Porsche 911 S 1971 engine "new special heads with new nimonic valves""

[expercat]

Hi Folks!
I write from Venice (Italy). I am rebuilding a Porsche 911S 1971 engine. The book “How to Rebuild and Modify Porsche 911 Engines“ by Wayne Dempsey is a very precious and valid help and I am reading its pages again and again. Some years ago I asked for six special heads to my machinist. A very expensive job! Nimonic valves (by Titanium company here in Veneto) with 8 mm stem and different profile, new guides, new valve seats, polished ducts. See at enclosed photos. Now after an accurate control I find all the height heads 0,50 reduced. Why did the machinist have this approach? Maybe the heads surface towards the camshaft housing were ligtly warped. Now I’ll have a perfect coupling (with Loctite 574) between heads and camshaft housing but the camshafts are 0,50 mm nearer to the heads. Correct?
I want to add the “new” inlet valves are 1 mm longer then original (115 mm versus 114 – 2.2 1971). So I think to have a double problem!
At the moment I don’t understand if these problems are superable because I am not so expert and in my area I’dont find anybody able to give me a final answer about this EXP engine with Wossner pistons 84.50.
The easier answer: you have to come back to original parts…….
Many questions…….. I’ll be graterful for any suggest about my engine rebuilding without problem.
Thanks.
Mike

[gled49]

Dry assemble, head, cam housing, cam and intake and exhaust rocker arms. See how far in or out the valve adjust screw is. Maybe the simple solution is to trim valve stems to bring adjusting screw into reasonable position.

[dannobee]

Are you sure that he didn't just machine the head to cylinder surface? It is rare to machine the cam housing to head surface.

If it's the head to cylinder surface, the 0.5mm can be taken up with cylinder base gaskets.

If your new valves are 1mm longer, you will need to add shims under the valve springs to correct the spring tension.

The valve adjustment screw (elephant foot) should have enough room to still properly lash the valves. Also, those valves will take different valve locks than the factory valves.

[expercat]

Hi!
thanks for your answers. I confirm only the heads surface were reduced not the camshaft housings.
I know it's mandatory to preassembly this engine after the deck height accurate control.
To put 0,5 gasket under the cylinders is a good idea but I'll miss compression. However I'll use Wossner pistons high compression so these pistons could reduce this problem.
I'll do an accurate control.
About inlet valves lenght 1 mm longer I know it's possible to trim them but there is a problem.
I miss the hardener treatment and the valve becomes weak. The best way to solve this problem is to buy six new valves with correct dimension.
About the heads resurfaced I thought to cut by laser six well shaped 0,5 copper gaskets to put between heads and camshaft housings. Obviously under the cylinders I'll put the 0,25 gasket if the deck height allows to keep this thickness. Do you have any experience about that?
Thanks

[targa72e]

Supertec has shims to go between head and cam housing already made. There is a picture of one in post two of this thread.

Old school with a twist




john

[expercat]

Hi!
thanks for your suggest about Supertec gaskets. I am not a professional so itsn't easy to plan everything about an "homemade" Porsche 911 engine rebuilding. In Italy there is a little difference about to share experience...... I controlled again the heads resurfaced job. For an accurate head height measure I have to use a large special micrometer because it's important to know the new distance between the surface inside the head towards the cylinder and the upper surface towards the camshaft housing.
Mike

[Henry Schmidt]

Originally Posted by targa72e

Supertec has shims to go between head and cam housing already made. There is a picture of one in post two of this thread.

Old school with a twist




john

Thanks for the reference but these shims were one off, made specifically for our peanut head project.
We can make more but the lead time and price may be prohibitive.


Cheers