Need some more help from the experts here... I spoke with my machine shop yesterday and went to conform today, my 76 block has some 1/16" casting porosity at the base of the rear lifter bores, right where they meet up to the mains. ou: The little suckers were cleanly hidden by the casting flash and discovered when the flash was being removed. So here's my question... is 1/16" deep enough to say scrap the block and start over if I'm putting in enough cam & heads to go around 480-500 hp? The deal is that the shop is going to eat the machining costs if I'll have to provide a new block, (I have a 72, 73, & 74 spare). My immediate thoughts are hey, it's all good to add in the protection and it's minimal cost to me... but is it worth going to the lower year block and losing the value of another block over this thing. Is porosity in the lifter bores really a danger knowing that most blocks get the main walk or rod damage first? I'm just not experienced enough to say if this is go-no-go... o No: any advice??
My idea of "porosity" is that the metal is there, but has microscopic pores through which fluid (air, oil, coolant, whatever) seeps. Loctite makes a product that can seal porosity. I'm thinking this is ordinary "blue" loctite, you pour it on and let it set for a few hours. It seeps into the pores and hardens, sealing them. Best to check the label directions, though, and I don't have a bottle handy. Sounds like your block is MISSING the metal. That's not "porosity" it's a casting flaw. (well, OK, porosity is a flaw, too, but to my way of thinking, a different kind of flaw.) Is your machine shop concerned about having the missing metal as a source of weakness in the block? Without seeing it, I'm kind of concerned that that might be a good stress riser, leading to block cracking. Yeah, I think I'd use a different block, especially since you have a few to choose from, readily available.
I'm definitely no expert, but I would do anything possible to avoid problems with the lifter bores. They are a known weak area in the block. Why take the chance they will break out and throw all that money out the window?
Yup, by porosity I'm referring to the casting flaw... a small spot where there's no metal, formed either by a bubble, casting error, or improper cooling rate. The thing is only a small hole, about 1/16" in dia, 1/4"length by about 1/16" in depth. Definitely a stress riser, even if radiused and polished out, however is it too much? My dilemma is caused by the fact that this block has the lowest core shift, ideal sonic, and is a 76 block with great meat to it. I'll be trading off these strengths going to one of my spares... I've looked around and cannot find much here or on the web about block selection w/ regard to casting flaws. Much help needed on this front...
