I have seen many cranks broken as yours is. All of them were externally balanced.
Some were traced to cheap harmonic balancers, some from loose balancer bolts and SEVERAL were the early design SCAT LS stroker cranks that needed 3 or 4 slugs of mallory metal in each end counterweight to achieve "proper" balance. Scat has finally changed all of the counterweights on the LS cranks, so they will internally balance like everybody elses units.
My new build uses a Scat crank that can be internally balanced, but I had to remove a TON of weight to achieve zero balance prolly because of the Wiseco pistons lighter weight. A lot of the weight savings is from a more normal weight piston pin. I believe anyone building an engine with stock replacement pistons buy a lighter set of pins, as stock ones are waaaay heavier than aftermarket ones. A better alternative is lighter aftermarket pistons anyway.
If you bring a Scat crank in to be zero balanced, expect to pay extra for the time for all of the weight that needs to be removed. I think its worth it in improved performance. Also, dont forget to balance the cast iron pulley spacer deal too, mine was way off, even tho it was factory balanced. It does hang way in front of the balancer, putting more load on the front of the crank.
P.S. I also zero balanced my stock flexplate and balancer rather than buying aftermarket, as mine is a "street car."
Thanks, taking the block to the machine shop to mag and see if the line bore won't be too excessive. Not sure how easy that call will be without more or less doing the job. Not sure if the bulkhead could be pushed forward also, not sure how to check. Lots of uncertainty, but would like to salvage if possible. I'll inspect the holes and measure the bolt movement side to side and front to back versus the other ones? I have a dial indicator to measure the movement."The rods were still on the journals but it did "grow" a little in length pushing the front crank snout forward. The crank locked up tight between the back of the #1 main cap and the thrust bearing".
When you are doing the suggestions already made, look very close at the entire ft bulkhead of the block. The hit with the crank side loading the cap bolts could wreak havoc with the threads.
When I was apprenticing in Toronto we had the contract for Blackwwod Hodge which was a large diesel rebuilder. I saw some seriously fucked up diesel blocks saved. Yours should be a walk in the park. I saved a ton of twisted diesel rods with the Robbie boring bar.Thanks, taking the block to the machine shop to mag and see if the line bore won't be too excessive. Not sure how easy that call will be without more or less doing the job. Not sure if the bulkhead could be pushed forward also, not sure how to check. Lots of uncertainty, but would like to salvage if possible. I'll inspect the holes and measure the bolt movement side to side and front to back versus the other ones? I have a dial indicator to measure the movement.
My 109 from Ruggles, not only cracked the crank, but spit the side of the block out on the track @ Reynolds.
Faulty boost controller put an end to it.
Sorry I can't help.I guess I'm lucky now that these blocks are $$. I'm in Woodstock GA, who is a good machinist in our area for Buicks?
Question. Did the new main caps have the 45 degree chamfer.I have never blamed the line hone. all was good and round in all position , back was a few tenths larger. cap being a little softer. don't know
Crank always turned very nice. I believe it was the inspection of the block not knowing what to look for. I believe as it came up to temp something was moving or when I pulled the heads down something moved. Rod bearing damage was just trash from the mains.
Again the only lesson to get from my mistake is get the machine work done buy a good Buick shop. It sounds like your block was under some stress.
Rings rotate on the piston in normal operation. That's why when doing a leakdown test, if u have a low cylinder, start it up, wing it a few times and recheck before getting excited....