Since some of you guys have Ls3's, a figured Id have better luck posting here instead of the c5 section. Maybe a couple of you might even have this same valvetrain.....

Any help is appreciated. This is a 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 an intake valve, from a broken outer valve spring on #2 cyl. I was 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.

 

all the installed height determines is the spring load on the seat. at 1.835 installed height you will have approx 129 lbs of force on the valve seat. most would just install the springs and not give it a thought, your 1.960 seems like a lot. was the spring sitting right on the head? stock is 1.800 you could put a .090 shim under each spring, but dont over think it, it's not an indy car.

http://www.kmotion.biz/instht.htm

 

I got into trouble once with a height mic , because the top had 3 different levels that different diameter retainers would set in . This led to the mic reading being a direct read out in only one position.

Something to check .

If the measurement is correct ; you need to shim.

 

I will give it a shot for you.

Ok so coil bind is 1.100, I like to be closer rather then farther from bind if possible so .060-.100 is a good area. That makes your stoping point at roughly 1.160-1.200. To make it easier lets just go with the 1.200 number.

Lift is .624 so add .624 to 1.200 and you get 1.824 minimum spring height which will give you the roughly 129lbs that is on the box for seat pressure.

You have a reading of 1.955-1.970 so you can either add the amount of shim(.130-.145) to get to the 1.824 number for 129 lbs or you can add less then that for less pressure.