Yes, thanks for the encouragement.
The clearance is set by CP at .030. from what I could find this is similar to the OEM pistons.
The method to set piston to bore clearance is by measuring each individual piston and then honing each individual bore to suit the particular piston. Thats it. Anything else is just an educated guess at what the clearances will be and an assumption of what the bore size was out of the factory and how much wear has occurred to the bore in the mileage the car has done since new. Drop in kits are the lazy mans mod for people with no idea about engine building.
Custom pistons to suit the bore size or fractionally oversize and hone to size. The drop in kits will shoot for an average piston clearance for a new block but although the coated bores in a B58 are hard wearing there is still a bore tolerance + or minus. Thats why any drop in kit will be a hit and miss affair. From what I've been able to deduce without a B58 shop manual for the B58 engine during assembly at the factory BMW use "selective fit" graded piston sizes to match with selective bore dimension to get the clearance correct. Same as Ducati' has done for 50 years with Nikasil coated cylinders. You have a cylinder with an A,B or C size grading and you need to use the corresponding piston for that bore OR the smaller size piston ( at a pinch) but never the bigger piston. So no A bore with a C piston. Mismatched pistons and bores are not optimal though. All this will be automated at the BMW factory by a dedicated measuring robot and match pistons to bores to get the optimal clearances.
I think given what others have said, it’s best to take the time to triple check everything and educate yourself along the way. The car is already torn apart, might as well ensure that you’re doing it right so you don’t have to do it again.
Good idea. You'll need a digital bore gauge or a set of telescopic bore gauges and a 75-100mm mike. A dial or digital bore gauge would be better but for a one off the telescopic gauges will suffice. These things are pretty cheap to buy these days and nothing wrong with Chinese stuff for your needs, just don't go too cheap. Vernia callipers won't be sufficient for this job either it must be a proper mike. Telescopic gauges can be fiddly to use and you'll need a little practice to get acurate results. Follow the piston manufacturers specs for the piston to bore clearances not the BMW clearance specs. Measure the bores across the block so you are measuring the thrust faces and at 3 locations from top to bottom. The pistons are usually measured 10mm from the bottom of the skirt or to the piston manufacturers requirements. Good luck and let us know what you find.
Thanks for the help.
