bad heads?

[Subzilla]

Took my 300k mile heads to the machine shop last week to have them reworked. Just talked to them and they said they're cracked, need all new valves and exhaust guides. I knew they had the typical cracks between the valves on the end cylinders so I asked him if they pressure tested them - he said yes. He could fix them by drilling and tapping the crack?? I'm a little head machining ignorant here but does this make sense?

My compression numbers checked out in the low 400's so would these cracks not create lower numbers?

I also asked him about the bad valves. He said the "card" said (I'm assuming one of his workers did the diagnosis) they were bad which means it could be worn stems or ends - he wasn't sure.

Guesstimate of $650 to do the work. The shop was recommended by a friend so I'm not necessarily accussing them of trying to rip me off. But does what they say sound right?
:confused:

[arveetek]

Sounds pretty typical. When I took the heads off my running '82 6.2L (I was just doing a refresh job from a cracked piston), I found out my heads were "junk." I went through three sets of used heads before I found a good set.

Most of the time these heads can be patched and reused, but it is expensive as you've found out.

My engine didn't show any signs of bad heads. It ran great, except for the smoking caused by a cracked piston.

Casey

[john8662]

Yeah, welcome to head rebuild hell.

Pretty sure I've got a few sets of bare 6.2 crack free heads. I'd have to talk to my machist to see what can be done with them. He's working on getting the precup problem solved while using his Serdi.

I'm running 6.5 heads on just about everything now.

[Subzilla]

You ain't wrong! I know that most of the hairline head cracks we see are OK but how can one tell the "experts" that? I'm not sure if they just don't know or if they know and they're telling me the truth. The shop came recommended by a friend and they said they've done 6.2/6.5 head work before.

Yup, I'm considering just buying some new 6.5 heads I found on line now. Pretty much the same price as this shop wants to rebuild my old ones!

I seem to recall some mention of injector line angles being different?? Are the 6.2's different from the 6.5's? This is going on my '83 Suburban.

I'm assuming the 6.5 heads would give me more power with less mileage??

I'm putting on my ATS turbo so should I consider getting the short injectors or will my good long injectors work just fine?

Lots of questions.........

[Robyn]

The heads used on the 6.2 up until about 90 were mostly the same except that the real early ones had the coarse threads in the injector holes.

The changes came when the 6.5 came about and the addition of the turbo.
They then used the slightly different angled heads that were designed for the 6.5 along with the slightly shorter lines.

The valve diameters changed a bit too over the 82-90 time frame.

The precups took on various incarnations of port size and shape.

The precups with small ports are mileage getters and the larger ones with the T and the diamond were the power makers

The cups can be swapped around to suit, just make sure they are from flush to no more than .002" above the deck with all things clean and tidy. (ALL cups must be the same)

The cup can't be below the head surface, Not even.

Pretty forgiving amount of combinations.

The late 6.2 engines were built using the 599 Block and the same crank as the 6.5 (one piece rear main) just smaller bores is all.


Missy

[Subzilla]

That's what I was afraid of. It seems every modification keeps requiring more money. Clearwater has new 6.5 heads currently for $300 each. They don't offer 6.2 stuff. I know how you feel about those folks, Robyn.

Hmmm, if I get these heads, guess I'll have to do some shopping for new injector lines.

[john8662]

I'll get out the Magnafluxer and the camera around this weekend and show everyone what to look for, things you can and cannot see without the tool.

A few cracks between the valves can be overcome, cracks that start off a set and head across the fire deck, or appear to start that way, should be discarded.

You'll need 6.5 MFI lines to do the newer heads.

J

[Subzilla]

Thanks John! That would be great and that would reveal the great head mystery that some of us have!

Still can't decide which direction I want to go with my situation........

[Subzilla]

Got the heads back from the shop. Asked the guy how they determined these were beyond the acceptable crack tolerance for these heads. He hesitated and only said "well, we pressure checked them". Wouldn't say much else. Here are some pictures of the end cylinder valve holes. These appear "hairline" to me but as is obvious by my posts, I'm not the expert here.
http://http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0346.JPG
http://http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0345.JPG
http://http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0347.JPG
http://http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0344.JPG

[Subzilla]

I messed up the picture uploading on the last post, it's been a long day, so here you go..........

It may be hard to tell from the pictures. The third picture down doesn't really even show a crack.

http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0344.JPG

http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0346.JPG

http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0345.JPG




http://www.thedieselpageforums.com/photopost/data/500/medium/IMG_0347.JPG

[Burbinator]

What exactly is needed to hang a set of 6.5 heads on a N/A 6.2 block aside from:

injector lines and injectors from a 6.5
head gaskets (any head or block mods required?)Any spacing or milling of the intake required?

[Robyn]

Heads will bolt right on.

As you mentioned, having the injector lines that go with the heads (injector angle and the shorter 6.5 injectors)

The real early 6.2 heads were different in that they had one odd water passage.

Lots of 6.5 heads have been swapped onto 6.2 engines.

The only real difference between the 6.2 and the 6.5 is the Bore diameter.

The real late 6.2 engines shared the same Block casting (599) as well as the one piece rear main crank.

The 6.5 was never produced with a two piece rear main seal.

The rods are the same as well as all the other internal parts (except) the reluctor/lower timing sprocket and the shorter hub on the ballancer.

GM even made the pistons on the 6.5 weigh the same as the 6.2 so that the ballance would remain the same and the cranks, flex plates/flywheels would all work.

The intakes are all the same EXCEPT the ones used on vans. These had a different angle on the intake flange and are Van only. Some HHMV's used the van type intake. (Mostly the rear mounted turbo stuff)

Your pretty much good to go.


Missy