Gents, need advice with a concern I have with my new engine. I'm in the process of measuring for proper pushrod length and have some concern about what seems to be a wide range of measurements for either the intake or exhaust valves. I've not built a lot of engines so I'm not sure what is an allowable variance. I realize it will never be the same exact measurement for each intake or exhaust valve but this variance has me worried.

Let me explain my procedure first to see if there is an error in my way of doing this. Since it's rather difficult for me to get my fingers underneath the rockers to change the length of the pushrod checker, I have put a slight crimp in the checker making it require slightly more effort to turn. Also, I ensured the checker was properly seated in the lifter on EVERY valve and checked it with a light.

Setup is a Gen IV iron block with ETP heads and stock rockers with the trunion upgrade. I am using the ETP rocker stands for stock rockers as well. Johnson link-bar lifters with .035" preload I believe.

Ensuring I was at TDC on the compression stroke for cylinder #2, I started with #2 intake valve. I adjusted the checker to zero lash and it measured out to 8.174" (baseline). I am fairly certain it was set to zero lash as the rocker was still rocking back and forth until the last 32nd or so of a turn on the tq wrench.

Without changing the checker length, I moved over to #2 exhaust. After torquing down the rocker arm, I could still rock the arm back and forth. I used a feeler gauge and put just enough pressure on the pushrod end of the rocker arm to seat it on the checker ( I'm very certain I didnt push the lifter down) and measured .008".

All is well. I moved on to cylinder #4 and repeated the process. #4 at TDC on compression, pushrod checker still set to 8.174". Tightened the rocker arm down on intake, perfect to zero lash. Moved to the exhaust side and the rocker was extremely loose still. The largest feeler gauge size I have, .025", was still loose in the gap between the rocker tip and the valve stem.

I completed the rest of the cylinders and measured anywhere from 8.174" to over 8.200" on intake and 8.182" to over 8.200" on exhaust.

I measured 5 valves that were more than .025" over the 8.174". I dont know how far over 8.200" those 5 are yet. I am going to lengthen my pushrod checker .025" and remeasure those 5 to get an exact measurement.

Only those 5 in particular, they are at least .025" over the baseline. So the question is, how much of a variance is too much?

Thanks gents.

 

What did you do that makes you think you need different push rod length, I recently did a ls3 heads and cam and milled the heads 0.020 and still used the same push rods there's less pre load but worked just fine.

Don't see the need to use filler gauge to aid in seeking push rod length.

Is best to have soft springs for this purpose in place of valve springs, (though not necessary) good to use center piston on top dead center on each cylinder bank put the adjustable push rod checker to zero lash remove the push rod and measure, add length to the push rod to obtain pre load you want and measure again to obtain the length.

you may want to check in several other pistons to make sure the intended length is just fine.

I personally like 20 to 25 thous pre load for street performance you may also find out how much lifter travel till it bottoms out just so you know your parameters.

 

I'm not even to the point of trying to establish preload yet, CAMSTER. I'm just measuring for zero lash. Preload I can add in later. I checked every valve on the engine and have exact measurements for all valves except the ones that measured over 8.200". But even without the exact measurements on those valves, I'm seeing a difference of 0.025" in pushrod length to reach zero lash. Hope that clears things up a little.

 

Use the length checker to determine the length with the preload. Adding it in later is a bad idea.

What I do is select a pr length.
Tighten the rocker bolt by hand untill there is no slack between the rocker and pushrod. This is zero lash.
Then using a dial indicator on the rocker measure the actual preload. Tighten the rocker to spec.

Adjust the length for proper preload.

Feeler gauges and adding preload is asking for the wrong size.

KISS

Tim

 

I do the same. For most combos with the stock block and heads, I'll start with 7.400" and see what that gets me. Then adjust accordingly.

As far as variation, I have two different length pushrods in my car. The old heads required two different lengths, 8 pushrods being roughly .025" longer than the other 8. The heads I just put on don't, so just to see what happens, I put the shorter pushrods on one cylinder bank and the longer on the other bank. Runs fine. No noise or anything. Once I gets tags on the car and take it to the dyno, I'll play with the pushrod length and see if there's any power on the table.

 

The only thing that could cause this is the valve job. Double check your install height on the valves to make sure they are all the same. (easy quick way would be a straight edge across the valve tips) To a particular engine builder .025 would be unacceptable between valves.