Got a 400 sbc from ebay a while back, said it was magnafluxed. Just got a call from the machine shop, left a message before I got here saying the block was cracked... Guy said the engine had previously had a rod knocking, and a main bearing chewed up the crank, so I am assuming it may be cracked down near the main bolts, or maybe by a steam hole. Have to call back tomorrow or stop by to see.

What is the opinion on welding cracked blocks to repair them? I guess it may depend on where the crack is I suppose. This is a stock bore 3951509 400 block, so I'd like to save it if possible, as it';s a better casting than my other two 400's that have slight coreshift (one is a 4 bolt, the other 330817).

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'71 RS/SS project: full roller 406sbc / 9.76:1 w/ E-Tec Al. heads / 750 Competition AFB / big 4 whl discs, 1-5/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

[This message has been edited by Chuck78 (edited June 14, 2005).]

There are procedures to weld cast iron, nickel rod and preheating, maybe (probably) something newer these days, but I've never seen it actually hold up worth a darn. If just sealing it up, maybe, but if you're investing some serious money in it, I'd sure get an expert opinion before going any further.

Not worth the cost
Will probably crack next to the weld

Although I have never welded a block, I have done a quite a few cast iron repairs. IMO, utilizing a furnace for pre/post weld temp control is the key. (unless the part is really small) It is too difficult, if not impossible, in most cases to properly control the overall temperature of the part with torches and accurately controlling the rate at which cooling takes place is vital to success.

As mentioned previously, it’s not going to be cheap.

The block is cracked in the lifter valley, between there and the coolant passage on the side where the valley starts sloping up to the deck surface. So if you visualize it, the side of the water jacket opposite of the cylinder wall towards the center of the block. Guys at the machine shop said they had never seen a block crack there, and said that they definitely wouldn't recommend welding it.

Sounds like a complicated process. Very strange area for a block to crack, wonder if other areas of the block are stressed, or if this was some weird weak spot in the casting, that only needs to be repaired to keep from having a coolant leak??? I'll take my other two 400 blocks down to have them magged later this week, and pick this up so I can maybe take a picture and see what you guys think.

Any opinions on this so far?

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'71 RS/SS project: full roller 406sbc / 9.76:1 w/ E-Tec Al. heads / 750 Competition AFB / big 4 whl discs, 1-5/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

Actually that is one of the more common spots for cracks. There along with just below the head surface in outside of block. Other than that they usually crack in cylinders. I wouldn't use it being that you have others. You would be better off with a jb weld or epoxy if you were to fix it. I have seen them used in stock cars. They jb, or epoxy them then paint the lifter valley with an epoxy paint. And make sure to use barsleak or something along those lines. Hope it helps, Jeff

If the crack is where I think it is there is actually coolant in that area, and the irontite or "drill, tap and taper pin" repair method is 100% successful if done properly.

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Custom Auto, your source for quality machine work, cores and new parts at competetive pricing right here in British Columbia 1-888-563-4050
A Canadian, EH? (with a 10 second street car)

can you explain this method? Are you talking about drilling, tapping, and pinning at the ends of the crack so that it doesn't spread? Irontite?????

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'71 RS/SS project: full roller 406sbc / 9.76:1 w/ E-Tec Al. heads / 750 Competition AFB / big 4 whl discs, 1-5/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

I think it is called "lock-stitch" crack repair.

I just found this link...

http://www.racecar.co.uk/L%26S/?CategoryID=20

Here it is!!!

http://www.locknstitch.com/Sitemap.htm

Good reading AND yes, this is a VERY good way to fix cracks!!

pdq67

You start with the outer ends of the crack and work inwards, interlinking the "stitches" one by one until they meet in the middle. I've saved a pile of heads and blocks using this method.

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Custom Auto, your source for quality machine work, cores and new parts at competetive pricing right here in British Columbia 1-888-563-4050
A Canadian, EH? (with a 10 second street car)

I have JB welded a couple of blocks there - no problems.

Heck - I just JB welded the outside of the original 350 in my friends 78' Z28. It had frozen and pushed out a 6" long section of the block on both sides about a quarter inch.

JB welded that sucker and its working fine now! We are going to replace the motor eventually, but he needed to get the car on the road since his daily driver died.