All of these heads are prone to crack from an exhaust port directly beneath a seat, across the deck and over to an adjacent coolant port. 99% of the time the cracks occur on interior cylinders, 2, 3, 4, 5 on the six cylinders, 2, 3 on the four bangers. Regardless of the location, we have made this repair very routine, and affordable. We remove the exhaust seat and mill out the crack. When making the weld repair we add a significant amount of additional material. I'm not sure why BMW got so skimpy on the aluminum in this area. If the head gasket is placed on the head you can see that the opening in the gasket is much smaller than the opening in the head. After the weld repair is done on the M50's and M52's the coolant passage is remachined with a ball nose end mill for additional strength and to enhance coolant flow in this area. This operation is not applicable to the four cylinder models because of the different coolant port shapes. With all models the repaired unit is stronger and machined to factory specs for a fraction of the replacement cost. Over the years we've seen a few repaired heads return following another overheating episode. In each of these cases the heads cracked in another location, but the repaired area remained intact.

Here's a M50 cylinder head being prepared for our head straightening service. This service, and many others, are available from HAM Inc.

A curious tendency with these heads is that when overheated, almost without fail they will either crack or warp. Rarely do they suffer both at the same time. It is common for the chambers in overheated heads to sink, meaning the pressure of combustion pushes the overheated chambers towards the cam. This is usually accompanied by warpage. We correct this condition by straightening to restore the cam alignment, followed by resurfacing the deck and correcting the valve stem heights.

When these heads overheat it is common for the hydraulic followers to suffer damage as well. We disassemble the followers and inspect them for wear. If they pass inspection we hot tank them, apply pre-lube and reassemble. Even if the followers don't suffer damage we have found that in most cases the lifters are gummed up to the point that many are stuck in position and not able to adjust to normal valve-train wear. This leads to ticking followers, or worse, burned valves. Rebuilding the followers is an affordable way to ensure proper valve-train operation at a fraction of the cost of new followers.

Of course we offer performance upgrades for all of these heads. For most street applications there really isn't much to do. These heads are great performers right out of the box. Even so gains can be made by smoothing out casting marks and blending the as-cast portion of the ports to the machined area beneath the seats.