PORSCHE TECHNICAL TOPICS
Technical problems solved
Last month, you might recall, I began this column by describing some of the work that my friend and colleague, Rob Nugent at BS Motorsport in Buckinghamshire, was carrying out on his own 996 engine – a 2000-model 3.4.
He had stripped it in order to track down and hopefully cure the inevitable spurious noise that had developed, discovering in the process that a previous owner, or perhaps his mechanic, had comprehensively butchered one of the cylinder heads. All six of the M8 screws securing the exhaust manifold had broken, presumably while being undone on some previous occasion, and our hapless technician had somehow managed to drill them out so woefully inaccurately as to render the head – and even the manifold – almost fit for the scrap bin.
It wasn’t a problem for Rob, though. I demonstrated last time how, using both his then newly acquired Stomski Racing jig and a pillar drill, he had accurately excised the remains of either the old screws or the threaded inserts that had been ‘fitted’ to replace them. Next step – shown in the first photo below left – was to cut a suitably coarse M14 thread into each now obviously much larger hole, and then a matching thread on a length of lightalloy rod of the appropriate diameter. This was divided into short lengths, and each one screwed tightly into position via a simple slot cut in the protruding ends.
Lacking suitable laserwelding facilities, Rob had to farm out the next stage to a local specialist who, as I think you will agree, has made a spectacularly neat job of rendering each rod effectively an integral part of the cylinder head (below). All that was necessary after that was to mill the face of the head perfectly flat, and then, using a good second-hand manifold as an initial template, to drill the first new hole, carefully position the jig, and finally drill out the remaining five. More easy drilling and tapping for some M8 Time-sert inserts, and the job was done.
Cost? Around six hours of Rob’s own spare time for the light-alloy rod and subsequent drilling – plus £200 for the laser-welding and another £400 or so for the Stomski jig. (And that will surely more than pay for itself in subsequent repairs on customers’ cars. This is a problem that isn’t going away any time soon.) But that was immeasurably cheaper than a brand-new or even a sound, used head, and brings with it the satisfaction of knowing that, with decent manifold screws instead of the rubbish Porsche items, the repair should now be good for the life of the car.