With all the talk about the good and bad castings, here is the question that I have.

"If you have a block that is of the "bad" numbers and Foundry and now its about 25 years from when it was cast, if it is not cracked now, will it crack?"

I have seen cylinder heads that are noted for cracking, that are not cracked. The people that weld and repair cast heads have said that after that many years of heating and cooling, if it is not cracked now it probably won't.

This is what we would call a seasoned head or block.

To be perfectly honest, over the years if a customer brought in a 400 block from his vehicle, and it was the wrong numbers & code, I have NOT talked him out of it.

We would check it for cracks like always, probably paying even more attention.

BTW when we build an engine for someone, we do go with the request that they want, and we do always purchase only the good blocks.

Just a thought,

 

I agree. If it hasn't cracked by now it most likely won't. The whole cracking issue has been over analyzed on the message boards. Back in the 80's when there were no good aftermarket heads and blocks, most guys I worked with looked for high mileage truck blocks as they felt if those could survive that abuse, then those would be well seasoned for the strip.

 

Where I work, I do a vibratory stress relief on our weld laminations. This prevents cracks, the same way preheat and postheat does. these 3 things are what an engine goes through. If it hasn't cracked early, it probably won't crack later. In talking with the "stress-relief-machine" representative, he says they all put the vibe to their new cars/trucks to get more mileage out of them. I take that with a grain of salt, but it's hard to prove wrong.

 

I used to agree until 2 acquaintances built mild to moderate engines using questionable blocks and both had them crack post break in. IMHO the "it hasn't cracked yet so it won't" theory is good until the blocks are subjected to stress being relieved and then reapplied.

 

Odds are is that those blocks were already cracked below the surface, and the stock build didn't offer enough abuse to cause the crack to worsen and become visible, well maybe anyway.

From my understanding of metalurgy through my welding engineering degree and from how most cracked blocks came in, what most likely caused the cracking issues was improper cooling of the blocks after initial casting, as aren't the blocks of cast iron, or some form of correct? Due to cast iron's chemical structure (high carbon content is the main issue, if i'm correct about what the block is made out of) if said object is cooled to quickly then excessive martensite will form creating a brittle object or area of the casting. Now this is just my $.02 from what i've learned through my schooling, now i have not personally seen or know of the exact alloy/material used in the blocks or the method (start to final machine) of casting of the certian 400 blocks prone to cracking, so i'm not sure of what caused the issues, what i stated is just speculation based on the kiss principle.

 

Well let me add this, the old 2.9 V6 used in the ranger had the reputation of cracking the heads. But with this theory of if it hasn't cracked yet it probably won't that would mean an engine with say 130,000 miles on it should mean it's safe, yet I have had to replace 2 engines with more miles than that when the heads cracked after those miles. I also worked for Chev dealer as many know, well the old 305 blocks had the reputation of cracking too, but we had a guy bring one in with 250,000 miles on the block with never a single idication of antifreeze in the oil (they were known for cracking in the lifter gallery about 1 inch below the deck) we had the block checked 2 different ways and then bored .030 and rebuilt it. 2500 miles later he was getting water in the oil and upon disassembly found the block cracked 1" below the deck surface in the lifter gallery right were all the rest cracked. That block was paid special attention to in that area and it was perfect yet it cracked almost immediately after rebuild. To each his own but I am always suspicious of those pieces with the reputation and avoid unless no other option is available

 

TMI Tim being new here, 3 months, what are the , "bad" numbers and what foundrys. Where does one look on the block to find these casting numbers.

I can't afford to stay at a Holiday Inn Express, that's why I ask so many questions

 

Here is a link that should supply answers to your questions. Check out the whole site and bookmark it, for future reference.

http://home.earthlink.net/~bubbaf250/parts/parts02.html

 

I figured this would rattle some cages.

Here's what I am getting at.

As I stated above, when we purchased cores, we obviously select the best possible cores.

But over the 22 years I have been doing this, I have seen a lot of examples and there are many more. So it is very hard for me to tell a customer who had a fine casting, even though it has a bad reputation, to throw it away and find another.

This not only applies to the 400 but other blocks and heads.

Monsterbaby, you have listed 2 big examples I have seen in the industry.
2.9 & 4.0 were horrible for cracking, I bet I can safely say I have seen over 100 pairs of those heads. Funny that a very large percent of the times only 1 of the pair is crack. I don't recall if any of the customers that had 1 of the heads cracked, repleced both heads, because they were know to be bad.
And yet I don't remember hearing anybody coming back with the other head crack later.

Many head rebuilders have said that repairing a head that is cracked can be better than it was new becasue the "stress" that is in the casting is now gone. And as long as they repair it correctly and not add more stress, it will be a long lasting casting.

I have welded aluminum heads for many years and had great success with that, I don't weld cast iron, but I do "pin" block. This has been a very good repair also. The question arises then, is it cheaper to repair or find a different casting. My opinion is the 400 is easier to find a different casting as compared to repairing. Cracked 400 heads, same story.
Cracked 302 Boss block, I'd repair it in a heart beat!!

Hope this stirs a few thoughts, remember this is only my opinion, just like everybody else's opinion, it's only an opinion.

And I know there are many people who can state examples opposite of mine, and that's fine.