Would anyone be kind enough to make sure my lifter preloaded is correct or if I should get a shorter pushrod?

IM using ls7 lifters, 7.375 pushrods and stock rockers, on average, once I established Tdc and zero lash, it took 1&3/4 turns to reach 22 ft/lbs. Some rockers took a little more, some a little less.

 

What was the length of the PR checker @ zero lash?

 

I didn't use a pushrod length checker, I read a few different posts where people said to just find zero lash, then count the turns until you reach 22 ft/lb on the rocker arm bolt.

 

At 1 3/4 turns, your preload is at 0.1110 inch.

 

Thank you much, looks like I need a shorter set of pushrods

 

Maybe, but I think you will find a number of folks running that much preload with those lifters. The original calculation associated with that method (counting the number of turns to reach 22 foot pounds) lists (incorrectly) the preload associated with 1 3/4 turns as being 0.0823 inch. In any event, it reportedly works for some.

 

It's .082" so you're fine.

 

.047" of preload per turn?

 

Yes. Some people have argued that the number is different. But the bolt doesn't move down into the head fully as it is threaded in - which is their argument. The math of the thread is closer to .065" or something. There is preload on the bolt itself and it doesn't travel for the last third of a turn as the bolt stretches. So there is no additional movement at the lifter. It averages out to roughly .047" preload at the lifter per rotation.

 

The 0.111 inch preload is based on Vettenut's calculation:https://ls1tech.com/forums/15087505-post42.html.

Vettenut's calculation differs from the linear .047 method in two respects. One is Vettenut's recognition that 1/3 turn is associated with bolt stretch as opposed to preload. JakeFusion, based this and other threads (https://ls1tech.com/forums/showthrea...544&styleid=25) apparently agrees with Vettenuts on this fact. The second difference in Vettenut's calculation of preload that differs from the linear 0.047 method, is its recognition of the rocker ratio 2.7/1.7. I cannot tell whether JakeFusion agrees or disagrees with this aspect of Vettenut's calculation. In any event, the three methods would put the 1 3/4-turn preload at 0.0823, 0.1110, or 0.0667 inch depending upon one's point of view.

The good news is, everyone seems to agree that 1 3/4 turns is acceptable.

 

Thanks guys, this is some really great info

 

For another data point...
Stock LS2 rockers/ stands/ valves
Stock LSA pushrods
LS7 lifters
Comp Cams 54-426-11; 222/224 Duration @ .050, .566 /.568 Lift, 112 LS
Felpro MLS

I was measuring:
.085" preload on the first turn,
.112" just as trunion bottoms out (snug before torquing) at a bit less than 1.5 turns,
.115" when torqued to 22ft-lb - at 1.6 turns.

All 16 were in the range of 1.5 to 1.6 turns.

I find this is fairly close to the center of lifter plunger travel as there was another .099" of available displacement.

All according to the dial indicator probe located on the rocker adjacent to the oil hole - not ideal as there is some monkey motion as the rocker pivots off the valve as its pulled down to the stand.
Regards
mk

 

get a pushrod length checker and a set of 8" calipers from harbor freight. then you won't have to guess on length or on what your preload is.

this counting turns business is about as precise as using a shotgun to open a bottle of beer.

 

I do use a pushrod checker. I also send the mocked up pushrod(s) to the pushrod vendor. I was advised against measuring the pushrod with calipers due to the ball end and oil hole shape. The effective length of the pushrod is longer than what is measured with calipers due to the hole in the ball end, correct?

I can't measure lifter preload with pushrod checker and calipers, once I have the "correct" length pushrods installed and wish to final check the assembly. I need to measure the lifter plunger displacement. The best I can do is measure the rocker displacement "as close to" the pushrod as possible. All I am trying to share is that the "count the trunnion bolt turns" was in strong correllation to that rocker displacement measurement - sample size = 16, so was just adding to the forum sample size.
All 16 were in the range of 1.5 to 1.6 turns.
All 16 were in the range of .100" ~ .115" measured at the rocker.
I guess for a correlation I really should have documented the degress of rotation Vs displacement for each valve - and paired up those #s statiscally, but I stumbled on this thread after I assembled the valvetrain.

This 'counting turns business' goes way back - it procedural on adjustable rocker hydraulic lifter engines like old school SBC's.

CK - how are you measuring the lifter plunger displacement?

mk

 

yes, but this may not be a problem if you specify to your manufacturer that your measurements are for an overall length rather than a gauge length. there are other ways to get around that though.

Just because it's been done forever doesn't mean that it's accurate. Not a big deal if you have a .100" preload window but it's not going to work for short travel lifters. Either way, I wouldn't want to be guessing.

I documented the process I went through for both pushrod length measurement and lifter preload measurement in my build thread (linked in sig), starting on Page 10. Basically fixtured up an indicator directly inline with the oil hole of the rocker arm, zeroed it at "zero-lash" and watched it as I torqued it down to 22 ft-lbs slowly. Tedious job.

The moral of the story is that if you measure your zero-lash lengths accurately with calipers, your actual preload will be pretty much dead nuts on to your theoretical values by +/- 0.001", depending of course on the manufacturing tolerances the machinist is able to hit. No guessing involved.

 

I would not run anything over .070 personally. If you do not have a pushrod length checker and you dont know your measurement in inches, then you are just guessing.