I have been reading many of the posts and think I have this figured out. I just want another person(s) to review what I think I have figured out and confirm I am on the right track.

I'm building an 02 5.3L engine for my sons truck. I have replaced the cam with a Howards cam (knock off of the GM Hot Cam). I also replaced the lifters with what are supposed to be LS7 lifters. They are "take outs" with zero miles on them and came in a white box. I also had the factory heads milled .020" as the machine shop said there was some warpage present and they wanted to mill them to get them straight.

So, I got the long block together and find that the factory length push rods are too long. I got the intake valve in the closed position (exhaust valve just opening) and then set the rocker bolt by hand to zero lash. Then I put a torque wrench on it set to 22 ft. lbs. and watched how far the bolt turned before I reached the 22 ft. lbs. The bolt turned 2.5 turns. This means the push rods are too long. I then built me an adjustable push rod to measure more accurately. I got the adjustable pushrod to a point where I can just snug the rocker bolt and there is no up-down movement of the shoe on the valve tip, but you can still move it side to side. No freeplay, and true ZERO lash, and ZERO pre-load. I then took my push rod to my local machine shop and they measured it.. Here's the math;

Adjustable push rod length: 7.250" + .060" Pre-load=7.310" is my desired length. They could only order 7.300" or 7.350". I went ahead and ordered the 7.300" as that will put me around .050" pre-load. Had I gone with the 7.350" it would put me at .100" pre-load.

Does anyone see any problems with this? Should I try and find a company that will make me a custom length push rod to get me between .060-.075" which would be 7.310-7.325 in length?

 

You'll be fine with what you ordered I think.

Typically if you measure pushrods with a caliper, they are about 0.015" longer than the declared length. Example a set of comp 7.400" rods will measure 7.413-7.417 all day long on a caliper.

 

Darth, I think that is because they account for the ball ends on the push rod to sit a little lower in the socket on the rocker arm, and the cup on the lifter plunger. So, I probably could have gone with the 7.350" and would lose some of that pre-load from the depth of the rocker socket, and plunger socket, ends. This is why it is so confusing for me. I guess I'll run with what I ordered and if it is noisy after run in, I'll know I need to order longer pushrods. Using my adjustable length push rod though *should* have accounted for the extra seating depth in both sockets so I hope I'm good.

When I get the new push rods in (tomorrow) I will measure them with calipers and see exactly how long they are from ball end to ball end. If they are a little longer than 7.300" I'll be happy.

 

Yes, they do. But I can measure at home with caliper and when I order, I specify "as measured by caliper". I definitely wouldn't go to 7.350", because they'll be 7.365 actual. If you do end up needing a custom length, manley and manton both make them.

 

Darth, appreciate the information. I will most definitely have my machine shop measure them when they come in tomorrow. The machine shop ordered them for me so I can measure a new one while I am picking them up. I will post results tomorrow.

 

The gauge length, used by Trend and others, is measured from a point on the ball that is 0.140" in diameter. This is due to the inconsistency of measuring end to end because of the hole in the ball. As stated, they will be slightly longer measuring overall length and may vary as a result of the hole. The inconsistency isn't as critical with a hydraulic lifters, which for the LSx motors, is actually pretty forgiving on length. Some pushrod manufacturers, Manton, use the overall length for ordering pushrods.

One thing to note on using bolt turns is that part of those turns are for bolt stretch and won't impart any lifter preload. When I did my testing I found that once the rocker bottomed, it was about an additional 1/3 turn to achieve the 22 lb-ft of torque. So if using this method it is not as straight forward as counting turns. You must also use the rocker ration to get the final preload by using parallel triangles.

 

How long we been preaching this gospel, brother? At least a year?

 

I typically recommend Manton pushrods because they nail the OAL every time. Plus their pushrods and service are ****. Trying to explain gauge length and tangent intersections to some customers is a royal pain in the ***!

Here's my preload calc that takes into account rocker ratio and thd pitch.

 

Quick update.. I just got the pushrods in today. They actually measure 7.315" from ball end (hole to hole?) to ball end. This works perfectly with my calculations as it gives me .065" pre-load which I believe is acceptable.

I got the Comp Cam 7609-16 Magnum 5/16" diameter.

This web site, and the people that make it up, is a wonderful resource!

Thanks for the help!