Engine pushrod /rocker geometry question

[Jerry G.]

I have converted my roller rocker motor for the race car to a stamped steel rocker valvetrain. I'm trying to get the point of contact and sweep of the pushrod on the rocker to move more inboard(closer to the center pivot). I think I'm supposed to shorten the pushrod but I've tried that and don't see much difference. It could be that it just isn't that sensitive to the pushrod length. Any engine builder experts out there with a thought on this?

[Clem Z.]

Re: Engine pushrod /rocker geometry question

I have converted my roller rocker motor for the race car to a stamped steel rocker valvetrain. I'm trying to get the point of contact and sweep of the pushrod on the rocker to move more inboard(closer to the center pivot). I think I'm supposed to shorten the pushrod but I've tried that and don't see much difference. It could be that it just isn't that sensitive to the pushrod length. Any engine builder experts out there with a thought on this?

start with at least .050/.100 shorter to see what happens

[Duke W.]

Re: Engine pushrod /rocker geometry question

Also pay attention to actual rocker ratio. My measurements on an OE 327 yielded about 1.375:1 at the lash point on about 1.44:1 at maximum lift with a 0.3" lobe.

Ideally, to minimize side load the rocker tip should be on the center of the valve stem at about mid lift, and moving it outboard might improve rocker ratio, but I did not test this or the effect of pushrod length.

Duke

[Michael H.]

Re: Engine pushrod /rocker geometry question

I have converted my roller rocker motor for the race car to a stamped steel rocker valvetrain. I'm trying to get the point of contact and sweep of the pushrod on the rocker to move more inboard(closer to the center pivot). I think I'm supposed to shorten the pushrod but I've tried that and don't see much difference. It could be that it just isn't that sensitive to the pushrod length. Any engine builder experts out there with a thought on this?

It takes quite a bit of push rod length change to have much of an effect on valve lift. If I remember correctly, a shorter push rod decreases total valve lift?? Either way, the chanhe isn't substantial.

Valves that contact the rocker arm closer to the tip will result in slightly more lift around the maximum lift point on the lobe but at the expense of reliability, and it does almost nothing at low lift. It's not worth it for the small amount you gain, if you actually do see a gain.
Did lotsa dyno testing with rocker geometry in the early 70's and most of it was a waste of time and material.

(pssssssst..... big block rocker arms CAN be fitted to small blocks)

[Clem Z.]

Re: Engine pushrod /rocker geometry question

(pssssssst..... big block rocker arms CAN be fitted to small blocks)[/quote]
you have to move the location of the studs to do this. you can use pontiac rocker which are 1.6 and if you can find super duty ones they are 1.65

[Jerry G.]

Re: Engine pushrod /rocker geometry question

It takes quite a bit of push rod length change to have much of an effect on valve lift. If I remember correctly, a shorter push rod decreases total valve lift?? Either way, the chanhe isn't substantial.

Valves that contact the rocker arm closer to the tip will result in slightly more lift around the maximum lift point on the lobe but at the expense of reliability, and it does almost nothing at low lift. It's not worth it for the small amount you gain, if you actually do see a gain.
Did lotsa dyno testing with rocker geometry in the early 70's and most of it was a waste of time and material.

(pssssssst..... big block rocker arms CAN be fitted to small blocks)

my problem is not trying to get more lift. The problem is the contact point is too far out near the tip. i'm trying to bring it back to center more. my question is do I reduce the length of the pushrod to do this. I think Clem answered it by suggesting I reduce the lenth by .050 to .100

[Clem Z.]

Re: Engine pushrod /rocker geometry question

jerry try one of these as the are pretty damn accurate. make sure you get the proper one for the diameter of the stud you are using. http://store.summitracing.com/partde...part=MAN-42137 i never used the adjustable push rod i just used a feeler gauge on the side that came up short to see what i needed.

[Joe L.]

Re: Engine pushrod /rocker geometry question

Also pay attention to actual rocker ratio. My measurements on an OE 327 yielded about 1.375:1 at the lash point on about 1.44:1 at maximum lift with a 0.3" lobe.

Ideally, to minimize side load the rocker tip should be on the center of the valve stem at about mid lift, and moving it outboard might improve rocker ratio, but I did not test this or the effect of pushrod length.

Duke

Duke-----


That's one of the problems with stamped steel OE rockers. Some aftermarket rockers are much better at providing the GM-specified 1.5:1 ratio for small blocks and 1.7:1 ratio for big blocks. Examples are investment cast Comp Cams roller trunnion Pro Magnum and Hi-Tech Stainless as well as Crower Stainless.

All rockers for GM Gen III and Gen IV engines are roller trunnion, investment cast steel. I would not be surprised if precise control of rocker ratios was ONE of the reasons for changing to this type rocker.

[Jerry G.]

Re: Engine pushrod /rocker geometry question

Thanks Clem. That is what I used and I did the correction for lift variance from what it's calibrated to(.600 at the valve lift) maybe i just don't know what the right spot is supposed to look like but i don't like where it's at. Jerry

[Don C.]

Re: Engine pushrod /rocker geometry question

Jerry

I've just completed some rocker geometry testing using a 327 block and 461 heads on a bench test set up my workshop. I did this to learn more about valve train geometry and particularly how it is affected by pushrod length, valve spring pressure and rocker arm ratio using stamped steel rockers. My conclusions from the data I collected are pretty much summed up in Micheal Hanson's reply to you. My test set up used an old crane power max cam (.312 max lift intake) - lift verified to be .312. I simulated 6 different pushrod lengths by coverting 6 hydraulic lifters to solid lifters with the plunger fixed at differing heights. I also used different valve springs and three different rocker arms.
On the GM rocker and '068' valve spring set up, the difference in max valve lift between the shortest pushrod (-.095) and longest pushrod (+.110) is about .015 with the longest pushrod producing the highest lift. The most dramtic changes in lift happened at the too long end of this spectrum. The valve stem pattern however was way too far to the outside and actually rolled to or off the edge of the valve at max lift. I also found that too long pushrods produced more rocker stud flex than just right or too short pushrods, suggesting more valve train stress on installations with excessive pushrod length. I have some fairly defintive photos of the valve stem pattern of the different pushrod lengths. With all my testing, I found the best way to get the correct set-up is to mount a dial gauge to measure perpendicular travel of the pushrod as close to the top of the pushrod as you can get. Starting at zero lift, set the dial gauge to read zero and then observe the amount of lateral travel of the pushrod as the engine is rotated to max valve lift. You should expect to see the pushrod move away from the valve for a portion of the travel and then return to the zero postion at max lift. I found the best set-up would generate about .009 - .012 pushrod outward travel and then almost return to or go slightly past the zero postion at full travel (+ or - a couple thou). I saw very little 'scuffing' produced by the stamped rocker. It kinda rolled across the top of the valve stem as the lift increased - the rocker ratio increasing as that end of the moment arm length increased.
If you wish to drop me an email I can provide additional data and photos.
I also used the bench set up to measure the rocker ratio of all my installed rocker arms. The max lift ratio ranged from 1.43 to 1.51.

Good luck on your build.

Don

[Michael H.]

Re: Engine pushrod /rocker geometry question

I've just completed some rocker geometry testing using a 327 block and 461 heads on a bench test set up my workshop.
I also used the bench set up to measure the rocker ratio of all my installed rocker arms. The max lift ratio ranged from 1.43 to 1.51.


Don

Thanks Don. Very interesting.

[Clem Z.]

Re: Engine pushrod /rocker geometry question

if you are using 3/8" studs i would use a stud girdle of some type because those 3/8" studs flex at high RPM if you are using heavier than stock springs

[Jerry G.]

Re: Engine pushrod /rocker geometry question

Jerry

I've just completed some rocker geometry testing using a 327 block and 461 heads on a bench test set up my workshop. I did this to learn more about valve train geometry and particularly how it is affected by pushrod length, valve spring pressure and rocker arm ratio using stamped steel rockers. My conclusions from the data I collected are pretty much summed up in Micheal Hanson's reply to you. My test set up used an old crane power max cam (.312 max lift intake) - lift verified to be .312. I simulated 6 different pushrod lengths by coverting 6 hydraulic lifters to solid lifters with the plunger fixed at differing heights. I also used different valve springs and three different rocker arms.
On the GM rocker and '068' valve spring set up, the difference in max valve lift between the shortest pushrod (-.095) and longest pushrod (+.110) is about .015 with the longest pushrod producing the highest lift. The most dramtic changes in lift happened at the too long end of this spectrum. The valve stem pattern however was way too far to the outside and actually rolled to or off the edge of the valve at max lift. I also found that too long pushrods produced more rocker stud flex than just right or too short pushrods, suggesting more valve train stress on installations with excessive pushrod length. I have some fairly defintive photos of the valve stem pattern of the different pushrod lengths. With all my testing, I found the best way to get the correct set-up is to mount a dial gauge to measure perpendicular travel of the pushrod as close to the top of the pushrod as you can get. Starting at zero lift, set the dial gauge to read zero and then observe the amount of lateral travel of the pushrod as the engine is rotated to max valve lift. You should expect to see the pushrod move away from the valve for a portion of the travel and then return to the zero postion at max lift. I found the best set-up would generate about .009 - .012 pushrod outward travel and then almost return to or go slightly past the zero postion at full travel (+ or - a couple thou). I saw very little 'scuffing' produced by the stamped rocker. It kinda rolled across the top of the valve stem as the lift increased - the rocker ratio increasing as that end of the moment arm length increased.
If you wish to drop me an email I can provide additional data and photos.
I also used the bench set up to measure the rocker ratio of all my installed rocker arms. The max lift ratio ranged from 1.43 to 1.51.

Good luck on your build.

Don

Most impressive. This tech board is great. Where else could you connect with so much knowledge and great people. Thanks. Jerry

[Duke W.]

Re: Engine pushrod /rocker geometry question

"I also used the bench set up to measure the rocker ratio of all my installed rocker arms. The max lift ratio ranged from 1.43 to 1.51."


If rocker geometry is in the proper range - rocker tip at/near the center of the valve stem at about half lift, side load is minimized and the radius of the rocker tip should "roll" not slide on the valve stem. This is why "roller-tip rockers" are basically worthless, however it appears from your research that ideal rocker geometry reduces maximum achieved rocker ratio. It can be easily made up with more lobe lift, but that will reduce maximum revs for a given spring. In most cases the loss of a percent or two of peak power is a good tradeoff for the extra couple of hundred revs before false motion sets in.

You've done a great job gathering data on how rocker arms behave and the effect of pushrod length on rocker geometry. Most guys don't have a clue.

Duke

[Don C.]

Re: Engine pushrod /rocker geometry question

Duke et al

I also collected data on rocker flex and found that on the valve opening ramp, the stud flexes towards the valve .003, and on the closing ramp flexes away from the valve .001 using the correct length pushrod. With the longest pushrod (+.110) the outward flex increased to .004.The flex motion changes direction as the lifter traverses the nose of the cam. With 300# crane springs and same OE rocker, the flex is .0035 and .002 respectively. Changing to 1.6 Proform rockers using the OE spring the numbers are .003 and .002 respectively. The 1.6 rockers and #300 pound spring generated .005 and .002. This is all in a static measurement state. In a dynamic operating environment I can only imagine that the effect is amplified. It indicates to me that changing to 1.6 rockers and stock springs introduces some level of additional stress on the valve train; but less so than increasing spring pressure - as found within the parameters of my testing. I'm hoping the additional lift of the 1.6s will get me me at least as much power as increasing spring pressure to get a few more revs. I did a lot of this testing to help me decide whether to install 1.6 rockers on the intake side. It seems I can't stop the search for more power on a basically stock GM components 327 (exception headers and bigger carb). Yes, I'm still running ignition points. Hoping to break into the 12 second range this summer. Got to 13.16 at 108+ last year and feels good to match or beat some stock c5's - just for fun.