM/GEP block outright (despite the many chinese knockoffs being advertised on ebay and elsewhere as "AM/GEP updated blocks"). The only way to get it is to buy a brand new engine off the assembly line or buy a used HUMVEE takeout from a military salvager - which you would then have to take apart anyway to verify its condition..

The easy way to find the cracks is to spray the area with brake clean and then have a camera ready as you observe it evaporate. The crack will weep oil out at the last phase of evaporation and be visible for several seconds.

Wow great detail

Boat anchor:-(

A team of engineers should be a shamed:-(

Ryan

I believe they traced the cracking problem to the fact that they were machining the engine blocks while they were still too "green" and the tolerances were changing after the block had some seasoning to it. Hence the cracks in the corners where they join with the main caps, and the main bolt hole cracks. Remember that these are low rpm engines - under 4,000 rpm max.

Back then they were making these engines as fast as they could churn them out, and selling them as fast as they made them. When the military HUMVEES went to the 6.5, AM General bought the rights to the engine and completely redesigned it to get all the stupid issues solved - cracking blocks, cracking heads, bad coolant flow to cylinder 7 and 8 (exactly where my headgasket blew out in 2103).

At least I can pride myself on the fact that the inside of the engine was spotless - no sludge, grunge, or caramelized residue anywhere...and for a diesel no less! I guess that's what 22 years of oil changes at 3,000 miles can do. All I ever used was the Rotella 15W40 and AC/Delco or Napa Gold filters.

Great thread. Well done.

BTW, let this be a lesson to not leave your tools out when you're done with a job...

...The wife saw the cherry picker in the driveway and got an idea to use it to pull out some tree stumps. It actually worked pretty darn quick. Kind of like pulling a tooth. Took maybe 10 minutes once it was set up, instead of 4 hours the last time she made me chop one out of the ground with a pick axe.

resourceful !


Tommy

I remember doing that at my 1st home. My neighbors were watching and my wife and I got a round of applause when the stump was freed!

Option B, may have been to tie the Suburban to it and pull it out in low gear. Option A seems much safer!

Yeah option B is not an option after the number of youtube videos I've seen of things flying into the back of the pull vehicle when they finally let loose. That, and the fact that we had a downpour last night which would have turned the front yard into a mudbog-a-palooza-fest for all the neighbors to enjoy.

Finished the autopsy today on the old engine. Here's some photos.

Pulled the heads off. Some of the chambers have the normal cracks between the valves. GM considered this "normal" wear in their TSB.

The valve covers were immaculate. (The black painted one is the NOS cover replaced during the headgasket job in 2013)

Camshaft and lifters looked nice - normal wear.

Looks like the cam bearings were showing copper on all of them.

The upper halves of the main bearings all were flaking like the lower halves.

You can see the difference in the main cap mating area where the crack goes through the bolt hole.

Looks like most of this stuff is going to the scrapman in the next few weeks. The old mill had a good life. Gonna be sad to see the big ol' hunk of iron go.

Looks to e FUBAR to me ... TAZ

Yeah. I guess running 22 to 1 compression for 22 years is a bit stressful for the too-thin main web area. Seems like the pistons were trying to shove the crankshaft out the bottom of the block. The new blocks were redesigned to handle this stress (and made out of a different iron formula, too.

I remember when my uncle bought a new Olds with a diesel -- they sold him a separate "insurance" policy for the engine ... I asked him why he thought that was necessary? Yup -- less than a year later it spit the crank out the bottom of the motor ... TAZ

He sold that thing ...

Just for comparison sake I'd thought I'd post a good oil analysis.

Just got the oil analysis today for my 1989 John Deere 185 riding mower. I bought it used in 1990 and have been mowing our couple of acres for over two and a half decades since. I tricked both kids into learning how to drive by making them mow the lawn for years with this thing. They then proceeded to break everything breakable on the tractor but it stills keeps going. For the longest time I thought my daughter had a kickback scheme going with the local JD dealer. She'd break something - like the hub out of the wheel and I would bring it into the dealer and the parts guy would usually say "I have never seen one of those break before." And then I'd pay a ton for a new wheel, bracket, pulley, etc. I have since resorted to ebay for a lot of used parts since the dealer prices have gotten insane.

I change the oil every year or two whether it needs it or not. It runs a Kawasaki engine. Looks like Blackstone likes this sample from their comments. Interesting how they noted a high silicon result from possible dirty air filter. Turns out the air filter is clean but there is a big gap between the air cleaner duct and the carb inlet that is letting a bunch of unfiltered (dusty) air get through. Time to get out the duct tape and seal that up.

Just got back from the vacation trip to Lake Placid. Total mileage on the new engine is around 1,200 miles. The highway mileage on the uphill route to upstate NY was 17.0 mpg. The "city" fuel mileage for the 200 miles around town while we were up there, was 14.5 mpg.

I changed the oil the last night when we got home and saved a sample to send in for baseline analysis. Magnetic drain plug was clean.

I just got back from filling the tank to the top. The fully loaded return trip (downhill from 2,000 foot elevation) got us 18.31 mpg highway. A new record! Not bad for a 8600 lb GVW Suburban with 4.10 gears and Yokohama Geolander 265/75x16 tires

The truck ran flawlessly. No noises, glitches, twitches, drips, etc. I am very pleased with the results and the new low compression AM/GEP engine. Very smooth running at speed.

I was just thinking this morning "NJSteve has been very quiet". I was looking in the wrong place. I go straight to the Pontiac section.

LOL. There was no GMC section so I threw it here.