Viper

iTrader: (6)

I just found some new sites and great reading information I'd like to share.

http://speedtalk.com/forum/viewtopic.php?t=2459

http://www.mid-lift.com/ - take the time to read through their definitions page

Quote from Buddy Rawls:

"Pushrod Length- Incorrect pushrod length can be detrimental to valve guide wear. Most sources say that centering the rocker contact patch on the valve stem centerline at mid valve lift is the correct method for determining the optimum pushrod length. This method is wrong and can actually cause more harm than good. The method only applies when the valvetrain geometry is correct. This means that the rocker arm lengths and stud placement and valve tip heights are all perfect. This is rarely the case. To illustrate this, think of the valve angle and the rocker stud angle. They are usually not the same. If a longer or shorter valve is installed, then the relationship of the valve tip to the rocker stud centerline has changed. Heads that have had multiple valve jobs can also see this relationship change. Note, the rocker length (pivot to tip) remains unchanged, so the rocker contact patch will have to move off the valve centerline some particular distance for optimum geometry to be maintained.

The optimum length, for component longevity, is the length that will give the least rocker arm contact area on the valve stem. In other words the narrowest wear pattern. This assures that the relationship is optimized and the rocker is positioned at the correct angle. This means that the optimum rocker tip contact point does not necessarily coincide with the valve stem centerline, and probably will not. What is the acceptable limit for being offset from the valve stem centerline? That will depend on the set-up. A safe margin to strive for is about +/-.080" of the centerline of an 11/32 diameter valve stem. This means that no part of the wear pattern should be outside of this .160" wide envelope. As the pushrod length is changed, the pattern will change noticeably. As the geometry becomes closer to optimum, the pattern will get narrowest. If the narrowest pattern is too far from the valvestem centerline, then the valve to rocker relationship has to be changed. In this case, valve stem length will need to change."

vettenuts

iTrader: (4)

I have been to that site, he has a lot of good information but also promotes his rockers (as he should). He is developing LSx shaft rockers, but the last time I contacted him he wasn't sure of the date. He wasn't too friendly either.

One other note, he shows many of his pictures with the roller starting towards the intake side, rolling across the center and then back towards the intake side. I have found the LS1 rockers that I have examined start on the intake side and go towards the exhaust side until max lift.

Viper

iTrader: (6)

vettenuts

You and I are drawn to the rocker arm discussions.

Perhaps because if you get it wrong, you lose power. Important to set it up right the first time. How are the cranes working out for you? That site mid-lift has some interesting viewpoints on 'quick-lift' technology. But as you pointed out, they are selling their own rocker arms.

BTW, I just picked up my stock rockers modified by Harland Sharp. Turns out their shop is 15 minutes from me. They look a lot better than stock, that's for sure! A little too cold to put them in though, only in the 30's here.

Greg Fell

iTrader: (9)

I'm going to be using a large lift cam with my ls7 top end, and ordered custom lash caps to lengthen the valves, to get the geometry dead nuts on. I'm a believer in proper geometry as well.

heavymetals

iTrader: (3)

Just installed a Comp Cams #1500 system in my LS6 (CTS-V).

Instructions are lousy.

System is awesome.

PREDATOR-Z

One thing that a lot of poeple confuse is that geometry and preload are the same or adjusted the same. Not on our LSx motors.
As mentionned before geometry is veryfied by a correct center wipe (adjusted by shims)
Preload is adjusted by length of pushrods (non adjustable rockers)

This is different than STUD like rockers, where p-rod length adjusts geometry and preload at the same time.

Viper

iTrader: (6)

Agreed, but Buddy still had good points on the geometry. We just have to use shims to move the contact point IF ( and a big if ) it needs it. With stock pedastal style.

PREDATOR-Z

Correct,
Now this is necessary once we put longer valves, aftermarket head castings, aftermarket rockers etc...
Basicaly once we modify the geometry.
Otherwise, on cam only swaps, the p-rod length is our only concern for lifter preload adjustment (and vital too)

Viper

iTrader: (6)

Do you know whose 'aftermarket head castings' apply here?

Many times I ask these type questions in the event people are searching in the future.

For example, a common misundertanding is milling affects geometry when in fact it does not. Same with base circle on a cam, it does not affect geometry but it does affect preload.

Here's an older good thread ( I had to find it on a cached google page as LS1Tech's search doesn't go back to 2005 )

https://ls1tech.com/forums/showthrea...1&page=1&pp=20

Take the time to read this whole thread. It made me head hurt last year but now I understand it a lot better.

vettenuts

iTrader: (4)

I haven't corrected my problem but have learned a lot over the winter (since the car is in storage) and I think my problem comes down to two things, I have too much lifter preload and if I were a betting man, I bet my wipe pattern is off. Since I plan on doing heads when the weather breaks good, I am going to measure everything on my current setup so I can do a post-mortem and figure it out. I see a lot of guys running the Crane 1.8 rockers with absolutely no problems and they are really happy with them. They run them to 7K RPM with the Crane springs. In the end, I installed them by the book but didnt' measure anything, so I guess I can only blame myself if this is the problem.

I do like the Crane rockers though, and picked up a set of 1.7's for my new Dart heads.

Viper

iTrader: (6)

I'm convinced this is the key : "with the Crane springs" with those rockers, or with AFR heads to get the updated springs from Tony. At least if you're going to run the 1.8RR's. Good luck man! Want to see what you run and put down when you're done. I too learned a lot over the winter and ended up remeasuring everything. Ended up with 7.300 PR's to get .030 preload on my Morel lifters, stock rocker arms rebuilt by Harland. Still need to buy a new battery, a set of Nitto DR's and realign my exhaust AGAIN before she's road ready.

02RedHawk

iTrader: (17)

Assuming the usage of stock rockers, how does the effect of longer valves (.070") change the wipe? (ie, how much of a 'shim' under the rocker is needed?)

Doesn't the lift of the cam also affect the wipe?

Viper

iTrader: (6)

I can't answer exactly what shim, but i can help you with why the valve height changes the swipe:

http://www.mid-lift.com/TECH/TECH-UNDER-ARC.htm

http://www.mid-lift.com/TECH/TECH-OVER-ARC.htm

http://www.mid-lift.com/TECH/TECH-Installed-G1.htm

http://www.mid-lift.com/TECH/TECH-V-Tip-Height.htm

PREDATOR-Z

Of course this should be actually done by wipe test but the shim I would first use to check is .070/1.7= .041 (or .040 shim)

02RedHawk

iTrader: (17)

The valve-height would not only be affected by the length of the valve, but by also the amt the valve was sunk into the heads, correct?
(so the shim needed may then need to be .041" + .XXX", where the XXX would have to be known by the porter. Which, for the end user, would still mean we'd have to check and recheck the wipe with various sized shims...)

vettenuts

iTrader: (4)

I went with the Morel's as well, and I think they will help with solving my problem.

PREDATOR-Z

Yeah, this is why I said it has to be done physically, but that is where I would start.

Viper

iTrader: (6)

02RedHawk

Didn't you and Predator-Z go over this here:

https://ls1tech.com/forums/showthrea...t=rocker+stand

I apologize for giving you the links on valve stem height, it seems you already know the answer. Same with the lift of the cam affecting swipe.

02RedHawk

iTrader: (17)

No don't apologize... Not sure why you would want to. Confusion still runs rampant within, and getting other opinions helps cement them as 'fact'.