Twin Plug DIY?

[David]

Anyone out there do their own head machining for a twin plug mod? As I look at the vast expense of my engine project, knocking off $500 for the twin plug machine work would be nice. I don't have a twin plugged head for reference and I'm a bit apprehensive about going off pictures so I'm looking for someone that's done it and that's not worried about giving away their trade secrets.

[garibaldi]

What equipment do you have? You cant do it with a makita and a tap set. You need some pretty special fixturing and tooling, which would cost you more than what you have been quoted to get it done. Spend the $500 and get it done properly, if you mess up, there goes the head.

[David]

I work in an extremely well equipped machine shop, so the only cost would be my labor. I'm still leaning toward sending them out to EBS for everything, but the idea of saving $500 makes it tempting to do myself. My main concerns are that in some of the pics I've seen it looks like the 2nd plug is at a different angle from the 1st (not just opposing angle) and maybe a different plug size.

Anyone have a trashed head they'd like to sell?

Here's a pic of the shop where I work from the the 100 ton crane, this is the center bay, the east and west bays house the smaller machine tools:

[garibaldi]

Cool, then you can set up off the other spark plug angle, 65 degrees front to back, and 80 degrees side to side.

[MT912RS]

Thanks, I was actually getting ready to post the same question.

[David]

Do most people machine the second hole exactly the same as the first but on the opposite corner? Do they machine for the same spark plug dimensions?

[afterburn 549]

some use a smaller plug,i went with same size.

[Grady Clay]

When twin plugging a single plug head I prefer a 12 mm spark plug, stock is 14 mm.

It fits properly, a twin plug 911 was designed for this.
You can use short plug connectors that fit inside the valve cover.
Less metal removed (better cooling and maintains high compression.)

Best,
Grady

[emcon5]

My twin plug machine work cost $350.

Tom

[CliffBrown]

Tom

Did you use a local shop for the twin plug machining?

Email the shop info if you don't wish to post it here.

Thanks,
Cliff
Clifton_Brown@hotmail.com

[TimT]

German Precison did my twin plug (well Ted did a few twin plug machinings for me) conversion..

Ted is a stand up guy, and $350 seems like a good deal...

I do remember someone bashing GP awhile back... in all Ive dealt with him for almost 10 years and have not had a problem...

[David]

I've been staring at pics in books and it looks like some of the 2nd plug holes are at a different angle from the original. Does anyone have a twin plug head laying around that could take a visual check of how the second hole looks compared to the first?

[emcon5]

Originally posted by TimT
German Precison did my twin plug (well Ted did a few twin plug machinings for me) conversion..

Ted is a stand up guy, and $350 seems like a good deal...

Ted did mine as well. $350 was in addition to the top end work he did. The total, parts and labor for the top end work, with new springs/guides/seals and twin plug conversion came to ~$1450.

Ted's number is (408) 747-0728

Originally posted by 125shifter
I've been staring at pics in books and it looks like some of the 2nd plug holes are at a different angle from the original. Does anyone have a twin plug head laying around that could take a visual check of how the second hole looks compared to the first?

The plugs are offset. The top set is angled in from the right, the lower set from the left. Here are the heads:



And here is a good shot showing how the plug wires line up.



Tom

[David]

Thanks Tom,

Could you tell if the 2nd hole angles are a mirror image of the first or are the angles a little different? The four heads in the bottom of your picture make it look like the angles are different, but the two on the top look like the same, but opposing angles.

[garibaldi]

You can set up using the same angles the original plug uses, I have seen others that deviate slightly from that as well.

[David]

In this picture from Wayne's book it looks like the 2nd plug is drilled at a much different angle than the 1st one:

[Jay Auskin]

I have a trashed head if you want it, I'll just charge you shipping. The only damage is the combustion chamber had a valve pounding on it so it looks like someone hit it with a small hammer 1000 times. It should serve your purpose as a set-up piece.

Just PM me your address.

[emcon5]

Originally posted by 125shifter
In this picture from Wayne's book it looks like the 2nd plug is drilled at a much different angle than the 1st one:

I think that it appears that way because the camera is off to one side a little bit, and tilted, relative to the head.

The term "Parallax" comes to mind, but I don't think that is the right word.........

Tom

[David]

I figured out what my confusion was. The hole for the 1st plug is closer to the exhaust side head studs, so my idea of lining up on the 1st hole and rotating the head about the head stud center would put the 2nd hole about 1/2" or so off alignment with the 1st. Now I understand why the 2nd hole recess is closer to the exhaust side stud recess.

On a side note, I picked up a 12mm plug out of curiousity. I bought an NGK, maybe others are different, but the porcelein is smaller than on the 14mm plug so I'd be concerned that a standard size plug wire boot would not seal out the elements.

Since I'm an amatuer machinist (I have made some intricate precision parts though), I alway consult with the pros at work and one recommended putting clay between the fins when machining to prevent damage. Another thought it wouldn't be a problem with mill at an angle, but I'll air on the conservative side and wedge some rubber between the fins.

[Grady Clay]

David,
There are plug connectors designed for use with 12 mm plugs. The 12 mm plugs are what Porsche used in all the race engines.

Best,
Grady