PR Length - Check My Math Please
 

I'm installing a new shortblock and wanted to check my valvetrain geometry this time around. According to my calculations I need 7.250 PR's and I've been running 7.400's for 20,000 miles. (valvetrain always was fairly noisy with crummy idle, though I attributed that to the fact that I never idle tuned it)

AFR 205 heads milled to 62-63cc (maybe .040?? - cant recall)
7.400 PR's currently
Cometic .040 gaskets on both builds
"Mamo" cam 224/228/114 - can't recall if I bought it from AFR or not.
Stock 2002 Lifters in past, though I've got the Caddy racing lifters now.

Checked for TDC in #4 with borescope and I used an adjustable PR checker....tightened rocker bolt just finger snug where I could not move the PR, but could move the rocker up and down a little but not make it tick on the top of the valve.

From that, length of PR checker was 7.175" (7.25 turns (anything 7.00-7.50 felt good)), I added about .075 for my Caddy lifters preload and got 7.250" PR length.

I'm concerned because this seems to be an odd size and my heads aren't milled that much. The car made 431whp with the 7.400's and only valvetrain change being the lifters.

You did what?

Must people run the improper size length pushrods because they never bother to measure it. 1st torque your rocker down than you turn your adjustable pushrod. Basically you take all the lash out of the adjustable pushrod while the cam is on the base circle. Just make sure you are not compressing the lifter. I would shoot for .020"-.040" preload. Terry Manton can make you custom length pushrods and try to get the thickest pushrods in you can, maybe 11/32?

Your math is correct tho' I think your method of finding zero lash is incorrect. The rocker needs to be tightened to 22 ft lbs (with pushrod measuring device in place). You then oen the pushrod device until the rocker does not tick anymore. The rest of the math calculating you seem to have a handle on. The piston should be at TDC on it's compression stroke and personally the preload numbers given above seem a bit shallow. I would run at least the .075 you wanted. When I ran the Caddys I ran them at .90 and all was well.

^^ Thats it (nitroused383) in a nutshell here is a good read for you as well.

http://www.circletrack.com/techartic...ech/index.html

So it sounds like I need to recalculate with the rocker bolt TORQUED, not finger snug. After re-reading it sounds like I interpreted "snug" as finger snug, not wrench snug.


Here's the copied instructions I used, from this thread.
https://ls1tech.com/forums/generatio...-engine/911392

This is a post from Vettenuts about measuring pr length,

Each turn of the pushrod is 0.050". When fully closed, it is 6.800". This is pushrod "gauge length" so you can't measure it directly as the pushrod length is actually based on the length between the ball ends where the ball end measures 0.140" in diameter. Assuming you are using stock rockers or a non-adjustable rocker.

1. Open the adjustable pushrod to the same length as your stock pushrods
2. Close it down two turns
3. Put your rocker rail on the head
4. Make sure you cylinder (typically #1) is at top dead center on the firing stroke so both valves would be closed
5. Put the pushrod in place on the intake valve and make sure it is in the lifter cup
6. Install the rocker and snug down the bolt (don't need to torque, just make sure it is snug)
7. Lift rocker tip up and down, if it "ticks" the pushrod is too short. If you can't easily move the rocker the pushrod is too long.
8. You can try and adjust the pushrod in place but my fingers are too fat so I end up pulling the rocker and adjusting the pushrod length. Go either shorter or longer 1/2 turn and try again.
9. You are trying to get to the point where the lifter doesn't "tick tick" with the pushrod in place nor is the rocker snug. When you get the pushrod length such that you just barely get rid of the "tick tick", you have found "zero lash".
10. When you have found zero lash, carefully remove the rocker and pushrod without rotating the pushrod.
11. Tighten the pushrod until it is fully closed counting the turns as you go.

To figure out your pushrod length you do the following. Let’s assume it took 10-1/2 turns to close the pushrod down to its shortest length after you reached zero lash. Each turn is 0.050".

Your length is then: 6.800" (fully closed length) + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So for this case:

6.800 +10.5 X 0.050 = 7.325"

This is the length you measured to zero lash without any lifter preload. Now let’s say you want to have 0.075" lifter preload, you add that to the measured number and you end up with 7.400" pushrods.

Now repeat for the exhaust valve to verify the length. If you have something like Yella Terra's, it is the same procedure but you must snug down the rocker pair rather than the single rocker.

Finger tight would actually work fine. The method you described was that you used the rocker bolt to achieve zero lash thats the mistake I saw in it.


The adjustable pushrod is what should achieve your zero lash.

This is where you went wrong it sounds like.

You want to bring the pr up to the lifter cup (by unscrewing it) you do not want it in contact when you tighten the rocker down (in this step). Then add the correct pre-load for the lifter you are running.

You had everything right except it needs to be either torqued to 22ft lbs or at least just wrench tight, then adjust your adjustable PR out to where the rocker has no lash. I would go for as close to .080" preload as you can get.

Unfortunatley, I don't think closing it down 2 turns before torquing the rocker will be enough in my case.

Read these for a little preload info

http://www.hardcorels1.com/vbulletin...ead.php?t=1815

http://www.hardcorels1.com/vbulletin...47&postcount=1

Two turns should be roughly .10", that makes your 7.250 about a 7.350 but you need to be sure.

Good job checking them, not enough guys do.

:jest: then close it more. It will shrink to 6.8

Yeah, I think I noticed.:|

After torquing them down it looks like I need a 7.200 PR.

Does that sound obnoxiously short for my setup?

Who sells decent PR's in that size if I really do need them that short? TR/TSP don't have them listed anywhere near that small.

I'm curious too since I'm currently installing 62cc AFR 205's and it will be with .040" cometics. 7.200" sounds short but I don't know that for sure. I'll be measuring PR length later this week when I do mine. Just to be sure you had the heads milled about 0.024" right? AFR says .006" per cc of reduction.

just to clarify, i think you need to make sure the lifter is hitting the cam. i remember when i did mine the lifter would be in the tray but i had to push it down with the pushrod a little bit before it hit the cam. someone can let me know if this isn't right.

You can get them from a few different places, we use Manton for a lot of custom PR's

I can't recall the milling that was done on my heads, but I'm thinking tony recommended 63cc just becasue I do a lot of track days.

I'm pretty certain the lifters are down out of the tray on the cam.

I still find this to be very short...