found a crack in my sb400 block

[74k20]

Got some bummer news this morning.  Trying to start my sb400 built.  Builder found a small hair line crack in the lifter valley.  Going to try and find another 509 casting sb400 block at a reasonable price.  If not, I got a spare 350 block for a 383 route.  Don’t really want to spend the extra money on a 350 block to convert to a 383, and would rather apply that money towards another 400 block.

Sort of venting, yet willing to listen to pros / cons.

’74 K20, th350, np203.  Currently very smooth running low HP original 150k sb350.  Goal of drivability, reliability, better towing, NO racing/mud bogging goal. 

[beastie_3]

if your looking to go 383, summit has a 383 block for about 600 i think. good price IMO, i think its a brand new block too.

[beastie_3]

http://www.summitracing.com/parts/SUM-150100/

[VileZambonie]

Your block looks rusty. It's hard to see the crack but what's your analysis? What do you think caused it? Was it frozen? Were there any issues with the 400 when it was running? The block can be repaired but you need to determine how much $ you want to sink into it.

[74k20]

The only real history was that the freeze plugs rusted out.  However the heads were replaced at some point (with other 400 heads).  The "rust" is only from the wash tank, wipes off with the finger.  The block was mag flux checked, which showed the hair line crack, so it was not just a visual check.

I would rather find another 509 casting 400 block, instead of doing the 383 route but we'll see.  Kind of wanted to use my 400 rods and save that money.

Part of the reason for this post was to brainstorm options.  I have $1000, and was hoping to get the lower unit gone through, assembled, and balanced.  Crank has already been turned for the 400 direction.  Now with the extra block cost, I'm not sure my best direction.



 

[VileZambonie]

You could always repair the crack.

[74k20]

yea I know it's possible, but worth it??  not sure.  This will not be a resell car/motor.  Want it to last a Looooong time.  The builder is going to check a core type shop for another 509 casting block, already cleaned and checked for around $250.  It will cost to weld and have risk, or cost to mod a 350 block to a 383.  So I'm hoping the cost is best spent finding another block.

we'll see.  Keep options coming.

[fitz]

If it makes you feel any better, my 509 block is in worse shape.

[74k20]

Fitz   -  OUCH... that had to hurt.

Another little option keeps floating in my head.  I got a complete Cad 472 (was suppose to be a 500ci - oh well) in my stock pile.  Someday I plan on freshening up that motor with a 500 crank, mild cam, intake, fresh bearings/rings, reworked heads.  LOTS of torque, and lighter then a BBC.  Not sure how a car long shaft BOP TH400 would adapt to the t-case.  Don't think I'm ready for this swap yet. 

Would rather stick with the original sb400 goal.  I'm keeping an eye on Craigslist, so we'll see.   

[jaredts]

Is he sure its a crack?  Does it look like it has any depth?  Surface imperfections can light up in a mag as can scratches.  It doesn't appear that he ground on it to be sure it has depth, which is standard practice in the mag operations I've been around.  I know nothing of engine block cracks and inspecting them, though.  Does your crack look typical for a crack in the lifter valley?

[74k20]

I've been lightly asking around on the checking process.  Seems legit.  The shop has a good rep and seems very honest.  Being an engineer, I have to watch asking too many questions.  I've been know to accidently pissing people off by being curious and "insulting/questioning", so it's that fine line I have to walk.  NEVER want to get on the bad side of a shop that's doing the work. 

Here's a closer picture.

[fitz]

The caddy motor would make killer torque.
As far as the tranny, I think all you have to change the output shaft with 1 from a 4wd turbo 400. I don't think it would cost a fortune to have a tranny shop rebuild the 400 and swap out the shafts.
It would be different to see a caddy motor in there.

[big bear]

id like to see that myself

[VileZambonie]

As Jaredts pointed out, why don't you investigate that crack.

[Engineer]

Ditto on the "check out that crack" posts. How deep is the crack? Does it hit water?

That is a very odd spot for a crack to form. There is little to no stress on that point. Even severe detonation shouldn't make a crack form in that spot......And knowing how little c.r. the 400s had, I doubt you had any detonation anyway.

What ever you do, do not throw that block away. It can be fixed.