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Valve spring compression results, I need help confirming results

Help! I just checked all my valve springs at work today on an Instron 3700 series tester (great piece of equipment) and would like anyone's help with confirming my data. I am going off of Bruce Anderson's 911 Performance Handbook, page 115, checking all the valve springs before installation. (Quote) First, check the spring pressure at 30.5-31.00 mm (1.201-1.220 inch) which will simulate the spring in the valve open condition. The pressure should be 80kp (176.4 lbs). Next, check the spring pressure at 42.0-42.5 mm (1.6535-1.6731 inch) which will simulate the seat pressure; the pressure should be 20kp (44.09 lbs). My data on the low end of these measurements is not on these values but still within my range, is this acceptable? I am building a 3.2l with Euro compression. Thank you all!

"W" Exhaust
Seat Pressure @ Open Condition @
0.207 in 0.227 in 0.660 in 0.679 in
(lbs) (lbs) (lbs) (lbs)
Small Valve 44.90 49.93 177.70 185.30
Large Valve 43.59 47.72 172.90 179.70
Average 44.25 48.83 175.30 182.50
Should be 44.09 lbs 176.4 lbs


"Z" Exhaust
Seat Pressure @ Open Condition @
0.207 in 0.227 in 0.660 in 0.679 in
(lbs) (lbs) (lbs) (lbs)
Small Valve 42.38 47.84 174.40 181.60
Large Valve 42.16 47.61 172.50 179.80
Average 42.27 47.73 173.45 180.70
Should be 44.09 lbs 176.4 lbs


"Y" Exhaust
Seat Pressure @ Open Condition @
0.207 in 0.227 in 0.660 in 0.679 in
(lbs) (lbs) (lbs) (lbs)
Small Valve 41.97 47.43 174.60 182.00
Large Valve 40.70 46.57 171.80 178.60
Average 41.34 47.00 173.20 180.30
Should be 44.09 lbs 176.4 lbs
__________________________________________________ _

"B Exhaust
Seat Pressure @ Open Condition @
0.207 in 0.227 in 0.660 in 0.679 in
(lbs) (lbs) (lbs) (lbs)
Small Valve 42.16 47.74 177.80 184.30
Large Valve 45.27 50.39 179.70 186.30
Average 43.72 49.07 178.75 185.30
Should be 44.09 lbs 176.4 lbs


"C" Exhaust
Seat Pressure @ Open Condition @
0.207 in 0.227 in 0.660 in 0.679 in
(lbs) (lbs) (lbs) (lbs)
Small Valve 42.37 47.66 175.60 183.00
Large Valve 43.03 48.91 177.70 185.30
Average 42.70 48.29 176.65 184.15
Should be 44.09 lbs 176.4 lbs


"D" Exhaust
Seat Pressure @ Open Condition @
0.207 in 0.227 in 0.660 in 0.679 in
(lbs) (lbs) (lbs) (lbs)
Small Valve 44.21 49.59 179.80 187.10
Large Valve 43.19 48.73 177.30 184.60
Average 43.70 49.16 178.55 185.85
Should be 44.09 lbs 176.4 lbs


Thanks for your help and Best Regards, Alex

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Old 02-09-2005, 09:39 PM
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Valve spring check

Alex;

I can't tell from what you wrote but:

Be sure that you check the valve spring compression numbers with the spring seat installed on the bottom of the spring pair and the spring retainer installed on the top of the springs. While this proceed is not explained carefull in either Anderson's or Wayne's otherwise excellent books it is cleared layed out in the factory shop manuals.

Needless to say adding the retainer and seat will raise your values a bunch over testing a bare spring pair.

Good Luck
Scott
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Old 02-11-2005, 12:08 PM
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Scott,
Correct me if I'm wrong, but valve spring specs are usually measured w/o the retainer or spring seat included in the spring height.

Alex's valve springs look pretty close to spec.

Sherwood
Old 02-11-2005, 12:25 PM
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Gentlemen,

Thank you both for your help, I performed the test with the springs in there upper and lower retainers plus I made certain the inner spring was properly seated. I did this after carefully looking at the picture in Anderson's book, it showed the lower retainer in place and I could not identify if the upper was there. I had to guess a few things, for example, I measured the overall length of the spring/retainer assembly (1.880 inches) then subtracted the specified test compressions from the book (1.201-1.220 inches for valve open condition tests and 1.6535-1.6731 inches for seat pressure condition tests) to determine the delta (difference) test compression values (1.880-1.220=0.660/1.880-1.201=0.679;these were my compress to values for the valve open condition test and the same approach for the seat test but subtract the 1.6535 and 1.6731 to get my other compress to values), in simpler terms…how far down to compress the spring if the top of my spring/retainer assembly was ‘zero’ reference point. It did come out very closely to factory specifications but I wanted to be certain that I did it right. My big concern was on the low end of the tolerance, a few were just below but the designated value but it was clearly within tolerance if I compressed towards the nominal or upper specification. I'm going to try to upload my excel spreadsheet again for a clearer view. Thank you both for time and support. I still am a bit confused and I'm not certain if I need new ones because of the lower end tolerance values measured.

Best Regards,
Alex
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Old 02-11-2005, 04:53 PM
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just as a reference, Smart Racing race srpings have 120 lbs seat pressure.

Jim
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Old 02-11-2005, 08:45 PM
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Alex;

After only a casual inspoection of your data and reply it look sto me like you did everything correctly according to the Factory Workshop manual and your values are indeed just at the lower end of the allowable range.

Sherwood;
I just double checked my factory workshop manual. It very clearly shows that the measurements refered to in valve spring checking are including both the upper and lower retainers. Obviously checking only the spring will give substantially lower readings (ask me how I know). Having recently performed this check myself I was surprised that all me springs were shot so badly untill I checked THE book. After adding the retainer and seat ......bingo! So I thought perhaps Alex made the same mistake.

Scott
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Old 02-11-2005, 09:59 PM
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Scott,
I was looking at the repair manual and indeed, it says:

"Test on a valve spring tester together with spring support (valve spring retainer) and valve seat." (valve spring seat).

However, it seems curious to me why they would include the retainer and spring seat in the valve spring pressure equation.

The spec is to compress the spring assy. to various lengths (as you did) and check the spring pressure. However, what if the retainer and spring seat thickness vary in thickness (as in using aftermarket valve spring retainers?). I would think any plus or minus deviation from the factory retainer thickness would yield different valve spring pressures at each of those compressed heights.



For example, if an aftermarker retainer were thicker than the factory retainer, then the valve spring would be compressed further than normal, resulting in a higher spring pressure at the standard "B" spring testing height.

And conversely, if the retainer was thinner; the valve spring would be longer at each test height and tension would be lower than spec.

Just curious,
Sherwood
Old 02-12-2005, 12:33 AM
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I love this site! Thank you all again for the additional information and feedback. The example was fantastic also. Can I ask for vote on what everyone would do with my springs, I only provided data for one set of heads, the other data was slightly better so I did not post it. I interpret my springs to be still usable, any advice or recommedations?

Thanks,

alex
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Old 02-12-2005, 08:42 AM
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Sherwood;
Re: Your question as to why the factory would include the retainer and seat. I dunno? But I'm pretty sure Porsche didn't bother considering the what ifs of using non standard seats or retainers becasue they didn't need to. They were writing a manual to help us repair engines to stock conditions. You are of course correct that any variation in those parts' thickness's would affect the spring load.
If I recall my physics correctly; coil springs have a linear compression rate. In other words F=Kx where F is the spring force, K is the spring constant and x is the displacement of the spring so one could calculate the change in spring force due to a change in x pretty easily. We could calculate K from the factory data.

Alex:
I am not knowledgable enough to offer much guidence to your question of: Should you use your springs or not. However it should be pretty easy to shim them back into spec especially since yours are just at the low end of the range. Notice that there were several shims under the spring seat when you disassembled the head. These were to adjsut the installed height of the spring and can be used to adjust the initial spring force too. All you have to be concerned with is not running into coil bind.

Hope this helps.
Scott
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Old 02-12-2005, 02:52 PM
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Scott,

Thank you sir, I did find 5-shims where you said. This is my first rebuild at it's very exciting but I want to proceed with caution with doubt arises. Thanks to everyone!

Best Regards,


Alex




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Old 02-12-2005, 03:32 PM
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For me this shouldn't even be an issue. Valve springs do weaken over time especially with an air-cooled engines rapid heat cycles.

I would never consider shimming a used spring to spec back to what pressure is needed. New stock or upraded performance valve springs are cheap by comparison to other parts in the engine assy. Yet if they fail the results are catastrophic.

On any performance engine where the rebuild was even just a freshen-up I still replace the valve springs. It's just good insurance for a happy engine.
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Old 02-13-2005, 07:57 AM
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asphaltgambler,

Your point is very well made; this engine already had one catastrophic failure already when I bought it. I agree that it is not worth the risk again. Thank you for your time. I've been looking at street performance springs with about 100-lbs at .50 inches, what do you think?

Best Regards,

Alex
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Old 02-13-2005, 08:40 AM
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I'm fairly new to the p-car scene so it took some time to sift through all the ad hype. I found John (the camgrinder) to have an excellent reputation and knowledge.

He sells camshafts and spring kits. Contact him through here and ask his reccomendation. I think his prices are very competitive.
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Old 02-13-2005, 08:47 AM
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Do not shim to set valve spring load! Shim to meet the installed height spec. If the springs are well used, even if in spec, I would suggest replacing them. Why? Because springs have a limited lifetime in the number of cycles thay can survive before breaking. Used springs have undergon a largeand unknown number of cycles. Therefore replace them, they are relatively inexpensive.
Old 02-13-2005, 08:56 PM
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Thank you Snowman,

I have decided to replace them, thank you for your time and feedback.

Best Regards,

alex
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Old 02-13-2005, 09:56 PM
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