Valve spring pressure - Page 2

Neil Harvey · 12-03-2018, 07:55 PM

Quote:

Originally Posted by Trackrash

So, from your chart the installed seat pressure is 60 -65 lbs?

Yes.
You would add shims to obtain the required seat pressure. But, you have to measure the actual retainer height of each valve, then use this as the measured installed height. From this you shim so all seat pressures are the same. I used the 34.50mm as it was asked at this height.

Neil Harvey · 12-04-2018, 06:45 AM

Something I think I should add here. Valve springs should never be installed on their installed height, rather on their measured installed pressure.

Springs sag over time, along with other factors and the aim here is to put the same amount of pressure on each valve to seat when closed and the same force over the nose of the cam on opening.

Typically, the springs are "over sprung" for most applications. I think this is done for many reasons, the main being nothing is ever measured and "its safe" and wont be a problem. True enough, but your engine has to turn against this added un needed force and when you make 180- 250 BHP, you are giving away free HP.

bdonally · 12-04-2018, 02:07 PM

Just to make sure I am clear on the data presented, is the 1.358" (34.5mm) dimension is as shown here?:

Neil Harvey · 12-04-2018, 04:23 PM

Yes.

bdonally · 12-07-2018, 02:00 PM

Ok got a set of stock springs.
Measured a few of the retainers and seats and found some variance, so used one set for checking the springs.
Based on 5 springs checked so far, I get results similar to the info posted by Neil, using my at-home tester:

Then I took everything to a local engine shop and borrowed their little Intercomp tester and checked each spring/retainer/locator assembly, determining the installed height to achieve both 60 and 65 pounds. Based on the 65 pound reading, I added 11.5mm to get the valve open force.
Interestingly, there is 0.5mm of variation in the height to achieve either of the loads - I guess that is why measuring is a good idea, although based on the spring rate 0.5mm amounts to only about 6 pounds.

The force increase as 11.5mm lift is consistent at 140 pounds.
So all is good EXCEPT that the installation heights using 65# result in a spring height(for comparison to the Porsche spec) of 35mm; 60# is 0.4mm more.
If I shorten the installed height to 34.5mm, the force will be 72#.

Given this is a more or less stock engine, probably the spec height is OK but there has been discussion about these forces being on the high side, so my dilemma is what height ( or, really, what installed force) to use.

On a side note, the "racing" springs that were installed be a previous owner are, as in my earlier emails, very strange and I cannot fathom why they were ever made, much less purchased and installed. They have a 15% lower spring rate than stock, but are much longer, so that even with a minimal thickness locator the installed force is 125# or so. The force with the valve open is 45# higher than stock, but since the spring rate is lower, the increase in force as the valve opens is 125#, 15# lower than stock, so the higher open force is achievedby increasing the installation force by 60 or 70 pounds. Seems goofy.
Especially since the increased forces are likely, upon reflection, the cause of the IM gear failure.
And especially because it has stock cams.

Anyway, any input regarding the installation force will be appreciated.
FWIW, as mentioned earlier, the motor occasionally runs up against the rev limiter at 6800 RPM.

racing97 · 12-07-2018, 03:15 PM

Now that you have the parameters of installed height and load you may want to take note of how much lift your spring will tolerate before solid height comes into play.

regards

bdonally · 12-08-2018, 11:23 AM

Quote:

Originally Posted by racing97

how much lift your spring will tolerate before solid height comes into play.

Yeah - I have 2.5mm +/- before coil binding on the intakes.

How many shims are normal? I am shimming 2 to 2.75 mm, so quite a lot of shims.
The valve length (projection above the head) is all within spec.

I've decided to set the installed height so that the force at 11.5mm lift is targeted at 205#, and let the force when the valve is closed to float. This approach results in the closed force to be 59 to 65# and the installed spring length 34.5 to 35.3mm.
I noticed a small but repeatable difference in the spring rates, ranging from 313 to 320 lb/in; this approach compensates by setting the fully open force.

lvporschepilot · 12-09-2018, 06:03 AM

General rule is to defer to the slightly higher pressure and/or having a 5-10% additional force as insurance for overrevs

Neil Harvey · 12-10-2018, 03:19 PM

If you set your springs up equaling the nose pressures, that is Ok too. Just a little harder often when you are dealing with stock springs. Just make sure you have enough on the seat too.

Cam design, engine use, seat widths etc., all dictate the seat pressure. Nose pressure is about engine RPM, valve train part weights and cam design.

Be careful here. Just make sure you know the weights involved as well as the cam design. If the cam design is a copy, make sure its a good copy as this can have detrimental effect on the valve control over the nose and back onto the seat.

Setting up the valve springs is not just about sticking 3-5 shims under the spring base and forgetting it. Unfortunately this is common practice in the production head repair business.

bdonally · 12-10-2018, 03:44 PM

Quote:

Originally Posted by Neil Harvey

If you set your springs up equaling the nose pressures, that is Ok too. Just a little harder often when you are dealing with stock springs. Just make sure you have enough on the seat too.

With the stock springs I have, If I set them to 34.5mm, the seat force is 61 to 71 and the over the nose force is 205 to 215.
Working with 0.25MM shims, I can get the over the nose force to be 205 to 208, with the seat force 61 to 65.
Or I can add force in 3# increments using 0.25mm shims.
Question is whether 205 over the nose is enough with stock cams and valves, and 6800 rpm redline. Seems to me that it should be OK as the forces are in the range that using the 34.5mm spec would achieve.

Quote:

Originally Posted by Neil Harvey

Be careful here
Setting up the valve springs is not just about sticking 3-5 shims under the spring base and forgetting it. Unfortunately this is common practice in the production head repair business.

Understood. ON the other hand, I suspect the springs in my engine are now the most-studied stock springs ever:-)

Neil Harvey · 12-10-2018, 04:05 PM

That is good. Well done.

I am pleased to read about someone who has taken the time and care to do this correctly.

Its a shame that many in the head repair business don't.

Trackrash · Trackrash's Garage

^ Agreed.

I should add that I discussed this topic with my cam grinder, John D, and followed his advice on my spring pressure.

I wonder how many builders actually measure the valve's installed height or the spring height for that matter.

racing97 · 12-10-2018, 05:41 PM

Gordon you did the right thing talking to John

safe · safe's Garage

Quote:

Originally Posted by bdonally

With the stock springs I have, If I set them to 34.5mm, the seat force is 61 to 71 and the over the nose force is 205 to 215.
Working with 0.25MM shims, I can get the over the nose force to be 205 to 208, with the seat force 61 to 65.
Or I can add force in 3# increments using 0.25mm shims.
Question is whether 205 over the nose is enough with stock cams and valves, and 6800 rpm redline. Seems to me that it should be OK as the forces are in the range that using the 34.5mm spec would achieve.

Understood. ON the other hand, I suspect the springs in my engine are now the most-studied stock springs ever:-)

Interesting thread.
Stock springs are fine on a 3.2 to 6800, with both stock cams and slightly hotter like the DOUGHERTY 993SS.

I bought some aftermarket "sportier" springs for my 3.6. I measured these carefully, height and pressure. I arrived to the conclusion that the supplied information on spring height was spot on and very equal among the springs.

bdonally · 12-17-2018, 11:53 AM

Spring installation is finished, heads given a light spray of WD40 and bagged til spring.
Thanks for all the input - it has been an instructive project.
At the end, I shimmed the valves targeting a fully open over-the-nose force of 205# at 11.5mm lift.
The results are the force ranges from 205 to 208. A 0.25mm shim increases the force by just over 3#, so this was as close as I could get.
The closed seating force ranges from 60 to 65. Essentially any differences among the spring assemblies is taken at the seating force.
Of course, the exhaust valves only open 10mm, so the forces on those are lower - 186 to 189 over the nose.
Interestingly, the above resulted in the spring height, specified at 34.5mm, being between 34.5 and 35.2. If the springs had been installed at 34.5, the forces would vary spring to spring by 8.5#, compared to the 3# I achieved by measuring each spring.

It seems to me that for a more or less stock engine, in particular with stock cams, the variances outlined above are not enough to compromise the performance.
No reason to not go through the exercise, though, other than it was a lot of work.

I'd be interested if there was any data around that showed the torque required to turn the cam versus spring pressure.

Otherwise, seasons greetings to all, and thanks again.

Walt Fricke · 12-18-2018, 11:57 AM

Bob - I've tried to find the orange strain gauge/fish scale/whatnot in the measuring setup you pictured earlier, but couldn't. Any idea what brand it is? Some guys use old style analog spring fish scales to measure ring tension by pulling a piston through a cylinder, but nothing I found is set up for the forces you measured.

The setup looks like it is within my goober welding abilities to fabricate.

I think a lot of us would be interested in any answer to your broader question about quantified parasitic drag. I think minimum or nearly so rates for the job should have benefits in reduced wear. But in an assembled engine, when one lobe is acting as a lever resisting crank rotation, another one somewhere is pushing in the opposite direction due to its spring. No free lunch, but perhaps just analyzing a single lobe might not give the whole story?

bdonally · 12-18-2018, 05:37 PM

Digital Scale,Klau Portable 150... https://www.amazon.ca/dp/B07BHPDSKR?ref=yo_pop_ma_swf
Amazon Canada but should be on Amazon.com.
Here's some notes in case you are making something similar - there are a number of areas that could be improved, not the least of which is the build quality. TRhe base is 1-1/2" x 0.10" tube - but could be anything.

About driving the cam, I don't think the forces balance out but I think it would be interesting to check the torque when I put the motor back together.

Walt Fricke · 12-21-2018, 02:40 PM

Thanks, Bob

I don't know how pressing down on one lobe while pressing up on another works out quantitatively over 12 lobes. But I do know that things are more likely to stay put with all the springs in. This manifests itself in doing leakdowns - the tested piston stays at TDC and the air pressure doesn't make it rotate - and setting cam timing - loosening the locking nut or bolt doesn't result in crank movement. While I time my cams with just one rocker in place for #1, and then just one more for #4, when retiming with all rockers in to fix some issue I have been amazed at how stable things are. I've fixed untightened 3x6mm bolts holding the aluminum annulus holder part without having to retime the cam. I had checked before and after, and no change.