Accepted Valve Spring Height?

ernestedward · 05-20-2006, 06:59 AM

Doing a valve job on an 87 944. Need to know the proper heights for the valve springs uncompressed and compressed (at a certain amount of compression force). I think I found the uncompressed height in the shop manual:

Intake Valve: 41 +- .5mm
Exhaust Valve: 40 +- .5mm

But my neighbor who's helping me with the job says there's another set of numbers I need, the ones mentioned above. Can anyone help me out here or point me to another resource?

Thanks,

Ned

SoCal Driver · SoCal Driver's Garage

I just checked the reference that I have and there is no mention of the stem height. Besides the compressed height of the springs the stem hight is critical for proper lifter displacements.

Best measure this before disassembly and compensate after the seats and the valve face are cut and lapped in.

rudidelange · 05-23-2006, 06:54 AM

The stem heightt is measured between the tip of the stem and the surface of the head - my 83 model is specced to between 13.65 to 14.5 (I hope I remember correctly), the installed spring heightt is measured between the seat of the spring and the retainer on top of the valve spring (the space that the spring occupies). If a seat is machined too much then the stem heightt will increase. The installed spring heightt will also increase but can be corrected by shims underneath the seat of the valve.
The installed spring height is different for the inlet and exhaust (earlier models) but was later corrected for later models were they are the same. Porsche machined the head where the shims and seats are seated.

I found a good explanation how to measure the installed spring heightt in Rennlist, somewhere in 2002.

The questions that I still have is:
How important is the valve stem heightt and the installed spring heightt?

I guess that an incorrect installed valve spring heightt will affect the "pressure of the spring" and a wrong valve stem heightt will affect the proper functioning of the lifters.

If a seat has been machine too much and the valve stem heightt is more than the 14.5 mm, can a person get the heightt correct by removing some metal from the tip of the valve stem?

I hope this helps
Let me know if you learn more

SoCal Driver · SoCal Driver's Garage

Yes remove material from the end of the valve stem to set the stem height. Shim the springs to correct their compressed height.

ernestedward · 05-23-2006, 02:27 PM

Great, thanks. That's what we went ahead and planned on - removing material from the top of the stem to get to the correct height. I'll let you know what the final procedure was when I hear back from the shop.

Rud - you seem to be describing the same procedure I was following from the factory workshop manual. 14.5mm is the tolerance noted there. Thanks again.