The L98 engine in my '89 is essentially stock. I am about to replace my stock pushrods. The engine has GM Performance Parts' hardened guideplates and I want to replace my stock pushrods with a set of hardened pushrods (preferably from GM Performance Parts). The "best" pushrods that GM Performance Parts sells are are made of 1-piece 4130 steel tubing 5/16" dia. with 0.080" wall thickness (P/N 10134309). Everything about these rods sounds great, except they are 0.100" longer than the stock units. Does this additional length make a difference to valvetrain geometry assuming I'm running my stock self-aligning stamped steel rocker arms?

Thanks in advance.

 

Yes... .100" longer pushrods will change the valvetrain geometry; ideally you want a consistently equal pattern the rocker travels on the valve stem. I would suggest measuring your factory pushrods and buying a set from Comp or Federal Mogul (which, BTW, builds the GMPP stuff).
-Jeb

 

Thanks Jeb. The problem I'm currently experiencing comes from the fact that my machine shop put hardened guide plates on my heads when I had them rebuilt, but I'm still using my stock (not hardened) pushrods. I tried to use a set of non-self aligning roller tipped rockers (I didn't know they weren't self-aligning) on the car and now because of side-to-side movement of the rockers my pushrods are scored baddly.

Thanks again.

 

YOULL NEED TO CAREFULLY CHECK YOUR PARTICULAR ENGINE!
heres a simple way to get close to the correct length
BUY ONE OF THESE


http://www.jegs.com/cgi-bin/ncommerc...67&prmenbr=361

after making sure the valve springs are correctly installed you drop the checker in place on the rocker stud and install your adjustable pushrod
adjust the length to fit and measure the resulting length if its within twenty thousands of the stock length its fine for most applications, if its more than 30 thousands long or short get the closest length set available

btw, if your one of the people that still does not own an adjustable push rod! you can easily make your own by cutting a stock pushrod in 1/2 (2 pieces), removeing 1 inch from the total length an then with about 2 " of a 4 inch section of 3/16 or 1/4" thread rod installed and (in one section epoxy it in place leaving about 2" sticking out thread two nuts onto the thread rod and slip on the other end of the cut pushrod,(no epoxy) use the two nuts to adjust to stock length and let the epoxy harded in the one section[/color] now you can easily measure and order custom push rods useing the pushrod checker and adjustable push rod as tools
AND YEAH IT ONLY WORKS WITH THE CYLINDER HEADS ON AND THE INTAKE REMOVED BECAUSE THE HOLE IN THE CYLINDER HEAD that GUIDEs THE PUSH ROD WON,T ALLOW THE NUTS ON THE ADJUSTABLE PUSHROD TO PASS THRU, UNLESS YOU PLACE THE CUT ABOUT 1" from the UPPER END OF THE ADJUSTABLE TEST PUSHROD BUT I prefer to place the adjusting nuts centered as I like to watch for all clearances with the intake manifold removed while manually checking as I turn the engine over by hand durring assembly, and at that point, while checking all the clearances, I use test springs which apply very little load on the push rod


http://www.jegs.com/cgi-bin/ncommerc...72&prmenbr=361

HERES OTHER TOOLS YOU MIGHT NEED








SOMETHING TO READ
http://www.compcams.com/information/Products/Pushrods/

CCA-7705 5.800 in. to 9.800 in. adjustment range, Master pushrod length checker 4 piece kit ... $78.69

here





[Modified by grumpyvette, 7:59 PM 6/13/2003]

 

get rid of your guide plates, and get the right size of plates to match your new push rods. this should eliminate the need for self-aligning rockers. plates are cheap too. the +.100 rods are designed to help correct the geometry if your running a higher lift cam typically. check your stock lenght push rod by taking off a rocker and mark the top of the valve with a permanent marker. put the roller tip back on(with the right plates you could use your roller tips again and not need self aligning) and rotate the engine a few times. look at the wear mark on the valve, if it is the correct length the wear mark should be across the center of the valve tip and about .030 wide.
if it is near the outside of the valve, you are to long, inside you are to short.
figure using the stock length as a bench mark.
look on e-bay for the plates and rods and it will only cost you about $60 for both. i got my pushrods from EPN and seem to be a very good piece for cheap. they have held up in my 500hp 383 at 7000rpm {with the correct geometry of course}
remember the roller cammed motors are a 7.195 lenght compared to 7.794 for a standard sbc, take note. :cheers:
drive it like you stole it, fix it, repeat!! :steering: