Installation length of valvesprings?

[Hebster52]

Now trying to figure out the Installation length of Valve Springs.

The heads are marked 7/68 and 8/68. Valve lengths are around 113,5-114mm which would point out the engine is a so called 911 T 1969? According to this the valvespring length should be 36,0 +-0,3.

The -68 and earlier should have 35,0 +-0,3 according Wayne's book. Those should on the other hand have shorter valves? (111,15 - 111,75)

Is there any differences in the rockerarms etc. in the two mentioned above? How can I verify what is correct?

[Walt Fricke]

Rockers are all the same dimensionally.

The springs are all the same, so valve length is immaterial, really.

The shorter the installed height, the more seat pressure (and full open pressure) there will be.

Differing valve stem lengths would only affect how many shims you use to get a given installed height. It is really the cam you are setting the installed height for.

[Hebster52]

Ok. So as long as I keep the installationlenght within the specs for the valvelenght it will be good as this is going to be a stock 2,0L T-engine?

[Walt Fricke]

Well, that's what I would do. But maybe one of the professional engine builders will chime in.

Did you measure installed height as you took the heads apart? Or note how many shims went with which valve so you can go back and measure that?

[Hebster52]

Ok.

No, couldn't measure as the engine and heads was allready taken apart when I bought it. All the parts I have are form the original engine though. The valve seats etc. have been reworked anyways.

Thanks!

[Walt Fricke]

Right - cutting the seat will raise the valve. Cutting the valve will raise the valve. Hence the need to check to see if more shims are needed.

[Hebster52]

Yes, first checked that the valveheight still was within tolerance. (measurement from springseat bottom to top without shims etc.)

[racing97]

If I had no instructions I would start by installing a retainer and keeper on a bare head no shims or spring seat installed, then using a vernier from the top of the retainer to the bare head at the spring base, this will be compromised by the angle somewhat but will work and this will be the
installed height no matter what. Next take the entire spring and base package to a vise and compress it to the dimension from the head. The important spec is where the spring is compressed to solid height you will always want to be 1.25 mm from total compression.
Measure the cam and subtract the narrow from tall and multiply by 1.42 the rocker ratio, compress the spring this dimension from the installed height (first measurement) and take up the difference less than 1.25 with shims.

Well nobody answered and you asked