I need to order a set of pushrods today so i can sneak my new heads on while the wife is away for the day next week. I know I should probably measure and go that route but surly enough people have done similar swaps that their should be a good guess. I don't want her to know I'm working on my car again, she would kill me.


I have a Comp. 224/228 581/588 112 with a set of Patriot Performance stage 2 heads that have been milled .010 perimeter style since this is on a 98 C5. I'm thinking the 7.4 stock length should be fine. What do you guys think?

Thanks again

 

What's your head gasket thickness? I have the same cam and used AFR 205's milled .010" with a Cometic .040" thick gasket. I used 7.4" pushrods and was fine. My guess is you will be too. I would invest in a set of hardend pushrods. With stiffer springs the stock ones will flex more.

 

Yea thats my plan. i was running the stock pushrods with the comp 918's just because i wasn't sure what heads i was going with. probably just go get stock head gaskets. i guess haven't really thought about them.

 

if you don't want to invest in a pushrod length checker--I would at least install one set of rockers and pushrods---1st marking the top end of the valve tip with a felt marking pen---then install the set--turn the motor over several rotations with the starter--make sure all other rockers are off--plugs out too--Then remove the rockers and check to see where the rocker has worn off the covered mark from the felt pen .
If correct the worn off ink should be in the center of the valve tip. If it is way off or too close to the edges--either way--you will have problems--

 

Pushrod length will not affect the wipe pattern, it is fixed. You need to shim the rocker base to change the wipe. Pushrod lenght only affects the lifter preload.

However, I do agree that checking the wipe pattern on the stock rockers is worth doing, but don't be surprised at the results. I found the wipe pattern to be very poor and went to fully adjustable roller rockers.

 

What adjustment can you make with a fully adjustable rocker that you can't make with a non-fully adjustable?
I was thinking it was just a lash adjustment, but if you can change the installed hight, that would be what set up the wipe pattern.

 

With a stud mounted rocker, you can set the wipe pattern and the lifter preload by using pushrod length and setting on the rocker adjustment. For example, on my Morel lifters, the required lifter preload is in the 0.030" - 0.050" range. I found a way to obtain a good wipe pattern with the heads on the bench by using the depth of the stud inside the adjustment nut. Once I installed the heads, I knew what the stud depth needed to be (a way of measuring the rocker fulcrum height that is fixed on the stock rockers) and then used an adjustable pushrod to obtain a measurement to zero lash and added in my lifter preload. Since the pushrods come in increments of 0.050", the rocker height has enough flexibility to correctly set the lifter preload and still maintain a good wipe pattern.

 

For stock rockers the ONLY way to be sure is use a adjustable pushrod and have a 8" caliper. It is quite a job but there are lots of variables involved with head milling, cam base circle, head gasket, lifter variances. You are probably ok with 7.4 but you will never know for sure.

 

If you use calipers, you also need to subtract the approximate 0.017" for the gauge length measurement that is used for pushrod length definition.

 

Yes:
or measure the actual length for stock 7.4s and subtract the difference and add that back onto your new required length.
The "measured length' is longer than actual length due to oil flow holes in end of rod.

 

So, if I go with a hydraulic roller (G5X3), get my LS6 heads ported and polished and they are not cut, but I use non-adjustable Harland Sharps, do I need to buy and adjustable push rod set up and measure for custom rods if I use the .040" gasket?

 

The best anyone can say is "probably" not.

You will have ~.015 difference in head gasket. The LS6 heads have different geometry and the cam base circle is different. All of those things change.
You want .040>.100" (depending on who you listen to) preload on lifters.

 

A checking pushrod is $20 and taking the measurement is actually quite easy. I would take the measurement and then get your pushrods, especially since Comp now makes pushrods in 0.025" increments near the 7.400" length expressly for the LSx engine series. That way you know you will have a correctly set lifter preload and avoid later issues. Don't forget, in addition to all the variables mentioned by see5, you are also changing the cam base circle. If the Z06 heads kept the original valves they will be one length, if they are replacement valves another length. If they worked the seat at all that could change things as well.

Above there is discussion of the wipe pattern, with re-worked heads the valve height in the seat will alter the wipe pattern to some degree, that is worth checking first then measuring for your pushrods. Sounds like a lot of work, it isn't too bad and you will get a good running setup with minimal valve guide wear when you are done.

 

Great post!!!!

bc

 

Boy, I'm really going to mess things up by getting the heads done. Yes I wanted to up-grade the valve sizes.
I wanted to go 2.02/1.60, and de-shroud the valves.
The push rod checker is $20? Where? Or are you saying to go get an eight inch dail caliper intead?

 

Here's one of many sources:

http://www.thunderracing.com/catalog...d=106&pcid=171

 

Wow! I actually started a thread that was helpful for more than just myself. I will double check mine with a pushrod checker when everythings ready but I sure hope the 7.4's work cause i scored some new comp's for $82 and they came with a t shirt thats way to big LOL


Thansk for all the great input

 

After reading your post i decided to read the instructions on my Yella Terra NON ADJUSTABLE full roller rockers. It says exactly OPPOSITE than what you have said--It says Quote --"Geometry can be changed by fitting different length pushrods or valve lash caps.Shorter pushrods or lash caps will bring the starting point on the tip further back from the center of the valve and longer pushrods will have the opposite effect"
AND :
Lifter preload--" Tighten capsrews until all freeplay is taken up......Torque the screws to 25 FT llbs ,Ideally this should be between 1/2 and 3/4 of a turn. More than 1 1/2 turns will require the installation of SPACER washers supplied in the kit to reduce lifter preload "

So pushrod length adjusts the strike surface on the valve tip--- and the pedestal washers simply adjust the lifter pre-load--not vice versa--the 2 aren't related--This is for NON adjustable rockers which all ls1,ls6 and Gen 3 engines come with stock.the most popular aftermarket rockers SLP-Yella Terra are NON adjustable. Some aftermarket rockers are the Adjustable style which require completely different procedures for installation,machining-different pedestals-spacer plates--different length valves--95% of typical LS1 installations would have no use for this type of set up--No advantage on a hydraulic roller motor--too much room for error on installation

 

With a fixed pedestal rocker installation, like the Yella Terra's or the stock rockers, the intial contact position on the valve stem is set by the design of the rocker itself. Once bolted in place, the pushrod length will not change this position on the valve, it can't because the rocker is already fixed in place by the bolt. Adding a lash cap will raise the height of the valve stem and push the initial contact point in towards the center of the motor. Adding a shim will move the initial contact point out towards the exhaust but now you will need a longer pushrod.

The Yella Terra instructions are actually doing the same thing. For example, by you installing longer pushrods, to keep the lifter preload in the correct range would require you to shim the rocker pedestal because you would end up with too much preload. That in turn changes the wipe pattern because now that the rocker pedestal is shimmed, the intial contact point has been moved outward on the valve stem.

However, lets suppose you haven't installed any shims but your initial contact is too far out, you can't cut down the pedestal on the rocker to get it to sit lower so the addition of the lashing cap becomes necessary to make the adjustment.

I did a quick google on this and found this article. It probably explains it better than I can and uses some photo's.

Valve Train Article

 

Cool, now I know where to go when the time comes.

Are the Harland Sharps comperable in terms of strength/value?
Thanks for the link. I understand now.