Here are 2 short videos that will be of interest to folks that are unsure of there lifter preload after making a cam change, or having the heads milled, or installing aftermarket rocker arms, or installing aftermarket heads.

All of the situations above will more than likely require either a longer, or a shorter pushrod in order to achieve the correct lifter preload.

Ideally, the most accurate tool that can be used to measure lifter preload is a dial indicator (which many of us don't have)

The next most accurate way is to use an adjustable 'checking' pushrod ..... But there is another way that I found out that works great ... Below are two short videos. The first is for folks that are have 1.7 ratio rockers in there engine. The second video is for folks that have 1.8 ratio rockers in there engine.




The above videos gave the lifter preload on the LS engine using one turn of the rocker bolt ... but how about if you have more or less turns than 1 turn? ... Well, below is what some other various turns of the bolt will give you for lifter preload

From everything I have read, most of the well known professional LS engine builders recommend approx .070" - .080" for lifter preload when using GM OEM lifters (aftermarket lifters such as Johnson, etc may require a different preload than the OEM lifters)

Note: Remember, when checking lifter preload, the lifter first needs to be on the base circle (heel) of the cam lobe before turning the rocker arm bolt and counting the turns until it's at 22 Lb/Ft.

Note: If the bolt rotates 1 1/4 turns, you would want a pushrod that is .025” shorter than stock

Note: If the bolt rotates 1/2 turn, you would want a pushrod that is .025” longer than stock
_______________________________________

1.7 Ratio Rocker Arms:

1/2 . . . .Turn of the rocker arm bolt = .040” lifter preload

3/4 . . . .Turn of the rocker arm bolt = .059” lifter preload

1 . . . . . Turn of the rocker arm bolt = .079” lifter preload . .

1 1/4 . . Turn of the rocker arm bolt = .099” lifter preload

1 1/2 . . Turn of the rocker arm bolt = .119" lifter preload


1.8 Ratio Rocker Arms:

1/2 . . . .Turn of the rocker arm bolt = .038” lifter preload

3/4 . . . .Turn of the rocker arm bolt = .057” lifter preload

1 . . . . . Turn of the rocker arm bolt = .076” lifter preload . .

1 1/4 . . Turn of the rocker arm bolt = .095” lifter preload

1 1/2 . . Turn of the rocker arm bolt = .114" lifter preload


.

 

So, the moral of this story is ... One you have set 'zero lash' on the rocker arm for the cylinder that your checking, you then turn the bolt down until you get 22 Lb/Ft torque ... Your lifter preload will be well within normal limits if that bolt has turned approx 1 full turn.

End of class ... Students dismissed

 

BTW ... I posted this info above because there is too much misinformation as to how much lifter preload actually equals 1-turn of the bolt.

The numbers are all over the place.

 

I agree as I tried doing this once and got three different measurements on the same cylinder. I then had a friend try it and he got a fourth different value. People frequently give me grief over this but I simply calculate pushrod length using basic math.

Assuming you're starting with a good known setup (i.e. completely stock) any differences get added or subtracted accordingly. If the only thing you changed as one example was to mill the heads .030 then you'd need a .030 shorter pushrod to keep everything as it was. If you did something more complex like deck the block by .005, mill the heads by .020 and run an aftermarket cam that had a .015 smaller base circle that then you'd need a pushrod that was .040 shorter.

Sometimes the math leaves you needing something shorter by an odd number like .033, but in that case going with a pushrod that's either .030 or .035 shorter will work.

 

Another source of confusion is due to the fact that the last 1/8 ( or maybe a little more) of a turn gets you no more preload. You're just stretching the bolt getting to 22ft/lbs.

 

Very true .... Once it's 'snugged down' good, it ain't going any more other than stretching