It can help stabilize the bores, but it doesn’t really do much to keep the mains from moving around.
The Engine Performance Expo was about 2-3 weeks ago. They had a sort of round table with Kieth Dorton. He was working with Chrysler TA blocks, so you know that was a long time ago. Anyway, they were having some main issues so they changed the way they did the main line, and then they had a mandrel made up that was .001 under main bore minimum. Once they finished the main line, they’d slide that mandrel through the mains. If it slid in nicely, they new that had the main bores in line.
He was doing these blocks for himself and at least one other customer. So that customer had a mandrel made up so he could double check the main line before they started assembly.
Dorton gets a call from this customer and he says his mandrel wouldn’t go in the main line. And it wasn’t even close. Dorton knew they checked it before it left so he grabbed his mandrel and ran over to the other shop, and sure enough, neither mandrel would go. Not even close.
They thought about it for a bit and then he said let’s take it off the engine stand and set the block on the bench with the China rails down. And sure enough, both mandrels slipped right through.
So the TA block, for as good as it was at the time will bend enough hanging from an engine stand to not let the mandrel get through the main line. That’s how much these blocks flex. And that was just hanging from an engine stand.
So think about the loads the block sees when it’s running. That block is moving all over the place. The X blocks were a bunch better than the TA stuff and the R blocks are better than the X blocks.
I took a bellhousing I had laying around and put it in the mill. I took a slitting saw and cut the mounting flange off the rest of the bellhousing. I’d torque that up before I put the block in the hone just to try and duplicate the stresses that he open when you bolt the bellhousing on.
I’ve also seen blocks (not just Chrysler stuff) that have been chained down or had a turnbuckle affair to keep the engine from moving around and you can see where that load pulls the bore out of round. That’s one reason why motor plates are used. You aren’t loading the lugs on the side of the block.
It’s crazy how much these things move around. And the thinner the block the worse it is.