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A tale of distributor rotors
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Frederik
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PostPosted: Thu May 16, 2019 3:22 pm    Post subject: A tale of distributor rotors Reply with quote

I get a lot of questions (from buyers) about distributor rotors and if they fit Porsche and I thought I should share my answers here as well. I'm not saying that it's the whole truth but it's my tale of rotors. Lets start from the begining.

If we talk about old original rotors for Porsche 356 and 912 cast iron distributors VJ4BR9, VJ4BR18, VJRBR18, "022" and VW 36hp VJ4, VJR4, VJU4, VJUR4 BR.. (Yes they use the same rotors) we can divide them into two groups "no-resistor rotors" and "resistor rotors" (the resistor works as a noice suppressor for radio) which each divide into two sub-groups "for dust cover" and "no-dust cover".

We then get 4 different rotor types. Below with old Bosch "ZV.." part number and new Bosch 10 digit part number under. All fits Porsche 356/912 cast iron distributors as above.

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Example of resistor rotor vs non-resistor rotor. In their earliest form it was easy to spot them as they didn't have epoxi over the brass arm (or resistor in the earliest resistor rotors). The "R" in VJR stands for that the distributor was fitted with a resistor rotor from factory.

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The "dust cover" rotor had a groove in the shaft that fits snug on a matching
edge on the dust cover. Of course you could use a "dust cover" rotor without the dust cover (they just didn't do anything extra then).

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Picture from gallery, user tasb. Dust cover.

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Different design of the same rotor/ part number: I don't know the exact year, but sometime in the late 50s - early 60s (going by pictures in Bosch spare parts book from the time) they change from the "round style" rotor to the "counter weighted" model with the large counter weight. This style was still in use when they in the early mid 60s changed to the 10 digit part numbers (as seen on the rotor to the right) and I don't think they changed to the smaller counter weight (in the bottom of picture) style for this group of rotors up until the 70s.

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Today most use the 1234332088 (04008) for replacement for all the above. It's a later replacement part and have no pedegree to the earlier versions above nor does it have a "old part number". It resembles in design of the 1234332107 (04012) to the right of the "088" in the pictre, used in late 60s aluminium VW and Porsche 912 distributors, but don't fit the same. Bosch today cross reference Porsche 61660222102 both to 1234332070 (resistor, non dust cover above) or 1234332088 (resistor, for dust cover).

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More on the design change and some aluminium distributor rotors. The "031" and "061" Porsche 912 aluminium distributors originally used the 1234332107 (same as late 60s VW). It still have the system with a groove for the dust cover. In the 70s (many of) the VW distributors went over to use the 1234332215 (04033). The "215" rotor fits the same as the "107" (minus the dust cover) and can be used in it's place in Porsche 912 aluminum distributors (not cast iron) if it's not fitted with old style dust cover. Also in my 70s-80s Bosch part list the 1234332074 (old part number ZVVT5Z6 z) is listed as spare part for VW instead of the "107". It's a "resistor, No-dust cover" rotor" therefore"107", "215" or "074" can be used in alu 912 distributors. Bosch cross referens Porsche 61660222105 to both 107 and 215 today.

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As a sidenote to the picture above one can easy spot a German 215 rotor from a later "non-German" Bosch by the color, light brown vs more orange (Same with caps). You also get the difference between the light brown and dark brown rotors. The really dark one ("107") is that of age/usage, oil and dirt/carbon (they always get a tan when old).

With the "215" the dust cover design went simplier. The rotor shaft is solid and simply fits down the center hole.

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Earlier "dust cap rotors" also fit (some a bit snug).

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Last edited by Frederik on Thu May 16, 2019 4:32 pm; edited 2 times in total
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tasb
The Distributor Distributor


Joined: April 27, 2002
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PostPosted: Thu May 16, 2019 3:48 pm    Post subject: Re: A tale of distributor rotors Reply with quote

I find that the fit of the combination immediately above is a bit too snug and the dust cap may get mis-alligned during use. There were other aftermarket manufacturers of these rotors and the designs metamorphose. This is a good analysis of the Bosch units.
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Frederik
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PostPosted: Thu May 16, 2019 3:55 pm    Post subject: Re: A tale of distributor rotors Reply with quote

Yes the one in the picture (and other early "ZV..-style" dust cover rotors) are a bit too snug. But the later "107" (and "088") rotors fits perfect.
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Frederik
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PostPosted: Thu May 16, 2019 4:10 pm    Post subject: Re: A tale of distributor rotors Reply with quote

So what rotor is "correct"?

If you have a 356 with a VJ4BR9 or VJ4BR18 (nov 1955- nov 1957) your distributor should probably have had a ZVT53Z9z rotor.

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If you have a 356 VJR4BR18 your distributor should probably have had a ZVVT5Z4z rotor.

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Nowhere does Bosch/Porsche list a dust cover rotor for the above or a dust cover version of the distributor (that I can find). That not said you couldn't have had one ordered or fitted from Porsche.

If you have a "022" distributor it could have had a ZVVT5Z4z or 1234332070. But a dust cover was listed and so a was a "dust-proof" distributor "023". Dust proof meaning just that it was fitted with a dust cover and rotor ZVVT5Z5z from factory.

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So what rotor should you have?

Any of the ones listed in the first post fits. It's a matter if you care about it being period correct or looking period correct, if you don't want a resistor rotor (cdi ignition or don't like the idea of resistors everywhere), have a dust cover installed or do not have it and think it looks silly with a dust cover rotor without the cover or if you just want to buy a new replacement in store (who cares about rotors!?)
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Steve F
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PostPosted: Fri May 17, 2019 3:36 am    Post subject: Re: A tale of distributor rotors Reply with quote

Well done! Thank you:<)
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We Sell Ice
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PostPosted: Tue Nov 24, 2020 11:31 am    Post subject: Re: A tale of distributor rotors Reply with quote

Thank you, nice post!

I have some ZVVT5Z6 / 1 234 332 074 here. Looking like RESISTOR - NO-DUST-CAP, numbered as ZVVT5Z4 / 1 234 332 070 in your table.

Frederik, do you know the difference between 5Z6 vs 5Z4?
I'll try to post a picture.
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We Sell Ice
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PostPosted: Tue Nov 24, 2020 12:15 pm    Post subject: Re: A tale of distributor rotors Reply with quote

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I do not have a ZVVT5Z4 / 1 234 332 070 for comparison.
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Frederik
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PostPosted: Tue Nov 24, 2020 12:36 pm    Post subject: Re: A tale of distributor rotors Reply with quote

The ZVVT5Z6/ 1234332074 (non-dust cap) fits the same as 1234332107 (dust cap) rotor used in late vw and porsche 912 aluminium distributors (031/061). You have one in the pictures of the aluminium distributor rotors. 1234332215 also fits in place of them but use a different dustcap (if used). All of them are with resistor.
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We Sell Ice
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PostPosted: Wed Nov 25, 2020 12:34 pm    Post subject: Re: A tale of distributor rotors Reply with quote

Thank you! So nothing for cast iron...

Now I also got the difference. Embarassed The inner diameter of all rotors is the same measuring on top, but there is a cone for a smaller shaft diameter at the cast iron distributor rotor versions.
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