ready to install springs and valves. when installing springs to spec. height what are the acceptable tollerances ? shims come .06, .03, & .015. and is it better to error on the plus or neg. side.

thanks.
mike

 

The install height has to allow for your max valve lift, AND provide enough spring pressure to seat the valve without bouncing. A lot of factors come into play like the mass of the valve and the ramp rate of the cam. If you're talking stock cam, then there is no problem with needing more pressure unless you've swapped to heavier valves.
Aftermarket cams usually have recommended seat pressures, so you have to pressure test your springs to see what install height gives you this minimum required pressure, and then measure to make sure they will not bind or allow the retainer to hit the valve seal or guide at max lift.

I'm not sure what you're running, but stock L98 heads & cam run with a 1.73" install height with only 70 lb pressure on the seat & no shims. That's very weak, but if you shim the spring you limit yourself too much on the lift capacity.
Unless you had the spring pads machined down quite a bit then you probably will not want to shim a stock type spring for an aftermarket cam.

Oh and it's usually better to error on more clearance before bind, so that would mean thinner or no shim. As long as the pressure is enough you're fine without shims. If you're running aluminum heads, then you have to run a spring seat or cup to protect the head. Again I don't know what you have.

 

im usins a set of 441 casting 350 heads they have been previously machined for screw in studs, guide plates, positive type seals, ported and decked. i want to use comp cams xe268 grind, 12-242-2. i also purchased new springs and lifters installed height of 1.7" all parts came with kit. im just learning head building and books have been ok but dont go into much detail so all the info you can give will be great. let me know if you need any more details ?

guess im going to have to buy one of those spring pressure dohickeys .

 

A machine shop would probably test one of your springs for free if you're nice.

The install height you get by mocking up a valve & retainer in the head and measuring it. It's not something you get off the box the springs came in or look up on the web.
It will vary due to any previous machining of the seat or spring pocket, and with valve length and retainer/keeper type.
It's pretty important to measure the height correctly to at least an accuracy of .010" so eyeing it with ruler is a poor choice.

Anyway once that is done, make sure the seal is in place and bottom the retainer against the top of the seal and measure that height. This is the heads lift limit.
When the shop measures the spring pressure, get them to tell you the bind height as well, so you know the springs lift limit.

Check your cam-card or the manufacturer. A cam like that usually specs around 110 lbs on the seat for the heavier 2.02 /1.6 valves people often put in 441 heads. If it specs a generic value of maybe 100 lbs on the seat then it's probably for the lighter factory valves. Valve weight matters for spring pressure. Heavier needs more pressure.

You say your cam & springs came as a kit, then that's good. All you have to do is install the spring at the required height by either machining the pockets, or more often using shims.
For a 1.7" height it's common to need a .030" shim, but you HAVE to measure to be sure for reasons stated above.

Is this helping?

 

thanks your helping alot. my previous post was short because i wanted out of the office to start that long weekend. heres the specs i have.

cam lift .477 / .48

springs, installed : 105 lbs @1.700"
open : 295 lbs @ 1.250"
spring rate : 417 lbs/in
coil bind : 1.150

i do have a spring height micrometer, example: when i measure a valve i come up with 1.89" that would mean i need .19" shim which means i need 3, .06 shims for a total of .18" .

am i thinking right ?

 

think i found what im looking for. went to comps web site and found an article on installing springs.

compcams.com/information/products/valvesprings/

thanks again.

ill be back with more questions before its all over.

 

Which valve spring height mic are you using? I'll bet it's the Comp Cams one, right?

Couple of things that lead me to this question..... it's damned near impossible to hit an installed height that tall in a SBC with stock length valves and the fact that not all height mics read accurately with stock diameter (1.25") retainers. Some units (like the Comp one) you have to subtract .150" from the raw reading to get the true installed height- and NO, they don't tell you this with the instructions for the unit.

You might want to go check for a post with a lot of replies in it by me (Damon) over on MontecarloSS.com a couple of months back. Something about valve springs, installed height, etc. I went 15 rounds with a guy doing this for the first time and I bet if you read the thread I'll answer 90% of your questions as well.

It all sounds so simple until you actually do it yourself for the first time, right?

 

I agree. His install height is probably 1.74 so he would only need one .030" shim.

Give the man a link so he can read your explainations.

 

Here you go:

http://www.montecarloss.com/ubb/ulti...329;p=1#000013

 

thanks. will read your post.

your right, it looked easy at first. but once i get through this first set of heads ( without destroying my motor ) i should have learned alot.

 

ok think i got it. ill try to lay it out as simple as possible for any one else who may try this for the first time. please comment on any thing i miss or that will make it simpler.

first thing that confused me was info that comes with springs (installed 105lbs @ 1.7") this is a referance of the pressure the springs have at 1.7" not the installed height you need.

1: install valves with retainer, keepers and spring height mic. record measurements for all valves. find smallest reading. this is the installed spring height for your heads.

tip: if using standard height mic and small retainers that fit into the mic and dont rest on top of it subtract .15" from your readings.

2: put spring in spring pressure tester and compress it to your reference measurement then record pressure.

3:now reference cam card and find recomended spring pressure. typically 110lbs. then add shim to spring and tester to get desired pressure.

4:now that you have the propper spring pressure for your reference valve add the required shim to your remaining valves to make up for seating differences.

this is a simplified example for a sbc head. there are alot of options for making up the propper installed spring height. to many shim washers is not good. from what i understand you can use options such as. spring retainer cups, thicker spring retainers, different length valves, larger springs ect.

hope this helps someone, i know i was confused as heck when i started, especially because instructions are non existant when you buy these parts.

 

Yep, you can also have the spring pockets machined deeper as well. This is a nice option because it allows you to run springs that handle more lift.
Also it's not required to run the same exact pressure on every spring. It is required that you allow clearance in the process. It is perfectly fine to run exhausts with less pressure on the seat due to the exhaust valve usually being lighter in weight. This can be handy when your exhaust lift exceeds the limit of a spring that has been shimmed to match the intake height.
It's also good to run a higher seat pressure on the intake valve when running boost. Generally if you make 10psi of boost, then you need another 10psi on the seat.
Remember that when you swap to larger size valves, springs, and retainers that you will need to increase pressure on the seat to control the heavier weight. Sometimes heavy steel roller rockers will also need more spring pressure to control.