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 »

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
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Martin Benade
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Re: Distributor Drives

#2 Post by Martin Benade »

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 »

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 »

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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Harlan Halsey
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Re: Distributor Drives

#5 Post by Harlan Halsey »

I have a pair of cam drive distributers which lack the rotors and caps. Which caps and rotors are they? Neither the V-drive Carrera nor the 356 rotors fit.
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Jacques Lefriant
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Re: Distributor Drives

#6 Post by Jacques Lefriant »

Hi Harlan
maybe the early flat angled cap from a preA.
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Bill Sargent
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Re: Distributor Drives

#7 Post by Bill Sargent »

Porsche recognized the distributor wear Jeff mentioned and offered a kit to retrofit the cam driven distributors to the 60 degree crank nose drive. The 60 degree drive then became the standard until, I think, the 692 series motor superseded the 547 series. My guess as to why Porsche went from the narrow 60 degree crank driven distributor drive to the 90 degree version is cost.

With the cam driven and 60 degree drive distributors, one distributor rotated counter clockwise and the other rotated clockwise. This necessitated different gears at the bottom and a different shaft for each distributor. This different shafts were due to advance weight rotation direction and the direction of the de-oiling spiral groove on the shaft.

With the 90 degree drive, both distributors rotate clockwise so they are identical, interchangeable and overall cost was lower.

Jacques - please correct me if I am wrong 😁.
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Martin Benade
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Re: Distributor Drives

#8 Post by Martin Benade »

I can’t think of a reason why at 60 degrees (but not at 90 degrees) one distributor needed reverse rotation. Can you explain it?
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Re: Distributor Drives

#9 Post by Bill Sargent »

In a 4 cam motor camshafts on one side rotate clockwise and on the other side they rotate counterclockwise. Thus one cam drive distributor rotated clockwise and the other rotated counterclockwise. Porsche needed to accommodate this when they introduced the retrofit 60 degree drive. Is you examine a 60 degree drive there is one gear on the shaft turned by the crank nose. The distributors are offset along this shaft such that each runs on a different side of the shaft. See photo below.
IMG_1949.jpeg
On a 90 degree drive the distributors are in the same plane and oriented such that each distributor runs on the same side of the shaft, offset by 90 degrees. See photos below.
IMG_1950.jpeg
IMG_1952.jpeg
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Re: Distributor Drives

#10 Post by Martin Benade »

The 60 degree drive was designed to use the cam-driven distributors?
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Re: Distributor Drives

#11 Post by Bill Sargent »

Yes.
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Re: Distributor Drives

#12 Post by Jacques Lefriant »

hi Martin
both 60* and 90* use clockwise dist that come off the flywheel end of the engine if cam driven. have to install a helical gear similar to the 911.
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Re: Distributor Drives

#13 Post by Martin Benade »

Jacques and Bill, thanks for satisfying my curiosity about something I’ll unfortunately never have.
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Re: Distributor Drives

#14 Post by Jeff Adams »

Harlan - The distributors you have are an interesting pair. The VES4R2 distributor would have been original to a 550 Spyder engine, with the "R" in the part number indicating a right hand (clockwise) rotation. Cam driven distributors used on 550 engines were installed on the flywheel end of the engine, for mid engine cars only. The similar but different VES4L2 distributors were for 356 Carrera engines and installed on the pulley side of the engine. Again, the "L" in the part number indicating counter clockwise rotation. The 550 and 356 Carrera distributors used the same advance curve and tune up parts, but the internal advance mechanism parts were mirror images of each other so the flyweights would operate according to the direction of rotation.

Your VES4R2 distributor has a hand etched ZV2/6K10 number on it, which matches the stamped number on the other distributor. So I would assume both distributors are clockwise rotation 550 units. If in doubt there should be an arrow stamped into the top of the distributor shaft which shows which way it is meant to turn.

The rotor and clip on cap used on the VES series distributors were unique and not the same as either a pushrod engine or later four cam engine. These tune up parts were very similar to what was used on an early 50's VW bus, but had Bosch part numbers that were exclusive to four cam engines. In a pinch the VW parts can be used but the real deal Porsche parts are better, especially the rotor.

Sometime in 1957 the VJS series distributors came out which used a much different cap and rotor, both of which bolted to the distributor.

The narrow angle V drive setup came out in 1956 for the 550A engines, and could be retrofitted to engines with cam driven distributors. All V drive distributors turn clockwise. The narrow angle V drive distributors had different mirror image gears on both the bottom of the distributor shaft and V drive shaft, but the end result was both distributors turning clockwise. The wider angle 90 degree V drive used the same distributor for both positions and was driven by a single gear.

The VES series cam driven distributors cannot be converted for V drive use, at least not easily.

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Re: Distributor Drives

#15 Post by Harlan Halsey »

Jeff Adams wrote: Sun Sep 10, 2023 1:01 pm Harlan - The distributors you have are an interesting pair. The VES4R2 distributor would have been original to a 550 Spyder engine, with the "R" in the part number indicating a right hand (clockwise) rotation. Cam driven distributors used on 550 engines were installed on the flywheel end of the engine, for mid engine cars only. The similar but different VES4L2 distributors were for 356 Carrera engines and installed on the pulley side of the engine. Again, the "L" in the part number indicating counter clockwise rotation. The 550 and 356 Carrera distributors used the same advance curve and tune up parts, but the internal advance mechanism parts were mirror images of each other so the flyweights would operate according to the direction of rotation.

Your VES4R2 distributor has a hand etched ZV2/6K10 number on it, which matches the stamped number on the other distributor. So I would assume both distributors are clockwise rotation 550 units. If in doubt there should be an arrow stamped into the top of the distributor shaft which shows which way it is meant to turn. YES THEY ARE BOTH CW DISTRIBUTERS.

The rotor and clip on cap used on the VES series distributors were unique and not the same as either a pushrod engine or later four cam engine. These tune up parts were very similar to what was used on an early 50's VW bus, but had Bosch part numbers that were exclusive to four cam engines. In a pinch the VW parts can be used but the real deal Porsche parts are better, especially the rotor.

Sometime in 1957 the VJS series distributors came out which used a much different cap and rotor, both of which bolted to the distributor.

The narrow angle V drive setup came out in 1956 for the 550A engines, and could be retrofitted to engines with cam driven distributors. All V drive distributors turn clockwise. The narrow angle V drive distributors had different mirror image gears on both the bottom of the distributor shaft and V drive shaft, but the end result was both distributors turning clockwise. BEEN A LONG TIME SINCE I LOOKED INSIDE OF A V DRIVE BUT I THINK THERE IS A PAIR OF BRASS BEVEL GEARS BACK TO BACK, LIKE THE A AND D GEAR DRIVE, AND THE ONLY DIFFERENCE BETWEEN DISTRIBUTERS IS THE SHAFT DRIVE PINNION. THIS IS WHY THE DISTRIBUTERS ARE OFFSET. The wider angle 90 degree V drive used the same distributor for both positions and was driven by a single gear.

The VES series cam driven distributors cannot be converted for V drive use, at least not easily.
Jeff, Thank you for the detailed explanation. Those distributers came with a disassembled 1500cc engine I bought for $800 about 1975. I had to EDM a broken cylinder head stud from the crankcase, had the crankshaft rebuilt by Wellington or Doyle, had the cylinders iron spayed, and swapped the pistons for RS pistons with Bill Doyle. I assembled the engine up to final cam timing, and the distributers, but I never ran it. I turned my attention to the 1600cc V drive engines I ran in the 1959 GT Carrera which I ran at the MHAR 1981 to 2005 or thereabouts. Now I am looking at the 1500 and thinking maybe I should get it complete. I had always assumed that the distributers were Carrera, but I you point out that they are Spyder, and the diagram, pg46, of the Carrera Guide confirms that the intake cams rotate CCW, so I guess I'll have to pick up a Spyder for a road test.
The distributer bodies are 65mm in diameter, like the 356 iron distributers. It might not be too difficult to modify a 356-distributer cap to fit. The rotor mount is 14.5 mm in diameter, while the 356 is 13mm. This might pose a problem, although the larger cam drive could be reduced to fit a later rotor. A better solution would probably be to go to an electronic crank pulley trigged system and do away with the distributer points and advance altogether.

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