Help with push rod size

HwyStar

Registered User
Thanks to Stan W. for filling me on on some things about this engine that would have held me back if I didnt know. By the way, Tim did spend a little money on a set of nice pushrods, but I dont think I can use them.

comp7940.jpg


Man those things just look cool! I didnt realize what they were till i went to put on a rocker and watch it travel the stem.

rocker003.gif


Ok, my situation looks exactly like the bottom example. From zero lash finger tight to 19ft/lbs. it only took 3/4 of a turn, which is correct per the Scorpion Perf. instruction. So, since they offer shims in .020" thickness, should I install a .020" shim and go for a .020" longer push rod? My concern is what if I need .040"? Can I figure whats right with the pushrods I have and just work out which length pushrod I will need in the end? Anyone have experience with this?
 
Dave Dalke has a great post on here on how to adjust lifter pre-load. I believe that is your question but not sure. The 7.2 inch pushrod is the typical length folks on here use when using a custom grind cam. I use that length pushrod as well. The shims I use come in increments of .010 and .030.
 
Been reading around on the LSx forums of all places, and something someone brought up was lifter preload. Im guessing that my lifter preload may be off while im checking the roller wipe across the valve tip. Once the wipe pattern is right, find out how many turns from zero lash finger tight Iam, then compare that to allowable preload. According to Scorpion Perf., allowable preload from zero lash finger tight is half turn to one turn. With a dial indicator i can find that number. Then, take what ever the distance i actually am over or under and that would be the difference in the pushrod. Iam really thinking aloud here, but it seems to make sense. Am i wrong?
 
Huh, odd, tried to view it and i get a warning that says i do not have permission to view....
 
Read this careful and understand it so you don't screw up. Zero tolerance occurs before you tighten the rocker bolt all the way by hand. It also occurs before the rocker seats to the head.
Whatever cylinder you are working on, you need to get the camshaft 180 degrees out from the tip of that lobe. So now that your at that point install your 7.2 pushrod and start to screw in your rocker with your 10 mm socket and a short extension by hand. Before you are able to screw in the bolt far enough by hand that it will seat the rocker to the head you will actually be compressing the lifter a certain amount. You need to figure out the exact point in which you start pushing the lifter in and stop at that point, go slow and you can actually feel it or have a flashlight looking at the lifter to see it happen is the best way.

From there, get your rachet on the their and tighten the bolt down the rest of the way until the bolt seats to the rocker(zero torque) just seated. In that space is where you should get between 1/2 to full turn out of the bolt. If you don't you will have to shim to get their or get longer pushrods.

This half to full turn indicates roughly how far you are pushing the lifter in until the rocker seats. Every 90 degrees that you are able to turn the bolt before the rocker seats equals roughly .020 that you are pushing into the operating space of the hydraulic lifter. It is safe to say you can't push the lifter more than .120 before bottoming out and actually pushing the valve open, so .060 or 3/4(270 degree) of a turn would be roughly right in the middle of your lifters operating range and would be a perfectly safe place to stay close to.

If this all makes perfect sense to you, then you are good to go. If all of it doesn't you need to read that post or find someone to help you out.

Chris
 
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I used to be a dues paying memer, does that count??

Yeap, i understand that. Maybe, part of my question is what the right preload on the lifter is good for these engines? I know a 302 is .030-.060".
 
I would do .060-.080 on this engine and use the longest pushrod you can for the best rocker geometry, then shim to get you where you need to be. That's just nitpicking so if your 7.2 pushrods work you might as well go with those.

Chris
 
The SCP Scorpion Performance non adjustable. Very nice looking. But, the roller wipe pattern definetly shows the rocker is low. Im going out to the machine shop tomorrow to drop off a 1.6d head for porting. Im hoping they might have the shims i need. If not, ill probly be waiting another week for the shims to come in. Not sure that the speed shops around here would have them.
 
That pushrod size is typical that Ive seen for a motor with a reground cam. I measured and that was the size I ended up needing on two different motors and then shimmed for proper preload. Summit sells a nice FMS shim set. If you think its the wrong lenght for proper geometry get an adjustable pushrod and check that way..then shim fo rproper preload
 
I think im going to shim it up and give it a shot. Im not sure how much it will take to get it right, but hopefully its within tolerance and i can use the pushrods. Work, wait, work, wait, work, wait.... Good thing i have plenty of other things to keep me busy and my mind off it when i cant move forward. Im dying to get this car done after having it sit for so long.
 
The SCP Scorpion Performance non adjustable. Very nice looking. But, the roller wipe pattern definetly shows the rocker is low. Im going out to the machine shop tomorrow to drop off a 1.6d head for porting. Im hoping they might have the shims i need. If not, ill probly be waiting another week for the shims to come in. Not sure that the speed shops around here would have them.

The shims are a pretty common part, since the Windsor V8s use the same ones. Someone around may have them.

http://www.summitracing.com/parts/fms-m-6529-a302
 
Yeah, thats what i ended up ordering. Theres only one FMS dealer in the hampton roads area, and they didnt have it. Machine shop didnt have it either.
 
I think im going to shim it up and give it a shot. Im not sure how much it will take to get it right, but hopefully its within tolerance and i can use the pushrods. Work, wait, work, wait, work, wait.... Good thing i have plenty of other things to keep me busy and my mind off it when i cant move forward. Im dying to get this car done after having it sit for so long.

Keep in mind the pushrod sets the angle along with the ratio of rocker. The shims juts set preload. Good luck!
 
This is what i came ot with when i checked the wipe pattern. What do you guys think? The wipe got narrower with more shims, but still high on the stem. I tried .030", .060" on the exhaust, and with the intake i also tried .090". Putting even the .030" shim in left me with movement up and down even with the rocker tightened all the way down. So, i went on to check anyway. That means 7.20" + .090" => i need a 8.10" pushrod set?

Exhstem.jpg

Exhaust stem with .030" shim.
Exhstem2.jpg

Exhaust stem with .060" shim under rocker.
Intstem.jpg

Intake stem with no shim under rocker.
Intstem2.jpg

Intake stem with .030" shim under rocker.
Intstem3.jpg

Intake stem with .060" shim under rocker.
Intstem4.jpg

Intake stem with .060" and .030" stacked under rocker.
 
Pay the $20 and get access to the article. You are going to get a wipe pattern. That is unavoidable. The Question is where it starts and where it stops should be in nearly the same spot.

PS 7.20 =0.090= 7.290
 
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