Drawing for twin-plugging of heads (3L SC engine)
 

Hi

Is there such a thing? A drawing that shows angles/measurements etc.

Cheers!

/Johan

I don't have a drawing but here is a tutorial on how I machined my 2.4L heads

http://forums.pelicanparts.com/911-engine-rebuilding-forum/584651-twin-plugging-using-14mm-plugs.html

Great writeup neilca....balls of steel! :D

(loving that mill....I so need a mill in my life)

Not sure I have the balls to do that :)

Hoping for a drawing which I can't take to a machine shop in order to help them set it up

Here is a short vid of mine, I can get you the degrees I use on the mill but to position the head and set depth I use a jig so I am trying to figure out how I can translate the jig into a measurement?

<iframe width="420" height="315" src="//www.youtube.com/embed/br6R5bTS05k" frameborder="0" allowfullscreen></iframe>

Definitely not for the faint of heart. I documented the procedure so folks could understand what all goes into twin plugging. Now you won't feel so bad having one of the machinist on this board do your heads. ;)

Best to have a couple of scrap heads to set up on before you commit to the good heads.
Just an FYI 2.0-2.7 heads are different than 3.0-3.6 heads.
Frankly it might be worth the shipping to get an experienced shop to do this.

FWIW,..I've had all the fixtures to do this since 1976 and we do a lot of these for other people as we'll as shops. :) :)

I would never trust my random local machine shop to do this. I'd send them to Steve.

I twin-plugged two sets of 2.2-2.7 heads myself about a year ago with the help of cgarrs and neilca earlier posts.
Bought M12x1.25 roll tap and proper drill for that roll tap. Made fixture beforehand with correct angles and rest was a breeze.

Wouldn't want to imagine the cost of sending two sets of heads over to US and back...

cgarr is the man. Word apparently has gotten out because he's always got a set he's working on every time I talk/text him.

One may be surprised by the number of shops that have the fixtures and can do this work. We use a local shop that has done many sets for us. We have 2 shops to chose from here locally. My suspicion is that a fair number of large cites have shops that have the fixtures to do this. Out local machine shop has heads sent from all over the world, but plenty of choices exist. If you can find a local shop you save the shipping to/from and the risk of damage during transport... The catch is your local shop needs to do the work correctly. But Porsche heads are not any more difficult to machine than any other head once the fixtures are available.

I don't have the luxury of locations when I am on my phone. At my desk now.

Talk to Stig's Garage and Lars Schonemann. Excellent air cooled shops in Scandanavia.

24 and 12.5 degrees for the mill head, 1000 rpm using a ball end mill, no cutting oil.

Thanks Craig for the degrees, much appreciated.

Not a bad idea Matt, actually think Schonemann is not too far away.

Cheers!

/Johan

Twin plug in Sweden
 

Try Perrys Motor ,Strömsholm 0220-43558

Shipping my heads, rods, and Ps&Cs to Craig was about $105. So maybe ~$80 for just the heads?
He was cheaper and faster than the local machinist that everyone recommended, even factoring in shipping. And he does nice work.

I have shipped stuff to US and with the weight of two sets of heads the shipping is ~200 and then I would need to get them back too. Remember, I am on the other side of the pond lol..

Total cost for me when I did it myself was ~100 usd total for the roll tap and special drill for it plus my own free time.

Why did you use a roll tap?

Although when used correctly there may be some advantages in using Roll Taps they do have their problems.

Torque to tap is commonly 2-3 times greater than with a conventional tap and they need much better lubrication to avoid galling

The control of the hole diameter is much more stringent for a given Class of Fit compared to a conventional tap.

The recommendation for class of fit often changes from an H5 to an H7.

The Roll Tap is also much more likely to cause burrs at the entry to the thread and will almost certainly need a generous chamfer.

I read about using roll taps on this forum for cleaning out head stud threads on engine cases and bought an M10 x 1.5 Roll Tap with some enthusiasm.

I noticed that the fit of the studs in the engine cases seemed quite loose after using this tap and spoke to the manufacturer.

I now use an ARP thread chaser for heads and we cut plug threads in our Twin Plug heads using a conventional tap.

We always use a 14mm plug and cut the fins to suit a 964 plug with a reduced body.

I used roll tap mostly because it creates a stronger thread by deforming material instead of cutting it. Also with roll tap the plug sits tighter in the thread compared to the regular tap kit I have for M12x1.25.
As for requiring more torque, I tapped it using a mill where I twin-plugged the head, so neither torque nor orientation of the tap was not an issue.

Agree with the hole diameter, it needed a special diameter drill.

As for burrs, it did produce burr but plug opening in the combustion chamber needed a chamfer anyway so it was a moot point.