How to do certain rebuilding tasks

[Neil Harvey]

Today I had a telephone call from Gary from Indiana who is rebuilding his 911 engine. I believe it is a 2.7L engine. He is doing most of the work himself including the Cylinder heads.

His questions was, how come some youtube video's show one way and another shows another way.

My answer was as I have suggested to others asking similar questions, there are many ways some good some bad. Its all opinion. I suggest a certain way because that's how I was taught and what I believe is the correct way based on good theory and principles.

What it has done is to give me pause to think that maybe there is room for an in depth Porsche 911 engine building class where all areas of rebuilding an engine are covered including the machine work.

The question that Gary had was about the Valve spring set up. He was correct in his assumption that the specified installed heights given by Porsche, are a way that most can measure. It would be unusual for any one at home to measure the pressures as a way of equalizing the pressures.

Having equal seat and open pressures is the proper way of installing the springs, but Porsche figured out no one could do this at home or even at some repair shops.

How we do this procedure may be different how others do it. We have the ability to measure the retainer and base thicknesses, retainer heights, camshaft gross lifts, rocker arms ratio's, ask for any seat, open pressures and calculate the coil bind distances etc. Then have the shimming calculated for the required pressures. The linear graphs show any odd issues with any of the tested springs.

I can say with conviction that any engine valve springs assembled using the factory heights only, will not fail. Years of running have proven this to be true. Our way is more involved and informs us of a lot more info so we can build an engine with tighter tolerances.

[Dpmulvan]

https://patents.google.com/patent/CN110375905B/en?q=~patent%2fUS3640129A