Technical 392 Hemi block with crack OK to use?

I've got a 392 hemi block with a crack in the rear main cap area. Its where the oil pump shaft goes through the block. If it's useable I'd use main studs and get it align honed. Here are the pictures.

 

It may be doable, but I think I'd loose sleep running with it. Got to wonder how it got that way to start with.

 

pin it , weld it or cross your findes and JB it.....However it if breaks loose and gets caught between the rods.......well you know the story.....seized oil pump pushed the shaft to the side and cracked the block...that is why u bought it so cheap.....

 

Nope I foresee that cracked bit coming off . Find another and line bore.

 

The machinist said there's a sleeve that goes in that hole and when the main cap didn't come off easily a previous owner may have "tapped" it with a hammer too hard and cracked the corner loose.

I may have him break that off and align hone it. He thinks there's enough material remaining to easily support the bearing. Also I can have him bore the sleeve hole deeper and use a longer sleeve.

I don't want it to come off later. 392 blocks are made of gold and I'd like to use it if I can.

 

I would guess it was a bad casting from new. I might be tempted to just break that piece out and run it!
You kinda said the same thing as I typed this.

 

Were it mine, I'd try to save it. I don't think it provides any substantial support to the bearing loading.
'vee' grinding the crack in the bearing seat and the side of the bearing web and brazing. Boring the pump shaft passage for a full length sleeve, possibly even counter sinking the block at the cracked end of the shaft bore, creating a 'vee' to braze the new sleeve to the block were it protrudes from pump shaft bore, would tie together the cracked wedge and block in three places. And, of course, align honing the main bearing bore and ensuring the main cap seats around the sleeve correctly.

 

Another way to deal with the problem is machine off that corner, have a special rear cap made with a "filler piece" so the bearing is fully supported, line bore the block and run it.

 

If your spending the $$ to get it align honed get another cap and fix it proper.

 

Who makes a rear main cap for a 392 that would have extra material above the crankshaft centerline to fix this?

 

That's what I wold do. It is a non-structural corner for the block. You just need something there to support the bearing.

 

It seems to me the bearing cap has nothing to do with this. Since it wasn’t mentioned by the OP one can reasonably expect the cap is fine.

Further, if one did “make a new cap” with an ‘extension’ to fill in for the removed wedge, how would one get the ‘wedgie’ in behind the bearing shell, which is curved, and especially with the crankshaft in place?

 

Gee is that the block not the cap? Looks like a cap sitting there?

 

Go to the junk yard and get another one
That's the traditional Way

 

At a glance, it does look like it could be. But looking closer, it appears the block is sitting on end, with the back of the block on a bench. Looking just above the rear main one can see the bottom of the rearmost cylinder on that bank and all of it is one piece.....the block. And, the OP specifically describes the crack problem as being the block.

 

The cap is fine, if that was the problem it'd already be replaced. The crack is in the block.

If this was 1965 I’d just go to the junkyard and get another block. I just need a time machine.

I agree the corner needs to be repaired or removed, because it could come loose later and that could be very bad. I’m a little worried that if the corner is repaired it could still break off later.

 

I think a good machinist/welder could repair that. with piece in place,just finding the right guy is the trick!

 

looks like a great place to try Mig brazing. Supposed to be able to do it without lots of preheat. And, it doesn't have to be super strong, just not falling out loose. Note the wear pattern on an old upper main shell, not much 'push' in that corner.

 

If you're going to hot rod it, get another block. The rear main cap carries a lot of stress. The aftermarket caps sold were all for the center 3 caps. They were to convert to 4 bolt mains. I'm not lucky enough to try that block.

 

Knock it out and run it. That bearing is way wider than all the others. Be sure to install a steel sleeve on the bore to support the remaining material.

 

W.W.B.D.D.?

(What would Big Daddy Do?)

 

This would be the ticket. http://www.hothemiheads.com/main_caps/main_caps_severe.html

 

FOR THE LAST %@$&# TIME, THE MAIN CAP IS NOT THE PROBLEM!

In addition, there is no visible damage to the rear main cap bolt hole in the block. Nor path for crack propagation. If this block had satisfactory strength for it’s intended use before the crack occurred, it still has the same strength now.

The concern appears to be two-fold.....maintaining some degree of support for that corner of the bearing shell in a low stress location.....and cosmetics.

 

I agree with most of this. But... if the remaining part is not supported, it is extremely likely that another small chunk will crack/ break out. The bearing shell is held in place with crush. So even an engine that isn’t running has a load on that small triangle. Remove the rest, or support what is there.

 

Post 14.

Maybe he’d just go get a new main cap?
(Duck)

 

I'm no hemi builder, but I'd grind it off and use it. If you hammer it off you may cause the crack to creep farther. It sounds like the sleeve that guides the oil pump could be brazed in place? If that is really needed to support the pump drive, do it. The lack of support behind the bearing right there wouldn't worry me. It's a shouldered bearing that limits crank end play, right? That adds even more support and the bearing shouldn't deform too much.

 

I would either just remove the cracked piece or fill the removed spot with brazing and remachine as needed.

 

No. That is a flat bearing. The thrust bearing is in -#3 main. This is #5.

 

Find a machine shop that has a metal spray torch.
https://www.bing.com/videos/search?...C344F7FE8EF86F3992C2C344F7FE8EF86F3&FORM=VIRE

 

That's pretty amazing! If it works as good as it looks rare pieces could be saved.

Dave