340 block question, opinions please

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marksmopars

marksmopars

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I am assembling a 340 for my 70 dart, original 198 /6, and got a 69 +30 340 block on the dl from a bud. The block will clean up easily at +40, question is the corner of the block is broken and I am not certain if it is a concern or not. The rear corner is broke through the locating pin hole. I have an option as a 84 318 block, which has roller lifter. I took it apart as a parts donor anyway, but am really interested in your opinions on this. I have a stock forged crank and a set of J heads with hardened seats which I would place on either block. Your opinions please, is the 340 block ok or should i use the 318, or is the 340 ok but use the 318 anyway?
 

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If you can find someone that can weld cast then it is repairable. I have a local welder that has a great shop with the right equipment and he could weld that up with no problems. They weld cast on heads all the time now.
 
If you can find a good welder/machinist that can weld cast iron, it can be fixed. Keyword is good. Not some hack with a stick welder and a hand grinder. They need to be able to build it up & then machine it flat & precisely relocate the dowel hole. It would be a heck of a lot easier if it was aluminum...
 
I got to tell you, i'd be real tempted to give that 340 a go. But, since you don't have a lot of coin in it at this point, and have the roller teen waiting in the wings, that's probably where i'd end up. Just get the compression up in a good spot, and build it just like you were thinking the other engine. With the reground roller option, i doubt you'll notice much difference in power on the street with a few less cubes. I would though, keep the 340 under the workbench for a future project.
 
Thanks to all for thoughts, much appreciated and that is what makes this a great place. I am real tempted to go with the 340 as the pin hole has enough material to accept the dowel ant the other will allow a bolt to be inserted. Not certain about who could weld it for me. Thoughts to ponder and thanks again.
 
My initial thought Mark, was a few extra lbs/ft on the other bolts would get the job done. But it would be a gamble that I wouldn't really recommend to someone else. If it was mine,??? Maybe :D.
 
For what its worth, I ran an oval track street stock small block with a missing bolt ear for 2 seasons without a problem.
 
for a driver/cruiser I wouldn't worry about it
if you plan to race it or beat on it, that's a different story

(I want to get my 318 blocks sonic checked and bore one out to 340!)
 
I'm not sure exactly what you want from this build, but...a decent compression, streetable, roller 318, with large port heads, should be capable of close to 350hp. That should be a really fun ride in a regulation weight "A"body for the street.
 
I've heard of people lighting a large campfire and leaving a cast iron engine block on a grate over the hot coals overnight to preheat it, then stick welding with nickel electrodes.
 
The problem is the movement of the casting when it's heated cooled - and the locating of that dowel. The bolt - while important - isn't that big of a deal. But the alignment dowel - that makes a huge difference. So you've got the repair/wedling, then the milling of the mating surface, and the locating and re-drilling of the holes with the alignment dowel being critical. Unless they have the right machine that dowel locatiing deal will be very tricky. Or - you can take that 318 and only be short a little on the bore and do everything just like it was a 340. There's NO difference when you're starting from a clean slate in terms of engine design - between a 340 and a 318 with the exception of bore size. So why spend money to repair junk?
 
That portion of the block doesn't get hot enough expand and contract. We fixed breaks like that in the textile mill all the time. Carbon plugs to fit/fill the holes, build the material with nickel rods and ark welder, remove the carbon, a bit of finish grinding, done.
In other cases, removing enough of the area to bolt on a steel scab worked just as well. You have to be sure the scab isn't going to interfere with adjacent parts, and precise location of holes needed in the scab was doable or not critical.
Bottom line.. Anything can be repaired. if you didn't have other options you wouldn't have had this question. In plant maintenance it wasn't about other options but about down time.
 
I had a X block at Shady Dell and they broke both sides off. I welded it with shartanium rods. . You could also have it spray welded.. Make sure you have a bell bolted up and indexed. The pin was welded in on both sides on my block. If it wouldn't have been that the motor was done . I would have trashed it. They broke both sides bolting it on the dyno. The motor ended up being junk anyway the machine work was not done correctly. Lucky me.
 
caferacerx said:
for a driver/cruiser I wouldn't worry about it
if you plan to race it or beat on it, that's a different story

(I want to get my 318 blocks sonic checked and bore one out to 340!)
Click to expand...

My personal philosophy is "build em, beat em break em and repeat em"!
I appreciate all the thoughtful input.
 
My 340 has the same problem , only its broke a little farther in.
I have a friend thats an excellent welder, I plan to call him to see what he thinks.
What do you guys think ?
I purchased this 340 and unfortunately did not see this until I got home.
 

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**** id use it, you got 5 other bolts holding it in place, if you dont wanna use it send it to me
 
caferacerx said:
for a driver/cruiser I wouldn't worry about it
if you plan to race it or beat on it, that's a different story

(I want to get my 318 blocks sonic checked and bore one out to 340!)
Click to expand...

Will you be running balled up paper for pistons as well?

I don't see this ending well.
 
motobro said:
My 340 has the same problem , only its broke a little farther in.
I have a friend thats an excellent welder, I plan to call him to see what he thinks.
What do you guys think ?
I purchased this 340 and unfortunately did not see this until I got home.
Click to expand...


I sent him the email with the pics , he said no problem he welds cast all the time. From the other stuff that I have read, its not the bolt hole thats important its the dowel. If the dowell cant hold the trans case in the exact right position then you got problems
 
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