I've seen several threads over the past couple weeks dealing with people either just slamming on a set of aftermarket valve springs or asking about shimming springs etc., so I thought I'd post my method of assembling a head intended for performance use, more specifically setting spring pressures etc..

Why? Because even springs within a brand new set can have pressures that vary a few pounds and also no head will have all 8 valves with the exact same installed height. To make up for the variables you'll want to shim the springs to get the desired pressure. It'll help the engine run that much smoother and squeeze out another bit of HP

Installed height = distance from the spring seat to the
bottom of the retainer
Coil bind - the maximum amount a spring can be compressed
before the coils touch, and bind.
gross lift- measure of how far the valve will open including
rocker ratio

First you'll want to measure for coil bind. Stick the spring in a vise and compress it until the coils touch each other and measure the lenth of the compressed spring. Lets say it measures 1.500". Now add .100" clearance (many engine builders will use less, from .060"-.080"). So to be on the safe side, our coil bind will occur when the spring is compressed to 1.600" .

coil bind + .100" clearance = absolute max lift before bind

Now go to your cam card and find what the gross lift is (intake AND exhaust, most of the time they're different so you'll have to do the math twice ) . Let's say we're doing the intake first and lift with a 1.5 rocker is .500" ( if you've got 1.6 rr's divide .500" by 1.5 then multiply that number by 1.6). So take your gross lift and add that to the coil bind (1.600") and this will be your minimun installed height which in this case will be 2.110". If your installed height is less than this number, you will reach coil bind and break parts!!

max lift before bind + valve lift = minumin installed height

Now stick an intake valve in one of your heads and put a retainer and lock on the valve with no spring. Measure from the seat to the bottom of the retainer. Lets say it measures 2.500". This is your current installed height. Now you'll need to check the spring pressure. You can rent or buy the tool to check them. Use the tool and compress the spring to 2.500" and note the spring pressure. Lets say that it reads 120#. This is the seat pressure, or the pressure on the valve when it's closed. For a hyd. cam with stock lifters, 130 is a good starting point. So in order to get out 120# spring to 130# we need to put some shims under it to preload it a bit. Now compress the spring until the gauge reads 130# ( or whatever seat pressure you want to run) and measure the height. Let's say it measures 2.550" at 130#. Thats a difference of .050", so that's how much shim you need to put under the spring to get the proper spring pressure. Shims come in different thicknesses, .015", .030" and .060" so you'll put a .015" under it. Now put the shim on the head and the retainer and locks and measure your installed height again to make sure it's not lower than the minimum you calculated (2.110"). If it's not, then put your valve seals on and install the spring. Do this for all 16 valves. You'll never get them all perfect but you'll be able to make up for most of the variations in the parts.

inst. height - height required for intended pressure= amount of shim required


Keep in mind I just pulled the numbers out of my head.

 

thank you muchly, this will come in handy soon...


I've never seen the valve spring compressor/pressure indicator for rent before... is there a more accurate name for that tool?



also, if you need more height (ie. you have lots of lift, and stock heads say), what are your options? lets make a list, including what is feasible:

-retainers with .050" (or another value) offset, good idea, as hopefully you can do your measuring with your old stock retainers, then if you need others, you can go buy these...

-machining down the valve guides (may be done when machining for positive stem seals as well. is there a limit as to how much can be machined down?)

-machining the spring pockets, deeper/wider. is this a good idea?

- any others? I thought RB had a post a long long time ago about this, and there was another, something about shimming it one way or the other... I can't picture it right now...?

 

A quick and cheap way to check valve spring pressures at various installed and open heights is to get a run of the mill bath room scale. Put a pieace of plate steel across the scale to distribute weight, then put the scale on a drill press and use the head to push your spring down to the desired height and read the pressure off the scale. It worked great for me.

I wouldn't go so far as to say that evening up your spring pressures will make the engine run smoother. It's worth checking just because of factory tolerances suck. I wouldn't worry if your pressure's varry + or - 5 lb's. As long as you have enough pressure to fight valve float and you don't have any interference you'll be good to go.

Retainer to seal clearances can vary wildly from head to head, and even valve to valve. It seems that GM didn't pay much attention here because they had enough of a safety factor built in for the small factory cams. I've seen some factory heads that would hit the seal at .460 lift, and some that would clear .490, Measure for yourself and avoid a rounded lobe.

 

That's good information. One thing you left out is measuring retainer-to-guide clearance (with seal installed, if applicable). While most aftermarket heads have PLENTY of room in there even with the seal installed, most stock heads do not. It's not at all uncommon to run out of retainer-to-guide/seal clearance on a stock head LONG before you get near the spring's coil bind height. Much like approaching a valve spring's coil bind height, you want to keep at least a .050" safety margin beyond the cam's maximum lift between the retainer and guide/seal.

Also, reference should be made to using the same retainer and locks on a given valve OVER AND OVER AGAIN. If you start to play mix-n-match with retainers and locks on different valves you will get a significant difference in their actual installed height (+-.010" difference from one set to another not being uncommon). Once you have a set of locks and retainer selected for a given valve keep using it on that same valve- don't just throw all the parts in a box and then pull them back out randomly on reassembly.