Twin Plug Dual distributor build

[volkaholic1]

No, it is my own design. I did not know about your parts at that time. Great work you did.
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Volkaholic

[Rwoodshvac]

Can you post pictures of the head work and plug placement.would like to see the plug placement from the combustion chamber . Nice work
Thanks
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57 Ragtop Semaphore Sedan
48 Aluminum Case drilled tapped, Full Flow Filter
Porsche 356 B Crankshaft 74mm
Porsche 356 B Rods
Shasta Cylinders with JE Pistons 80mm
WW Okrasa Heads worked by Ron Chuck
Speedwell Ratio Rockers 1.25
Dual Valve Springs w/Lash Caps
Blackline Racing Lifter Inserts, Manton Push Rods
34 Pbic Carbs rebushed by Mr Okrasa
Custom Okrasa Intakes enlarged to 34mm
Gene Burg Sump
Fram bypass Filter with Okrasa Oil Cooler

[Ninamashr]

Sorry for the delay but after looking high and low I finally found the *&^%*% disposable camera I used to take pictures of the head work I did in making my heads twin plug...

I needed a small plug in order make this work. Used an M10 x 1.0 sparkplug with a 1/2" reach. It was hard to get it at the correct angle but it worked...

Tooling:
Extra long 9mm endmill, Extra long 5/8" endmill to create the flat gasket area where the sparkplug seals, Extra Long 7/8" endmill to hog out the fin area so you can install the sparkplug with the socket, and finally a m10 x 1.0 thread pitch tap...

These are all the pics I have, I lost a few in the roll due to heat and it being in the garage for years behind my bench. I hope this helps anybody that wants to attempt to do a twin plug. It's not for everybody, it does take a long time, but it was worth it for me.
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1957 Karmann Kabriolet "Franky"
1957 Allstate trailer

[volkaholic1]

GREAT PICS! Thanks so much for the angle information. When I tried doing it myself, my problem was drilling from the fin side, snapping off fins, and if you are off even a small amount, when you flat spot the bottom for the spark plug seat, you can cut into the combustion chamber. I was surprised to find that a Forstner bit cut the aluminum amazingly well when combined with a good cutting fluid at 10% concentation. I use Master Chemical TRIM E206.
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Volkaholic

[Ninamashr]

Volk, It was very hard to get the fin area right, I had our grinder take down the neck on the 7/8" end mill to about .400 in order to clear the fin area where the push rod covers meet the head then I used the adjustable stop on the Bridgeport to take off the fin area .010 at a time. Big endmills tend to dig into the material so using the stop kept it from pulling into the material and snapping off a fin. I did not use the same end mill that was used to clear the fin area to make the seat for the reason you mentioned. In order to not cut into the combustion chamber I took a 5/8” end mill, also had the neck ground down to .400, and used it to make the seat area. Making the holes was hard compared to making the dist drive.
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1957 Karmann Kabriolet "Franky"
1957 Allstate trailer

[henry roberts]

great info. you haven't had any issues with the plug threads glowplugging?

[Ninamashr]

I don't know what you mean by plug threads glowplugging? So far I have not had any plug issues. Every month I check that the lower plugs are firing by taking the off the upper plugs coil wire and they are all working. The only issue I have had is that every once in a while, one of the lower plug wires falls off it's plug, I can hear the arcing when it happens so I just turn the lowers off, reach into the lower tin opening and put it back on.
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1957 Karmann Kabriolet "Franky"
1957 Allstate trailer

[gears]

I think what Henry's concerned with is the exposed threads overheating to the point that the they pre-ignite the charge. I've heard of this happening. I suppose you could mark the exposed threads requiring polishing?

The 36hp head is one of the few I never examined for dual plugs .. it appears from your photos to have far less material behind the combustion chamber than 40hp & later.

Does your top plug protrude more than stock ?

For some reason, I didn't have the fin break-off problem during machining that I had initially feared. In a week or so, I'll locate the various cutters etc that I had to assemble, as well as a demo head .. perhaps even a 36 hp head from somewhere. I'm curious if there's any possible way to get both sides to point toward the exhaust, like these dual port heads:

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aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[Ninamashr]

[gears]

I went through a few heads finding that sweet #2/3 plug angle .. and it was "barely". It might not be possible to place that plug exactly where we want, but a 36 hp collapsable pushrod tube might allow it.

Yes, I'd put in the shorter reach 10mm plug. You're already way ahead of of the curve with dual sparks, so I don't think you need to protrude so much.

A secondary issue with exposed plug threads is carbon buildup. This can chew up the threads when the plugs are removed.
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aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[gears]

I don't know how much this post will aid in dual-plugging 36hp heads, but hopefully most of it is applicable. I'd still like to find an old 36 hp head locally to play with.

My original goal was to find positions for both lower plugs that were as "straight in" as possible, with both angling away from the intake valve, and with both easily accessible (without having to first remove other parts).

It's difficult to begin a straight hole in an angled surface, so I modified the tip on one of my long drills to act as an end mill.

After drilling my 5/16" hole all the way through the chamber and through the fins, I flipped the head over, enlarged the drilled hole to 11/32", stopping just short of the chamber. I then used 7/8" and 5/8" end mills, as well as my custom lengthened 10mm tap, stopping short of threading into the chamber.

In order to keep from breaking fins, the head must be solidly mounted (steel or iron mounts) in a Bridgeport mill. With even the slightest unwanted vibration, chances are high that fins will snap off .. so I opted to mount the head as solidly as I could and adjusted the milling head for final angles.

I took pains to keep the lower plugs out of the airflow as much as possible. The sharp machined edges in these photos still require smoothing out (this is merely a pattern head).
#1 plug: https://www.thesamba.com/vw/gallery/pix/1027340.jpg
#2 plug: https://www.thesamba.com/vw/gallery/pix/1027341.jpg
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aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com

[WorkerB]

This is a great thread! I found it when searching for any info on dual plug ignition setups. My search brought me to a page in the middle of the thread. As soon as I realized that I went to the beginning and then couldn't stop reading until I got to the end.
What is the center-to-center distance of the two dizzies? I may have a different application using two larger diameter Bosch distributors.
Thanks.

[Ninamashr]

[[email protected]]

[gimmesomeshelter]

If your request doesn't work out, here's another option.

https://willhoit-auto-restoration.mybigcommerce.com/porsche-356-912-twin-plug-distributor/

"WR offers a complete Twin Plug Kit for $2,850. The kit includes this distributor, a preprogrammed and wired MSD CDI box, Magnacor plug wires, two coil options, upper and lower NGK Iridium plugs, and complete easy to follow instructions for installation. The MSD box is mounted under the passenger's side floor board and a period correct wiring harness connects it to the distributor."
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"I would rather have questions that can't be answered than answers that can't be questioned."

Richard Feynman

[volkaholic1]

wow - that looks dangerous just like the twin plug distributor i used to build, hahaha, things come around and go around, i think i sold my distributor for 1/2 that price! ripping myself off i guess, way too busy now to build them anymore.

actually, if you got access to a lathe, or can farm it out, i can sell you PDF plans, build it yourself, includes parts list, where to get stuff, and instuctions. pm me if interested
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Volkaholic

[[email protected]]

[volkaholic1]

i started with 009, then switched to new pertonix, then back to 009
you got to check, 009 from different places are slightly different dimensions

datsun twin plug cap and rotor, adapter for rotor, adapter for cap, add dual ignition moduals
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Volkaholic

[Alstrup]

I used a 009 as a base too in the beginning, but I chased the typical ignition shudder with these. Also, the distributor looks odd, even after streamlining the adapter, so I converted to billiet distributors which are more precise. Most of the systems I have been making I have used a programmable unit on the side. You can use an AL2-programmable, CB black box, Daytona TCS-1 and most likely also other fair priced stand alone units.
On the last 2 I am working on now (On and off) I have simply gone crank trigger and WS. It took a while to figure out how. I thought I could just copy the Alfa 155TS system. But it was not that easy, but it works now.

But the classic look with the dual distributors is hard to beat on the cool factor.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[volkaholic1]

oh yeah, 2 distirubtors is way cool, here is my 1st distributor, made by HASSAD in the 1970's, i had these pics on my website, then it guy you made them found me, we had a nice talk. found the dis at a swap meet in houston. this is like 1 of 5 he made, it uses a belt drive about the timing plate, so both have the same timing, i only had room for 1 pertronix, ran points in the other - had it on a 1915 turbo in my blue ghia

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Volkaholic