Build Thread Engine Build - Take #2

Build Thread Engine Build - Take #2

Bedford, NH
8 jeeps
So, last night I was able to get the "new" block into the engine bay...

I was exhausted, but it is in there.
Since I am new to the forum, I will explain in a nutshell what happened.

and here it is...

The other block cracked.
I have heard theories, no one really knows why it happened.
Magnafluxing the block didn't find it.
It ran a couple times before it really leaked.

So, here are the pictures of the crack

I am open to theories on how this might have happened, because I am about to start the new block up maybe at the end of the week and I would like to avoid this again.

Here they are:

1) Freezing - water/anti-freeze mix was not enough for cold NH days... block may have been too cold when water was added?

2) Tapping in freeze plugs too hard caused a crack?

3) Block was bad before and they didn't really magnaflux it. This time around they did it 3 times. Once when they got the block, once after it was cleaned, and again after the freeze plugs were put in. They didn't want any chance of it not being done I suppose

4) It was always there, machining it and such caused it to come out... not sure I buy this one.

5) mishandling of the block... upon getting home, if I caused damage to it by falling, etc.

Other then that, I am open to any others.

That's a strange crack. Right between the large core plug and the core plug. I'm not sure a 258 even has 'real' freeze plugs. Most of those holes are for the sand removal from casting but that really doesn't matter. Does it span the entire length? It looks like it does.

That looks like a very high stress area - and thin. I bet that area would be one of the first to 'burst' out when a freeze hits.

Sorry to hear about that crack but a competent machine shop shout have easily seen that under magnafux, it would have floressed like crazy!
I have to vote for the freeze on this one. Tapping in the freeze plugs? No. Machining brought out the defect? Not in that area. You mishandled the block and broke it? Only you know ;). More info on how it happened and how quick might help.
that's a pretty thin part of the block, and I have seen a builder crack a block right there with a missed hammer blow installing freeze plugs. Not saying that is what hapened to yours, but It do happen.
What about vibration?
I was just looking at the exhaust... now I doubt this could cause it, but the down pipe goes to the back. If the pipe was rigidly mounted, would the vibation cause stress on an area like that from the exhaust manifold?
I tend to doubt it (and I don't have my exhaust rigidly mounted), but I figured I would say something as I noticed it tonight when I was putting the exhaust manifold back on...

I did all the "underneath" jobs tonight so I can go in an shower up... WHAT?!?!?!?! it is a monthly thing ;) LOL.

I just don't see any binding or vibration from the exhaust causing that. Maybe crack a port flange on the head but not a block.

I still think freeze or even a crack that was there before but undetected.
I wish I could go back and time and smack myself in the head, but basically, the "air" temperature in the small workshop I have is like 35-50, depending on how much time I give it to warm up with the space heater... the good news is, no outside weather... no rain, no snow, no wind... but it isn't like working in a shop.

So, with that being what it is, the block was continually cold, but I am not sure how cold... maybe some night it got below 32... but when I started it up the first time, I put in anti-freeze... not water... I only topped off with distilled once it was running, so putting it into a very hot mixture, I would assume would have warmed it up.

Anyway, this time around, I am starting it only once I realize that the temperature in the garage is 40 and above for a few days in a row... then I know we are good to go... also, only antifreeze!

So I guess the first time the freeze plugs showed no sign of pushing out or anything? You just got the fatigue in the block? I had a 304 and it just puked 2 of them out literally. My stuff was always outside. Maybe it was an imperfection ?
I can't say, no idea what happened.
I wish they popped out, but they didn't, so I was just left with fixing it or replacing it... I chose to replace it.
I didn't know the history of the first motor... I know a bit more about the 2nd motor... but usually with all the engines I have had "checked out" I never saw any issues once the machine shop said it was good to go.

Not sure what happened.

Had a friend in the early 80's who had a new CJ8 with a 258 whose block cracked in the same place. He was stressing his engine while recovering another truck out of a lake. His block actually split. AMC replaced his engine. Local dealer said they had several failed blocks due to thin wall castings.
well since no one else mentioned it I will….damn good looking motor and Jeep:chug: i love it when someone paints them something other than black

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