356/912 Porsche Cylinderheads

We have many years of experience with these heads ranging from stock restorations of severely damage heads to CNC ported race heads.

It would take hours to detail all of the services we offer for these heads, but the photo’s below offer some visual evidence of the extreme repair techniques we can employ to restore and reclaim severely damaged castings.

The 912 chamber crack in the following photos was as big as any I can recall. A repair of this magnitude requires years of aluminum casting repair experience (owner Len Hoffman has 30 years of said experience) and much machining prowess. In the photo of the excavated crack you can see that even after massive material removal in one of our Bridgeport Mills, the crack ranges further into the casting. From that point the remaining crack (between the red lines) was excavated by hand with a carbide burr.

The weld repair was done in 8-10 minute intervals after which the pre-heated head was returned to the casting oven for no less than an hour to even out casting temps, thereby minimizing shock to the casting. This is a drawn out process which in this particular case spanned two days as the other chambers were also cracked. Not visible in the photos is the skillfull tie-in to the bottom of the fins where the crack had ranged from the chamber. This is critical for proper heat extraction when the engine is up and running again.

Following the weld repair the weld was peened from both sides, which is akin to cold forging. The finished repair is actually stronger than the original casting. The photo of the machined valve seat counterbore reveals consistent machine surface texture and bore dimensional uniformity of  <.0001″ when measured in the X and Y planes, indicating a successful repair.

Also pictured is an example of our refaced exhaust flanges with new exhaust studs. This not only ensures a good sealing surface, but saves the engine installer the nightmare of busted studs when finishing up the install, a common scenario with these old heads. Even when the studs look fine, they are typically brittle with age.



A quick word or two, with photos, about why I’m not a fan of 86mm big bore kits for these engines. Simply put, they dig into the heads. The cylinder walls are too thin. I long ago lost track of how many heads I’ve machined that required excessive flycutting to correct this etching. The supporting photos are at the extreme of this condition, but not uncommon.  These jugs shorten the life of the heads and can lead to head leaks.

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