Valve stem seals crushed, LS7. More spring?

[mdrew]

I'm in the process of trying a different cam/head combination in my Z06. Round three.... Will be looking to improve off idle, lower rpm street manners thing time. Less cam, and the heads have not been ported nearly as much as the heads I have been using.

I just broke the heads down and all but two exhaust seals are crushed. None of the intake seals were damaged, but one was very loose and popped off when I removed the spring.... They are the type that is set to the top of the guide. When I installed them I removed the springs and filed the lips down a touch. The engine never gave me any indication of valve float. Not that I could tell on a dyno or seat of the pants. Before I assemble and bolt new heads down, figured I'd better seak some wisdom here...

Cam that I have been running is a Comp, HUC lobes. 235/255, .654 /.670.

Comp 26926 springs with Ti retainers.
I set the intake up at 1.835" +/- 0.002".
I set the exh up at 1.845" +/- 0.002".

The spring listed specs are below, and I did check load. They were spot on.

O.D. Outer Spring: 1.320''
I.D. Inner Spring: .654''
Spring Rate: 505 lbs/in
Seat Load: 129 lbs @ 1.835''
Open Load: 470 lbs @ 1.160''
Coil Bind: 1.100''

The O.D. of the seals are 0.060".

Spring locator lip O.D. is 0.060". The lip is 0.120" in height.
Measured clearance between the retainer and top of seal is 0.160" at 0.670 lift.
Morel 5294 lifters. 0-30 oil, 0.070" pre-load with 0.150" measured total plunger travel.
Crower Shaft mount rockers with Trend .080" wall rods.
Fuel cut off is set at 7200, and I hit it from time to time.

OEM Ti intake valves: 77 grams
Ferrea hollow stem exh vavles: 85 grams
Retainer weight with locks: 15 gram
Spring weight: 100

I ran this same set up with OEM rockers, and the lighter OEM SI valves the second time I rebuilt the engine and heads. No damaged seals. The only change was the Crower rockers and heavier Ferrea exh valves. I'm assuming the added M-MOI of these rockers has upset the valve train dynamics. Is it possible the inner springs started oscillating, danced around, and came into contact with the seals?

Not enough spring load? Anything else?

I will be buying new springs, but need to get a cam spec'ed out first.

[CGT]

Interesting. Ive been unintentionally playing with the limits of hydraulic rollers lately. My inclination would obviously point towards the rocker arm, provided you are going to stay with them. LS rockers are very light on the valve side.

If it was mine i would be looking into a slower ex lobe, which could actually help power, along with a heavier oil.

I have not had luck and have seen power losses with 0wt oil and hyd lifters on the dyno.

The valve weights are still very light. Could end up having to be a balance of more spring and thicker oil.

[user-23911]

Too much lift.

Maybe take the top off the valve guide for clearance?

[turbo2256b]

Too much lift.

Maybe take the top off the valve guide for clearance?

+1

[mdrew]

How much clearance should I be shoot for between the retainer and seal? I'm not going with less lift, so I need to figure this out. The reason I went with these rockers was due to the OE rockers taking out the valve guides from too much side loading the last engine irritation.

Sorry about the oil... I have been using M1 5-30. Not 0 weight.

The HUC lobes are supposed to be pretty gentle. Kind of a marine lobe design. That's why I went with them. Makes great power (more than my driving skills can handle to be real honest about it), but I'm tired of the low rpm reversion issues. Makes the car is not-fun to drive in traffic. I may try one of Jone's cams this time.

[MadBill]

o Were the springs, especially exhaust, still 'spot on' for load when you tore it down?
o Many rockers have more than advertised ratio; did you measure actual lift and retainer/seal clearance with checking springs and verify seal location on all valves? .
o Having only 6 seals crushed means something's different on the bad six. Less clearance, lower spring load, worse lifter pump-up, six valves that aren't hollow...

[RW TECH]

I think your system isn't happy & that may be why the seals got hammered.

You've added ~8 grams of exhaust valve weight, ~4-5 grams of retainer & lock weight, 30 grams of spring weight, and a significant amount of rocker arm weight. It doesn't sound like you spend a lot of time at high RPM so I have to wonder how you arrived at your current valvetrain combination?

The following configuration has completed over 3,000 racing miles (see pic below) up to about 7500 RPM peak (long total run time per event). Actual limiting speed in that system (defined as .010" bounce at closing & not cleaning up 100 RPM higher) is about 8200 RPM.

-GM catalog hyd. roller cam (aka Stage 3 LS Cam)

- 1511ML springs, set up at 1.820"-ish

- Stock retainers & locks

- Stock rockers
*No "trunion kits"....completely 100% straight off the production line and zero failures in several engines like this & 2,000 or more racing miles. Trunion bearing failure was a 2007 era field concern that was fixed for later production. From a geometry standpoint the stock rocker arms will not cause problems if actual (net) lift is .650" or less. Above that you will have trouble. Otherwise, the stock guide material isn't extraordinary or great and earlier heads (2007-2008-ish) had machining issues that caused excessive guide wear. I assume you had the guides sleeved or changed somehow?

- Stock LS7 pushrods
*Actually delivered best stability with certain hydraulic roller cams & same ancillaries in comparison with a variety of same & larger OD & thickness 4340 1-piece pushrods.

- Stock valves (exhaust too).
*The exhaust valve problem on LS7 engines was fixed after 2008 and I never had any problems with the newer exhaust valves even with .800" lift solid rollers in a similar application to the link turning about 8,000 peak RPM. 100% of the 2013-newer COPO engines have the stock valves that include material & process changes after 2008.

Engine in chassis:


I wouldn't necessarily climb all over the idea of adding more spring force because the combination really needs to be verified on a spin test rig but essentially you've added a ton of weight and you have about as much spring force as a decent beehive like the PSI 1511ML. BUT - with the disadvantages of additional spring/retainer/lock mass plus the dynamic stability disadvantage of straight wound springs (vs taper-wound like the beehive).

If it was mine to deal with I'd get the existing parts on a spin test rig (bet $100 you find the exhaust is pissed off), then compare to the proposed parts to make sure your system is correct/happy. What ends up being the best may surprise you.

[Geoff2]

Twenty degrees of extra exh duration [ compared to the intake ] will give you plenty of reversion issues....

[Warp Speed]

Twenty degrees of extra exh duration [ compared to the intake ] will give you plenty of reversion issues....

Huh?!?

[mdrew]

o Were the springs, especially exhaust, still 'spot on' for load when you tore it down?
o Many rockers have more than advertised ratio; did you measure actual lift and retainer/seal clearance with checking springs and verify seal location on all valves? .
o Having only 6 seals crushed means something's different on the bad six. Less clearance, lower spring load, worse lifter pump-up, six valves that aren't hollow...

Thanks for the questions.

I have not checked spring load, yet. I, uh...er....kinda ran over my tester with a four wheeler and am waiting for a replacement to show up.... - long story.
I did not check total valve lift with the Crower rockers! Should have when I was checking PTVC. Good idea and I will when it goes back together.
All exh valves weigh the same. Intake too.

[mdrew]

I think your system isn't happy & that may be why the seals got hammered.

You've added ~8 grams of exhaust valve weight, ~4-5 grams of retainer & lock weight, 30 grams of spring weight, and a significant amount of rocker arm weight. It doesn't sound like you spend a lot of time at high RPM so I have to wonder how you arrived at your current valvetrain combination?

The following configuration has completed over 3,000 racing miles (see pic below) up to about 7500 RPM peak (long total run time per event). Actual limiting speed in that system (defined as .010" bounce at closing & not cleaning up 100 RPM higher) is about 8200 RPM.

-GM catalog hyd. roller cam (aka Stage 3 LS Cam)

- 1511ML springs, set up at 1.820"-ish

- Stock retainers & locks

- Stock rockers
*No "trunion kits"....completely 100% straight off the production line and zero failures in several engines like this & 2,000 or more racing miles. Trunion bearing failure was a 2007 era field concern that was fixed for later production. From a geometry standpoint the stock rocker arms will not cause problems if actual (net) lift is .650" or less. Above that you will have trouble. Otherwise, the stock guide material isn't extraordinary or great and earlier heads (2007-2008-ish) had machining issues that caused excessive guide wear. I assume you had the guides sleeved or changed somehow?

- Stock LS7 pushrods
*Actually delivered best stability with certain hydraulic roller cams & same ancillaries in comparison with a variety of same & larger OD & thickness 4340 1-piece pushrods.

- Stock valves (exhaust too).
*The exhaust valve problem on LS7 engines was fixed after 2008 and I never had any problems with the newer exhaust valves even with .800" lift solid rollers in a similar application to the link turning about 8,000 peak RPM. 100% of the 2013-newer COPO engines have the stock valves that include material & process changes after 2008.

I wouldn't necessarily climb all over the idea of adding more spring force because the combination really needs to be verified on a spin test rig but essentially you've added a ton of weight and you have about as much spring force as a decent beehive like the PSI 1511ML. BUT - with the disadvantages of additional spring/retainer/lock mass plus the dynamic stability disadvantage of straight wound springs (vs taper-wound like the beehive).

If it was mine to deal with I'd get the existing parts on a spin test rig (bet $100 you find the exhaust is pissed off), then compare to the proposed parts to make sure your system is correct/happy. What ends up being the best may surprise you.

RW - glad to see you respond. Always enjoy your insight. I've actually had the heads work twice now. This will be the third (new OEM heads with new MS 90 guides, mild port work retaining the swirl damn).

Long story short, after the heads were ported the first time, I had a cam spec'ed from the port work data, and it's what's in the engine now. I kept the OEM valves, had guide liners installed, and used stock rockers. After about 5K miles, I tore down the heads to find the guides wiped out again. Mostly top side wear. Sent the heads out again and had the guides replaced with new PM guides, and milled the rocker stands down for the Crowers. Kept the same springs as before. Went with the slightly heavier exh valve.

Decided to do something different over this winter, and found what I found, hammered seals. Good news, is that guide clearance looks perfect.

My personal experimentation with the OEM rockers on these heads, is the pad moves off center and starts side loading, right around .625" lift. Instead of fussing around with bolt on roller tipped rockers, I just decided to go with the Crower set up. Jesel was way too expensive for a street car.

I suppose I could always blow a bunch of money for spin rig testing, for a personal car.... but that's not happening. I'd love to, and completely understand the value, but for a one time deal??? I ain't made out of money.

[RW TECH]

RW - glad to see you respond. Always enjoy your insight. I've actually had the heads work twice now. This will be the third (new OEM heads with new MS 90 guides, mild port work retaining the swirl damn).

Long story short, after the heads were ported the first time, I had a cam spec'ed from the port work data, and it's what's in the engine now. I kept the OEM valves, had guide liners installed, and used stock rockers. After about 5K miles, I tore down the heads to find the guides wiped out again. Mostly top side wear. Sent the heads out again and had the guides replaced with new PM guides, and milled the rocker stands down for the Crowers. Kept the same springs as before. Went with the slightly heavier exh valve.

Decided to do something different over this winter, and found what I found, hammered seals. Good news, is that guide clearance looks perfect.

My personal experimentation with the OEM rockers on these heads, is the pad moves off center and starts side loading, right around .625" lift. Instead of fussing around with bolt on roller tipped rockers, I just decided to go with the Crower set up. Jesel was way too expensive for a street car.

I suppose I could always blow a bunch of money for spin rig testing, for a personal car.... but that's not happening. I'd love to, and completely understand the value, but for a one time deal??? I ain't made out of money.

The stock rocker has a peak valve lift (by design) of 0.6567". After that you get into a tighter radius on the slide surface and that'll cause fits. Of course this assumes all dimensions like valve tip height are where they need to be.

The spin rig testing can be fairly cheap, especially compared to mixing & matching parts and hoping the combination is right. Maybe $350-$500 will get you taken care of but you will have to confirm pricing with a source of your choice.

Compare that to the prices of the parts you have & it starts to look like a cheap date. Especially when you compare content of the valvetrain systems in the example I showed or the COPO Camaro to what you have.

I've spent a fair amount of time with this stuff so I'm speaking from experience and my heart when I suggest that you get your combination verified on a test stand.

Just as an example, a cam sourced through a popular vendor that, combined with the same ancillaries I described above, created a hot mess that wouldn't run clean past 7100 RPM. Change cam lobe design (same lift) & poof - it rocked on up past 8,000 RPM without any trouble. Then there were the dual springs (all that were available on the open market) that didn't rev nearly as high as the beehive, the solid stem exhaust valve that knocked over 1K RPM off peak limiting speed, trick lobes from popular vendors that would break spring tips like clock work, and on and on and on.

[randy331]

Twenty degrees of extra exh duration [ compared to the intake ] will give you plenty of reversion issues....

Huh?!?

Huh ? Was my first thought too.

I guess we can cure the reversion issues by adding intake duration ?

Randy

[pamotorman]

question is that picture a 4 WD off road race truck ???

[RW TECH]

question is that picture a 4 WD off road race truck ???

Yes. Ultra 4/King Of The Hammer.