lots of good info here.

Thanks for the descriptive post truedualws6. Lots will benefit from this post and should be considered for a sticky.

Lloyd

 

This is the way I have always done it, but many claim that this is not right since the sweep width will be wider which would result in robbing duration and lift from the valve.

They are simply saying that sweep width is primary and pattern close to center is secondary. It appears for most by moving the pattern off center towards the exhaust side then the sweep width will decrease.

When mine were set up in this more off centered fassion after installing Comp pro-mags I noticed average .070" guide plate wear on EVERY slot and one wore so bad a valve fell off the rocker. When running my pattern centered as described above there is not even a smidge of guide plate wear.

Even with my psycho nuts high lift cam I am not concerned with losing a tad of lift, I just dont want rockers falling off. Who the hell knows?

 

So how do you measure that?

BTW, I forgot to mention that I also substitute the hydraulic lifter with one that I have removed the spring from and replaced with washers to make it solid.

 

Excuse me for partial ignorance on this subject, but I am going to try to lay this out in layman's terms.

Your trying to achieve a small sweep pattern on the valve tip when checking PR length right? (smaller window of contact from roller tip to valve, measured by sharpie wear etc.)

Now what your also saying is that it is not necessary to have that pattern fall in the middle of the valve tip, but closer to the exhaust side?

When doing this how do you know how far is too much toward exhaust side?

And so this will create a more correct geometry reducing guideplate wear etc?

Can this accelerate roller tip wear on a rocker, by not being centered?
This is one of my next steps on my engine and want to get it right.

 

There is really nothing wrong with that method and it's the method I have been using when forced to use stud mount rockers. But it's not ideal. That link to the Miller engineering web site in the 1st post is eye-opening. Ideal pushrod length is what gives the minimum sweep not in what gives the centered mark. They say that usually perfect geometry does not put the rocker tip in the center of the valve tip, (but sometimes you can get lucky).....and that is due to longer valves, sunken valve seats, whatever would cause the valve to be further or closer to the rocker stud....But you would want the rocker tip in the center of the valve tip AND have the minumum sweep in a perfect motor world.

Not that reading that web page makes any of us experts in this subject.....but now we have food for thought. The minimum sweep of the rocker tip would give the least amount of scrub--waste of energy---and also give the most force directly down to open the valve. That minimum sweep is obtained by that "mid-net-valve-lift" measurement method at Miller Engineering web site. It all makes sense.

But it's true that this trying to eek perfection out of the valvetrain may not show up to help anything. Not on the dyno. Not on the track. Not even in longevity. But it might.

Shaft rockers are easy for sizing proper pushrod length because you just get a pushrod that fits where the shaft system just so happens to sit on the head...after you shim or don't shim, (or mill the head rocker stud bosses).

I also like that Miller Engineering method of getting the proper geometry with a shaft system, (they call it a stand system). You measure and then determine how much to mill off the shaft stand. The stand they supply is extra thick,(tall) and so is designed to be milled.

This is not to say that Jesel and T&D and all the other shaft systems do not give proper geometry, (minimum sweep). They all can be set up for perfect geometry and it's just in how high or low the stand is set on the heads. I've been shimming (or not shimming) the Jesel shaft rocker systems to get the rocker tip centered but I should do it the Miller method and it's possible that proper geometry will not be with the rocker tip centered on the valve tip....who knows....I am curious to measure now.

Sticky vote: yes.

Karl
Ellwein Engines

 

You need to read the link about mid lift in the very first post. You may need to read and go over everything in that link several times.

 

I did it exactly the way you describe above myself, to the letter. I even have a lifter
that has the spring removed and is set to a solid height equal to 1 turn with a 7/16-20
rocker stud. Set up this way I know my sweep is .080+ becasue I measured it, and
I have some photos of the stock sweep and it's about half what it is now.

As already stated, you need to read the mid-lift info. It took me about three reads for
the light bulb to go on.

 

I still don't see that affecting your guideplate wear. Maybe you have truly hardened guideplates now?!

 

I would think your guideplate wear was related to something else. As you go shorter
and shorter with pushrods, you lower the axis of the rocker trunion which in turn will
move the pushrod at the rocker arm end very close to bottom of the guideplate
slot. There is a point, probably at a pushrod length of 7.05" or less where contact
with the bottom of the slot will occur. I noticed this with my install and it's mainly a
result of the longer valves. The only negative I can see in the mid-lift setup is that
the rocker studs that are available for LT1s may not be long enough and I'm hopeful
that this is not the case.

 

Karl, I would be very interested in hearing what you find out as you play around with
this. Please share it with the board. I would think that the difference between a
centered .080" sweep pattern vs. an off-center (but safe) sweep pattern of .030-.040"
would be worth a few ponies on the big HP motors. For mine it's probably not detectable,
but for me it's the reduced side loads on the valve stem that has my eyes open.
From an engineering (or materials) perspective, the valve stem and tip is like a column.
Because it's a very rigid structure it can support off-center loading and transfer that
load without any negative side effects provided you maintain a safety margin so
the roller does not move off the valve tip. With all the harmonics going on in a high
rpm engine it's probably a best practive to not allow the sweep to move too far off
center. As stated in some of the linked material and in my original post the .070-.080"
from edge of sweep to OD of stem was presented as the limit.

 

Been there done that. Even made up a dial indicator tool as shown in the Speedtalk thread.

Problem was my sweep was almost at the edge of the valve towards the exhaust side. The total sweep was .031" at that point. You will notice in the post by jimil that you should not be any closer than 25% of the valve diameter from the edge of the valve for the center of your sweep.

So in order to do that I had to shorten my pushrod back up and I wound up with a sweep of around .041". In my case it was a compromise because I did not want to change my componets except for the pushrods of course.

By the way the stock pushrod length on my car is 7.200" For mid-lift it would have been 7.500". I wound up with 7.365" for my pushrods.

Unless you are very lucky with a stud mount system you will most likely not have the sweep centered on the valve stem.

 

the tool they say not to use because it is only measuring a symptom?

 

I will share and I am going to measure as many systems as I have available to me right now. (T&D, Crane, Jesel, Probe). I keep thinking back on my builds and it seems that when I set up the Jesel shaft rockers and start with the .100" shim under the stand I get the rocker tip way out toward the exhaust side of the valve tip (but the witness mark is a tiny sliver). So I take the shim away and I get a nicely centered witness mark, (but very broad). This is on TFS LT1 heads. I'm sure different heads will have different results.

Karl

 

I seems to me that off center loading puts the the line of force (not an engineering term but I don't know what else to call it) of the rocker tip pushing down on the valve stem in a direction that is not concentric with the valve stem axis. Therefore won't that will put a side load on the valve stem against the valve guide at one point and cause premature wear?

 

Where did you end up relative to the rocker stud threads and number of turns
on the locks? The minimum should be equivalent to one stud diameter or about
8-9 turns. It seems like you would need to go with a longer stud.