6.5 cracked heads/cracked precups hood?

[2INSANE]

Quick question! I have pulled a 6.5 motor apart and found cracks in the precups and between the valves on the 6.5 heads. I remember reading that they can still be used and won’t cause a problem as long as the water jacket is not cracked. Is this correct?

Sorry about title. IPhone typo...

[Robyn]

Just a personal note from experience.
I would not spend a dime on a head with cracks between valves.

Precups can be changed out with good ones....Be sure to use the same type (Diamond, one dot, two dots, a square...yada yada yada...all must match)

Be sure the precup bore in the head is spotless and the cup is NOT below the head deck and up to .002" above is fine.

Cracks between the valves on a slop together get rid of the beast engine ???????

A build you are wanting to get a bunch of use from....NO WAY....Not if it will leak...JUST WHEN.....

AMG heads can be had new in the box....zero hours and far better castings......

I have used the Chinese made "Clearwater cylinder head" units on a build I did on a 94 Burb....I put over 50K miles on the engine before selling the truck.

I would not hesitate to use a set of the CW heads again......

I would basically say this...If a GM set of heads is not absolutely perfect....use them as door stops.....

Coolant leaks are a nasty thing to deal with...... and once your project is done ....you are not gonna be happy having to tear back into it.

You have made mention of wanting POWER....Cracked heads will come back to haunt you...GUARANTEED THEY WILL.

[JohnC]

I'm with Robyn on this, however, I recall there is a process to sleeve the heads where the cracking is. I expect it's in one of the books you received recently. (Or I may be missremembering....)

[DmaxMaverick]

I'm with Robyn on this, however, I recall there is a process to sleeve the heads where the cracking is. I expect it's in one of the books you received recently. (Or I may be missremembering....)

Correct. The cracks between the valves can be sleeved with a valve guide tube. It's a permanent fix, but I'm with y'all. I wouldn't spend $100+ for a repair on heads worth not much more than that.

[sctrailrider]

The newer GEP heads are said to be better, however I have not seen proof by metallurgy testing, GM heads are older, GEP isn't quite as old, but I have seen many of GEP heads & blocks cracked in the very same places as the older GM stuff, the GEP so called better heads are still induction hardened for seats, that is a contributing reason why they crack between valve seats, induction hardening cast iron makes it brittle... The P400 heads are a very different casting altogether different from all the others and they have real seats and no hardening ...

[sctrailrider]

And the only way to get real inconel precups is to buy real GEP/P400 heads... all the aftermarket cups are stainless steel...

[2INSANE]

Thank you all for the quick reply! I have 4 motors I am working on right now. 2x 6.2 diesels and 2 6.5 diesels. All 4 are removed from the vehicle. The worst of the 4 motors is the one in question. It will be disassembled and the good parts will be kept. Since the block is cracked as well, I think these heads are for sure not worth repairing. Thanks again for the advice!

[Robyn]

Had the bean counters been rained in a bit the 6.5 could have been a great engine....and been close to the legendary mouse motor.....

The 6.5 was not junk by any means....but the issues it had/has should not have happened.

A deep skirt block with cross bolted main caps, more head bolts and a bit better head castings with better coolant flow and hardened valve seats (Press in)

The changes that GM made as well as GEP were basically bandaid fixes.....

They kept things as close to original so everything would fit....but did slight mods to try and improve things.

Deep skirt block
Forged steel crank
More head bolts
Direct injection heads (They did try this on a couple X engines along with a common rail system)

Ah yes....20/20 hindsight

Not until the Dmax did GM get it together....and even the early Dmax had some issues.....

Bean counters will save lottsa $$$$$ and cost the company more $$$$ and ruin the reputation......