Pushrod Length - NJFBOA - Home of New Jersey's Camaros and Firebirds

zraffz · 07-01-2012, 11:03 AM

I don't understand what I am doing wrong when measuring the pushrod length on this motor. It's a 1997 block, stock lifters, mild cam, crane cams gold 1.5 rockers, unmilled heads/deck, .016" compressed head gaskets.
In order for the pushrod to contact the bottom of the rocker with a hair of drag, the pushrod needs to be set at 7.55"... anything less and the pushrod isn't contacting the rocker throughout the cycle. Naturally without any pushrod, the rocker is sitting too far forward on the intake valve.

I've only been pulling measurements of cylinder 1's intake valve. Is it possible when the machine shop drilled for screw in studs that he didn't drill them strait?

This was set at 7.40", the pushrod was so loose that it barely sat in the rocker's pushrod cup.

No pushrod:

A little easier to see the top of the valve:

Any ideas?

S.J.SLEEPER · 07-01-2012, 11:30 AM

stock pushrod length is 7.200 I believe. which is shorter than what you are using. this is telling me that either you have the trunions on rockers flipped, or wrong rocker studs.
are they the correct rockers for your motor?

with rockers adjusted properly, the roller tip should be a lil bit towards the outside of the valve, when rocker fully compressing on valve...the roller should be just passed the center point of valve.

LTb1ow · 07-01-2012, 11:39 AM

I am not sure you are doing this right.

You need a weak spring, or a solid lifter to measure correctly. A full HR lifter and new spring will not work.

Featherburner · 07-01-2012, 11:40 AM

Did you make it so the lifter can't collaspe? If not you need light weight test springs for set up.

Edit: Matt is a faster typer than me!

S.J.SLEEPER · 07-01-2012, 02:23 PM

^ what they said, I assumed you are using a solid lifter, or a old hydraulic lifter that has been shimmed internnaly to act as a solid to determine your pushrod length. If you dont know what you are doing, than either read a book or give it to a professional.

zraffz · 07-01-2012, 03:16 PM

Quote:

Originally Posted by S.J.SLEEPER

^ what they said, I assumed you are using a solid lifter, or a old hydraulic lifter that has been shimmed internnaly to act as a solid to determine your pushrod length. If you dont know what you are doing, than either read a book or give it to a professional.

I've been pumping up the lifters before measuring each time... wouldn't that be more accurate?

LTb1ow · 07-01-2012, 03:18 PM

Quote:

Originally Posted by zraffz

I've been pumping up the lifters before measuring each time... wouldn't that be more accurate?

No by nature a HR lifter is gonna bleed down.

You need it to be a solid lifter and then mark the valve stem with a sharpie, and get the sweep pattern to your liking. Then measure what the PR checker length is.

zraffz · 07-01-2012, 03:35 PM

Will I damage a lifter if I take it apart? Otherwise I have a new set of LS7 lifters and some old LS7 lifters I can take apart to make into a solid lifter.

LTb1ow · 07-01-2012, 03:36 PM

Take apart an old one, don't ruin a new one

zraffz · 07-01-2012, 03:37 PM

Alright thanks. Zero experience with a hydraulic roller motor lol.

S.J.SLEEPER · 07-01-2012, 03:48 PM

Quote:

Originally Posted by LTb1ow

No by nature a HR lifter is gonna bleed down.

You need it to be a solid lifter and then mark the valve stem with a sharpie, and get the sweep pattern to your liking. Then measure what the PR checker length is.

Quote:

Originally Posted by LTb1ow

Take apart an old one, don't ruin a new one

follow instructions above

zraffz · 07-01-2012, 04:34 PM

So I switched from the stock Vortec lifters to the LS7 lifters (which are a hair taller). I had a new set of LS7 lifters laying around and an old set. I checked to make sure they were the same size, I took apart an old LS7 lifter and cut a bolt to fit inside it - filing it to final size. Now the lifter has no play inside it.

I remeasured, got a bit closer to having the mark on the center half way through the cycle and came up with a 7.35" or 7.4" pushrod. I was almost expecting to be under the 7.2" stock size since the head gasket is significantly thinner but these new rocker studs are physically a hair taller at the seat. Think now I'm getting the results I wanted but I'm going to have someone come over and double check my work.

LTb1ow · 07-01-2012, 04:49 PM

IDK how you are doing this but this is what you should be doing.

http://www.compcams.com/Products/CC-...rods%27-0.aspx
http://www.compcams.com/Pages/417/va...-geometry.aspx

Like so and what not

zraffz · 07-01-2012, 04:52 PM

Exactly what I am doing.

LTb1ow · 07-01-2012, 04:59 PM

Ok, next question would be, can you get a pair of calipers to measure the adjustable pushrod? You may just be reading it wrong for that extra ~.2

zraffz · 07-01-2012, 06:06 PM

I'm using the comp cams adjustable measurer. Closed it's 6.8" and every turn is .050". Is 7.4" ridiculously big compared to 7.2" stock?

LTb1ow · 07-01-2012, 06:10 PM

Yea, considering stock is 7.2 and you have a thin HG on it .

zraffz · 07-01-2012, 06:42 PM

But my rocker studs were originally pressed and my new ones are thread in (which have a taller seat and taller overall length).

I guess I'll have to pull some measurements off the knew lifters and knew rocker studs to get a rough idea if that's causing the larger reading?

zraffz · 07-01-2012, 10:52 PM

Figured it out. Was looking at the stock rocker studs and the new ones (GMP).
The ones I had put on are meant for self aligning rockers BUT the base (where the nut is to screw the stud into the head) is physically too tall. This makes the rocker rest on it and cause a reading of 7.35" at a minimum (at which point the rocker arm is rubbing on the nut on the rocker stud).

The ARP rocker studs appear to have a shorter collar.

Don't ask me why it took me forever to notice that...

S.J.SLEEPER · 07-02-2012, 08:26 AM

Quote:

Originally Posted by S.J.SLEEPER

stock pushrod length is 7.200 I believe. which is shorter than what you are using. this is telling me that either you have the trunions on rockers flipped, or wrong rocker studs.
are they the correct rockers for your motor?

umm......

zraffz · 07-02-2012, 06:40 PM

Quote:

Originally Posted by S.J.SLEEPER

umm......

I'm aware. They are GM Performance studs for an LT1; meant for use without guide plates. My rockers were rubbing the collar of the stud/nut. Go figure, Summit said that's what people use when they don't run guide plates and they were wrong as usual.

Ordered a couple of individual studs to figure out which one will work best. I know the Trick Flows I had in the basement work but they are for another motor laying around and something had to be machined on them.