I usualy do it before machining. Recently, I did it for the first time, after the block was going to recieve no further machining or honing. Its my own personal engine, so, I figure, if it turns out to be a problem, then I won;t have a mad customer, but, I will say, after filling the block, and re-measuring, no dimension changed even one tenth. Had the mains tqed. Measured the cylinders before and after, ZERO change in size, measured the mains, ZERO change in size.
If you read the bottle, I used Moroso block filler, which I like better, its not as chunky, and flows better thru voids and hard to reach areas, where there is no hole to pour it in, so, you have to move it around with a wire, to fill in spots you can;t access. I have used Hard block plenty of times also, just prefer the Moroso stuff. But, my point is, it says the stuff is non shrinking, and, it doesn't expand either, so, with that said, its not putting any mechanical strain on the cylinders, or mains, by tweaking on them, due to the stuff shrinking, or expanding, so how can it be an issue? The only thing you do need to worry about, if you do it after the machining, is that the bores are a bit bigger, by about a thou or so, .001 in piston to wall clearance. Due to hotter running cylinders, which causes the pistons to swell a tiny bit more. My block is a used piece, I had, that was .060 out, and after freshening the bores with a tq plate, they were about .001 looser than what the piston man. calls for. The original plan wasn't to use the fill, but after I got into the build, I put it in there.
Frank
Advanced Performance
www.get-ap.com