Distributor Drives

Discussion of 4-Cam Type 547 engines (and all the Fuhrmann racing variants) and cars that powered them.
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John Clarke
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Distributor Drives

#1 Post by John Clarke » Sat Jun 05, 2021 10:54 am

Hi
See that there are various cam drive angles from the crank and location as per cam driven or crank driven. Were the cam drives too far away from the crank to give accurate timing with all those bevel drive gear's backlash ? Just interested. I hope to be able to own one of these engines in the future if I ever win the lottery :P
Jay
 

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Martin Benade
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Re: Distributor Drives

#2 Post by Martin Benade » Sat Jun 05, 2021 2:29 pm

I think the cam drives shook the distributors to death as the cams don’t rotate smoothly. I am no expert though, I’ve barely even seen a four-cam.
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Jeff Adams
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Re: Distributor Drives

#3 Post by Jeff Adams » Sat Jun 05, 2021 4:49 pm

Backlash in the cam drive, action of the two lobe camshafts among other things did contribute to the early distributors wearing out prematurely, as well as less accurate ignition timing than the later crank driven setups. The first factory service bulletin related to four cam engines said distributors from racing engines should be sent to Bosch for rebuild every 5000 KM. The bulletin did not say why, but for those of us who have rebuilt early distributors the reasons can be easily seen - the internal advance mechanism bits and pieces get very worn.

The first engines to get the crank driven distributor drives were the 547/2 550A engines in 1956. There were a few different variations over the years, the most obvious being the narrow angle more upright drives and later 90 degree with the rightmost distributor being at a flatter angle. I am not sure why the angle was changed on later engines, but my guess is that the engines used in 356 Carreras got the 90 degree drives to make room for the muffler support rod which came down from the base of the generator stand.

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Harlan Halsey
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Re: Distributor Drives

#4 Post by Harlan Halsey » Sun Jun 27, 2021 5:35 am

A friend of mine, Chuck Forge had a 1957 GS Carrera which he drove on the street in the mid 1960s. One day coming home from an autocross across the Bay, the engine began to run rough and blow smoke. On disassembly, he found that a cam drive distributer had failed and gone beyond full advance. This resulted in a holed piston. He also found that the engine was completely worn out at 40,000 miles. The wear he attributed to running Castrol R. He found the Castrol R very difficult to clean from the engine parts. The only thing which would touch it was hot Toluene, and a lot of it. And Toluene was expensive. So he built a version of a vapor degreaser in the back field: A wood fire heating Toluene with Carrera cases suspended above, and a sheet metal condenser/collector overhead and around. (Ahh the time and focus we had in those days!) Wellington rebuilt the crank. Chuck reassembled the engine, I think with a Vee drive. 20 years later he was pushing a 300 SL Gullwing at Laguna Seca at the MHAR and had just passed when.....but that's another story.

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