Forgive me ahead of time but I've done a search and haven't come back with anything. I'm fairly mechanical and have adjusted valves on "old" small blocks as well as late-model LT1 cars but am new to LS1 mods. I have the C5 apart installing new valve springs as well as a cam. Here is the story on the cam ... it's a legal Pure Stock cam (IHRA Stock Eliminator) which means it has stock lift and stock duration. When I go to put the rockers back in how do I "adjust" them?

Thanks.

Scott

 

1/2 turn past 0 lash i think.

 

The valve train rockers are NON ADJUSTABLE!


The rockers sit on a pedestal and the bolt is torqued to (if I remember correctly 22 FT/LBS) Dont quote me on that torque value.

You adjust the lash with different length pushrods Its not really lash in a LS engine It's lifter PRELOAD.

MAKE SURE that you put the rocker stands/ perches under the rockers when you reassemble the valve train. If you dont you will bend ALL your valves.

Dont know what year C5 you have but, Have you considered up-grading your rocker trunions to the better heavy duty trunions?? The early stock GM Trunions are well known for puking out all the roller bearings.

Bill

 

Yep ... 22 ft-lbs.

 

Also when installing the rockers, the lifter for that rocker must be on the base circle when you torque it to 22ft lbs.

 

Write up located here: http://forums.corvetteforum.com/c5-t...e-pattern.html

 

That is a good write up, for Yella Terra rockers.
It's not applicable to the stock rockers.

The 22ft lbs has nothing to do with the preload, it's simply the torque spec for the bolt that holds the rocker to the head.

Scott, is the cam in yet?

You are replacing the pushrods, right?

If your new cam (are you sure the duration is the same as stock?) has the same size base circle......as the oem cam.....you just buy better stock length 7.400 inch pushrods and put it back together.

Do you have a pair of digital calipers?

Ron

 

this works great

http://ls1tech.com/forums/12334324-post12.html

 

Wow, I didn't know setting valves was going to be such an ordeal.

Ron,

Here is what my cam card from Bullet says:

Intake Exhaust

Duration at .050 196 207

Lobe Lift .2740 .2810
Separation 116 OP-CL OP-CL
Timing Events .050 -17 33 40.5 -13
Duration at .006 247 258
Gross valve lift .466 .478
Valve Lash (hot) .000 .000
Degree Intake Lobe to 115

I had to contact a GM representative (Mark Kent) to get the OEM cam numbers to get the car approved for IHRA competition so the lift and duration numbers have to be the same.

No, I wasn't planning on replacing the pushrods and no I do not have digital calipers.

Am I going to have difficulties? I'm still doing the disassembly and hope to install it one day this week but am in no real hurry.

 

As Ron said above, if the new cam doesn't have the same base circle as the stock cam, then it's best to check for correct pushrod length. You might need different length pushrods to provide the correct lifter pre-load.

The absolute best way to check is with a pushrod lenght checker tool. It's basically an adjustable pushrod for length to determine when zero lash is with the new valve train setup, and then you add the desired lifter pre-load to that measurement to get over-all pushrod length. There are hundreds of threads about how to this on the various LS and Vette chat boards.

 

So I'll need to call Bullet and see if the new cam has the same base circle?

 

That would be good to do. If the base circle is the same, then you have to worry about correct lifter pre-load because the same lenght pushrods can be used. That is if you haven't also changed something else in the valve train besides the cam.

 

That is for the adjustable rockers on the C3 style engines. you tighten the nut just until there is no play in the rod and then go 1/2 more.

 

Thanks. I'll call them Monday. No other changes other than PAC springs but they are OEM specs.

 

Yes, that's how I adjusted valves on my LT1s in the late-model Impala SS cars.

 

wrong!!!!!!!

 

What I do for my 68 mustang and 72 vette 454 is do the 1/2 past zero to get a baseline and then crank it up to get it warm. remove the valve covers and crank and let it idle. i then loosen each rocker until i just start to get a clack then tighten until the clack just goes away. then 1/2 turn tighter.

 

I would think this is a bolt in and go. I would strongly recommend hardened .080" wall pushrods. Stock length.

Bullet has done something with those lobe profiles to add power...otherwise, how would it make more power than stock? My guess is even though the timing numbers are stock, once the valves starts to open, they open it real fast.

I would just talk to Bullet and ask about the pushrod length etc.

Ron

 

Thanks Ron. I'll call them tomorrow. Pushrods would be cheap insurance since it's all apart now. Also, I have no idea what they do when they grind them ... the guy talks so quickly and in terms that I don't understand but he felt very confident that just from the cam (even with stock lift and duration) he could get 3 tenths out of it. I'm sure he, and the other cam experts at Bullet, have forgotten more about cams and valvetrains than I'll ever know.