altarchsa

Anyone know the valve spring pressure spec? '89 C4 stock.

Machine shop is waiting for me to give them this to finish the job today. They say it's not in the 964 spec book I left with them.

Thanks Rennlisters.

Geoffrey

What book does your machine shop have? The spec book says that the installed height for the 964 is intake = 34.5 +- .3mm and the exhaust is 33.5 +- .3mm. He can take the spring and put it on his Robec spring machine and measure the seat and nose pressure which will be approximately 45lbs on the seat. IMO the stock spring pressure is the minimum you can run the 964 at.

altarchsa

I told him I thought I had read 45 lbs somewhere, but I didn't want to rely on memory. I gave him the 964 spec book which has the picture of the white coupe on the cover, same as Streather's Enthusiast's Companion book. He said he didn't see a spec for the pressure, just installed heights.

After a broken valve within 4 month's of a total rebuild, I'm a little nervous about running additional spring pressure.

Thanks for your help.

Geoffrey

The valve did not break due to additional spring pressure, it broke for a different reason.

The specification is in the 911 Carrera 2/4 Technical Specifications book on page 100 and in Volume 1 (maintenance/engine) of the 911 repair manuals chapter 15 page 14.

If you are using the stock springs, be aware that the outer springs have tighter wound coils on one end and they need to be installed towards the head, not the retainer.

altarchsa

Thanks for your help Geoffrey.

I understand that the spring probably broke due to the extra heat generated from worn guides, but I would think that high spring pressure could accelerate that.

Thanks for the reminder on the springs. I'm using an engine shop that's very good, so I assumed that they would be aware of the variable rate spring orientation. But since they're not Porsche specific, I think I'll give them a call.

Geoffrey

Stock springs are pretty robust. They usually break only when run to coil bind which can happen if the seat pressure has not been set high enough and the rockers come off the nose of the cam.