This is probably not a news flash to anyone. After months of gathering parts, waiting for machine work, and time wasted working overtime to make money to feed this project, a crack in your block will really ruin your day. There is no easy way around this. If your working on a production 400 based project, magnafluxing is mandatory!! Through a miscommunication with the seller of the block, I failed to do this and am paying the price. The block was vatted, bored with deck plates, line bored, had the lifter valley polished up and deburred, was Hardbloked, etc. all for nothing. I can count at least 3 occasions where 400 blocks I planned to use didn't make it through magnafluxing. One was a four bolt that cracked at the main web, another four bolt block that had a cracked bore, and a two bolt block that cracked at the steam hole stretching all the way to the nearest bolt hole. Just a friendly warning so others won't suffer the same heart ache. And it is a heart ache to have your car sit....again.

 

I think you'll find that 400s are no different from any other 30-yr-old cast iron in that respect.... it's one of the unfortunate hazards of the hobby. People with old 50s & 60s 283s and 327s and such have even more trouble with it.

Moral of the story: if you haven't been running the block yourself and are familiar with it and know it to be good, the VERY FIRST MACHINE WORK you should have done to one, is magnaflux and/or pressure-testing.

 

The crack from the steam hole to the nearest head bolt hole is not necessarily fatal. I ran one with THREE such cracks and I didn't blow anything up or leak coolant into the combustion area. That 400 got beat on HARD by me. Daily driving, TOWING and high 11 second nitrous-assisted passes all on the same block. I first did it almost out of a morbid sense of curiosity to see how far it would go before breaking in half. After a while I stopped even thinking about the cracks- it just kept going and going with no problems. Then I retired the motor briefly just to rebuild it ONE LAST TIME for my brother's fuel injected 87 GTA (cracks hadn't gotten any worse but obviously hadn't "healed" themselves, either). It went thousands more miles in his car running high 12s at the strip and seeing regular duty at the local roudy-round track on "wacky wednesdays," again having the snot beat outta it. The motor got sold to a friend of his who put it in a drag-race RX-7 and ran low 11s on it for a season, even overheating the motor once. And it KEPT ON RUNNING. I lost track of the motor after that but I no longer freak out about cracks between steam holes and head bolts on stock 400 blocks.

Cracks in other places (like the main webs) are obviously much more worrisome.

 

Damn, why can't I have that kind of luck. I hate you, Damon. LOL!!