SBC push rod checker?

[rod]

i read the entire discussion about push rod lengths. all very interesting.
so i want to know your thoughts on the push rod length checker [manley or proform].
what is the correct way to use this and what are the secrets to success using this checker?
thanks rod in AZ

[Alan Roehrich]

If you're talking about the old red plastic "tool" that slips over the rocker stud, the best way to use one of those is to use it to take up space somewhere out of the way.

What you need is an adjustable pushrod length checker, Comp Cams has them. Use that on your engine, either mocked up completely (head gasket thickness included) or assembled, combined with a dial indicator that you can use to read valve lift at the retainer. Adjust the pushrod length checker until you get the correct lift and geometry for each valve and each lobe. Measure the over all length of the pushrod checker with a dial caliper, and order the correct pushrod. Thicker wall and larger diameter is better.

[Reed Granrt]

Originally Posted by rod

i read the entire discussion about push rod lengths. all very interesting.
so i want to know your thoughts on the push rod length checker [manley or proform].
what is the correct way to use this and what are the secrets to success using this checker?
thanks rod in AZ

What most of the checkers that you see or saw on the market dealt with trying to get the rocker arm in the middle of the valve. At that time, most people thought that was the best rocker arm geometry. Today, we know that is not true. You may end up with a rocker in the middle of the valve, but you just got lucky. In today's racing mode with angle milling heads and moving of valve guides even slightly, being in the middle of the valve is damn lucky. And also what contributes even more to this is the accuracy or lack of, is the rocker geometry. The short side of the rocker could be accurate and the long side could be long or short or vice versa. So you may could never get the valve in the middle.
reed

[Grant Eldridge]

Originally Posted by Alan Roehrich

If you're talking about the old red plastic "tool" that slips over the rocker stud, the best way to use one of those is to use it to take up space somewhere out of the way.

What you need is an adjustable pushrod length checker, Comp Cams has them. Use that on your engine, either mocked up completely (head gasket thickness included) or assembled, combined with a dial indicator that you can use to read valve lift at the retainer. Adjust the pushrod length checker until you get the correct lift and geometry for each valve and each lobe. Measure the over all length of the pushrod checker with a dial caliper, and order the correct pushrod. Thicker wall and larger diameter is better.

Alan, I have just been working through this on my BB chev stocker, but after reading the previous thread am not so sure I'm correct in looking at just correcting the spec lift at the valve by lengthening the pushrods. I noticed that the longer pushrods create a wider "swipe" pattern on the valve stem, even as the lift is increasing at the valve. In my case, my cam lobe lift is .240" so would theoretically produce .408" at the valve with a 1.7 rocker. In fact, with light checking springs it was more like .420", way over spec. With a race spring and the same .120 wall pushrod, valve lift dropped into the low .380" range, to my thinking a huge difference. After installing a .100" longer pushrod, lift increased into the upper .380's, still way short of my legal max at .398".
The rockers are the re-inforced Holroyd units w/ his oversize studs, so hard to imagine that kind of deflection mainly in the rocker body, but these are the numbers I've been seeing. I'm now questioning whether the objective might not be to achieve the narrowest contact pattern on the stem tip, thus minimum side thrust and drag, then consider grinding even more lobe lift into the cam? Another poster suggested that, if I understood him correctly, that the pushrod tip and valve stem tip should each be at 90 degrees to the rocker stud and in line with each other with the lobe and valve both at half lift. I'd like to hear more feedback on those points from anyone who's researched this topic. I'm an old dog, but still tryin' to learn a few new tricks. Thanks to all who are contributing to this interesting subject!
Grant Eldridge
E/SA 6650

[Bub Whitaker]

Grant says
" I'm now questioning whether the objective might not be to achieve the narrowest contact pattern on the stem tip, thus minimum side thrust and drag, then consider grinding even more lobe lift into the cam? "
Bingo, you got it...

[Reed Granrt]

Originally Posted by Bub Whitaker

Grant says
" I'm now questioning whether the objective might not be to achieve the narrowest contact pattern on the stem tip, thus minimum side thrust and drag, then consider grinding even more lobe lift into the cam? "
Bingo, you got it...

The correct rocker arm geometry WILL result in the least amount of swipe across the valve. Setting the correct lift is not getting the correct rocker arm geometry. You can check for correct rocker arm geometry without even having springs on the head but do use the checker push rod to get you the correct length. But remember that is the correct length unloaded. Some where along the line, you will need to assemble the head to get the correct length LOADED. The length doesnt change, but when loaded, the pushrod may no longer be that length.
reed

[Alan Roehrich]

The only problem with the idea of altering lobe lift is this: If you alter your valvetrain geometry so that you reduce the lobe lift necessary to achieve near maximum lift, you may change your rocker arm ratio so that it is outside the legal limit for your particular engine.

This can go either way. You could end up needing more lobe lift, meaning your rocker arm ratio has been effectively reduced at maximum lift. However, you could also end up needing less lobe lift, because you have eliminated lost motion, and effectively increased your rocker arm ratio. As far as I've read, and from the answers I've been given, if you end up with less than maximum rocker arm ratio, and needing more lobe lift, you are technically legal. If, on the other hand, you end up needing less lobe lift, because you end up above the maximum rocker arm ratio, you are illegal, even though you have legal rocker arms.

For example, let's say you are allowed 0.520" lift, using the rectangle port solid lifter big block Chevy cam engines. You're allowed a 1.7:1 rocker arm ratio, according to the blueprint spec, and your lobe lift will be approximately 0.306". Suppose you correct your geometry, and eliminate the scrubbing and thrust caused by lost motion, so that 0.306" lobe lift yields 0.540" at the valve. You have effectively increased your rocker arm ratio, even though you have not changed the rocker arm. So, your rocker ratio at max lift is now 1.76:1. You now need a 0.295" lobe lift, to get your valve lift down to 0.520". We'll ignore the fact that you really want it around 0.515" so that you're safe going through tech.

The problem is, if you go back and read NHRA Division 3 tech guru Travis Miller's posts, is that NHRA is not going to like your new effective rocker ratio, since it now exceeds 1.7:1, the maximum allowed.

Now, you might get through "basic tech" where they pop a valve cover or two off and check lift at the valve, but if they check lift at the valve and lift at the lobe, or even the end of the pushrod, and do the math, guys like Travis are known to do so, you may fail tech.

A rocker arm is not a constant ratio device, it is a constantly variable ratio device, the ratio changes as you move through the lift curve. You alter that ratio as you change pushrod length and or valve length, and the relationship between them, as well as where the rocker arm is on the stud when valve lash is adjusted.

Yes, as Bub stated in reply to Grant, getting the scrubbing and the thrust to a minimum, thereby reducing the force necessary to open the valves, is what you want. However, in Stock Eliminator, if you substantially alter the rocker ratio in the process, you can find yourself in an unhappy situation in the tech barn.

Remember, when you change camshafts, you may or may not get the same exact base circle, if you do not, you will have to start all over again. You will also find that your cam grinder may not have the lobe design you need with the lift you want. Now, if they use a CNC grinder, they may be able to easily go in and change the lobe lift. However, in doing so, they may alter the lobe design. If their Stock Eliminator cams are ground from masters, or they are unwilling to write a new CNC program, you may be stuck. This is where you need a really good relationship with your cam grinder. Adding or subtracting a few thousandths of an inch of lobe lift is not nearly as simple and easy as changing deck height or pushrod length.

[Maverick]

A few years ago, my pushrod length was off and I had to come up with something to make it easy for me to believe. My guy at the time said you could mark the valve stem and measure how far it walked across the valve stem and try to make it the minimum distance. I ended up making a dial indicator that was mounted on the valve retainer, and have the tip of the indicator against the center of the roller tip. It would measure how far it swept across the stem and I would have a number for a certain length pushrod. You change the length of the the pushrod and it changes how far it swept. Made it real easy. This was on stud mounted rockers. I picked up considerable et, and everything seemed to work. Now I got new heads with the valve cover rail real high and I can't use that tool for these heads. But I got my video camera and used it to look at the movement across the valve with different length pushrods and made my length off of what I seen in the video. i have seen a advertisement a few years back and it was called Off Your Rocker, and he sold a package with for a dial indicator that basically did the same thing. I am no expert, but I have seen other people ask mne what I did to drop the et and they ended up using it to find out where they were. Just think about what you are trying to do. I had to put in a lot longer pushrod and then put head washers under the rocker stud to get it up where it needed to be. It is fun when you can see the change.

[Reed Granrt]

First lets make sure that we understand. You cannot make the rocker arm have any more rocker ratio than what it is. If it is a 1.7 then it is 1.7. None more nor non less. If you want to delay the full ratio to come in later in the lift, then yes you can have the cam read too large on lift, but only if the cam is GROUND wrongly to start with. By wrongly, I mean it was not ground correctly to start with to get minimum scrub pattern and minimum friction losses thru out the variable ratio of the rocker arm. The cam grinder ground it to have the pushrod some length other than perfect use of the rocker geometry. Is that what you want? I dont know any good cam company today that doesnt use a CNC cam grinder some place in their facility. And believe me they can repeat within a couple of tenths of a thousands. I have worked in a facility that would grind a 100,000 shafts per week and hold +/- .0002 per shaft. That camshaft will be much closer in tolerance than you will ever be able to measure. If you want the camshaft to your spec, they can grind it. If they cannot, why are you purchasing from them? One thing I do know, you never ever get what you do not pay for. If they cannot hold the accuracy, whether it be master or CNC, on one lobe, then what makes you believe that all 16 lobes are exact. No matter what push rod length you have, the lobe has to be correct to start with and no matter what lift you have, YOU want to get to that lift with the least amount of frictional losses available. TO ME any thing else is unacceptable.
Damn here i go again on my .02 cents worth. Geez I sorry
reed

[Robert Simpson]

Originally Posted by Bub Whitaker

Grant says
" I'm now questioning whether the objective might not be to achieve the narrowest contact pattern on the stem tip, thus minimum side thrust and drag, then consider grinding even more lobe lift into the cam? "
Bingo, you got it...

Bud you have a PM. Thanks.