Push rod length***AM I CRAZY?***

[northerngn]

Ok, so i installed the weak springs on the head and used and adj push-rod.
id set rocker to 0 lash then 1/2 turn on adjuster and kept changing push-rod length until roller tip left a mark perfectly center on the top if the valve stem.

just for ****s i compared it to a stock push-rod i had laying around and guess what...its the same length...so i install to stock push-rods and measure on both valves...see pic...does this seem right? am i just lucky?...i thought after building an engine the length would be drastically different from stock

-build uses champ heads w/studs rjc bulletproof h-gasks,comp cam hyd roller,com cam hyd roller lifters,and chev style scorpion rockers with a 1.55 ratio

-dan

 

[turboclam]

No you're not nuts. Mine came out the same, so I used stock length push-rods. Champion GN1 heads and roller lifters are taller than stock. Are the poly-locks and rocker studs brand new? What # springs did you go with? What cam, 212-212?

 

[bison]

Ok, so i installed the weak springs on the head and used and adj push-rod.
id set rocker to 0 lash then 1/2 turn on adjuster and kept changing push-rod length until roller tip left a mark perfectly center on the top if the valve stem.

Just to avoid others from thinking that the pushrod length/adjustment has an effect on the footprint of the roller tip i need to correct you there. The way you adjust the roller contact point is by raising or lowering the fulcrum point not changing the pushrod length/adjustment. It was just luck that your roller tips are nearly centered in your instance. Scorpion rockers dont make rocker geometry adjustments easy.

 

[northerngn]

hmm thats odd
i say this because it was AFTER 6 full turns that i reached the proper wear pattern
at original length(too short)... the wear marks were towards the top of the stem

by ONLY changing rod length the wear pattern slowly moved towards the center until the length was reached at the point where the pattern was perfect

also if you think about it...ok now think... the fulcrum point does change as the rod length does
you see the installed height of the valve spring is constant and the rod length is variable which changes the angle on the rocker ,which positions it at a different spot on the stem...

-dan

ps not to be long winded... i just put this post up cause i thought i was kinda ironic that after i spent the money on the checking tools and springs and took the time to do it that it happened to end up the same length as stock...

 

[northerngn]

bison--- not trying to bust your chops btw just telling you my take on it:smile:
turboclam3---all parts brand new!!!:biggrin:
-dan

 

[Ttype6]

kept changing push-rod length until roller tip left a mark perfectly center on the top if the valve stem.

As you lengthened the push rod,did the rocker open the valve or did the push rod move down into the lifter?

 

[earlbrown]

Going by the wear pattern is NOWHERE CLOSE to setting proper valvetrain geometry. Rocker location retaliative to the center of the valve is no indication of correct pivot point height, or pushrod length.

 

[pacecarta]

even if they did fit i stil wouldnt run the stock weak pushrods on a roller setup

and the pushrods on the gn1 scorpions roller almost always end up around 8.50 . cam and lifter choice can change that number as well as gasket choice , i never run stock height .060-.066 gaskets on aluminums but rather .040 cometics , with all the variables its possible the stock 8.70 worked out close enough for you but thats a fluke and really unimportant that it matches because it doesnt matter to the prod builders when you order good rods whether its stock length for a gn , they ship out just as fast

the correct way with scorpions is to use a chevy rocker tool and an adjustable pushrod , set the pushrod for zero then remove turn for preload and read the instructions and adjust pushrod length based on lift of cam

 

[turbo nasty]

X2 with Bison. The fulcrum point is fixed with a shaft style rocker setup.....unless you raise or lower the PIVOT the sweep across the tip of the valve will not skew with a long/short push rod.

 

[bison]

2010!!!


BPE2013@hotmail.com

 

[earlbrown]

X2 with Bison. The fulcrum point is fixed with a shaft style rocker setup.....unless you raise or lower the PIVOT the sweep across the tip of the valve will not skew with a long/short push rod.

That's another misconception too. As cam get bigger the rocker will pivot down further with the extra lift. On a roller tip rocker that will expand the wear pattern and move the 'lift' edge closer to the pivot point. On a shoe type rocker, the contact point moves outward as it rotates. Eventually the rocker will have almost as much energy wiping across the valve tip as pushing the stem downward.

With higher lifts you need lower than stock fulcrum heights. On my engine I lowered my pedestals .045" to get halfway decent geometry.

 

[turbo nasty]

Earl that's not the question......it's not a misconception......we are talking pushrod length and its affect on valve tip geometry......Bottom line......period......whatever cam you have with the stock style shaft style rockers the valve tip geometry is what it is. The sweep will NOT change with a longer or shorter pushrod to you will have to raise or lower the fulcrum.

 

[Ttype6]

Earl that's not the question......it's not a misconception......we are talking pushrod length and its affect on valve tip geometry......Bottom line......period......whatever cam you have with the stock style shaft style rockers the valve tip geometry is what it is. The sweep will NOT change with a longer or shorter pushrod to you will have to raise or lower the fulcrum.

I think Earl is agreeing with bison and you as he mentioned that he had to lower his fulcrum .045" to achieve a good sweep across his valve stems.

 

[earlbrown]

No. I don't give two craps about the sweep. It's a byproduct of how the valve are located relative to the fulcrum point (and the angle of the stem if it's threaded).

If the valve stem height is fixed and the fulcrum is fixed there is NO adjustment to geometry with pushrod length. Changing just that one factor will do nothing but alter lifter preload. ....or knock it out of acceptable range.

When you put in a 'larger' cam, you've actually put in a smaller base circle most of the time. That lowers the lifter in the bore more than stock and it take a longer pushrod to account for the added distance from the rocker just to maintain proper preload. After that's done the rocker will exhibit more rotational degrees per lift cycle due to the higher lift. If the rocker arm starts out of from the same angle of attack all those additional degree of rotation will be on the lift side. The more it rotate the less it pushes down and the more it wipes across the tip of the valve instead.

That' why I lowered my shafts. I wanted 1/2 the extra rotation to be equalized on the top and bottom of the lift cycle.


After spending MANY hours setting up my valvetrain, milling my pedestals, measuring pushrods, etc... I honestly have no idea what my sweep pattern looks like.

 

[Ttype6]

That' why I lowered my shafts. I wanted 1/2 the extra rotation to be equalized on the top and bottom of the lift cycle.

You did this to move the roller toward the exhaust side of the valve stem. We are all in agreement.

 

[earlbrown]

No, I have stock rockers and I wanted to put my extra degree of rotation from my 215/220 up top, not just on bottom. .... and you got it backwards. If I had a roller tip rocker, by lowering the fulcrum it would have moved the contact point towards the intake gasket.

To maintain proper rocker geometry when going with a bigger cam, you need to lower the fulcrum, raise the valve tips, or a combination of both.... to do it right. With our engines and stock rockers it's physically not possible to have correct geometry (Jim Miller holds the patent, and he told me he has no interest in making Buick V6 shaft rockers). But it is possible to not make things worse than they already are. The trick is to minimize the errors and find a balance point between the pushrod side being wrong and the valve side being wrong.

It also helps if you have access to a milling machine and a 13/16" ball mill.

 

[Ttype6]

No, I have stock rockers and I wanted to put my extra degree of rotation from my 215/220 up top, not just on bottom.

So your goal of splitting the difference of the extra lift resulted in moving the contact area of the rocker foot on the valve stem toward the intake producing a contact patch more centered on the valve stem.

If I had a roller tip rocker, by lowering the fulcrum it would have moved the contact point towards the intake gasket.

The same thing will happen if you have stock rockers.

To maintain proper rocker geometry when going with a bigger cam, you need to lower the fulcrum, raise the valve tips, or a combination of both.... to do it right.

With stock rockers.

 

[earlbrown]

So your goal of splitting the difference of the extra lift resulted in moving the contact area of the rocker foot on the valve stem toward the intake producing a contact patch more centered on the valve stem.
The same thing will happen if you have stock rockers.
With stock rockers.

Actually it made it wider. And it wasn't centered. As the shoe type rocker goes through it's motion the rocker ratio increases. That causes it to reach our further from the fulcrum. The difference between you and I, is you care about where it's touching. I don't.

Unfortunately I had to live with it as it's not possible to have correct geometry with a shoe type stock rocker. I just wanted to get the angles as square as possible at midlift on both side of the rocker, and minimize overarcing, underacring, wasting radial motion, and physically pushing on the side of the valve stem.

Since the rocker is wrong to start with, both angularity AND at the contact patch, it's just minimizing the evils.


Trust me on this one. I have a thorough understanding of converting linear motion into radial motion and back to linear motion, along with excellent spacial perception. I know how these things work together. If the distance from the fulcrum to the valve stem was adjustable, I'd adjust it..... AFTER the geometry was set and correct pushrod were in place.

On a fixed shaft system, with a fixed valve tip height, there's NO adjustment to move the contact patch, NONE. Jacking up the shaft just to get a centered pattern on the tip is going to be 100% wrong almost 100% of the time. It's the wrong approach to cure a 'problem' that's not really a problem. And the side effect is normally screwing up what valve motion the cam is trying to achieve.

 

[Ttype6]

Let's try this. The reason I brought this thread back to life was because northerngn stated that he was able to move the contact patch of his rocker rollers on his valve stems by changing the length of his push rods. Anyone reading this and believing it could run into problems trying to put this advise into practice. You,bison,turbo nasty,and I have stated that this is not true and that the way to change this is to move the fulcrum up or down. We are in agreement about this one issue. I think this correction will be helpful to some who read it.

 

[earlbrown]

If you change the length of a pushrod on a engine and nothing else, the ONLY thing that will change is lifter preload.