I am down to a bare block with my S52 and will be doing aftermarket pistons/rods/rings. I have decided to go with Molnar rods and JE pistons for the rotating assembly. I talked to the machine shop today and told them I was going to be ordering custom pistons and that once they arrived I would bring everything in for them to do the work. The engine ran just fine before teardown and the cylinder walls had some very faint vertical scores but nothing major at all. Factory crosshatch is still intact (everywhere in the bore I believe but it has been weeks since the block saw the light of day). So here's my question/dilemma:
The machine shop told me to bring the block in and they would clean it up and do the bore/hone and then tell me what size pistons to custom order to fit the bore. This seems a little odd to me as I was under the impression that each bore should be made for the corresponding piston and that the piston should be right in front of the machinist when the bores are done to get everything precise. The shop's logic is that they don't know how much they will have to bore out the block to get the cylinders perfectly round so they recommended not buying a set of pistons that could potentially be undersized by the time they get the bores where they need to be. Like I said, the bores LOOKED to be in pretty good shape overall and I was planning to go .1mm over at 86.5mm. He was saying that .1mm is .0039" so that's not much material to remove to get the bores straight and that he may have to take more off.
I have to place a custom order either way since JE does not have off-the-shelf 10.5:1 pistons and I also want to get a few upgrades they offer when they custom make a set for you. What do you guys think? Would you just get .2mm over to be safe and have them machine the block to each specific piston or would you let him bore out the block and hope JE get the dimensions EXACT on my custom order? FWIW this is a reputable shop in the area and was recommended to me by the local BMW race shop.
The machine shop told me to bring the block in and they would clean it up and do the bore/hone and then tell me what size pistons to custom order to fit the bore. This seems a little odd to me as I was under the impression that each bore should be made for the corresponding piston and that the piston should be right in front of the machinist when the bores are done to get everything precise. The shop's logic is that they don't know how much they will have to bore out the block to get the cylinders perfectly round so they recommended not buying a set of pistons that could potentially be undersized by the time they get the bores where they need to be. Like I said, the bores LOOKED to be in pretty good shape overall and I was planning to go .1mm over at 86.5mm. He was saying that .1mm is .0039" so that's not much material to remove to get the bores straight and that he may have to take more off.
I have to place a custom order either way since JE does not have off-the-shelf 10.5:1 pistons and I also want to get a few upgrades they offer when they custom make a set for you. What do you guys think? Would you just get .2mm over to be safe and have them machine the block to each specific piston or would you let him bore out the block and hope JE get the dimensions EXACT on my custom order? FWIW this is a reputable shop in the area and was recommended to me by the local BMW race shop.
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