How certain engine build tasks should be performed.

[Neil Harvey]

Happy new year to all.

This time of the year I get time to catch up on my reading and go through emails that I have unfortunately not had the time to respond to properly.

Just before the Christmas break, I had some emails and a telephone call from an owner who was rebuilding his 911 engine. I believe it was an early 3.0L engine. He, like many wanted to do most of the work himself. I admire that passion. I wish I had the same for some of the things I want to achieve. Sadly, I have not the time anymore.

His question was like many, “have you watched this video on You Tube about’, fill in the blank here. The questions are always, do you agree with how and what is been told.

My answer was and always is, maybe I do not but I do not believe my way is the only way. This may also be controversial; I often do not agree with how Porsche suggest it be done. I will agree that, built how Porsche suggest will always end in success. I also believe that another way will also be successful if engineering thought is invested into the solution.

Watching others can give another perspective and maybe you do learn something. That has happened in the past for sure.

The specific question related to the 911 2V valve spring set up and testing. I did watch the video in question. As for the testing results, it is always about the quality of the test equipment and the user’s ability to minimize the errors in its use. A poorly maintained machine with wear and tear can give the same results as a very accurate machine used by a person who cares less about accuracy.

My answer was, this is how we do it and we do it this way because. My first reaction was, I have never seen Porsche supply the seat and nose pressures for Valve springs. I must be missing this literature. I have only seen installed seat heights given. I have always thought Porsche gave this as it was an easy measurement for anyone to measure without other expensive tooling.

The other interesting thing was the dimension given for the overall height of the spring assembly. Another piece of information we have missed. I have only seen the installed height given as the spring height dimension, not including the upper and lower base and retainer.

We measure the retainer and base thicknesses and input these into our computer program. Having measured the Retainer height in the cylinder head, we know the total distance from the under side of the top retainer and the spring base. This is the maximum spring height possible. We input all the retainer heights into our program along with the cam information, any rocker ratio, lash required and the number of valves and cylinders to be tested.

Then one at a time we compress each spring with its retainer and base attached to coil bind height and the program shows a linear graph of the spring, force verses spring height. It gives us a read out every increment from 0.010” to 0.050” depending on how much info we want to see. With the installed force we want programed, this program gives us the height the spring needs to be installed at to achieve this seat pressure. It also gives the open pressure, coil bind distance, spring rate, clearance to coil bind and the shimming required to obtain that seat pressure and the possible lift that can be used. The linear graph immediately shows up any bad spring throughout its compression and allows us to match new springs into sets. Not all springs are equal. Its not just how much pressure is generated at open and closed numbers. It’s also about how the spring appears throughout its complete compression. Sometimes you will see bumps and dips in the graph, showing some manufacturing or extended use issues.

It needs to be understood that the seat pressure or closed pressure required is all based on the valve seat width and valve diameter. It has nothing to do with anything else. However, many increase this in error to mask the harmonics and poor control built into bad cam profiles. The open pressure is all about the engines’ ability to sustain control over the valve train weight at RPM.

Each cam profile may require the spring set up to be different. Lift numbers change the clearances. There are two clearances to be aware of. One is often forgotten. The clearance or distance to spring coil bind and the distance from the underside of the top retainer/locks to the guide seal.

We have already done the calculations in another program that tells us the forces required, both the seated and open forces for the Intake and Exhaust springs. Now we have an installed height and the shimming required. Then it’s simply an assembly task, adding the correct number of shims, the base, the spring, correct installed way if progressive, the Top Retainer and then the locks.

The last task we do is to repeat the vacuum test and make sure the valve is sealing.

We record all the dimensions and print out the reports for any of the programs used and these are filed in the build file for each engine. In the case of the springs, if the customer chooses to change the camshaft, we can quickly find out the new clearances that will result in any change in lift. In some cases, a difference spring will be required, maybe a different offset in the Top Retainer or base and or the locks. The platform in the head have been known to be machined as well to gain height and clearance, or the valve changed, and the lock position moved up towards the valve stem tip.

This is how we do this task. Others do it differently and how, they believe is the right way for them.

I saw nothing in the video that I would consider wrong. Some may say our way is wrong or too much and over the top. It comes down to each asking what is required, and what information do we want to know?

[Helix8]

Neil,

Happy New Year. I enjoy reading your posts and look forward to seeing more in 2023. All the best.

[Alan L]

Hi Neil,
Interested what vacuum readings you consider acceptable.
Regards
Alan

[Neil Harvey]

Originally Posted by Helix8

Neil,

Happy New Year. I enjoy reading your posts and look forward to seeing more in 2023. All the best.

Glad to give back in any way I can. I may add more to this with some added info. It doesn't matter what type of cylinder head you are rebuilding, the basic requirements are the same. The difference may be dimensionally, but the procedures are the same.

Having tooling and machines that make the work easier and quicker pays off when you are rebuilding 4V engines with many cylinders. V10 and V12 4V engines add time but the exact same work is required with the Porsche 2V heads. Just more parts to deal with.

I enjoy watching how others do certain procedures. You often learn something and compare tooling etc. We invested in machinery and tooling to make our work easier and more accurate. But its about keeping that machinery in good working condition so accuracy is achieved.

I question how we do things often, but it always comes down to how you were taught. What is considered important and what you are trying to achieve. The performance in any engine comes from the Cylinder head. Shame, many do not know this and "short cut" the work just to get it out the door. The customer just sees clean heads and assumes all is right.

The devil is always in the details.

[Neil Harvey]

Originally Posted by Alan L

Hi Neil,
Interested what vacuum readings you consider acceptable.
Regards
Alan

The machine we have that cuts the valves seats has a vacuum gage. It's dial has a green segment that starts at -0.7b. Typically, with Porsche 2V valves we see -0.75+--0.80b. A good sealed seat is considered in the "green".

You can tell a well cut seat and valve on how the gage reacts to applied vacuum. It pulls a vacuum very quickly and the needle in the gage quickly goes into the green.