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C6 Corvette ZR1 & Z06General info about GM’s Corvette Supercar, LS9 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track
Just bought this car 2 weeks ago. 2008 Z06 completely stock w/ 36k mostly highway miles. Never tracked. Oil changed every 3000 miles.
Wiggled the #1 intake and exhaust valves. Measured .0060" for intake and .0085" for exhaust. Service spec is .0037" for both. Glad I tested them before dropping a valve. At this point I don't see any choice but to pull the heads. I'll measure the rest of the valves after I get the heads out of the car. Also, can hear a sewing machine like noise between 1200-2200 rpm. Not sure if related. Just for kicks did a compression test on all cylinders and they seem to be holding pretty good pressure. between 180-190 psi. Not sure if there is supposed to be so much oil under the valve covers. My first time opening an engine.
What to do next? I am not looking for more power. I just want a car I can drive w/o worrying about losing the engine. Here are some pics so you can see the tear-down and my test set up.
I would just pull the heads and send them off to AHP or WCCH to have new valve guides installed. Might as well do a trunnion upgrade while you have them apart. No one likes needle bearings floating around and an 08 wont have mag plugs to catch them.
I would just pull the heads and send them off to AHP or WCCH to have new valve guides installed. Might as well do a trunnion upgrade while you have them apart. No one likes needle bearings floating around and an 08 wont have mag plugs to catch them.
Trunion upgrades are a waste, IMO. The needle bearing problem occurred during a very small time period, from January 07 through June of 07. For the most part, trunion upgrades are less reliable than the OEM rockers too. The only ones that seem to work well are the brass bushed ones. The long term jury is still out on those too. If anything I'd just replace them with a new set from GM. If you're compelled to replace them the only ones that I'd go with would be a fully rollerized set, T&D, Crower or Yella Terras. I've got 106K miles on my Z06 with OEM rockers and never have had a problem or excessive noise with them.
Undy is spot on. Needle bearing trunion upgrade is pure crap. Bronze upgrades seem ok for now, but need to get enough miles to evaluate, and may just have to replace the bronze pieces every 10k miles.
All 16 of my comp trunions were SEVERLY worn after ~10k miles. Metal dust/flakes all over. Grooves through bottom of the trunion. The crap metal they use can't take the load, and just gets worn away. Everyone I know now that is pulling their trunions apart is finding the same thing. So if you want an "upgrade" that dumps metal shavings/dust into your oil, go for it.
If so, your intake is "in spec", but the exhaust is pretty much at service limit considering margin for error on the wiggle test. Having said that...GM's "in spec" means nothing to me since its obvious that their quality assurance was all but absent with these cylinder heads. I still think pulling the heads and sending to somewhere like AHP for their very budget friendly package #4 is a wise choice. You will sleep much better knowing you have a good set of properly machined/concentric heads on your car.
Correct these are raw measurements, meaning from one extreme to the other extreme in terms of rocking the valve within the guide. I haven't seen where it says to divide the raw value by 2 though? Where is this stated?
Correct these are raw measurements, meaning from one extreme to the other extreme in terms of rocking the valve within the guide. I haven't seen where it says to divide the raw value by 2 though? Where is this stated?
Probably not discussed enough...but here's AHP's post (#47) on deciphering the raw measurements taken from their own "DIY" wiggle test thread.
This makes complete sense. Since the valve guides are 2" in length and if the measurement is taken .040" above the guide then doing some trig yields a result that is within .04% of the actual clearance when the raw number is divided by two.
I wonder how many people know about this when doing the wiggle test. Quite a few false positives if you forget to divide by 2.
This makes complete sense. Since the valve guides are 2" in length and if the measurement is taken .040" above the guide then doing some trig yields a result that is within .04% of the actual clearance when the raw number is divided by two.
I wonder how many people know about this when doing the wiggle test. Quite a few false positives if you forget to divide by 2.
Certainly possible if one isn't knowledgeable enough on the subject matter. The wiggle test has been scrutinized to death here, but at the end of the day its a good test to determine whether or not you have an issue that needs a closer (more invasive) look. You only sampled one cylinder, and in my opinion...you should have a closer look at your heads (i.e. send them out for a rebuild).
Undy is spot on. Needle bearing trunion upgrade is pure crap. Bronze upgrades seem ok for now, but need to get enough miles to evaluate, and may just have to replace the bronze pieces every 10k miles.
All 16 of my comp trunions were SEVERLY worn after ~10k miles. Metal dust/flakes all over. Grooves through bottom of the trunion. The crap metal they use can't take the load, and just gets worn away. Everyone I know now that is pulling their trunions apart is finding the same thing. So if you want an "upgrade" that dumps metal shavings/dust into your oil, go for it.
I have not heard of anyone having any issues with the CHE upgrade that I've gone to. I would never reinstall needle bearings.
Yours were severely worn because you installed comp's upgrade which has long been prone to failure. I removed mine less than 2 mos ago for inspection and there was no indication of wear whatsoever.
Last edited by User Omega; 08-23-2016 at 10:24 PM.
Reason: Can't think or type today...
Haha these are actually pretty good results. I wondered if those were the raw numbers too since you didn't show the math. I agree with the others about the rockers. No need to change them. I'd still do the heads personally plus who wouldn't want more power?
Send your heads to American heritage performance in los angles and for a little over 1300 they deck the head put new exhaust valves and powder metal valve guides in. Better then bronze guides.
You are out of warranty? if so its a gamble, for peace of mind get this handled now. I am in the same boat and following my exact advise myself.
Unless going to a roller setup....CHE, Straub, or leave the stock trunions. Nothing wrong with the stock rockers at all IMO, I just decided to go the CHE trunion route on my head rebuild because I didn't care for the side to side slop I've seen with stock rockers...however minimal that may be.
I would still love to see someone order a set of those T&D adjustable pedestal mount rollers and incorporate those into their build. But them I'm sure that will spark another spintron debate...
Crowers are a nice peice at a decent price point for what they are.
We like they but as mentioned by Unreal they can be "taxing" on some budgets.
If your on a budget a nice upgrade is the bronze bushings to the stock rocker arms. We recently started installing the bronze rocker bushings in house.
Looks like we are mixing 2 different wiggle test methods. What the OP pic indicates is his test was the Hib (Test indicator)methodology while the AHP's method and math is different. Both are good methods but need to make sure what method is used and how to interpret the results..
Looks like we are mixing 2 different wiggle test methods. What the OP pic indicates is his test was the Hib (Test indicator)methodology while the AHP's method and math is different. Both are good methods but need to make sure what method is used and how to interpret the results..
Well regardless his pass fail criteria for his results was wrong. These are actually pretty good numbers. Many are WAY worse than this. I know mine were.
Does anyone know what recently built heads usually wiggle at? There must be some clearance even new just not sure how much. 0.0005" or so of total clearance would be my guess.
Quick update. I got the intake manifold, headers off. Last thing to remove before I can pull the heads is the power steering reservoir and alternator bracket. What a PITA. After I get the heads pulled I will measure the remaining valve guides and send these heads off to AH. Hopefully I remember how to put everything back together.
Will probably have a few more moments of despair before she is put back together. I know the peace-of-mind will be worth it though.
Getting this deep into the engine makes you appreciate all the engineering that went into our cars.
08-23-2016, 03:28 AM
Failed wiggle test
