For those with Early heads.....
10-06-2011, 10:56 AM
#1
Thread Starter
For those with Early heads.....
How many shims were under your large valve springs? i have seen one, or two and i even heard of 3!
machine shop is getting ready to assemble my euro heads.
just wondering,
:-P
Duc
machine shop is getting ready to assemble my euro heads.
just wondering,
:-P
Duc
10-06-2011, 11:08 AM
#2
Archive Gatekeeper
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Isn't there some installation height spec that the machine shop needs to know, in order to be able to actually measure how many shims are needed for each individual valve?
Installation height* = spring height at coil bind + safety margin of 0.040-0.060” + cam lift - thickness of spring perch
Installation height* = spring height at coil bind + safety margin of 0.040-0.060” + cam lift - thickness of spring perch
10-06-2011, 11:44 AM
#3
Installation height is directly related to the tip/retainer height as well as the actual tension of the spring. The tension of the spring is either progressive or... I think
It's progressive- meaning that you will be determining the shims per the open and closed tensions. In many cases you will wish to match up the open and closed tensions with the weight of the valve assembly.
Open is higher than close as I said because the spring when compressed is creating more stored force than when its less compressed. Hypothetically, you would be using shims to account and facilitate the open and closed numbers within the exact compression charts that normally come with springs.
It's progressive- meaning that you will be determining the shims per the open and closed tensions. In many cases you will wish to match up the open and closed tensions with the weight of the valve assembly.
Open is higher than close as I said because the spring when compressed is creating more stored force than when its less compressed. Hypothetically, you would be using shims to account and facilitate the open and closed numbers within the exact compression charts that normally come with springs.
10-06-2011, 11:46 AM
#4
10-06-2011, 11:47 AM
#6
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10-06-2011, 11:58 AM
#8
Too many shims will kill the cam, or destroy the hydraulic lifter. Too little will allow the valves to bounce.
10-06-2011, 12:46 PM
#9
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Page 27 of the 80-84 Tech specs book, bottom of the page, says installation height is 38.2 +/- 0.3 mm, both intake and exhaust for non-S motors.. Then there's more stuff on pages 28 and 29 for S motors, with changes in 1981 and 1982.....
DISCLAIMER: I have never held an 8V head in my hands, so take anything I say with a large pinch of salt to taste, and I especially have no clue about which valve springs you're actually using (sounds like multiple flavors between 1980 and 1983) Nor do I know what is the right measurement on a hybrid motor, or whether it's different from the stock spec. But I do know that you have to measure these things to be able to calculate the # of shims you need. Otherwise,
The machine shop oughta be able to do it right. Pay them for their expertise.
DISCLAIMER: I have never held an 8V head in my hands, so take anything I say with a large pinch of salt to taste, and I especially have no clue about which valve springs you're actually using (sounds like multiple flavors between 1980 and 1983) Nor do I know what is the right measurement on a hybrid motor, or whether it's different from the stock spec. But I do know that you have to measure these things to be able to calculate the # of shims you need. Otherwise,
Too many shims will kill the cam, or destroy the hydraulic lifter. Too little will allow the valves to bounce.
10-06-2011, 12:46 PM
#10
Thread Starter
talked to the shop, of course they know what they are doing. after he has checked each spring out etc, he will let me know what other shims, if needed, are needed.
10-06-2011, 12:52 PM
#11
I had assumed if you had brought the heads to somewhere experienced, that it would work out fine. As long as they do not hammer cold guides into cold heads like blind monkeys, I think you will be okay.
10-06-2011, 01:56 PM
#13
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I misread your first post- didn't occur to me you were just asking RE: natural variation in shim #'s that people have seen.
10-07-2011, 07:26 PM
#14
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There exists more shim thicknessees than what PET lists. Porsche seems to have decided years ago those two are enough to get height within specs but they themselves used several different thickness originally.