Pat Hall

iTrader: (31)

Hey guys. I found a guy who has a set of Comp 4130, Hi-Tech pushrods for sale for a good price. He said the length is 7.100", and the stock length for hydraulic roller is 7.200". The question I have is this. I've got a set of AFR heads that I'm pretty sure have valves that are .100" taller than stock, according to the part# etched on them anyways. I guess this is a common upgrade since AFR has it listed as an option when purchasing new heads from them. Would the 7.100" pushrods work better with .100" taller valves as compared to stock length valves? I realize getting the tool and checking the actual length would be the most accurate thing to do, but for a ballpark figure, would the .100" shorter pushrods theoretically be better with the longer valves? In my mind, it makes sense that this would make the rocker arm geometry more even anyways. As always, any advice or input is greatly appreciated!

Ward

iTrader: (1)

Shorter pushrods in theory would be good with taller valves, since they should keep the pushrod from binding anywhere. As long as they don't touch the pushrod holes in the heads, I would think they'd be okay.

Edit: actually, after thinking that over, I think taller valves might be better with longer pushrods. This should get the pushrod angle back to stock. Basically, the rocker arm would move up a little, to match the longer valves and pushrods.

Pat Hall

iTrader: (31)

Yeah, that kinda makes sense too I guess. No worries about the pushrod holes though since they're AFR's. There's no actual "slots" for the pushrods, just the guideplates.

Damon

Longer valves, longer sticks. That's how it usually works. But checking for proper rocker geometry is always best.

If you need a quick-and-dirty way of checking I will direct you to the Moroso (or Mr. Gasket??) plastic push-on length checker. Looks kind of like a plastic rocker arm that you shove over the rocker stud. Costs peanuts, easy to use, and is accurate enough that it will almost always get you in the ballpark- close enough you won't have any problems. I've found it to give results +-.050" in pushrod length from true optimal every time I've used it. Not always perfect, but way better than just guessing at it, that's for sure!

onfire

Pat,

What you can do is put the rods in for the #1 cylinder. Then before you put the in/ex rocker on, mark the tip of the valve with permanent marker. Install and adjust the rockers. Roll the engine over 2 full turns to make sure you made a good mark. Then check your mark. The ideal is to be in the center and a thin mark.

I have attached what mine looked like. This mark was attained during tear down after I first broke in the engine. This then shows you if you have to get the adjustables out and get more accurate. I have no experience with that tool that Damon noted but is yet another way to acheive the same end result.


Rabi C.

lukn4trbl

You should be checking PR length at mid valve lift with a solid lifter.
Installing the incorrect pushrod could cost you a bit of lift (~ thousandths)
if the rod does not extend above the rocker centerline.

If you can't get a hold of a solid lifer, use a dial, achecking spring and an adjustable pushrod to get the correct length. The rocker tip should be at
90 degrees with the valve at mid lift for correct geometery.

It seems like a bit of work for a few thousands, but at least you have
options. A nicely set up valve train will also extend the life of the guides.

BTW: The rub mark in the photo shows an incorrect scrub pattern.

Pat Hall

iTrader: (31)

Thanks for the tip on that tool. I've looked at the different tools at Summit and Jegs, and I've seen the one you're talking about. Since I've never played around with valve train geometry, or I guess I should say since I've never worried about it before, I really have no idea which tools are easy or fairly effective to use. Hey Onfire, I've also seen guys use the magic marker trick to check the pattern. Kinda similar to checking the contact pattern on a ring and pinion. I guess as long as the line ends up close to the center of the valve stem, your geometry is pretty close right? I'll probably pick up that Moroso tool. I'm not overly **** about this kind of stuff, but I'll feel better knowing it's at least in the ballpark. In other words, if I don't end up with bent pushrods or a broken rocker stud, I'll be happy!

sofakingdom

iTrader: (1)

Actually, you want the mark to be as NARROW as possible; ignore where it lands on the valve stem. That doesn't matter. In fact, higher-ratio rockers will almost always move it over toward the exhaust side; they get their ratio increase partly by shortening the side toward the push rod (which is why the holes have to be lengthened alot of the time), and partly by lengthening the arm toward the valve (which moves the contact point outwards).

Imagine the rocker arm swinging in its arc. If the arc is EXACTLY centered on the valve tip over its entire length, then the rocker tip will start up closer to the stud at zero lift, move toward the exh side, reach max travel that way at half lift, then start to move back toward the stud as lift increase toward max. If it swings farther in one half of its cycle than the other (not centered, then the mark it leaves on the valve stem will lengthen.

A solid lifter and "check" springs work the best. It's almost impossible to get a reliable indication with a hydraulic lifter (unless it's filled with grease or Vaseline or something), because the plunger will depress and take up some of what shoudl be push rod length. You'll end up selecting push rods that are actually about .100" too long.

The more important benefit of getting the geometry right, is reduced side loading (and wear) on the valve guides.

Those little plastic tools are better than nothing; but they make ONE critical assumption, that's not always true. That is, that the rocker is level at the center of its arc. However, there's no inherent rule about rockers that says the push rod cup and the rocker tip have to be like that; so if they're not, then the little plastic thing, to the extent that it doesn't match the ACTUAL rocker shape, can be quite a ways off.

Pat Hall

iTrader: (31)

Hey Sofa, that's right, I knew I was forgetting something when I was talking about the contact pattern. I remember from other posts on here that a narrow line is a good indication. This probably indicates that the rocker is staying more centered throughout the lift cycle right? Centered, as in vertically, not horizontally. Am I on the right track here?

1989GTATransAm

iTrader: (3)

Yep, Sofa is correct for best lift. Look at it this way. The more side to side movement of the roller across the valve tip the less vertical movement there is that actually lifts the valve. I have found that usually requires a longer pushrod.

I actually made up a dial indicator similiar to the one in the picture to get mine dead nuts. However I made mine to clamp around the retainer. I was able to get it around .032" of total movement. My cam has .570" lift.

Damon

The geometry question is a more complicated one that it might at first appear. That's why I mention the cheap plastic checker tool- it's basically fool-proof and plenty accurate for what 99% of people need.

Going by rocker contact pattern is more difficult to do (easier to make a mistake or misjudge something), AND you will almost always end up with sticks that are longer than stock. This is often the case becuase the "minimum travel" method is NOT HOW THE FACTORY DOES IT.

The factory uses shorter sticks which create slightly more total travel across the valve tip. But, as with everything the factory does, there is a method to their madness and I spent many hours figuring out why they do what they do. As it turns out, they're no dummies. Shorter sticks cause more movement across the valve tip at low lifts, which valve spring pressures are lowest. But when you get above the mid-lift point, however, where spring pressures are high, the tip of the rocker doesn't move hardly at all across the valve tip. So they put less strain on the rocker, valve stem and valve guides when spring pressures are high. This is smart engineering, especially considering the factory never used roller-tips on any of their factory engines (at least not older Gen 1 small blocks).

I have now adopted the factory geometry method for ALL street engines I build (and I build almost nothing that doesn't drive on the street).

The plastic checker tool is set up to give geometry that is roughly equivalent to how the factory does things. It can NOT account for differences in max valve lift from cam to cam. It doesn't know what mid-lift point is for your particular cam. It is built around some "typical" street performance cam max lift number- about .500", near as I have been able to figure out. So it's not perfect. But if your cam is in the .450"-.550" lift range, it's pretty damned accurate. It also can't know what the geometry of your particular set of rocker arms is (yes, rockers can vary in where they place the pushrod cup and rocker tip in relation to the fulcrum point), but again, most typical bolt-on street performance rocker arms are set up very similar to eachother and to factory rockers. And the tool is STILL very accurate every time I've used it on many different engine combinations.

It is close enough that I always use it as my first check. Beyond that I get more sophisticated to dial in the final stick length (I spend a lot of time on rocker geometry- more than most people do). But that cheap little tool is good enough that if you trust nothing else, it will still give you sticks that are plenty close to optimal 95% of the time. Even if you build only one non-stock SBC engine in your life you should buy that tool.

1989GTATransAm

iTrader: (3)

"But when you get above the mid-lift point, however, where spring pressures are high, the tip of the rocker doesn't move hardly at all across the valve tip."

That is probably true and the lift probably does not go up much more either because it was used up on the wasted motion in the first half of the lift.

For those that are interested here is a link to a recent discussion on the subject by some of the best engine builders in the country. You be the judge.

http://www.speedtalk.com/forum/viewtopic.php?t=9556

Damon

If you can follow that thread then you're WAY beyond "I need to know what the right length pushrods are for my engine." That's post-graduate level discussion there. And it relates to Crane's "quick lift" rockers which are a whole different bag of gummy bears than more traditional universal bolt-on aftermarket rockers.

You need sticks that are roughly the right length and not make a valvetrain-breaking mistake by going too long or too short. That's job one. And simple is always better your first time through. That's why I recommend the cheap little plastic push-on rocker arm checking tool. It's easy to use, plenty accurate 99% of the time, and the interpreting the results is dirt-simple. Safe and effective for the first-timer.

sofakingdom

iTrader: (1)

What Damon says about the factory using shorter push rods is also true; the logic being, bias the arc toward where the rocker pushes straighter on the valve at high lifts (high pressure), and tolerate a little more error at lower lifts (lower pressures) where they don't cause as much guide wear.

You can accomplish the same thing by finding the narrowest pattern, and then simply rounding to the nearest stock length DOWNWARD (they come in .050" increments from the mfrs). Or, if you're right at a .050" increment, drop to one increment lower.

This whole deal is alot like degreeing a cam. Even if you don't DO anything as a result of it, just going through the motions enforces a whole bunch of discipline and rigor into your build, that can't help but improve your finished product.

Pat Hall

iTrader: (31)

Thanks again guys for the explanations and advice! Yeah, sometimes I like to read the really complicated articles just to see how long it takes for my eyes to glaze over. The DIY Prom board is where I usually go to accomplish getting confused very quickly. But seriously I have to agree with Damon. As I stated earlier, I'm not THAT **** about it. Just want to make sure the geometry is close enough so I avoid any damaged valvetrain parts. The shorter pushrod theory makes sense in that you run more risk of damaging things at higher lifts when the springs are under full pressure. In fact, I have to wonder if some of the major cam companies purposely make their standard length replacement pushrods a bit shorter for that very same reason. I noticed Comp and a few others, list the OEM, hydraulic roller pushrod lengths they sell at 7.195", instead of an even 7.200". Whatever the case, I should have enough understanding of it now to be able to set up my valvetrain safely. Btw Sofa, I have to confess another sin. I've never bothered degreeing a cam in yet either. I usually just line up the dots and call it a day. I'm just a lazy a s s when it comes to that stuff. Lol.

1989GTATransAm

iTrader: (3)

I will cut to the chase on the discussion I referenced to. Basically if you want the most lift and the valve to follow the profile of the cam the best use the mid-lift principle.

What I have found out is there are quite a few different methods people are using to figure rocker arm geometry. They all work to some degree. Some are better than others.

You should read the discussion on how to degree a cam. Especially when you have symetrical and assymetrical cams. You think there is one method? Not so.

Pat Hall

iTrader: (31)

Yeah I bet you could get some interesting results by degreeing an asymmetrical cam different ways. I guess you could kinda look at it as intially advancing or retarding the cam several degrees when you install it being the "roughing in" adjustment, then degreeing it a certain way would be the "fine tuning" part of it. If I were a professional engine builder, and putting together competition engines that are going to be judged against other ones, that'd be homework well worth doing. Most guys building a street engine don't usually go through that much trouble or attention to detail, but I have met a few that are picky enough to do so. A buddy of mine put together a supercharged, nitrous-fed, 383 LT1 motor in a 97 T/A, and he took the time to set up everything just perfect. He always shakes his head in dismay when I tell him "ahhh, I'm just gonna throw it together and see what it can do". Course he's military and puts jet engines together for a living. He's the type where his house, garage, car, everything is clean and perfect. Sometimes I wish I could be more like that, and other times I'm kinda glad I'm not.

sofakingdom

iTrader: (1)

I actually asked a cam grinder that very question here not too long ago. He tells me that you should use the actual peak-lift point of the lobe as the "lobe center", by dial indicator, at the mid-point of about the .005" points off of the peak. I've done em that way, and also by the mid of the .050" points, which was how they were done "back in the day"; doesn't always produce the same results on modern cams.

The thing about putting them together perfect and measuring and checking everythign, isn't so much that it's all right somehow; but when problems do occur, it sure makes it alot easier to identify and/or eliminate possible culprits. Things are alot less "fuzzy" when you go to work on it later.

Pat Hall

iTrader: (31)

Good point there Sofa. That kinda falls under the same logic that it's not a good idea to do a ton of mods all at the same time. When it ends up running horrible, it's a lot harder to isolate exactly which particular mod is causing the problem. When you throw too many variables into a combination, the end result can be a big, "fuzzy" mess. Sifting through that mess can be a real time-consuming nightmare. Having the combination of parts agreeing with each other is always my biggest concern when putting a new system together. If you have decent mechanical skills, putting everything together is the easy part.

1989GTATransAm

iTrader: (3)

Sofa, you are correct. Regarding the discussion about degreeing a cam on that website it came down to you better ask the person who ground your cam for what method to use. Sounds like with doing the .005" down from peak lift on either side you should be able to find the true intake center line. One of the arguments on the other site was the .050" method down does not always work depending on the cam lobe.

Regarding the "fuzzy". Again if you want to make the most horsepower from your combination you have to get the "fuzzy" or variables under control. Most people just say screw it and bolt the motor together.

When degreeing a cam you have to find true top dead center of the piston. How many people tripple check this to make sure they have it right. If that is not quite right and the next step is not quite right the "fuzzy" begins to build.

Joe Sherman was quoted as saying I can sell the same parts to my customers and when I build the same motor I usually make 40 to 50 more horsepower. I think that says it all.

1987CamaroZ28

This is an older thread, but a good one. Are people changing their OEM pushrods when going to a higher lift cam? I'm under the impression the answer will mostly be no.
I've got a stock short block LB9, with a comp cams 500/510 210/220 cam, ZZ4 heads, will be using 1.5 full roller rockers. Do i need to check and measure for the proper size pushrods, or can i re-use my stockers based on my changes?