How can you tell when the lifter is on the cam base circle to measure push rod Thanks

 

I am not an expert in this area however, I would think you could simply remove the valve cover, pull the rocker off and measure the pushrod length directly.

 

2 valves on each cylinder. When one is about half open the other will be on the base of the cam. The one on the base should have play between the rocker tip and valve stem.

 

Thanks FKING1 that's what i was looking for

 

That depends on which side of fully open your on. If the exhaust valve is on the leading side of fully open, the intake valve can be open some also. Also with hydraulic rollers there is no play, the lifter is supposed to be loaded, I'm not positive here but I think its .040 to .060. When the exhaust valve starts to open the intake valve is on its base of its lobe. When the intake valve has opened and is almost back to closed the exhaust valve will be on its base.

 

I thought that you measured your pushrod length by marking a valve with a sharpie then putting on your rocker arm, spinning the engine and checking where the wear mark is, when the wear mark is in the middle, that is the correct length pushrod. What you guys are describing seems to be measuring valve lash.

 

Measuring for correct p/r length, lifter is on the base circle of the cam and there is zero lash, just zero lash at the p/r cup of the rocker.

Checking the valve wipe consists of marking the valve stem with said sharpie, rotate crank at least 2 full turns, remove rocker to see wipe pattern. Optimum is thru the center.

Been told that wipe pattern changes when changing rocker arm geometry and it is 1st step when checking for correct p/r length.

Do a search, Mr Vettenuts has many excellent write-ups.....

 

My reply was to the the question: "How can you tell when the lifter is on the cam base circle".
I don't know what that would have to do with checking push rod length, unless its just a good place to be when removing the rocker.

 

With no load on hydraulic lifters there is no appreciable play, however you can wiggle the rocker arm as opposed to not being able to when it is loaded.

 

OK, so what I am seeing is that if you have too short of a pushrod, when you tighten the rocker to 22ft/lbs there will be lash. If the pushrod is too long there will be zero lash before you get to 22 ft/lbs?

I keep reading that if your valve wipe is off center then you need a different length pushrod but reading this it seems that will mess up the base circle/zero lash setup?

 

You adjust your valve wipe by shimming the rocker (do this first, then check push rod length off the cam lobe base). The only reason for changing push rod lenth on a LS motor is for lifter preload. Earlier SBC engines did change the rocker contact on the valve by different length pushrods. Whats up here anyway, why do you believe you need to change pushrod lengths. Milled heads, differant cam, differant rockers? Just interested to see what your going to do with this information.

 

planning cam and head swap, read time and time again on here to measure for the correct length of pushrods. never saw shimming come up to change valve wipe only pushrod length. this information looks different than what i have read before.

 

Keep reading, check this thread:

http://forums.corvetteforum.com/c5-t...e-pattern.html

It's got good pictures that show the shims. Think about it, these rockers are differant than the old style SBC's. by bolting the fulcrum of the rocker in place it keeps the arc of the rocker in one position. There for raising the rocker will change where the roller rides on the valve stem, just like longer pushrods did on the old SBC's. After the wipe patern is established then the push rod lenth needs to be determined.

If you really want some rocker arm geometry information go here:
http://www.mid-lift.com/INTRO-ML-BKGRND.htm
Jim Miller was the first to determine where rocker vs valve centerline should occure. I suspect his rockers are some closely guarded secrets in differant forms of proffesional racing.

 

I read that page a few times and it does make sense. I am just confused as to why most of the how tos dont really talk too much about doing it that way. You cant really go by the service manual on this one because the service manual assumes that you are using stock parts. vettenuts write up shows roller tips, how does this work for the oem rockers that have a wider contact point?

 

Hum, OEM rockers, why would you want to change from the OEM push rods if you're using stock rockers? Most everybody agrees there is minimal HP to be gained from the use of roller rockers, I personally like them for the reduction in sideloads on my valve stem resulting in less valve and guide wear. Another reason I'm installing rollers is the HP gained under the curve, that is a plus for me and I do not understand why it isn't motivation for others. One concern I have with the LS setup stock or aftermarket rocker is the small bolt that holds each rocker in place. I've broken many of the old SBC 3/8 th's studs and I think one 7/16 stud. For that reason I kindof wish now I had bought Shaft mounted rockers for the extra support. I hope you had a chance to read the artical from Jim Miller concerning mid-lift and rockers, it took me a while to understand that the contact patch on the valve stem not only needs to be in the center of the valve but it needs to be as small as possible, that is why he refers to some of the other rocker manufacturers design being wronge due to over arc situations. If he ever designs a set of rockers for a LS motor you can bet they will be state of the art and will have easy to understand directions on how to properly set push rod length. I hope I have not mislead you in any of this, This information is to the best of my knowledge and I in no way want to indicate I know it all, because I'm sure I don't. If I had a bunch of money I'd be dangerous though.