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Cracked Block Question

1K views 12 replies 11 participants last post by  OldTech 
#1 ·
Hi all,
New guy and a bit of a engine newbie here.

I think I know the answer to this question: Get a different short or long block.

Background
: I found a crack in my AMC 258 I6 block at just at the bottom of where the headbolt ends. The crack extends from the waterpump gasket on an upward angle to the head gasket.

At idle, there is no leak, but does leak at higher RPMs.

Question 1: Is there a reasonable chance that a fillet weld from a professional welder would seal this for any length of time?

I suspect the answer is: No, the crack probably extends around the headbolt hole on the block mating service around the hole.

Question 2: Any recommendations on reman engines? (This was an ATK reman with 20K miles)

Thanks in advance
JR
 
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#3 ·
I'd try a water jacket sealer first.

Welding cast iron is extremely difficult, complete disassembly of the engine down to a bare block is about the only chance you would have of making a successful weld, to try it on an assembled engine would be foolish.

I've seen K&W Block Seal and Blue Devil Block sealers both work amazingly well for something like this
 
#5 ·
I had a had a 283 freeze up on me once.Pushed the freeze plugs out & saved the block, but, the front of 1 head cracked bad.I used some JB Weld on it by smearing over the crack & using a small scraper to force it into & packing it into the crack.Prior this tho, I also flushed the cooling system as clean as possible.After letting the JB cure for 24 hrs, I added some KW block sealer.The crack seeped at 1st, then sealed up.I sold the truck about a yr later.It never leaked on me, but, the new owner let it run hot & said it started to leak afterwards.
 
#8 ·
Just an FYI, those plugs are core plugs used to seal the hole where casting sand was removed from the block. They were never designed as a safety feature to prevent cracking in the event of a freeze up. The core plugs are easily pushed out by expanding freezing water and probably do relieve some pressure but that is not their intent.
 
#6 ·
Back in '77, the night before a race day I installed my newly freshened 331 SBC in my gas Vega, found a 4" crack between #3 & 5 cylinders. Wire brushed it well, cleaned and used JB weld, plenty of it, put heat lamps on it at midnight. At 6 AM fired it up, no leaks, ran that motor all season at Alaska Raceway no problems.
 
#7 ·
Years ago at my bro in laws former work place they had a 76 Corvette on the lot. Somebody neglected to put any Antifreeze in it, the weather went down to a 3 day freeze and cracked the block right below the deck on both sides. So the engine was yanked and replaced. We took the cracked block, cleaned up the cracks, pack'em with JB Weld, built it with some performance parts, slapped it in a Camaro drag car, threw some Nitrous on it and had fun with it. It didn't leak a drop. Later on I found a 400 SBC cracked the same way only on one side it cracked right below the deck and to the freeze plug boss. Instead of trying to save it I scrapped it, as I thought if it's cracked to the freeze plug boss there's no way to fix it. I wish I hadn't scrapped it now.
 
#13 ·
A cast iron block can be oven brazed (using brass) and come out stronger than when it was new. It is likely more expensive than a used block but I have seen this done to engines, straight axles, and other cast steel and iron parts. It is impossible to hide the repair but it is strong and permanent.
Ifr it was me, I would just replace the block with a good used unit.
 
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