After having numerous people tell me my pushrods are too short, I decided to spend today measuring the preload on each lifter

My setup is a modest 5.3L motor, 799 heads milled 0.022" otherwise stock, LS7 lifters, LS9 head gaskets, stock rockers with Comp upgrade, Tooley dual spring kit, and a mild cam with 0.561" lift. For this combo I was using 7.325" pushrods. My logic what that the LS7 lifters sit the pushrods 0.050" higher, and the heads are milled 0.022". So rounding up, I figured I needed a 0.075" shorter pushrod, 7.400-0.075 = 7.325

During the install I used a pushrod length checker on just a couple valves and got 9 turns to zero lash. 6.8 + 9*0.05 = 7.250, plus 0.075 preload gives 7.325. So I put the 7.325's in an its been running fine for about 600 miles, minus a loud tapping sound near cylinder 5-7

Today I double checked the preload and was surprised. My goal was to get between 0.075 and 0.100 preload. I ended up using longer (7.350) pushrods on 5 lifters, all exhaust valves weirdly. The rest I kept 7.325. I used a dial indicator and checked each one at least three times.

Intake Lifters:
Cylinder Preload Pushrod Length
1......... 0.075.. 7.325
2......... 0.083.. 7.325
3......... 0.081.. 7.325
4......... 0.086.. 7.325
5......... 0.084.. 7.325
6......... 0.082.. 7.325
7......... 0.081.. 7.325
8......... 0.078.. 7.325

Exhaust Lifters:
Cylinder Preload Pushrod Length
1......... 0.079.. 7.325
2......... 0.092.. 7.350
3......... 0.080.. 7.325
4......... 0.094.. 7.350
5......... 0.091.. 7.350
6......... 0.096.. 7.350
7......... 0.084.. 7.350
8......... 0.075.. 7.325

I guess the point here is that there can be a large variation from valve to valve, and it's good the check the pushrod length on more than one or two valves. Also, if these results look strange, or familiar, please chime in.

 

did that quiet it down?

 

When I measured mine, I checked all of them for accuracy. #2 cylinder (Both Valves) measured needing a longer push rod. I made them all use that size (7.375")

Your variation is all over the place...The remaining 14 valves were almost exact.

 

Not really, the loud tapping is still there, the rest of the valvetrain sounds normal.

 

Did you use a dial indicator? With the adjustable pushrod I figure I could only get it accurate to 1/8-1/4 turn, which is 0.00625"-0.0125".

 

I measured all of mine several times as I am running short travel lifters. I measured a peak to peak variation across all valves oaf around 0.020". Tony Mamo has told me this is pretty typical with what he sees. Looks like you see 0.021...completely normal in my experience and understanding.

 

.020"? or .0020"?

20 Thou seems like a huge variation to me. That means you have some valves requiring .020" smaller and bigger than the mean.....

You would have pushrods .040" longer than the shortest

 

Richard at WCCH says most factory heads have a variation in valve height of around 0.02, as in the difference between the shortest and tallest valve. The variation in valve height is divided by 1.7 to get the variation at the lifter. So a valve that sits 0.02" higher will have 0.012" more preload at the lifter.

 

Gents. To be clear Im not talking about valve installed height. I am talking about the pushrod needed to achieve the same preload on each lifter...so that rolls all tolerances into the same number. Ferocity, your measurements are 100% in agreement.

From what I have heard the majority of the variation is determined by the rocker tolerances.

 

To conclude this thread, I found the issue. The heads had six 1.59" exhaust valves and two 1.55" valves, they should all be 1.55". The 1.59" valves couldn't sit as deep in the seat since the seats were machined for 1.55" valves, and thus their stem heights were lower than the rest. That's what I get for buying heads on eBay.