Porsche 4-cam Engine Stripdown

I had an interesting visit to Tuthill Porsche at the weekend. Francis took one of his 4-cam 356 Carrera engines out of storage and brought it into the engine workshop for the team to carry out a complete restoration and rebuild, including upgrade to 904 spec (pistons and cams ready and waiting).

The 587/1 GT engine was found sitting in the corner of a garage many years ago. It had been in a fire and done a bit of damage but nothing too serious. Fran took it home and started rebuilding it with the help of a friend who made valve guides for Formula 1 engines and had rebuilt a few race engines also. They rebuilt the bottom end, bought new valves from Porsche and made a full set of valve guides (superb things to look at) but never got around to doing the top end. Now the Tuthill engine builders will get stuck into it as a special project and I am excited to follow the work.

The 4-cam engines are a bit of a minefield, but no doubt when they work they are pretty special. Ferry Porsche had a 4-cam in several road cars and put a fascinating piece about development of the first Fuhrmann 4-cams into his autobiography, which offers an excellent insight into how the factory was operating at this time (late forties).

“For some time, our total work force comprised less than a hundred men, but we made good use of the cramped and limited space (a 600m2 rented workshop in Stuttgart) and even managed to find room for a diminutive test and racing shop, which held just two cars. It was shielded from prying eyes by an ancient closet and a primitive sliding curtain.

“We knew when we started using the Volkswagen engine for our Porsches that the maximum to which we would be able to increase piston displacement would be 1,500cc. The pushrod system of valve actuation, while completely reliable, also placed limits on engine revolutions. But we had foreseen this problem, and already by 1950 Dr Ernst Fuhrmann, an outstanding engineer on our staff, began designing our future Carrera engine.

“Different technical drawings were made which examined the possibilities of driving four overhead camshafts. One method was by chain, another by gear drive and so on. It seemed to us at the time that the best method to use would be a gear train, and that the distributor could also be driven from the end of one of the camshafts; but this arrangement led to difficulties.

“Each of the four camshafts operated two valves, and as the engine gained speed, a vibration began which ended up by destroying the ignition system. We therefore had to make changes in the ignition drive – not too much of a problem. The Carrera engine originally had a piston displacement of 1,500cc but was so designed that could be enlarged to 2 litres. However, we are anticipating a little, since another five years were to pass before we introduced this famous engine into our production line.”

Looking at the myriad parts spread out across the work bench in Tuthills, I simply cannot imagine how much effort went into making this thing work reliably. It is insanely complicated – the camshafts have flywheels and each camshaft is driven by a shaft which needs two position adjustments (one at each end and in opposite directions) to alter the cam timing. Even the flywheel is complex: it is fixed to the crankshaft by two tapered spacers, which interact under torque to lock the flywheel solid, but need huge torques combined with a specific routine of taps with a brass hammer to do their thing properly.

The first Type 547 crankshafts were Hirth roller bearing assemblies that came in separate pieces. Can you imagine starting an engine build by assembling a crankshaft? There is wonderful madness to an engine designed for production that took 120 hours to assemble and up to fifteen hours to set timing on. Compare this to the 41 hours often cited as start-to-finish build time for a complete 996!

Every single piece of it is outrageously complicated, making the flat-four 4-cam engine fascinating but frustrating. It leads me to wonder how much of Fuhrmann’s love of the complex fed into the convoluted, overweight transaxle cars which he had scheduled to replace the 911 before he was eventually replaced as Porsche CEO by Peter Schutz in 1980. An interesting question that would no doubt draw many comments on engineers as MDs, and the eternal battle between technical staff and accountants.

Setting aside my musings on four-cam contribution to Porsche boardroom history, this engine build is a fascinating project and one I am really looking forward to following. For example, valve lift on the 904 spec 587/2 engine is confirmed as 10mm exhaust and 12.5mm inlet. This would be mental enough with small-ish valves, but the 4-cam valves are huge and weigh a shedload. It is simply unbelievable and wondrously exciting!

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