Jim85IROC

iTrader: (2)

Last night I checked the sweep pattern for the rockers on the motor I'm setting up. It's a 350 that was in my IROC for a number of years with 461 heads. I swapped to Vortec heads, which were milled .007", and I used a .015" head gasket to maximize quench. Because of this, I expected my stock pushrods to be a tad long. What I found was a bit surprising. The stock pushrods, combined with the PRW 1.6 ratio roller-tip rockers resulted in a nice narrow wipe pattern, but it was really biased toward the exhaust side of the valve tip. I repeated the process with some 1/4" shorter pushrods I had around, and overall, things didn't change much. The rocker tip is still pretty close to the exhaust side of the valve.

Here's a pic with the PRW 1.6 rocker and my original pushrod:


I repeated with the shorter pushrod, and as you can see, it's not a lot different:


For a reality check, I put the stock self aligning rocker in, still with the short pushrod. Not surprisingly, the wipe pattern is wide, but it looks like it's a little closer to the center:


Lastly, I put the stock pushrod back in with the stock rocker:


All of these are favoring the exhaust side. What surprises me is how minimal the difference in position is from the stock pushrod to the 1/4" shorter one. I really expected it to move more than it did. I really can't imagine what would cause geometry to be so far off that I'd need to go to a pushrod that's 1/2" or more shorter than stock.

Is the location of the wipe pattern with the PRW rocker and the shorter pushrod "close enough"? I keep reading that the width of the sweep pattern is more important than it's position relative to the center of the valve stem, but I'm not really getting a warm & fuzzy from it.

AlkyIROC

Don't worry too much about where the sweep line is on the tip unless it's really bad. Technically, you want the sweep to be as narrow as possible. As close to the center of the tip is best but a narrow sweep off center will be fine. The wider the sweep, the worse the geometry is.

Rocker ratio shouldn't make any difference. The distance from the rocker stud to the valve tip doesn't change. To increase the ratio, the pushrod is moved closer to the rocker stud.

Use lightweight checking springs and an adjustable pushrod to determine which length gives the smallest sweep.

redneckjoe

idk if you used one, but dont you need a solid lifter to do this test correctly? might explain why the 1/4 inch different length pushrods didnt make much difference, if you were useing a hydraulic lifter?

AlkyIROC

Checking with a solid lifter is recommended but if you're using lightweight checking springs, the spring pressure keeping the valves closed shouldn't be enough to compress the lifter.

Jim85IROC

iTrader: (2)

I've got checker springs that I used on my LS build... I was just really hoping to get "close enough" and put the ***** together without going through all of that. I was also hoping that my "close enough" could happen with the pushrods I already have so that I wouldn't have to buy more stuff. What's got me concerned is that based on what I've seen so far, to get that wipe pattern centered on the valve stem is going to require a pushrod that's at least a half inch shorter than stock, and that seems drastic to me. It concerns me that something else is way off.

midias

Looks very similar to my pattern after my vortec head swap. I got some slightly shorter pushrods and I am looking forward to installing them.

redneckjoe

dont vortecs require self-aligners? i like self-aliners when not useing guide plates. i use them on old school builds. i woulda got screw-in studs if those heads went into a machine shop. idk the history though.

Jim85IROC

iTrader: (2)

Yeah, vortecs need self aligning rockers.

Tonight I played a little bit more. I took pictures from the side with the rocker installed with the 2 pushrods, as well as my checker pushrod. Apparently my estimate of 1/4" difference between pushrod lengths may have been exaggerated. The longest pushrod measures approximately 7.8" (i.e. stock length). The checker pushrod measures about 7.6", and obviously the middle one is somewhere inbetween. Apparently in the heat of battle, a .100" difference looks more like 1/4".

Here are the 3 pushrods:


With the "tall" pushrod (7.8")


With the shorter pushrod:


With my checker pushrod:


With that checker pushrod, the bottom of the rocker seems to be sitting awfully close to the bottom of the stud. From what I can see, the middle pushrod is likely to be my best option, though I'm going to install my checker springs and go through a full sweep pattern with the checker pushrod as soon as my stud-mount spring compressor comes in.

redneckjoe

i think the last pic looks correct, from here. lol. those valvestem tips look used? from self-aligners? are those new valve springs? dual springs, it looks like? im sure you know what your doing. im guessing your useing an ols-school hyd flat tappet with those measurements? sorry if im typeing bad, i ruined my shouler a few weeks ago. lol. but i see the dual springs, be careful on lift.

Damon

DO NOT STRESS OUT EXCESSIVELY OVER THE LOCATION OF THE CONTACT PATCH ON THE VALVE TIP.

Only rarely do they center up exactly right. This is normal and usually by design of the head manufacturer.

The sweep from closed to open is what's important. And, to let you in on a little secret, there are times you simply can't get it right. You have to make some compromises. Only in the very rare cases do you need sticks that are shorter than stock. Standard length works 90% of the time on non-aftermarket heads.

I use 6 different methods of cross-checking pushrods to make sure they are the optimum length. Yes, 6. I'm not only **** about rocker geometry I also know how to catch every "gotcha" ever encountered. Maybe there is one I haven't come across yet, but I won't know until I come across it. Then I'll have 7 checks instead of 6.

What works almost every time? LOOK AT THE ROCKER ARM POLY-LOCK. If it does NOT approach either end of it's slot too closely in either the valve-closed or valve-fully-open position, you're in the ballpark. If it's getting close to the end of it's travle at either point your rocker geometry is almost certainly out of whack. That is check #1.

When you say you are using pushrods 1/4 shorter than stock I suspect you are biased towards the end of the rocker's travel in the valve-closed position. The fact that switching to stock length sticks makes very little difference in the contact pattern tells me you're probably closer to optimum with stock sticks than you are with shorter ones.

Obviously, impossible for me to say just guessing over the internet. But if guessing is all I've got, that's my guess.

Damon

Oops.... you''re using stamped-steel rockers. Can't judge by the poly-lock. Gotta drop them on and look where the stud comes through on the slot in the bottom of the rocker arm. You want at least .080" of clearance left at the end of the slot in the valve-closed position.

Good pics. I always do a visual-from-the-side as one of my many checks.

I have to admist that somewhere between stock length and the slightly shorter sticks looks about right. The short adjustable pushrod in the bottom pick looks a bit too short.

But please remember that you MUST check with the lash set at the same point as you intend to actually run it. 1 turn down from zero lash effectively shortens the pushrod quite a bit vs. running it at exactly zero lash. You see my point?

All the talk about using solid lifters for checking is BS unless you intend to run your hydraulic lifters at exactly the same total stacked height as the solid lifter happens to be. Otherwise you're setting your final pushrod length to a fictional distance your acutal valvetrain won't be running at.

BTW- a typical solid lifter has the pushrod cup sitting further down than a typical hydraulic lifter with 1/2 a turn of pre-load. Just thought you might like to know.

Complicated? Yep. Sure as heck is. That's how I became **** about rocker geometry.

redneckjoe

i think theyre awesome pics. most posters cant help anybody out with a pic, and that just makes most things a guessing game unfortunatley.
are those used valves in there? could be the computer, but it looks like someone was useing self-aligning roller rockers?
what cam, and lifters are you running?
those sure look like the wrong rockers,...probabley why they are turning to the sides?

Damon

Oh, and another BTW- the factory puts the rocker nut down about 1 to 1-1/2 turns from zero lash. That puts them about in the middle of the hydraulic lifter's plunger travel.

Most home-gamers put them down only about 1/4-1/2 turn from the zero-lash point. That makes the stock sticks effectively "longer" than they are in a stock application.

Thin head gaskets and a slightly milled head is small potatoes compred to the difference in effective pushrod length from a full turn more of rocker arm nut pre-load.

I'm kinda hoping you read this and say "Ah hah! NOW it makes sense!".

You feeling any of this?

Jim85IROC

iTrader: (2)

You bring up a good point. The thing is, you face the same problem using checker springs too. If you tighten past zero lash, you'll open the valve before you compress the lifter. With either checker springs or a solid lifter, you need to check your geometry at zero lash, and add your desired preload length to the measured pushrod length to determine your ideal pushrod length. I went to great lengths to make sure my measurements were spot-on with my LS build. Truth told, I'm not really as worried about that level of precision on this motor. This time around, "close enough" is good enough, as long as I'm operating in a safe range. I'm still going to swap in a checker spring and see how things look, but right now I'm starting to think the middle pushrod is "good enough". The stock long one pushes my contact point too close to the exhaust side for me. I don't like that the roller tip is wider than the valve stem at that position.

AlkyIROC

I'm glad I switched to shaft rockers. So much easier.

redneckjoe

http://forums.chevyhiperformance.com...gth/index.html
heres a pretty good link about pushrod lengths.