LA 340 block crack in deck

[Peini]

Hi guys,

I am rebuilding my 340 and found a crack on each side of the block. The area looks quite strange to me since I could not find any pic on the internet where another block looks like mine. It looks a bit like some sort of plug but I am sure it is not. Can anyone explain what it is and how serious the crack in this area really is? Is the oil galley behind it or a water jacket?

Data:
LA 340
Casting Number 2760930-340-4
Built 6/22/67 (nightshift)

Engine was running before tear down, no smoke or other indicator for burned oil or water. No noticeable amount of oil in water (but a huge amount of rust in water channels and jacket)

Thanks a lot for your help!
Chris

 

[furrystump]

Pretty dirty, but looks like it froze once. Pushed that core plug out a bit. The crack in the deck, I think that is in the oil galley. The head gasket should stop oil from entering the cylinder or the cooling system. It might dump some oil pressure through the crack into the valley. I’m not sure that area is actually drilled on that boss.

 

[Peini]

Pretty dirty, but looks like it froze once. Pushed that core plug out a bit.

Might be...did not recognize until now to be honest.

 

[furrystump]

Not sure on availability for you, but if its original block for the car. I would clean it up and put it on a dolly. Find another 340 or easier/cheaper a 360 block and build that. Can it be fixed? Sure. Money and time can fix anything. When they freeze they crack in weird ways.

 

[Garrett Ellison]

When they freeze they crack in weird ways.

And it’s the potential cracks that are inside of the water jackets that aren’t all the way through that can be the real problem. Magna-fluxing or x-raying would probably show more cracks in it.

 

[Phreakish]

I don't think that's a core plug.
Looks like a datum target, or someone machined a flat for some reason. Pictures of other blocks with the same boss configuration don't show the flat spot.
The flat spot left a thinner wall adjacent to it, could have been clamped on for some work or the thinner wall might have helped initiate a crack. Hard to say. I don't think that boss has any oil in it (it doesn't intersect the cam tunnel the same way as the head-oil hole does).

It's probably a non-issue, but it's tough to say. Cracks have a way of growing, so I'd try to grind it out. What's there to lose? It'll have to get ground on to repair it too. It looks like other (maybe later vintage?) 340 blocks had those bosses reshaped to a smaller profile.
Here's a picture of a block without those big bosses:

and one with (but no spot faces on the bosses):

 

[Garrett Ellison]

Definitely needs a crack check at that core plug below the casting numbers in the first photo. I’m wondering if that greenish yellow color is tracer dye or coolant that has seeped through some micro cracks.

 

[Oldmanmopar]

There is nothing behind there that is the second one I saw like that and the other one was also cut into on a mill. Probably happened taking it out of the mold before those casting passaged were cut off. I wouldn't worry about it one bit. There is no passage drilled behind that that leads to th cam tunnel. Look at the cam bearing bore you will see there is nothing there

 

[Max1196]

My take on what you have is being that you have a 6 22 67 block, a portion of the casting mold program was carried over from the "poly" design. On a poly, that is a open water passage. This being so early, the hole was machined round and a plug pressed in. By 1968 this knob of deck surface had the hole not cast and then eventually not exist at all. This section is still a crack prone area BUT differently. Below 1970 block.

 

[Garrett Ellison]

Clean and pressure test would answer which direction you need to go next.

 

[cudamark]

I'd start by getting the block cleaned and magged. You might find something else wrong that will influence your decision. You might also get another opinion from your machine shop.

 

[Garrett Ellison]

Exactly!

 

[Peini]

Hi everyone, tooke some time but here is a short update: all drain plugs are out and one on each side was a little deeper than the others and that is way it seemed as if it was frozen once which pushed the drain plug out. Nevertheless I will definitely inspect for cracks carefully after I disassembled everything and cleand it up.
Look what I found behind the plugs:
On the left side some really gross mud and on the right side desert sand

So the right sand pretty likely did not see any water for a long time. Going to inspect the heads for warpage.

 

[rumblefish360]

Send that out to a shop and tell them it needs be checked out and made mint for service. Also say that you would like an estimate on welding the cracks.

It might turn out better than expected. But there is only one way to find out.

 

[furrystump]

The sand is casting sand, usually in there. The factory didn’t go crazy getting it out after casting. You can hose it out and take a stiff brush to it.

 

[Garrett Ellison]

My guess is the mud is some block sealer someone tried as a band aid. But the sand is definitely casting sand, and don’t be shocked if you find core wire in it.