Valve spring tension - advice required please...

[Jimmy]

Folks

What spring tension should I expect from a brand new set of dual springs for a 68 911T part number 901 105 901 51.
I have been told the springs now tested are out with the required specification and would need shimming though would prefer another set. I don't have my manuals to hand for me to reference spring compression distance / weight, what should they be? Is this common?
Advice would be appreciated.


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Jimmy

[haasad]

The spring tension is actually a weight that they compress a given amount for when it's applied.As far as I recall the shims under the spring base are for setting the correct height for assembly. Adding shims does not compensate for worn out valvesprings. It's common to replace valve springs when rebuilding. Make sure to note that on dual spring set ups the assembly has the coil wind direction opposing for the pair.
Happy to be corrected. Just refreshing my 911 motor knowledge in anticipation of some projects.

[fetuhoe]

You need to set the spring into a standard base and use a standard retainer.

The force displacement should be as follows;

B = 42.0 to 42.5mm Force = 196 Newtons

B = 30.5 to 31.0mm Force = 795 Newtons (Equivalent to 11.5mm Inlet Valve Lift)

B = 31.5 to 32.0mm Force = 735 Newtons (Equivalent to 10.5mm Exhaust Valve Lift)

The Outer spring is progressively wound and the closely wound coils should be installed on the cylinder head side which is the spring base.

These measurements are applicable to all dual springs as there is no difference in any standard 911 spring from 1965 to 1989 other than the 'Single' 911T Springs.

The installed length does change depending on the engine type and the Model Year.

The installed length of the spring for a 1968 911 T using Dual Springs Should be 35.0mm +/- 0.3mm (Dimension A). This is correct for both Inlet and exhaust



This is the length that is adjusted using shims. It is not necessary to check the installed height of the inner spring which is not wound progressively.

[haasad]

Much better description than mine ....

[haasad]

Much better description than mine ....

[Jimmy]

Very appreciative of both replies - thanks guys.

So, the springs removed from my car were singles, I bought replacement dual springs (new) as one single spring was out of spec. Having tested the new dual springs, these are all out of spec. ~2mm shorter than the originals and not applying sufficient force, adding shims onto the spacers doesn't seem right. I will give up on the replacements and will buy Kent springs matched to the engine needs. The car is a 'T' it now has the S Mahle pistons and cylinders with a hybrid E (ish) cams.

Thanks again

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Jimmy