What is the proper way to determine push rod length?

[A/Fuel]

For instance, say you are going from a standard rocker raito to a high ratio rocker. You can tell the pushrods are too short because the rocker adjusters screwed way down. So instead of just saying you need a 1/4" longer pushrod (which would probably work) is there a forumla out there based on rocker ratios, or what's the right way to do it?
For arguements sake, say I'm going from a 1.5 to a 1.7 rocker.

[JeffMcKC]

Re: What is the proper way to determine push rod length?

th easy way is to cut a push rod in two thread the inside and take a peice of threaded rod in the center. You are trying to make the witness mark on the end of the valve be in the center of the tip of the valve, it will move back and forwards as it travels. So you can blacken the end with marker. I have never had any luck with the checkers you buy that slip over the end of the stud and lay on the valve tip.

[BlackoutSteve]

Re: What is the proper way to determine push rod length?

I think those checkers are designed for stock cams and rocker within the stock geometry design..
I've got one and it disagreed with what I actually needed in pushrod length because I have 0.100" taller valve stems and a 0.700" lift cam.
It's not what the cylinder head designers had in mind.

[DanStokes]

Re: What is the proper way to determine push rod length?

I agree with the adjustable push rod method. I've made several and have had excellent luck with the method. As an experiment I used the one I made for the 5.8 and measured a stock 5.8 with it. I got pretty much exactly what Ford came up with.

Dan

[Scott Liggett]

Re: What is the proper way to determine push rod length?

I bought one from Comp, but they had all the measurements for my setup dead on. My Edelbrock heads, small base circle roller cam and matching lifters. I still used the checker, but the ones they recommended were spot on.

[MadmanMark]

Re: What is the proper way to determine push rod length?

Adjustable pushrod checkers are the only way to go.

There are different opinions regarding the pattern. It seems to me most experienced builders like a narrow pattern reasonably centered over a perfectly centered larger pattern.

On the Team Chevelle web site, there was an excellent write-up about how to get it perfect, which involves finding what pushrod length puts the line between the rocker stud mount and tip at a right angle to the valve stem:
http://chevelles.com/forums/showthread.php?t=284771

[REARSPROCKET]

Re: What is the proper way to determine push rod length?

I use the comp adjustable or a pushrod that's close, then I Sharpe the top of the valve stem, install rocker and pushrod and adjust or lash as normal, then spin the motor over two revolutions and remove the rocker and look at the mark on top of the valve stem to see if its centered or slightly off center towards the intake.

[TC]

Re: What is the proper way to determine push rod length?

On the Team Chevelle web site, there was an excellent write-up about how to get it perfect, which involves finding what pushrod length puts the line between the rocker stud mount and tip at a right angle to the valve stem:
http://chevelles.com/forums/showthread.php?t=284771

Isn't that what those plastic pushrod checkers do?? I think I'm the only one that used one of those and had it work.

Here's the problem I had on my 406, it has a small base circle solid roller cam, .100 longer valves, the block has been zero decked, and the heads have been milled, not to mention I run 1.6 ratio rockers instead of 1.5's. When I first put it together with the pushrods that came with the Crower kit the side of the pushrod actually hit the head where it went through the head. After using the plastic checker and an adjustable pushrod I was able to determine that I needed a .250 longer pushrod. So I order a set, installed them and I no longer hit the head and the the rocker tip ran in the center of the valve.

[JeffMcKC]

Re: What is the proper way to determine push rod length?

They never get close enough for my taste. Its the pattern I am after, I have to clearence most of my stuff to run the push rods I do at times. I have .750 offsets right now took a bit of grinding to clear even then

[TC]

Re: What is the proper way to determine push rod length?

They never get close enough for my taste. Its the pattern I am after, I have to clearence most of my stuff to run the push rods I do at times. I have .750 offsets right now took a bit of grinding to clear even then

Ya I had to do some grinding on the heads to, but I did it before I got the longer pushrods, so I'm not sure if I had to grind or not with the longer ones. As for the pattern, mine was pretty much smack dab right in the middle of the valve. And I'm not saying those checkers are perfect at determining pushrod length, more that they can get you to the general length your going to need and then you can fine tune from there. But then like most of the time I probably just got lucky. ;)

[malc]

Re: What is the proper way to determine push rod length?

Here?s a couple of CHP articles on pushrod length.

http://www.chevyhiperformance.com/te...gth/index.html

http://www.chevyhiperformance.com/te...ods/index.html

[A/Fuel]

Re: What is the proper way to determine push rod length?

Very intresting, I think we have an adjustable push rod somewhere, but now you guys made me think the valves could be a tad too short also.

[JeffMcKC]

Re: What is the proper way to determine push rod length?

Keep in mind: valve springs, and retainers, a lash cap maybe the way to go

[Loren]

Re: What is the proper way to determine push rod length?

Ya know I've never really considered where the rocker touches the valve stem as something that would determine pushrod length. I do check contact through the travel, using a light spring.

What I worry about is what I'd call the lever angle, for lack of knowing some proper term. And, for lack of having a better idea, this is what I do: with everything assembled incl. head gasket, I turn the crank to put the valve at half whatever the total lift with the installed cam will be (such as if it's a .550" cam, get the valve to where it's down .275" using a dial indicator). Then see that the angle the rocker arm makes splits the difference between the valve and the pushrod. Ideally at this point if you drew a line up the centerline of the valve stem, and a then a line from the top of the stem over to the c/l of the rocker shaft (on a Mopar), the difference between the two lines should be 90 degrees, and if you could draw a line from the shaft c/l out to the pushrod/rocker pivot point center, that should make 90 to the pushrod. If you can't make 90 by whatever adjustments available then at least try to get both angles the same.

I know that's not a very clear description, I could do better by drawing a diagram. Just know that by doing the checking at the midway point in valvetrain travel however you can possibly do so (it can take some creativity in methods), you are taking the total travel into consideration. Why would the beginning angles/dimensions between components be the same for a cam with .400 lilft and one with .600? That's what you get though when you stick to a "standard" pushrod length or checking device.

[JeffMcKC]

Re: What is the proper way to determine push rod length?

Over all, I don't know a simple way to reply to this one but,,, your looking for overall valve train stability.

Using small base circle cams, tall lifters, longer valves for bigger springs to not coil bind, different deck blocks, different length studs or a shaft assemblies. You can get the pattern in the middle more and keep it tight so your not adding to stability issues. Dealing with higher lift and bigger rocker ratio's keeping the valve under control at 7500 to 9000 be comes a bigger effort, this is where longevity of valves springs and engines can be saved, or lost, plus power by following the lobe of the camshaft.