spring height ?

[philippeF]

Hello again

another one, i've tried many solution to try to measure (accurately) the valve spring height, i'm not satisfied as i've found several values....
does any body here have a good idea to correctly set the spring height ?
thanks
Philippe

[cstreit]

Valve spring height tool works good!

http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911M&section=ENGwiz&page=3&bookmark=14&part_number=PEL-TOL-P228

[philippeF]

thanks Cstreit

you mean the "valve spring aduster", will it allow to find the right number of shims to achieve factory spring height recomandation ?

[cstreit]

It is my understanding that this tool allows you to measure the proper spring height easily. (Someone please correct me if I'm wrong, I have the machine shop do this for me)

Once you measure the "current height" you then compare it against spec to determine how many shims you have to add.

[stevepaa]

I tried using one of these on my 912 and worked pretty good. But the one I bought for the 911 had too much slop in it and was not correctly calibrated.

So I just made two height go/nogo gauges, one for intake and one for exhaust, from some 3/16 wooden dowel and that worked quite well.

[911pcars]

To measure the installed spring height, couldn't you just install the retainer and lock w/o the spring, then measure the space between spring seat and retainer, or am I missing something?

From my rapidly diminishing memory, I think the factory spec includes the height of the retainer. Please correct me if I'm wrong.

Sherwood

[philippeF]

i've tried without spring, there's too much clearance with the retainer to perform an accurate measurement...

[philippeF]

and... i don't really undestand (looking at the picture) how it works....

[911pcars]

"i've tried without spring, there's too much clearance with the retainer to perform an accurate measurement..."

Have you tried a lightweight spring for the measurement?

Sherwood

[TimT]

I believe the peilican tool has a light spring inside it.

the tool is a known height , it is used in place of a valve spring... the dimension in the "window" is added to the known height. Then shim calcs are done

I have used something like this for years, its a valve height micrometer. Replace a valve spring with this, screw it out until the valve is seated, and light resistance is felt, then directly read the measurement. Then calculate shim thickness requred.

[Henry Schmidt]

Cut a small piece of welding rod to the correct length and place it between the retainer and spring perch and if it fits tight you're close, if it's loose at a shim, if it won't fit in remove a shim. It's as easy as that. We have the tools and the rod method is faster and easier.
You should make a rod for each length you need.
Put a piece of tape around the rod to make it easier to hold.

[dweymer]

So what are the height specs for a 2.7? As I am going through the same thing right now.

[Henry Schmidt]

Spring height specs are based on cam profile not engine size.

A good rule of thumb is .070" from coil bind at full lift.

Take valve lift and add .070" and that will be the installed height. It will also give you max spring pressure for the given spring.

If you take this calculated spring height and check the pressure at the height you will have installed pressure.
Something between 60 and 90 lb will be normal.

If you add calculated height and valve lift spec that will give you pressure over the cam. I like to see somewhere between 230 and 260 lb.

Some of the new valve springs offered on the market today give you an over the top pressure of more than 300 lb. My feeling is 300 lb is way too much (high pressure generates friction= heat which adds to parasitic loss and excess wear). That is why we came up with a valve spring formula that gives us 80-90 lb of seat pressure and only 240-260 lb over the top even with high lift cams.

It has been my experience that if you use this method and the seat pressure is over 60 lb there is no need for special valve spring unless an RPM in excess of 7500 is projected.

[dweymer]

So if I understand this, for an sc cam:Intake=.450" lift, spring height should be .520" and Exhaust=.395" lift, height should be .465"

[Henry Schmidt]

I wasn't very clear with my description. You compress the spring to coil bind. Measure that amount , then add valve lift and .070" and the combined total is the spring height.

[dweymer]

got it, thanks Henry.

[philippeF]

thank you all, i know what to do right now...