Greg Fell

iTrader: (9)

What do you guys think could be causing my broken rockers? Just trying to get some thoughts on subject.

some useful info:

springs:
K-Motion K-800
Spring OD 1.460"
Coil Bind: 1.085"
closed pressure: 165# @ 1.850
open pressure: 470# @ 1.150
spring rate: 471 lbs./in.

we set our installed height at 1.900ish, for a closed pressure of 145ish.
plenty of PtoV clearance as we cut the pistons for the 12* head/valve combos and checked on motor stand with mockup and check springs.

ti retainers
10* beadlocks
LS7 heads shaved .040
morel lifters
ls7 rockers
comp cams 3/8 (5/16 tip) oil through pushrods: 7.650
cam motion 246/257 112+ 2 .669/.652
ls7 intake valves with .100 lash caps
ls7 exhaust valves tipped .015 with intake lash caps (.060 if i remember correctly)

We used custom thickness lash caps to get optimium valvetrain geometry and the wipe pattern in the middle of the pad. valvetrain is velvet and silent, the quietest i've heard to date (possibly due to morel lifters?).

we also custom fit some spring seats and there is zero slop in them. they are piloted very well with a very tight fit.

broke an intake rocker at about 2000 miles at the fulcrum. replaced all intakes w new.

broke an exhaust rocker at about 2200 miles at the fulcrum. currently replacing all 16 rockers with harland sharp fulcrum modifications.

cylinder compression test passed with low being 185ish and high being 200ish. one was 210, but this was due to the broken exhaust rocker (at that time we didn't know it had failed).

using new ls2 timing chain with damper. 4" cola crank. 4.100 diamond pistons. 6.125" lunati pro-mod rods. arp studs top/bottom

i cant think of any more useful info. i turn the motor 6800ish and rev limiter is 7200.

zero knock.

fwiw, the car ran like a mother when i got together. way more than my old 422 with 484/459. it dyno'ed lower than that the other day, and had been feeling lazy as of late. i want to blame the broken rocker arm but am open for ideas. i am not 100% positive it was broken before hand, although i strongly suspect it.

at any rate, i'm concerned about breaking more rockers and having another issue at hand. the springs show no sign of coil bind, and they shouldn't as they are good for over .700 lift.

Phil99vette

iTrader: (11)

We recently had the EXACT same problem with LS1 rockers. Everyone said we were the only ones to break them.

John B

iTrader: (10)

After breaking a rocker on my LS1 I was convinced that the metal used just wasn't up to par for what I would consider "extreme" duty use which is what your valvetrain consists of. I wish I could offer a better idea for you.

By the way, what width did you cut your spring pockets to enabling you to fit wider springs?

Greg Fell

iTrader: (9)

Thats kind of what we were thinking, but so many people tell us that they have never had issues with rockers breaking.

We cut my pockets to be 1.48, I believe. Maybe 1.50.

Beast96Z

iTrader: (21)

I'd say poor quality materials in the rockers combined with high spring pressures is causing your problem. The only other thing you could do is have your valvetrain parts run on a spintron or optron to see if there is any high frequency instability/vibration. I believe Thunder and Katech have those resources.

Richard@WCCH

iTrader: (3)

Greg, 450ish lbs. open seems like way too much for the stock rockers. IMO 410lbs would be pushing their limits. Can you pull a shim out from under the spring? Or increase the installed height? I believe your getting to the root of your problem here.

Richard

Greg Fell

iTrader: (9)

i didn't shim them at all, actually. i dont think it set up exactly like the stock ls7 (1.959?)...i think it was a bit less, but over 1.900. if i recall, it may be less than 400. I'm going to pull a spring off and put a valve height mic on it, recheck, and check installed spring height.

may also end up going with the PSI beehives. seems to me, they are too good to be true? .700 lift, a bee hive, and stock diameter even??? but, katech is conservative, and if they say they work, imo they work.

Richard@WCCH

iTrader: (3)

I'm intreseted in the actual installed pressures Greg. Let us know how this turns out for ya.


Richard

WKMCD

iTrader: (2)

Now I'm a little concerned. I'm installing a set of L92 heads with the offset rocker....

Katech_Jason

iTrader: (19)

Guys,

You know how many LS7s we have ran? We have NEVER failed a rocker.

Greg Fell

iTrader: (9)

Aren't most of yours also with less spring and less aggressive cams? In my case I'm not sure its apples to apples. Dunno

Katech_Jason

iTrader: (19)

Thats right. That is why my gut tells me its related to spring pressure and lobe profile.

Greg Fell

iTrader: (9)

Cool, thats what I'm hoping too. The Harland Sharp upgrades should be a good deal. May go with the PSI springs as well.

LSX Wizard

Stock rockers are/were tested for hundreds (thousands?) of hours with stock lobe profiles and spring pressures, near 360# over the nose. They were designed to live for those parameters only. Your over-the-nose pressure of 420ish is approaching 20% over stock, not taking in account the additional stresses of the more agressive lobe. You need to change either the spring, the installed height, or rockers, 'cause somethings gonna.... strike that.... something has given.

No insult intended, but the next thing I'm waiting to see is when the spring pockets crack from cutting them so oversized. The wall material left is very thin.

Louis

iTrader: (7)

GM would has more than a 20% safety factor, and thats not including shock loads and other oddball loads that are up to and over 1000#s. Seat and open pressure are only a few numbers in a big equation with something like this.

Greg, what is the lobe lift, and how much preload are you running?

Greg Fell

iTrader: (9)

I'm running .372/.362. Running about .040 preload on morel lifters.

Brian Tooley Racing

iTrader: (13)

I can tell you a 1.440 spring will not RPM with the 1.300 stuff most people run now. When TFS had their 215 head (1.300 Gold springs) against the ET 215 heads (1.440 dual springs) on the dyno, the TFS heads would pull 300 RPM higher and sounded better at high RPM. If both springs have the same pressure, the smaller spring will RPM better because it has less mass.

As far as breaking parts, you are better off with too much spring pressure then not enough (which is what I think you have going on) I have a customer that runs over one inch of lift, his seat pressure is 400+lbs and open is 1200+lbs and has not broke anything. I have seen guys with .850" lift break every component in the valve train and have 200-250lbs on the seat and they think they have enough pressure.

These competition hyd roller Ford engines we deal with have 200 on the seat and 500 open with .500"-.550" lift, all on stock lifters, and I have seen them go 8000 RPM on my dyno and not float with stainless valves, and also not break parts. Ramp rates have to be slow to do what you are trying to do, besides, a head with killer midlift flow DOES NOT need fast ramps. We have put slower ramp speed lobes in some of these cars and made more power everywhere.

IMO, your valve lift is WAY too high, we see some .5xx lift stuff make more power then some .6xx lift stuff. I would bet you don't have sufficient spring pressure for the mass you are trying to move. I would back the lift down to .630" or less, put on the beehive spring with the most pressure you think you can stand and hope for the best.

SLED28

iTrader: (7)

I beleive its way to much pressure! And a big bulky *** springs! We put the lightass .700 beehive's in haans249 LS7 heads and they pull to 6500 rpm no problem and there is 1200+ hard miles on the motor allready with no broken rockers.

Brian Tooley Racing

iTrader: (13)

We agree on the bulky *** spring part

How much valve lift are you running on the car you spoke of?