Michael_D

I deliberated whether to share this information on this forum or not. I do not like drama or bullshiit. I want no part of it. I do not want any part of personal agendas, sales pitches, or emotional based discussions either. I have yet to see a thread on this forum that doesn’t contain some of what I don’t want to be a part of; hence my deliberation. I'm just an old school mechanic who's been wrench on stuff for over 3 decades. I have nothing to sell, no agenda, nothing to prove. I know I don't have a big ******, and find no reason to prove otherwise.

The amount of incorrect information regarding this engine, and what one should do with it, compelled me to post this information. Do with it what you wish. It’s just numbers. I will have access to the heads today, but tomorrow they get stuffed in a box to go out for machine work. If anyone wants additional information, speak up quick while I have the measuring tools out.

Brief back story…

I bought this car used about four years ago; it is an 08, Z06. It had roughly 9K miles on it. The previous owner had a cam installed at 5K miles (QM-550). I did not like the way the engine behaved, so I decided to try and have it retuned. $500 and four different tunes files later, it wasn’t any better. So I tore the top end apart. I broke the heads down, took some measurements and sent them out for work. 5 guides had excessive clearance. All five valves had wear at the bottom of the guides. The cylinder head shop I sent them to preferred to address LS7 guides with a particular bronze alloy guide liner he has had good luck with. So that’s what I had him do.

After port work was done and the flow figures from the port work received, I had EPS spec a cam for the engine. Nothing too menacing, but not real tame either. Total lift on the intake is .646”. Exh is .670”. Those are cam card numbers, actual measured lifts are .650” and .674”.

When I had the heads off this engine the first time, I had planned to run a roller tipped rocker, but I did not like the bolt on YT rockers. Too nose heavy for what I wanted. I want this engine to rev to 7600 rpm. Reason being, I’ve seen that rpm twice now, and both times were due to me thinking I had the damn thing in third, shifting up from second WOT, but it was actually in neutral. The fuel cut off is set to 7200, so one would think the damn thing would not rev past 7200.... Well the first time I saw it, I did not believe it, and the second time it happened, I figured it would be wise to believe it. To keep peak rpm capabilities at 7600, light valves and rockers with minimal MOI are mandatory. Throwing spring pressure at a heavy valve train is not the best solution, and often just leads to cam lobe failure. I will not argue this point with anyone. If you don’t get something as simple as this, I can’t help you. Buy some books.

In keeping with this desire (light valve train, high lift, low valve side MOI, moderate spring rate), the OEM valve stems were micro polished and the valves re-used. I had CHE work the OEM rockers. Three years ago, choices for alternative exhaust valves for this engine were very limited. Both type and availability. I considered titanium, but couldn’t justify the cost, as they were a one-off, special order piece with a long lead time.

I am quite irritated with my decision to use the OE rockers with this much lift. I knew better. When I had the heads off the car before, I heard vastly different recommendations from “professionals” saying you could run them with a total valve lift of anywhere from .620” to .750”. Not believing any of them, I decided to experiment. I used a collection of springs, clamps, dials and braces to set up a rocker and observe it’s sweep across the tip of the valves at various lifts. I did this for both the intake and the exhaust. What I found, was the rocker tip would sweep the middle portion of the valve tip, just like it is supposed to do, up to roughly - .625” lift. I say “roughly”, as my test wasn’t terribly accurate, and had much room for human error. Anyway, at about .650” lift and greater, the tip would start to walk closer to the valve tip edge. Not a good thing.

Knowing this, but trusting “professionals”, I elected to stick with the OE rockers and save myself about 2 grand, as the only other roller tip set up I would consider was Jesel, T&D or Crower. With machine work, 2 grand is the price of admission. Even after I got the heads back, ran a sweep check on the valve tips, and not liking what I saw, I ran them anyway. I f’ing knew better, but I would have lost an entire season of driving time, as the heads would have to go back to the machine shop to be machined to run the rail rocker set up.

So fast forward to today, and 5K miles later……..

I’ve been chasing a rather irritating misfire for the last two summers (car goes into storage in the fall). I’ve tried a multitude of different tuning adjustments and tweaks. None have eliminated it. It’s not just reversion either… It’s a misfire. The next thing to check was the valve springs. While I had the springs off, I figured I’d check guide clearance with a dial. I checked three cylinders and didn’t need to go further. They were shot…….

Cylinder #1
Int: .014”
Exh: .009”

Cylinder #3
Int: .020”
Exh: .004

Cylinder #5
Int: .019”
Exh: .011

It is important to note the ALL movement is from intake port to exhaust port. The movement for/aft is tight. It’s also important to note that the vast majority of movement was towards the exhaust port, with very minimal movement towards the intake. This correlates with the peak lift push the OE rockers impart on the tip of the valve stem. Clearly, a peak-lift rocker side loading issue.

Here are the numbers I got with the bore gauge. One thing to note with the top and bottom numbers, is that they can vary a fair amount by just how far into the guide I position the gauge. I did my best to keep position consistent; at 3/16” from the most outer edge. If anyone has ever used this type of small hole bore gauge, they know what I’m talking about. The numbers are obtained by zeroing out the dial on the bore gauge with the valve stem diameter locked into a 0 – 1” outside micrometer. You set the mic, then roll the bore gauge into the mic, then zero the dial indicator gauge. All readings noted are intake side to exhaust side. Clearance for / aft were good on all valve guides.




You can see baked oil on the intake valves from the seals being shot. The exhaust valves don't look bad at all.....







In summery, if you are running a total valve lift in excess of .625", and using the OEM rockers, I suggest you check valve movement at 5K miles. It does not matter if you running bronze or PM guides. Side loading will eventually lead to wear and excessive clearance. Do not buy into the A-typical response you will get from bolt on guys on the internet; "I've done this a hundred times and you'll be just fine". Chances are, they are full of crap. Do yourself a favor and check clearance.

Technical questions with cognitive thought process and reasoning are welcome. There are some interesting discussion points based off of the measurements above.

PS: I refuse to use the words "wiggle" and "test" together, to form a sentence.

Rock36

This is an honest question, and I was dancing around asking the same question in the sticky guide wear thread, but what do you think is driving the greater wear on the intake side?

I completely understood your explanation, but my question is still why there was greater wear on the intake side compared to the exhaust side; especially considering the lift on the exhaust side is greater than the intake lift based on your cam specs and measured lifts. It would seem the exhaust side would be subject to greater side loading, and therefore more wear. What am I missing here?

Slightly related question. Would micro polishing the intake valves negatively affect the CrN coating to any meaningful degree?

Bad_AX

Subscribed, with full and undivided attention!

You are addressing some questions that I (and probably others) have had regarding the OE LS7 rockers. Like you, I want to maintain the 7000+ redline. I have a high interest in the Crower shaft rocker system, but I could not see a way to use these rockers without going to an old-school spring and heavy retainer to compensate for increased MOI of the roller tip rocker. It does not appear to me that a beehive spring such as the PSI LS1511 would have enough pressure to maintain stability at 7000 rpm and above, but data on the Crower rocker has been pretty much impossible to come by. I am highly interested in your valve train component selection this time around.

Question:

Given the following components

Cam with I & E lift not greater than .640"
Crower shaft roller tip rockers
OE Ti intake Valves
Ferrea Competition Plus Exhaust Valves F2042P (85 grams)
Ti valve retainers
Powdered metal guides by American Heritage

What springs will be needed to maintain 7000+ redline?

Thanks for posting about your experiences.
-Scott

Michael_D

Those are very valid questions, and I have been pondering over it….

I can only hypothesize at this point without validated my theory. Titanium is more malleable than stainless steel. Theoretically speaking, the intake may be bending more from the rocker push than the exhaust. This could be why the exh clearances are similar top and bottom. The other theory fluttering about between my ears, is the stem finish on the intake. But, if that were the case, I would have seen similar results when I inspected the heads the last time I took them off.

I tend to look for patterns. It’s something that I’ve learned over the years. Never jump to conclusions.

Micro-polish is to remove surface risers. There are different techniques. I’m not absolutely certain how these were polished.

wjnjr

Questions on one detail of the backstory:

In the first rebuild, were all the guides sleeved, or just the five that showed the worst wear?

And were the five bad ones all exhausts?

Michael_D

Mark and I have both been trying to get meaningful information from the various manufactures of rocker arms that would help determine the “change” from a known mass MOI (OE rockers), to one of the roller tipped models. It’s a hopeless endevour. The manufactures do not do any sort of comparative anallisis. I have actually spoken to the guy at Crower who designed there system. They do not know. About the only thing you can do to see what the difference is, and it is not very accurate, is to buld a trifoler pendulum and time each rocker osculation. Mark actually did this, the creative little bugger….

Out of the Jesel, Crower, YT and T&D, the nose weight is the only thing one can accurately measure and compare. The Jesel is the lightest, with the Crower second. The Crower is Stainless Steel, the others are aluminum. Jesel does make a steel version, but I don’t what it weighs. They are too proud of their stuff anyway. T&D will make you a chrome moly steel rocker, but that’s a $500 adder. I do not like aluminum rockers, in general. They flex too much at high rpm.

With springs, you are at the mercy of whatever rate is required for the lobe. Lift, coil bind and spring OD/ID are also factors. I like beehive and conical valve springs, but neither have one for this engine with the amount of lift I’m running. I could just yank the cam, but the thought of doing another in-car cam swap on this vette makes me cry like a baby.... I just don't want to do it.

It’s usually best to just get this info from the cam grinder. In my case, Skinner suggested the Comp 26926TI-KIT, that comes with Ti retainers.

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''

I prefer PSI or PAC, but they didn’t have a spring that was similar enough to the Comp spring, so that’s what I went with.

I have no idea what the peak rpm is on this engine. I do know it’s at least 7300 rpm. All I do know, is that I am not going to arbitrarily increase valve side rocker weight.

Also, don’t confuse the term “redline” with “peak rpm capabilities”. Two different terms with different meanings that I have had to speak to on this site, several times.

Michael_D

All guides were lined, honed to proper clearance, then the seats cut on some pretty trick machinery by a very skilled craftsman.

All five were still within spec, but at the outer limit. They were on their way out, so to speak. Two were intake, three were exhaust. The guy doing the work was able to check concentricity with an fixture he has, and all five were four thou or greater off. I just checked seat run-out, with a gauge I seamed to have misplaced in my frantic enthusiasm to move "stuff" around to fix a water leak. I'm a bit sore over that at the moment.....

'06 Quicksilver Z06

Interesting question, and I noticed that you and he had a brief discussion about sleeved guides between post 24 and 38 of the following thread.

https://www.corvetteforum.com/c6-z06...post1586353002

I wonder if this might have had something to do with the results he sees now.

I'm looking at Michael_D's numbers written on the tablet in the first post of this thread, and 15 out of 16 of those sleeved guides are shot.

I also noticed another comment and incident with regard to this technique in the case of forum member meanjoe.
http://forums.corvetteforum.com/c6-z...post1587022310

Michael_D

The guides (or sleeves if you prefer) are all out of spec. Please don't confuse the reason why they are toast, with the fact that they are sleeved. The material is a bronze alloy, with the rigidity of the PM parent guide surrounding them. They are worn as they are due to side loading from the rocker tip. As I said in my opening post, it doesn't matter the material is. Any guide would have eventually worn down.

Point being, check your heads, even if they have been worked and you are running lift in excess of about .620" and you are running OE rockers (or CHE bushed). Unless I happen to have a one-off set of heads with funky rocker location, and / or height, you may find similar results.

The heads are boxed and will be on their merry way to Kohle at AH. He may find something else to consider when he puts the heads under the knife.

Dirty Howie

Michael

I will skip all the stuff you don't want to hear and just wish you luck with your new setup


DH

'06 Quicksilver Z06

Thanks for the heads up, and this is interesting because there are so many cams out there with either an intake or exhaust lift at or around .620" and more.

If I'm following you, then you are saying that a roller tip rocker setup is a better option than the stock rocker for cams with lifts in this range.

This is really interesting when I think of many of the popular cams out there such as the Lingenfelter GT19 678/.688 and GT21 691/.702 , the Katech Torquer .615 / .648, and the new K501 . 657/ .660, the Black Widow QM series, and the Livernois Stage 2 2R and 3.

Michael_D

Ya, I know. That's why I felt compelled to post this information.

When the installer, (whomever that may be) installs the heads, he needs to check the wipe pattern. That is always telling. I may have an oddball set of heads, I really do not know. If the sweep pattern remains in the middle 1/3 of the stem, you should be just fine. Mine were not. Even the tips of the valves and lash caps show signs of the rocker rubbing the most outer side of the stem. I knew I was going to have troubles, but did not realize it would be this soon....

A roller tip isn't going to fix this, IF the rocker / rocker system does not allow for height adjustment. So some may not help the situation.

glenB

I've read a few articles where they've mentioned valve tip scrub while using the stock rocker and lifts over .625.

I understand the reason to reducing weight over the valve, valve float, using a bigger spring isn't an option like the older gen2 engines, although the Brodix head allows for a bigger spring but it also requires its own rockers.

So if you're using the factory head and stuck with relatively small springs, how about looking at camshaft design.

Comp Cams makes good cams, but to get extremely fast valve action they are hard on springs. EPS has stable cams, if you choose the profile using the Cam Motion Hi-Rev lobes, because EPS also uses Comps lopes.

Cam Motion makes stable lobes for the L76/92 head, basically an LS3 with a steel intake valve. This valve is heavy, way heavier than the LS7 valve. My point is if he can do a lobe for the heavy valve and still make great power, why not an LS7 with a roller tip.

Or just change to a head with larger spring pockets.

427ZM

Wouldn't lobe design play a serious role in this and not just raw lift? If your ramp rate is like a XER, your valve is much more likely to bounce than say a more stable lobe.

Personally, I just switched from a cam running LSL lobes (.657/.660) to a cam running QXX/HUC lobes (.701/.670) and my Valve train noise has decreased while power has increased substantially. Deal is, QXX and HUC lobes are more stable lobes; they are more soft on and off the seat.

The below is from Martin Smallwood of Tick in regards to my new cam:

"As you can see, the softer opening and closing ramps of the QXX intake lobe and the HUC exhaust lobe exhibit less valve train noise. The softer ramp as I mentioned before will also significantly decrease deflection in the rocker arm, at the rocker arm/valve stem tip meeting point and in the push rod."

So, before giving up on lifts higher than .625, take into consideration the lobe design.

Michael_D

Ummmm.... I had not intended to get into lobe design and valve train stability, again..

The entire point of this thread is to be informative to those who are running higher lift cams with OE rockers, and rocker GEO is not as good as they may have thought, or been lead to believe. There is a general assumption in the ol' interweb world that you can run the OE rockers on lifts in excess of .650" and not worry about it.

The cam I am running was spec'ed by Geoff. I wanted a very stable high rpm lobe profile that would capitalize on the port work done to the heads. The lobes are HUC: 13047R / 13054R. Cut on a 113.

Something else that is rarely discussed, is lifter wheels. The OE .700" wheel is not the best choice for more aggressive cam profiles. The .750" wheel is a better choice, but not an inexpensive one.

Mark2009

Well, excellent point, but to my interpretation the point Micheal is making on lift is mainly with respect to the OEM rockers and is twofold:

1. Higher lift is going to move the wipe pattern (rocker tip/valve stem tip) closer to the outside edge of the stem (assuming it is properly centered at stock lift). The OEM setup has no ability to adjust the rocker pivot (trunnion) height in order to compensate and re-center the wipe/sweep pattern.

2. Due to the design and function of the OEM rocker tip, at some point lift is going to exceed its design capabilities (the pad on the rocker tip will be pushed up onto its edge, which is a bad thing). Now exactly what the design limit is depends on who you talk to... some say .650, some say more, and maybe none of them have actually measured, plotted, and consulted with GM Powertrain or other professional engineers/designers. So, probably best to be conservative when choosing a limit.
.

MyLS1Hauls

I made it ~20k miles (~26k total) with a .675"/.675" lift cam (don't know detailed lobe specs...they aren't comp), before the guides were worn out. My wipe pattern looked pretty good. Had no noticeable wear pattern on valve tips/lash caps. My intake valves were much dirtier than yours, but I had 4 times the miles. I attributed it to PCV oil, coupled with carbon from reversion. Worn out guides had clearances between .0037 and .005. Running dual springs at 150#/410#. I've been told by a few that they like to see 150# on the seat, to lessen bounce. Take that FWIW.

Good luck with the updates, and thanks for the detailed info.

Mark2009

I was thinking that as a possible culprit on the OP's intake valves as well.

.

Michael_D

I am running a catch can.

double06

What shape were these in after 5,000 miles?