jimsalone

Ok guys here is the skinny on the valve guide wear inside my 2010 ZR1 with only 1,300 miles on it. I will quote the person at the head shop that was planing my heads for an upgrade. I will not give the name but here is the info:

"50% of the intake guides could not be measured due to the excessive wear at the top and bottom of the guides. They were off the dial of my bore gauge. The mid section of each intake guide measured at .0025" +or- .0002". The exhaust guides consistently measured .00024" at the top and by the bottom were at or near the max wear limit of .0037". Some as large as .0043" at the bottom."

Sounds really bad to me

forg0tmypen

Its really bad. 1,300 miles and already PAST wear limit near bottom of exhaust guides? Oh man. The excessive wear issue is not just an LS7 problem anymore folks. This is an LS7 AND LS9 issue. The prediction has always been, when enough LS9s get up in miles and track hours, theyll fail just the same way LS7s have. IMO, with this report, that is fast becoming more of a reality instead of a prediction.

NHRA95

GM has a BIG BIG problem on their hands... this is UNBELIEVABLE!

Shurshot

Bummer!!!!!

I was hoping the LS3 valve guides used in the LS9 heads would not inherit the well known problems with the LS7 heads.

Makes me feel better about not re-financing my house just to get a ZR1

No wonder they are saying there will not be another ZR1

timmyZ06

Im starting to wonder if im gonna buy another corvette, vibration, transmission, clutch excessive guide wear and e.t.c im glad its only 100k car!
shelby gt500 is more and more temping, i cant stand this s**t anymore.
Am i the only one who feeling this way?

range96

Did you forget to put oil in the engine after your oil change???
Seriously, were there any indication of worn guides prior to the breakdown?

I'm a little skeptical of this report from your mechanic. I would make him save these guides for prosperity.

Was your engine still stock or modified? Did you put 1,300 miles on the car 1/4 mile at a time?

Give us some history here. We have some cars that spent a lot more time on road tracks at high g turns, running near redline without incidents.

I'm not doubting you or your mechanic, but it's very surprising.

Just saw that you're doing Stage 4 at Katech. I'm pretty sure they are the one who reported guide wear on a previous car also. I'm still very surprised. Did you have any low oil pressure indication?

Dicecal

UFB! If true, listen up GM, and fix the problem and come out with a TSB. Dumped my Z06 in part because of the LS7 issues. I may dump GM & Corvette next!

OnPoint

Does anybody know what the specific/particular differences are b/n the LS3 head and the LS9 head?

barduch

Anybody else using ZDDP? Full flame suit on, I think it's cheap insurance. It seems like a lubrication issue to me. Another mitigant might be the use of Lenckite Avblend oil additive. I have used the Avblend in my turbocharged aircraft engines for 15 years. All of those motors have made it to their specified TBO (time between overhaul) interval with no cylinder, valve, or valve guide problems. Heat is the enemy of a turbo or super charged engine but it is a fact of life with compressors. Heat affects the ability of oil to do its job. The Avblend seems to be particularly effective as a penetrating lubricant that performs its magic when the temps are high and lubrication is needed the most.

jimsalone

My car has never been tracked. My car has never been raced. My car never broke down. It was running like the day I picked it up. My oil has been changed twice and it was at the Chevy dealership in my home town where I bought the car. They are very reputable and they only have 1 senior corvette mechanic that is allowed to "touch" zr1's. I did not post this to cause any problems. Actually I baby my corvette's which to some people may seem stupid. I payed 122K for this car and i would not dream of abusing it. It may in fact be silly for someone like me to even be getting more horsepower. As I stated Range...in my post where I said I had dropped my car off at Katech, the guys asked me to report the valve guide wear...so I did. It's that simple. i have had ZERO problems with my zr1 and love it and would not trade it for the world. The great news is that it is now getting bronze valve guides and Ti/Mo intake valves at Katech so at least the problem was fixed before the damage could have occured. Please be advised that Katech's name should not really be dragged into this and "you should never shoot the messenger". I'm glad they have fixed it before it really mattered.

Jim

range96

Jim,

I appreciate the feedback. I wasn't trying to "shoot the messenger" and I know Katech is very reputable. Just trying to make sense with this. It either had a batch of bad guides or the car had some oiling issues. I also have a '10 since new, so you know why I'm curious to find answers here. I road race and will possibly do some upgrades in the future.

Do you know what the factory guides are made of? I thought they were bronze as well.

I'm also completely puzzled that Katech offers Stage 1, Stage 2 and Stage 3 upgrades if they know the factory guides are bad. Something just doesn't add up here. They only put new guides in their Stage 4 and Stage 5 CONCEPT. Why increase boost if the guides are marginal? If anyone would know that the guides are bad they would. But then why offer increased boost and stand behind their work?

jimsalone

I'm not sure what the stock guides are made of. Good question. The answer I got from Jason leads me to believe that the stock guides were not bronze but I simply don't know. I never had an oil light and the oil was changes by a certified zr1 mechanic and it was changed at 600 miles and then again at 1,100 miles. I am willing to bet if you PM Jason he could provide you with very specific information...he has been very responsive and informative on each and every communication I have had with him....as a mater of fact I have kind of been a PITA with all the emails I have sent him and he answers the same day EVERY TIME. I am very glad I took my car to them and look forward to posting all the GREAT STUFF about it when I get it back. The waiting...is the hardest part...LOL

Jim

'06 Quicksilver Z06

Been there, done that. High ZDDP motor oil won't save you from valve guide wear. And I was using RLI. One of the motor oils out there with the highest ZDDP levels you can find. In a normal situation, if your valve seals are intact and doing their job, there'll be no oil on your valve guides and stems.

If you're to the point to where motor oil is getting between your guides and valve stems, then it's already too late.

range96

Jim, it is refreshing getting straight and objective information. Thank you.

mirage2991

so they measured the guides... that's nice... how about each valve stems and then substract the numbers to get actual valve guide to stem clearances, and the. comparin that to what it "should be"... whatever number that is... that would indicate much more that just stating " i have a hole this big"...

Dicecal

The stock valve guides are "powdered metal", the exact composition is unknown to me.

barduch

I agree with everything you are saying in regard to oil on the valve guides and you make a valid point. I guess that I am more focused on the heat retention factor. The following was lifted from an article by Kas Thomas. He is a highly respected expert/guru in the world of gasoline powered reciprocating aircraft engines.

"Valve sticking has been a problem for aircraft engines since the 1930s. The problem, in a nutshell, is that high-output air-cooled engines impose huge thermal loads on exhaust valves (and seats and guides). In addition, air-cooled engines run at very rich mixtures, for cooling purposes, and they use serious amounts of lead in the fuel (for knock suppression). This combination is ideal for valve sticking, since the combustion chamber now becomes a crucible for the formation of high-melting-point lead/carbon deposits which, given the opportunity, precipitate out on valve systems during the exhaust event. When the valve retracts into its guide in preparation for the next cycle (and remember, the valve spends two-thirds of its time closed), hot stem deposits transfer to the cooler valve guide. With time, deposits build up to the point where the valve has no running clearance at all. After a hot shutdown, especially as the rapidly cooling cylinder head and guide shrink onto the still-hot valve stem, valves and guides can cement together.

The problem is worse in engines with sodium-filled valves, because the sodium coolant carries massive amounts of heat straight up to the valve stem (the entire valve runs hot, instead of just the head).

Abnormal valve cooling only aggravates the picture. How does valve cooling become "abnormal?" Simple. When the heat-transfer path is broken, the valve overheats - that's all there is to it. For a solid -stemmed valve (which includes all Continental valves), the single most important heat-transfer path is the one formed by valve face to valve seat contact. This is where up to 75% of all heat transfer takes place (see SAE Paper 650484, May 1965, by Thompson valve engineer Cherrie). Anything that interrupts this path will cause valve temperatures to skyrocket. Bear in mind that the exhaust gases rushing past the open exhaust valve may be 1,600F to 2,000F or more, and at valve lifts less than about 0.1-inch, flow is Mach-limited. The "wind chill" is probably around 3000F. So poor valve seating, due to deposit buildups on the valve or seat, for example, can result in greatly elevated valve temperatures, and the increase shows up instantly.With sodium-cooled valves (as used on all current-day Lycoming engines), the most important heat-transfer path is via stem and guide contact. Here, valve guide wear is critical, because if guide clearances open up, not only is heat transfer impeded, but valve seating can be impaired by virtue of the fact that the valve isn't going straight up and down any more (it's wobbling around). Again, the result is skyrocketing valve temperatures.

Anything that can aid in achieving better valve seating, reduced guide wear, lower temperatures, and/or improved lubricity inside the valve guide should, in theory, help to reduce valve sticking, and maybe go a long way toward improving the overall TBO life of the engine (since valve and guide problems are often TBO-limiting)."

I know that this may be comparing apples and oranges in light of the fact that aircraft engines are air cooled and typically operate in a much more hostile ambient temperature environment. But when supercharging is added to any conventional automotive engine temperature extremes come into play and anything that can be done to help control those extremes should be beneficial.

svtkeith

Thanks for this info Jim...however this sux big time..like Dicecal one of the main reasons I got rid of my Z06 was that this problem was probable to happen and the step up to the LS9 was that it had more power and no more fear of the LS7 syndrome.

JetBlue427

be interesting to find out if these LS9 heads are built in Canada by the same company that manufactures the LS7s....regardless they probably both use the same powdered metal valve guides that are machined wrong right from the factory. And this extremely low mileage example is proof of that problem...you just cant get that kind of wear with 1300 babied miles.

FrankTank

In one of the guide wear threads in the ZO6 section last year I think , Jason from Katech mentioned they were also seeing some guide wear in the LS9 I think Wcch said the same thing . Looks like ZR1 folks are going to be joining the party . A party nobody wants a part of