ok, stealcomp you wrote me up something a while back that i printed out and I'm pretty sure i understand what your saying but i wanted to get your input as well as others like fiat, gofast, infomatic, and anybody else who knows what they are talking about.
From my understanding to get the perfect length i want to make sure the rocker is 90 degree to the valve stem while at mid lift. To find squareness to the rocker you talked about the trunions (sp) and i'm guessing, because i don't know for sure, that those are the axle type shafts that go through the middle of the rocker and the roller tip. You talked about machining marks and if i understand you correctly i should use the center of these two as a way to align my straight edge and then compare the square end to the the valve stem?
Here's a pic i took, kinda shows what I'm doing..
Another pic, but hard to see valve stem...
Also stealcomp, you talked about pushrod length not having anything to do with where the trip of the rocker is.... The more i extend the adjustable push rod tool the more forward the tip seams to be moving on the rocker.. Also i noticed a few time that the rocker was alittl off to the side of the valve tip, if i release the pressure on the rocker twist it a bit so that the push rod is centered on the guide and not touching one side or the other this is corrected... but whats going to keep things from not moving all over the place, do i have too much play in my guides or maybe this tool is just a bit skinnier than it should be? Now that i think of it there were two sized push rods that could be used 3/8 and 7/16 if i recall correctly, maybe i bought the guides for the beefyer pushrods? Just throwing that out there... i could be making no sense right now
Last edited by shaun; 11-17-2010 at 08:22 AM.
Yes the pushrod length does in fact have everything to do with where the tip of the rocker rides. This is referred to as the "valve train geometry".
From what I've been told by engine builders, the pushrod length should be a length that centers the rocker tip on the valve stem when the valves are closed. Some will say to center it with the tip just a "c-hair" towards the intake side of the head.
Looks good Shaun, since Scott started you off on this I won't interfere. But in case this hasn't been mentioned before, when you install the rockers check the guide plate alignment, the rockers should be centered on the the valve not off to one side, factory guides are usually out to lunch but some of the aftermarkets are pretty good, if you're using factory ones and they are off you can cut them, line them up and then weld them back up, common thing to do with factory guides!..
Meanwhile you can go here and read till your eyes bleed.
http://www.mid-lift.com/MASTER-INDEX.htm
gofast, the guideplates manelys if i remember correctly, would have to dig out receipts.. if i center the pushrod tool between the guideplates it aligns perfectly.. the guideplates just seam to allow alot of play, again though, the tool may be skinnier than the real pushrod...
Last edited by shaun; 11-17-2010 at 08:25 AM.
Probably your adjustable pushrods are 5/16". Your real pushrods will prolly be 3/8. Thus the play.
Here's a litttle diagram I did a while back that might help understand what's happening through the travel of the rocker. The main thing you want to concentrate on is getting the rocker at 90* to the valve at mid lift. You can't figure pushrod length correctly any other way, and this should be done with full valve train installed, or at least the spring you're going to run on that partiicular valve, when doing mock-up. This helps simulate the loads, which can change things a little. Some guys will over-arc their rocker by a small percantage, to make up for flex, but IMO, that's splitting hairs, and you can only guess at what that might be.
The tip of the rocker will be where it's going to be. You don't adjust the location of the roller on the valve tip with pushrod length. That's a function of the length of the rocker, and the distance between the stud and valve. It will start where it's going to start, and be at that same place at full lift, if things are correct. (Comp Cams, in their description of setting PR length coundn't be more wrong.) Installed height will also effect roller location...the taller the installed ht, the closer the tip of the valve is to the rocker stud, making the rocker seem long. This usually only haappens with 2.100 or more installed ht, so I wouldn't worry about it. Chances are, the roller will be toward the outside of ther valve tip, but as long as the sweep of the roller stays away from the edge of the valve tip, you'll be OK.
With the rocker at 90* to the valve at mid lift, you get the minimum amount of rocker tip sweep across the valve tip (see the diagram) Technically, at that point, the pushrod should be at 90* to the PR end of the rocker, as well, but with stud mount rockers, there's nothing you can do about that, so I wouldn't worry about it. With shaft mount rockers, you can adjust the PR cup, and really dial in the geometry, but that's another thread.
If you don't have this geometry correct, you're wasting crankshaft degrees of rotation trying to get the information from the cam, through the PR, through the rocker, to the valve. This will alter cam-crank timing and the cam won't perform as designed. It seems nit-picky, but IMO there's a lot of wasted power out there due to improper PR length. Aside from the cam-crank timing, you induce a lot of extra friction in the valve train when the geometry isn't correct, and that robs power, increases oil temp, and un-needed wear.
As far as the rocker being off to one side or the other, it's not uncommon to have to cut the guide plates, re-align the rocker with the valve, and weld the guide plate back together. That's a total pain in the ass, but if the edge of the roller is over the edge of the valve, you should take the time and do it. There's going to be a little slop in the PR slot, but that's typical. If you had the 7/16 plates with the 3/8 PR's, you'd know it.
Hope this helps.
http://www.***boat.com/image_center/...r_geometry.jpg
Looks good Shaun, since Scott started you off on this I won't interfere. But in case this hasn't been mentioned before, when you install the rockers check the guide plate alignment, the rockers should be centered on the the valve not off to one side, factory guides are usually out to lunch but some of the aftermarkets are pretty good, if you're using factory ones and they are off you can cut them, line them up and then weld them back up, common thing to do with factory guides!.. I had to adjust my plates from Comp Cams. They weren't even close, but with alum aftermarket stuff, you never know what's off, and what's right. Bottom line is, the stuff has to line up, whatever it takes.
NO SHORT CUTS!!
Yes the pushrod length does in fact have everything to do with where the tip of the rocker rides. This is referred to as the "valve train geometry".
From what I've been told by engine builders, the pushrod length should be a length that centers the rocker tip on the valve stem when the valves are closed. Some will say to center it with the tip just a "c-hair" towards the intake side of the head.This is such a misconception, and completely wrong. Once you establish the proper pushrod length through correct rocker geometry, the tip of the rocker will be where it will be. You don't alter PR length to adjust the location of the roller on the tip of the valve.
To help understand a little further, look at the diagram. If you notice, because the rocker is moving in an arc, the further you get from 90* to the vlave, the more horizontal the movement is, than vertical. If you exaggerate the movement, you could see that at the top or bottom of the arc, the rocker would be moving mostly horizontally, and very little vertical. This is why it's critical to keep the travel of the rockewr as close to 90* to the valve as possible...half the travel above 90*, and the other half, below 90*, therefore, 90* at mid-lift. You'll also notice that during the rocker's motion, the tip is moving outward before mid-lift, and inward, after. If the roller tip continues in one continuous direction throughout the rocker's travel, (like some descriptions will tell you), you've got things way screwed up. The sweep of the roller will be at it's max. at one half of the rocker's travel, from zero lift, to mid lift (or from mid to max...same distance). Then it starts it's sweep back in the direction it came.
http://www.***boat.com/image_center/...r_geometry.jpg
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