Carpenter's straightedge for block deck warpage?

[jerry598]

My 95 6.5 with 125k was pressurizing the cooling system and causing coolant burping within a minute or less after cold startup. Never did a compression check. Guessing it was just a blown head gasket, and lacking the equipment to pull the entire engine, I pulled the heads and found deep cracks between the valves and across the seats on the rear cylinders on both sides. I don't want to lay out the money for a remaned long-block at this time and I'm ready to order new heads from Clearwater after reading Robyn's posts. I've cleaned the block deck with stripper and a single-edge razor to the best of my ability. No erosion or other pits or cracks found. Cylinders and pistons all look OK to my untrained eye. I have a good 'carpenters' straightedge and used that with a feeler guage to check the deck surface for warpage. Didn't find any sign of warpage using the carpenters straightedge. Is using a carpenter's straightedge good enough? It's certainly not easy to reach into the engine compartment and check the deck with these tools at arms length. Is this procedure good enough considering that the new heads should be nice and flat? And, after reading all the horror stories of cracked main webs, etc, am I crazy to to put this amount of work and money into it without pulling the block and looking for bottom end cracks? The engine was running great before I tore it down.

[rustyk]

Usually, it's the heads that warp, not the block. A carpenter's straightedge is, IMHO, only adequate to check for gross distortion, but a machine shop should be able to check and even true for very little money.

I'd suggest posting photos of the cracks so that the more learned forum members can tell you if they're reusable, before you order new ones.

[Robyn]

Did you see anything nasty looking on the gaskets, such as a burned through fire ring??

This is common on the end cylinders where they border the large water passages.

If the heads are showing nasty cracks between the valves and this was the cause of the leak they should/could show rust from coolant seepage too.

Check number 8 cylinder for cracks (RH side rear cyl)

These can crack on the lower side about 1 inch below the deck.

Looking at the cylinder from the RH side of the truck a crack (if there) would be located at about 7 oclock

If there the cylinder will be discolored (sort of a satin gray look as compared to the slick smooth look of a normal cylinder.

If these things check out I would consider the options.

6.5 heads are generally IMHO not worth spending any $$$$ on once they have high miles.

If you can't figure out which one failed then both are suspect.

Get them pressure tested to see what you have to work with.

If only one is bad then possibly a good plan is to clean the good one up, find another good used one and bolt the beast back together with new "Felpro" gaskets

Use new bolts with the sealer already on them.

Be sure to reinstall the pushrods with the copper colored ball facing the rockers (very important)

A fresh set of rocker buttons would be good too.

A good bet is that the bottom end of the engine "COULD" have cracks.

Most all do once they get big miles on them.
If the cracks dont extend beyond the bottom of the bolt holes then it need not be a death sentence.
This is easily repaired but the block has to be apart and cleaned.


With a good set of heads (Replace the bad one) and some new gaskets the old girl should be able to go a bunch more miles before she has to come out.

Let us know

Robyn

[SmithvilleD]

I bought my '95 at 157k with a blown passenger side headgasket similar to your situation. Mine had been run long enough eating coolant to have some cylinder pitting so it was rebuild time.

The heads pressure tested OK but had the common cracks you describe. I think instead of installing valve seats in these heads, GM induction hardened that area & simply machined seats into the cast iron.

Here in Kansas City, there is a cylinder head shop that's done many, many 6.2/6.5 heads on Frito-Lay boxvans - so they've got some experience/track record on what's worked for them. They put valve seats in my heads & did the coolant passage (btwn the valves) repair where they put a sleeve in the passage to ensure it can't leak coolant.

As they've had consistent success on lots of the Frito-Lay vans, I took their word, had the work done, & it's worked fine. However, the cost ended up being very close to replacement heads. I mention this just to suggest you'll want to compare costs & choose accordingly.

My block's (929) deck surfaces were straight by a machinist's straightedge. But since it was at the machine shop being bored/honed anyway, we decided to do a small, cleanup surfacing. When doing this, it became obvious that while the deck surface had been straight, it wasn't square/equal height with the crank centerline. Don't know if it was sloppy machining setup at GM, or the block has "moved around" that much as it seasoned/relaxed going thru its initial heat cycles. Regardless, I was glad we did that surfacing to get those dimensions right.

The decision to go deeper checking the block for cracks, etc., is often a judgement call & also relates to how long you expect to keep the truck. For me, I keep these projects a good long time. Skipping any reasonable steps
tends to weigh on my mind soon as the engine's buttoned up & installed.

[jerry598]

Thanks guys for all the great feedback! Well, the almost microscopic cracks that I found between the valves of the rear cylinders (7 & 8, I think) go through the valve seat but I can't see any cracking below the valve seat (removed only one valve on each side). There is also no rust or erosion in the cracks. My machinist thinks he can see the crack going deeper but I think he is seeing things because I can't see it. My machinist also said he thinks the heads and pulled valves look really good with no stem wear or surface erosion but his opinion was to get new heads. I showed him the crack repair procedure but he still did not want to tackle the job. Should I find another machinist? I think Robyn said that if the crack goes across the valve seats like these do that the heads are toast. I am isolated in rural Idaho and the nearest good shop that might want to tackle the job is 150 miles away. Does anybody think the heads might be repairable or worth the cost? I would try to post a picture but I don't think it would show much of anything unless the light was perfect, because the cracks are so faint, especially across the seats. Everything else, including the block deck and cylinders, look fine, although I still have not found anyone with a machinist's straightedge to check the decks. I'd like to just slap heads (new or not) back on it and go.
Jerry
95 6.5 Turbo, 125k, 929 block, 4 speed manual, etc.