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Old 10-30-2011, 10:08 PM   #1
Bub Whitaker
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Default Re: SBC push rod checker?

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...
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Old 10-30-2011, 10:42 PM   #2
Reed Granrt
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Default Re: SBC push rod checker?

Quote:
Originally Posted by Bub Whitaker View Post
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

Last edited by Reed Granrt; 10-30-2011 at 10:55 PM.
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Old 10-30-2011, 11:14 PM   #3
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Default Re: SBC push rod checker?

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.
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Old 10-30-2011, 11:57 PM   #4
Reed Granrt
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Default Re: SBC push rod checker?

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
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Old 10-30-2011, 11:02 PM   #5
Alan Roehrich
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Default Re: SBC push rod checker?

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.
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Old 10-31-2011, 08:49 AM   #6
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Question Re: SBC push rod checker?

Quote:
Originally Posted by Bub Whitaker View Post
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.
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Old 10-31-2011, 09:15 AM   #7
Greg Reimer 7376
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Cool Re: SBC push rod checker?

Well, here I am at 6:07 AM on a Monday reading this. Here's two more cents. Since most of these stocker cams are ground with more precision and consistancy as to lobe lift and profile, which can be verified by checking all 16 lobes with the cam in the block, then the places correction is necessary would be in the rest of the valvetrain. If all 16 lifters check,then the pushrods, rocker arms, and the valve stem lengths have to be considered. The post regarding minimizing the sweep of the tip of the rocker arm across the tip of the stem revealed the secret to minimizing valve train friction, that sounds like the optimum goal. Variations in rocker arm ratio and valve seat depth and variations in stem length are the only variables left to play with. The actual ratio of rocker arms vs. effective ratio is one more thing to concern yourself with. Seems like these two threads have revealed more areas of thought to be considered than anything else I've seen in a long time.Yes, push rod length is more critical than most persons have probably thought.
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Old 10-31-2011, 10:10 AM   #8
Reed Granrt
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Default Re: SBC push rod checker?

Quote:
Originally Posted by Greg Reimer 7376 View Post
Well, here I am at 6:07 AM on a Monday reading this. Here's two more cents. Since most of these stocker cams are ground with more precision and consistancy as to lobe lift and profile, which can be verified by checking all 16 lobes with the cam in the block, then the places correction is necessary would be in the rest of the valvetrain. If all 16 lifters check,then the pushrods, rocker arms, and the valve stem lengths have to be considered. The post regarding minimizing the sweep of the tip of the rocker arm across the tip of the stem revealed the secret to minimizing valve train friction, that sounds like the optimum goal. Variations in rocker arm ratio and valve seat depth and variations in stem length are the only variables left to play with. The actual ratio of rocker arms vs. effective ratio is one more thing to concern yourself with. Seems like these two threads have revealed more areas of thought to be considered than anything else I've seen in a long time.Yes, push rod length is more critical than most persons have probably thought.
Greg
Several years ago, I made myself a rocker ratio checker. It is simple. Take a flat piece of metal and install a stud. Really needs to be what ever stud diameter your rocker system. Since I was using a small block chevy, I used a 5/16 steel ball out of a roller bearing. I then placed this on top of a gage block. It seemed easy to put 1 inch lift on small side of rocker ratio was easiest to use. I then put a dial indicator on the large ratio side. You can then measure the correct ratio of the larger side. I then went thru every stamped rocker arm I could find. I then put 8 together for the intake and 8 more for exhaust. All as close to each other as I could get. While doing this, for my stock rockers, I decided to check some roller rockers that I had (used-couldnt afford new ones). Man was I ever surprised at what I found. You have to remember this was several years ago and I found out later that some companies was still repeating the wrong way to build a rocker arm. I had no idea what was wrong but I knew it was wrong or the rockers did not make 1.5 (SBC). I was at one of the first PRI shows in Nashville, Tenn and I went to a presentation by Smokey Yunick. I waited until after his presentation and asked him. His comment was " Damn son, dont you know that cause it is new does not mean it is right" He then splained the world too me in a language that embarrassed me then. I came back and got a set of rockers (used)like he told me to get and they checked all the way thru a rotation. Apparently, people like he and Bill Jenkins new this but I had no clue.
reed
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Old 10-31-2011, 06:13 PM   #9
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Default Re: SBC push rod checker?

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Bud you have a PM. Thanks.
It's Bub... BUB
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Old 11-01-2011, 07:16 AM   #10
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Default Re: SBC push rod checker?

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It's Bub... BUB
Sorry about that Bub...
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