These heads tend to crack in the rocker chamber, directly beneath the cam. Another area they crack is beneath exhaust seats, across the deck out to a coolant port. The cracks beneath the cam can be terminal if the crack migrates through a cam bore. While we have the ability to make this repair, these heads are so common that they just aren't worth the expense. Cracks through the exhaust are another matter. Repairs here are routine and affordable.

Another problem arises with these heads when the timing belt breaks. Since M20's are interference engines, the pistons and valves collide. Aside from the bent valves and damaged valve seats, in some cases the valve-piston collision transfers through the rocker shaft into the head, leading to broken shaft bores. This repair is also routine for us. We weld in a replacement and align bore with the existing bores as a guide for proper shaft alignment.

These heads, like most BMW heads don't present many opportunities for high-performance improvements. We smooth out the as-cast ports and blend them into the machined area beneath the seats. As far as the casting goes that's about it. There are plenty of performance cam grinds available, and we'll be happy to discuss them with you, as well other component options.