Valve Train Torque
Thread Starter
Teching In
Joined: Jun 2011
Posts: 6
Likes: 0
From: Illinois
Valve Train Torque Have many of you torqued the stock valve train to 24 Foot Pounds and left it like that. Without doing the TDC / 22 lbft procedure. We set all mine at 24 and called it a day. So far so good. Having second thoughts now but wondering if other guys have left it like that and been fine
Stock 2000 LS1
799 heads
stock pushrods / rockers
Thanks
Stock 2000 LS1
799 heads
stock pushrods / rockers
Thanks
TECH Addict
Joined: Dec 2017
Posts: 2,177
Likes: 968
Only thing the TDC / rotate thing is for, is to make sure the valve spring pressure doesn't corrupt the torque measurement and leave the bolts loose. Not sure why those are called TTY; seems to me that around 20 - 25 ft-lbs is the normal-ish torque for that size as it is, can't see how 22 ft-lbs on a fine thread into aluminum is going to make em yield. Butt hay, what do I know...
I tighten them down by hand to compress the spring, then torque.works fine. If it is someone paying me and like a customer car I will roll the engine over and get it on tdc. Adjustable valvetrain of course it would be on tdc to set the valves.
Only thing the TDC / rotate thing is for, is to make sure the valve spring pressure doesn't corrupt the torque measurement and leave the bolts loose. Not sure why those are called TTY; seems to me that around 20 - 25 ft-lbs is the normal-ish torque for that size as it is, can't see how 22 ft-lbs on a fine thread into aluminum is going to make em yield. Butt hay, what do I know...
Torque is a crappy measurement of the bolt preload (very inaccurate and highly dependent on friction). Adding valve spring force to this inaccuracy only makes it worse. GM procedure tightens the bolts at TDC cylinder #1 and then TDC cylinder #6, i.e., set at TDC firing stroke for cylinder #1 and tighten specific bolts then rotate one turn and tighten other bolts at TDC firing stroke of cylinder #6. Those bolts tightened at each position are those on the cam base circle.
One of the many ls1howto short cuts is to tighten all at the same time and then rotate and check. Doing this doesn't account for static vs. dynamic friction so the bolts will always show tight, even though the actual preload may be low. In other words, if you tighten a bolt to a given torque and stop, it will take more torque to get it rotating again after which the torque will drop. You will see this with a needle torque wrench, not a clicker.
One of the many ls1howto short cuts is to tighten all at the same time and then rotate and check. Doing this doesn't account for static vs. dynamic friction so the bolts will always show tight, even though the actual preload may be low. In other words, if you tighten a bolt to a given torque and stop, it will take more torque to get it rotating again after which the torque will drop. You will see this with a needle torque wrench, not a clicker.
