If someone that has experience with this can help me, Id really appreciate it. This is a Camaro Ls3 engine, thats been swapped into a c5 Vette. I just bought this car a few weeks ago. The engine swap was done by the previous owner, and the engine mods were supposedly done to the Camaro (donor car), in 2010, by CBI Streetcars.

I bent intake valve on #2 cyl, from a broken outer valve spring,..... just while putting around town taking off from a red light. Started missing, ...and I had first thought maybe I'd fouled a plug or something. The inner spring (dual comp 926) kept the valve from dropping, BUT it must have floated a bit, and barely kissed the piston top.

I pulled the head and replaced the valve. Had the machine shop install a new guide (it got banged up) and check all the valves, while it was there. My bottom end wasn't hurt, thank goodness.

I also ordered a whole new set of Comp 926 springs (26926-16), and a new set of Ls7 lifters, ...not that there was anything wrong with the ones I have. Just want to do things right.

When I initially pulled all the valve springs, there were no shims under any of the seats. I want to make sure that the installed height is correct, on each one. I know theres some kind of formula used to determine what shims to use, ...but Im no engine builder OR math wiz.

Valvetrain is comprised of :

-Cam: 227/239 .614/.624 115 +3 (Vengeance Racing Stage 2)
-stock valves
-OEM LS7 lifters
-stock length 7.4" Comp pushrods
-stock 1:7 rockers
-Comp 926 dual springs with steel retainers.

This is a pretty dang basic valvetrain, so maybe you guys will know what specs to follow, right off the batt.

Spring specs, ....followed by space between seat and retainer, with valve fully closed, using a install height micrometer. They start at #2 exhaust, and move back. I need to figure out what the correct install height is, so I can use the right size shims.

New spring specs:


#2 exh.


#2 in.


#4 exh.


#4 in.


#6 exh.


#6 in.


#8 exh.


#8 in.

 

set them up at 1.800". That should give you roughly 135lbs of seat pressure. If true coil bind is at 1.100", your safety margin is 0.050", so your coil bind for you math will be at 1.150". your max valve lift is .624". 1.800" - 1.150" = .650" max lift that you can run. Hope this helps

 

Helps alot.....thankyou. The max lift advertised for these springs is .675" Does that change anything?

And how should I go about measuring? Do I set my micrometer at 1.8", pull the valve closed, and use a feeler guage to determine the shim I'll need?

 

You can measure that way to give you a quick value to start with, then install your shim/shims, and check like you are in the pics and go from there.

 

I think Im understanding this micrometer better.

#2 exhaust is showing 1.861", meaning I need a .061 worth of shim, correct?

Being that my exhaust on my cam is .010" larger...wouldn't that mean the install height would need to be more on the intake side?

 

Are you measuring the installed heights with the locators installed?

 

They springs are good to .675" but only if set up at 1.835" and using the manufactures .060" safety margin for coil bind. 1.160" coil bind -1.835" installed height = .675" max lift. some people use a .060" safety margin but most use a .050" safety margin. as long as the springs are new i see no reason to use a .060" safety margin .050" is what i always use with new springs. Keep in mind that the LS3 heads have a recommended install height of 1.800" not 1.835" so that will change things.

 

I have always measured the valve installed height without the locators installed. Then i measure the individual locator for each individual valve and subtract that number from the valve spring installed height for that given valve. When i measure and shim I treat each and every valve as if it were on a separate head. I'm sure not every one measures each and every valve on both heads but I do. What if you measured just one or two valves then shimmed all to right under coil bind. What if the manufacture had a tolerance in their machining of .010" or what if there was an error in machining and tolerances were way out .030" (or something crazy like that). I know that's why the safety margin is there but still could cause some issues in extreme circumstances.
I'm also a big fan of actually measuring for myself: the seat pressure @ given installed height, spring open pressure at max open and true coil bind height. I do this for each and every spring.

 

I think the reason your coming up with such high installed height is your not subtracting the thickness of the locator/seat. I think the springs you have come with a .060" thickness locator seat. Just turn it all into math and shim accordingly. FYI if ever needed, Texas speed makes some locators that are thinner (off the top of my head it think they are .030" thick).

 

We always measured every one, but there's no need to leave out the locators, it's just one less thing to mess with.


Since the thinnest shim is .015" the range that you can shim to is +/- .005", so it's not like you're going to shim within .001"

The 26926 springs really have too much open pressure for a daily driver using stock rocker arms. I've seen a few sets of damaged valve tips using the 26926 springs, stock rockers and .630"ish lift. That's why I recommend a spring with 400 lbs or less open pressure when using stock rocker arms. With that in mind, I wouldn't shim those springs any.

 

I can't tell from the pic too well, but make sure your retainer is sitting flush on the step inside the height checking mic. If you have interference with an inner step or something, it will be way off. The checking tools don't accomodate all the different retainer combinations out there.

 

An interesting day...... Maybe I can put this engine back together now?

I called Comp Cams today (since they made these springs, and ground the cam), and they said no shims are needed. Does the manufacturer really not know their ****?

Then went to the machine shop that replaced my guide, and checked my valves, .....and they said no shims are needed,.....ok.

Then, went by Thunder Racing. THEY said I need roughly .030" shims for ALL the springs, ...and these other guys don't know what they're talking about.

Also, BOTH the machine shop and Thunder Racing said that my measurements with the height gauge (pics above) are way off. A couple of guys at TR re-measured using my tool (yes, locaters installed, btw), but instead of centering the retainer in the tool, ...they moved the mic over slightly, to where the retainer was sitting up on the edge of the tool. They used their measurements along with my cam's lift specs, to determine that .030" shims would be good to use.

They said that shimming each springs differently (to the .010"), and testing each springs pressure at different heights, is something they only do with race engines. On a street car that doesnt turn more than 7k rpm, it's not necessary to do that. But that depends on who you talk to.

Jeez, I just want this thing to be right, and not break on me. I wanted a gen 4 engine because Ive seen stock ones take lots of abuse, and they make great power for a street car/highway cruiser, like this. I want to be able to bounce the rev limiter all day, if I feel like it (not that I would do that), and not worry about something breaking or letting loose. I sure am missing my turbo 6 cylinder toyota about now. It's stock, 18yr old (165k mile) long block and valvetrain, were rock solid.

 

It is VERY hard to tell from the photos, but looks to me like your spring retainers are sitting down inside the mic. It's too bad they make these things black because it's a bear to see where the retainers sit in a photograph!

They are supposed to sit on top of the top-most surface, which could explain why your heights are coming out too tall. Which lip are they sitting on? The very top or just on the inside?

I don't trust the off-center mic method to get the retainer on top because it may sit at a slight angle, giving you falsely tall readings. If your retainer is sitting at the next step down position, I would measure the step distance of the mic using calipers and subtract that measurement from what the mic measures in that position.

 

Seeing you are close to 1.960" there is 2 possible things here. Your on the second step of the tool, usually .100" step and do not have spring seats on the head, hence the extra .160" or you have a ls7 setup wich measures 1.960" from the factory.

PS #2 EX is 1.961" not 1.861".

Thanks,