The machining limits given in BMW’s Technical Data listings have been misinterpreted in some instances, resulting in replacement of parts that are still serviceable or replacement of parts due to listed specifications that should only be used on new components.
When a maximum tolerance of a part is stated in the Technical Data, it is the limit that that part may be machined and returned to service.
Example: the machining limit of the cylinder head height of an M50 engine is listed as 139.7 mm. When performing engine repairs, the cylinder head may be reused if it is at least 139.7 mm high and the sealing surface is flat, or if the height of the head is at least 139.7 mm after machining the sealing surface flat.
The maximum cylinder bore out-of-round is .005 mm and cylinder bore conicity (taper) specifications listed in Technical Data are for new engine blocks only. This means the engine has not yet been run.