Bosch Twin Plug Cap

[tenzing]

Hi there,

Looking to purchase a Bosch Twin Plug Cap or repair mine.
Here is a picture of mine, with worn tips, can the tips be replaced?




If can not be repaired, who has Bosch Twin Plug cap and rotor for sale?

Thanks,

Tenzin

[Rufcar]

I just went through this on my twin plug. There are no new ones like yours period! That said there are NOS one's for 3k and more yes 3K! plus the rotor. There are several black repos made (that's what I purchased) from about 350-550 depending on where you buy and the exchange rate. There is one supplier at the moment for rotors and he only does bank to bank transactions but he has both NOS and repos. He is 11parts in Europe. I could not use the new cap with my old rotor as these must be a matched set so I reinstalled my olds ones until I get my rotor. Those are supposed to be available by the end of the year but you never know. Id love to know if you make out better then me. Good luck. Jim F

[356RS]

I have a NOS set, Cap & Rotor for $2900.

[tenzing]

Hello,

Purchased 3 sets of rotors and caps from Marco at Elevenparts in Switzerland. They are excellent quality. So should be good for next season.

Mark, thanks for the offer. I am going to use these repros for now, but at least know someone who has a set.

Does anyone know who can repair these caps?

Tenzin

[MZ3 SBC]

Originally Posted by tenzing

Tenzin

Hi- I need some help with the wiring / firing order for the BOSCH twin plug on my 930. I took the distributor out and also removed he wires during an engine clean up. Car timing is off- so I am just not confident.

what does the red and black dots signify here....
Thanks

[fred cook]

I installed an Electromotive XDi twin plug system in my SC when I rebuilt the engine. No expensive caps or rotors to buy! And, the timing is fully adjustable via the timing controls. Also, not having a distributor in the engine helps clean up the engine and compartment a lot! System works good and runs great!

[MZ3 SBC]

Thanks for the note Fred. I want to keep the set up as it was built by Dawe Motorsport- he built a 3.4 twinsplug with 935 gears and LS diff.....I do not want to change anything ....its a piece of history as far as I am concerned.


I know the 930 dist counter rotates, and I know the firing order is 1-6-2-4-3-5, and timing is 10degrees advanced TDC....then I have to set the CYLINDER #1 to TDC - the question is how to address the second set of plugs...... so I am getting close....

[356RS]

It looks like the red and black dots are on a #1 & #4 marking. Looking at your photo of the top of the cap, the red marking @ 12 o'clock could be where the #1 B is and then CCW to the #6 B is a black marking. Same for the #1 A black marking @ the 1 o'clock position, CCW to the #4 A red marking @ the 7 o'clock position. The A connectors are on the outer plug connectors and the B's are the inner connectors.

[fred cook]

Originally Posted by MZ3 SBC

Thanks for the note Fred. I want to keep the set up as it was built by Dawe Motorsport- he built a 3.4 twinsplug with 935 gears and LS diff.....I do not want to change anything ....its a piece of history as far as I am concerned.

Wishing to keep it as built is understandable. I might do the same!


I know the 930 dist counter rotates, and I know the firing order is 1-6-2-4-3-5, and timing is 10degrees advanced TDC....then I have to set the CYLINDER #1 to TDC - the question is how to address the second set of plugs...... so I am getting close....

Set the #1 piston at TDC first, then adjust the timing. Once the #1A plug is timed correctly, all the others will be correct also as the rotor and cap are not adjustable. Once it is running, adjust the timing with a timing light to get it "right on"! Good luck!

[gumba]

I bought a cap & rotor for my Bosch 12 plug a few months back from here: shop

[gumba]

Here's a spark plug wire layout of my Bosch 12 plug cap for my 3.5 twin plug turbo

[356RS]

Well after looking at my engine with the Bosch Twin Plug Distributor I can see that the 2 red marks are for the #1. Bottom red is A and top red is B.

[MZ3 SBC]

This is a picture of the cap and rotar that came off the car as well as how the car was wired. you can see a hash mark on the distributor which I assume is for TDC on cylinder #1?

[MZ3 SBC]

4B and 5B seem to be flip flopped based on firing order.

[356RS]

Your T's are correct. Not the B's. Your labeled 5B should be 4B, and then your labeled 4B should be 5B. Fun stuff right?

[MZ3 SBC]

Originally Posted by 356RS

Your T's are correct. Not the B's. Your labeled 5B should be 4B, and then your labeled 4B should be 5B. Fun stuff right?

Thanks you guys helped tremendously- I caught the 4b - 5b reversal last night too.

Does the cap and rotor look toast? I am gonna replace with remanufactured. $700 is ridiculous! gotta be a better deal out there....

Gumba your diagram really helped.

I apologize for the noob questions. But once the light bulb goes of it is really much more simpl than I made it out to be....just need some help to get on track and you guys always step up.

Cheers......and hoping this turns over tonight.

[MZ3 SBC]

I managed to clean up the cap and rotor nicely and have been able to find TDC for either cylinder 1 or 4. I have the rotor indexed to hash mark at the Z1 setting.

I wish I knew for sure if this was the compression stroke for 1 or the overlap- but I guess I will go with trial and error and assume its compression and wire spark plug 1 T to the rotor. if it does not start than I know it was the over lap.

I tried a compression gauge on the cyl 1- but I would get pressure on every 360 rotation...and the gauge had a Schrader valve and a bleeder valve...so it holds pressure. so I don't get the benfit of the air leaking out when valves are open.

nice thing is a learned a lot again...and its so rewarding to work on the car.

I pulled the plugs and they are autolite...and the lower set of plugs are small plug conversion...so two different size sockets. The is a realtively cold plug as I understand.

What plug is being run on a daily driver ( not seeing track duty)....I would assume a hotter plug would serve me better.

I am expecting to have this running tomorrow!!

[MZ3 SBC]

When I was looking for TDC cyl #1= I would rotate the crank pulley 2 times which is 1 rotation of the cam gear / rotor. Each time the rotor cam around that gave me TDC...and I was thinking 1 rotation was compression and 1 rotation of the rotor was over lap.

So one rotation of the crank pulley is compression and one is overlap. Now that I have that resolved....the rest is extremely straightforward. I hope this helps someone else who is doing this for the first time.

Now that I know where TDC is - I know that the distributor was not put in correctly as TDC reads at 6 oclock and the hash mark on housing is at 3 oclock...and along with plug for cylinder #1.

I am getting a distributor wrench so I can rotate the distributor to move the rotor to the hash and the plug for cyl 1.

Then I will adjust the timing.

took advantage of the time to clean plugs, cap and rotor, re organize the wires.

I am looking forward to hearing this thing come back to life.

[Walt Fricke]

Easy way to confirm overlap TDC vs firing TDC is to pull the intake valve covers with the crank pulley Z1 lined up with the mark on the fan housing. If the @1 intake is loose (has the specified 0.004 lash), and the #4 is tight (but not depressed much), you are at the #1 firing point and #4 overlap.

[MZ3 SBC]

thanks- I found the easiest way was to remove 1 plug, attach a compression gauge and spin the crank pulley. When the gauge moves.....its TDC. borrowed one from a buddy, found the matching connector tot he plug size and done.

My confusion was in thinking that there was a 1:1 relationship with the distributor rotor and the crank pullEy when in fact its 2:1. So every complete turn of the rotor is 2 turns ( see z1 2x) if crank pulley.

On a turbo with a twin plug cap- you absolutely need this to tackle the distributor 13mm.




Once that epiphany...it was easy.