Correct Rocker install
09-20-2012, 12:40 AM
#1
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Correct Rocker install Does anyone have a site or anything that explains correct way to install rockers on the ls1? The guys at TSP said not to do it the way my chilton manual says. Wondering if there is anywhere that explains how TSP says to do it
09-20-2012, 04:01 AM
#3
I have posted the pages out of the service manual several times for the stock rockers. Unfortunately the host for the files is gone and I need to upload to photobucket. I can do that later if no one else answers this.
PS: LS1howto doesn't follow the GM procedures for stock rockers and it is not correct.
PS: LS1howto doesn't follow the GM procedures for stock rockers and it is not correct.
Last edited by vettenuts; 09-20-2012 at 04:10 AM.
09-20-2012, 07:05 AM
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I'm just reusing the stock rockers. I talked with Tsp and he said I needed to get cam on base lobe then torque to 18 lbs and can't remember what else. Was just curious to see if there was anything out there to follow. Just didnt want to write it down while talking to him to make him wait.
09-20-2012, 09:11 AM
#8
If you don't turn the motor over, you are torquing the rockers when they are on the cam lobe which might have worked, but I like to torque them when they are on the base circle like recommended to get correct torque...but everybody has their way of doing stuff
09-20-2012, 10:05 AM
#9
09-20-2012, 02:18 PM
#14
TECH Senior Member
The cam turns once for every two crank turns... so you would turn the crank 360°.
The GM Service Manual specifies 22 ftlb on the rockers that are on their base circle
[ the procedure in the SM has you torque down the all rockers that are on their base circle, then it has you spin the crank 1 revolution, and then it has you torque down the other rockers (which are now on their base circles) ]
The GM Service Manual specifies 22 ftlb on the rockers that are on their base circle
[ the procedure in the SM has you torque down the all rockers that are on their base circle, then it has you spin the crank 1 revolution, and then it has you torque down the other rockers (which are now on their base circles) ]
09-20-2012, 02:24 PM
#15
TECH Senior Member
If a rocker bolt is torqued when not on the cam's base circle, the spring requires some force to compress it, this increases the thread friction which uses up some of the applied torque... so the actual torque on the rocker bolt will be less than the perceived 22 ftlb.
09-20-2012, 03:47 PM
#16
^^^^
THIS!
you have to be on the base circle....it doesnt necessarily have to have anything pointed at TDC... but you need to be on the base circle with the valve completely closed.
you can use the EOIC method to help you determine this
Exhaust Open = Intake Closed
Intake open = Exhaust Closed
and proper spec is 22ft-lbs
also, you need to know your approximate preload.
GM specifies approximately .080~.010 preload on the stock and cam
but it is not the same for all cam's and all lifters..
material of the cam will dictate a lot of what it should be.
most cam manufacturers will tell you to shoot for .020~.060 (because it is a different material than a stock cam)
most engine builders will tell you to be on the low side of that.
you can count turns from zero lash on your stock rocker to figure out preload.
bolt is an 8mm x 1.25
one full turn = 0.049212598 (I just round it to .049 for the sake of this operation)
if you get past 2 turns, you definitely need a shorter pushrod
in an ideal world, you want to be at approximately 1/2 to 1 full turn. (.0240~.0490).
you will also find, that with less preload, you will have a quieter valvetrain.(assuming you dont have a giant agressive cam like mine slamming the valves down anyways)
less preload also = less friction = more potential power(probably not a huge amount, only a couple of ponies... but every bit counts)
09-22-2012, 09:30 AM
#18
^^^^
THIS!
you have to be on the base circle....it doesnt necessarily have to have anything pointed at TDC... but you need to be on the base circle with the valve completely closed.
you can use the EOIC method to help you determine this
Exhaust Open = Intake Closed
Intake open = Exhaust Closed
and proper spec is 22ft-lbs
also, you need to know your approximate preload.
GM specifies approximately .080~.010 preload on the stock and cam
but it is not the same for all cam's and all lifters..
material of the cam will dictate a lot of what it should be.
most cam manufacturers will tell you to shoot for .020~.060 (because it is a different material than a stock cam)
most engine builders will tell you to be on the low side of that.
you can count turns from zero lash on your stock rocker to figure out preload.
bolt is an 8mm x 1.25
one full turn = 0.049212598 (I just round it to .049 for the sake of this operation)
if you get past 2 turns, you definitely need a shorter pushrod
in an ideal world, you want to be at approximately 1/2 to 1 full turn. (.0240~.0490).
you will also find, that with less preload, you will have a quieter valvetrain.(assuming you dont have a giant agressive cam like mine slamming the valves down anyways)
less preload also = less friction = more potential power(probably not a huge amount, only a couple of ponies... but every bit counts)
THIS!
you have to be on the base circle....it doesnt necessarily have to have anything pointed at TDC... but you need to be on the base circle with the valve completely closed.
you can use the EOIC method to help you determine this
Exhaust Open = Intake Closed
Intake open = Exhaust Closed
and proper spec is 22ft-lbs
also, you need to know your approximate preload.
GM specifies approximately .080~.010 preload on the stock and cam
but it is not the same for all cam's and all lifters..
material of the cam will dictate a lot of what it should be.
most cam manufacturers will tell you to shoot for .020~.060 (because it is a different material than a stock cam)
most engine builders will tell you to be on the low side of that.
you can count turns from zero lash on your stock rocker to figure out preload.
bolt is an 8mm x 1.25
one full turn = 0.049212598 (I just round it to .049 for the sake of this operation)
if you get past 2 turns, you definitely need a shorter pushrod
in an ideal world, you want to be at approximately 1/2 to 1 full turn. (.0240~.0490).
you will also find, that with less preload, you will have a quieter valvetrain.(assuming you dont have a giant agressive cam like mine slamming the valves down anyways)
less preload also = less friction = more potential power(probably not a huge amount, only a couple of ponies... but every bit counts)
09-22-2012, 12:49 PM
#20
unless you get a one piece billet cam, the material is softer than stock, so you want a little less preload to keep from putting too much pressure on the lobes causing it to wear out sooner...
and even a billet cam will take some damage from too much pressure caused by preload
many times its the worn out cam lobes that destroy a lifter and not the other way around.
not only that, but less pressure = less friction = more ponies free'd from their stable
Originally Posted by vettenutts
Counting turns without accounting for the rocker ratio and bolt turns to "bolt preload" will not provide the correct preload estimate.
to correct my math....
Rocker bolt gets you motion from thread pitch
so 1.25 thread pitch = .0492
then we take into account for rocker ratio
1.7 rocker ratio on stock rockers.. we need to know the inverse because our pivot is now essentially the valve stem
so, to get our new value, we need to add the difference back into our value
effectively...
.0492 + (.0492/1.7) = .078
so 1 turn = .078
still want to be in that .020~.060 range
so 1/4 to 3/4 turn from zero lash to 22 ftlbs