Best blocks?

I was wondering what the top 5 best block numbers are for 6.2's and the top 5 are for 6.5's. Thanks, Bradley

The best all around block for Both 6.2 and 6.5 would be the 599 block

The late 6.2 used the same block and crank as the 6.5

The real early 6.2 red blocks were OK but still not imune to cracks.

The absolute best 6.5 is the really late AMG/GEP Blocks that are made after 2000

Date codes 00 00 H
00 00 J
00 00 K and so on H is 2001, J is 2002, K is 2003

There was a number of these blocks that got Loose from the vendors and ended up in the private sector.

Recently bought a J date block with rough bores (left way small)

Building a 6.5 with it.

The early 506 blocks for the 6.5 were JUNK and had the large outer main bolts at the center locations and had large squirt nozzles.

Prone to cracking.
The late 506 blocks (1998) also would crack the #8 cylinder wall.

Best block from GM is the 599

Some of the China blocks are ok, although I am told that these can suffer from core shift.

Missy

Thanks Robyn. Do you have a full block casting number for a GEP/AMG block? Also, what would be a good price for a fully reman'd 599 or GEP/AMG engine? Long block? Fully dressed?

Are the good blocks just randomly out there or can you tell by the year of the truck? Are there any differences between engines installed in the U.S.A. vs Canada for the same year of truck? Other changes don't seem to always match between the U.S.A. and Canada for the same year of truck.

I am looking at getting a Canadian 96 GMC 6.5 truck that was damaged in a minor accident to use as a donor truck for the drive train to use for my 86 GMC 6.2 (siezed). The 96 runs fine (I drove it) would it make a good rebuild engine?
Thanks for any info anyone can provide.

The casting numbers on the GEP/AMG blocks still end in 506

Its the julian date thats the important indicator. As I posted earlier in this thread about the date codes.

The older blocks with casting numbers ending in 599 were fairly good blocks.

Here it is, if you find a high mile block that does not have cracks in the lower end and is otherwise in good shape, its worth using.

Make sure the decks have not been cut previously before you spend any $$ on it.
You can check this (on an engine with the crank an pistons in the engine) by turning the assembly to place a piston atTDC (Do each side) The pistons should be flush with the deck.

If the piston protrudes above the deck surface then the decks have been cut previously.

These blocks are capable of being cut .010".

You can take them to .015" and still be OK, but .010" is the target maximum for machining.

Cylinders can be bored Oversize, I dont like to go more than .030"
Many high mile blocks will clean at .020" OS

The only way to really know what you have to work with is to clean the iron well and go over it.

Do not buy any used engine as a "BUILDER" without a guarantee against cracks and decks that are not machinable.

Complete engines, even one that run fine can be unuseable once you get them apart and inspect them.

Small cracks in the main webs right in the outer bolt holes that are not deeper than the bottom of the hole can be repaired quite well with the Lock and stitch "Full Torque inserts"

Cracks at the register fit renders the block useless.

Inspect the decks for any cracks in the head bolt holes. On occasion I have seen cracks that go from an outer hole to the outside of the block, and or to the lifter case.

Any cracks in the deck are a NO GO.

I have seen 6.5's with 200K ++ miles that were in fine shape and were put back into service.

I have also seen 6.5's that had very few miles on them (under 100K) that were junk.

There seems to be no real reason behind the failures either.
I have seen high milers that have been used hard last foreve, and a light duty Burb that was used only to haul the kids to school and get groceries go south ???????????????

Prices can vary all across the board. I have seen complete 6.5's for $100 all the way into the $1000 ++ arena

Rebuilts can certainly vary too. I am skeptical of rebuilts. Unless you know the shop that did it and their reputation is spotless, I would be wary.

AMG/GEP Blocks are basically non existant and to find one is a real rare find.

A few got loose back in 2001 when GEP took over production of the blocks. The Navistar plant was/is doing these blocks and they turned some semi finished blocks loose (without proper authority).

I found an bought one of these a couple months ago and paid $500 for the bare block, which was a steal to say the least.

The after market blocks have been doing fairly well though, but its a gamble.

New heads can be purchased from GEP for $1000 a pair.

The new after market heads from Clearwater Cyl head can be had for $670 a pair.

Canadian or USA, it makes no difference in this as the engine all come from GM and are subject to the same failures.

Failures are random, there is no way to predict what trucks will have a failure.

Buying used is a tedious proposition that requires careful inspection of the beast as it comes apart.

As I mentioned before, even a good runner can wind up being JUNK once you get inside the thing.

The absolute best choice, if you can afford it, would be a new GEP optimizer 6500 (complete long block)

Good luck and good hunting

Missy

Check out a # 141 block casting # from a late 1996 truck. Those have the dual thermostats. They also have the smaller out board bolts on the main caps. The smaller bolts are less likely to induce cracks the block.Look for A 96 year#141 block casting with dual T stats . Those engines have more stable coolant temps. = less chance to heat crack.

Hate to toss cold water on the campfire here, buttttttttttttt

The only blocks that come close to being reliable were the 599

The 92-94 blocks were fairly good.

The 96 and later blocks, although they had the dual stats were more prone to cracking the Number 8 cylinder near the top rear of the bore. (98 was common at this)

Even the 10mm outer main bolts were not a real fix for the main web cracking issue.

The early squirt blocks (oil sprays) had large outer bolts and large oil spray nozzles in the main webs.

These blocks would crack the main web right through the oil squirt holes and then up into the cylinders lower end and then into water.

Been there done that.

I would not recommend any of the later blocks that have squirts or even the small outer bolts.

The early 599 blocks seem to be more stable.

Find one thats crack free or at least has small cracks that can be inserted and your good to go.

After the squirts were installed the issues just seemed to multiply.

The only late block I would consider would be a really late block that has the Navistar diamond <> cast into the valley floor near the front of the block.

Some of the 2000 GM were ok.

The really good stuff came after AMG/GEP took over total control of engine production in 2001/2002

The dual stat option can be installed on any 6.5/6.2 and is not a real indicator of much.

Many myths circulate about these engines, one being that the old RED 6.2 Blocks were GREAT and did not have the isues that the 6.5 blocks did.

WRONGGGGGGGGGGGGGG I have seen the mainlines on these cracked too.

These seems to be NO real Rime or reason as to why these crack.

I had a 94 Burb with 230K ++ on the thing that blew a head gasket, the block was 100% crack free when I tore it down.

I have been around a few of the China Blocks that are coming in through Clearwater Cyl head and a few other places.

These are zero time blocks, the machine work is beautiful on these things.

I know of several locally that have been installed and are working fine.

The problem with the old GM iron is that its all at least 11 years old and as much as 19 years old.

If you find a good crack free early (92-94) block its a good bet that it will stay crack free.

The duty cycles (hot and cold) are numerous and the block has cycled through expansion and contraction a Bazzilllliion times.

All internal stresses in the casting are long gone by now, so a freshen up and refit should net you a great engine.

Missy