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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
I finally decided to get my guides checked at a Motor Sports Shop in Mooresville, NC. Dropped the car off yesterday afternoon and the owner called me to let me know what they found. Heads were removed from the car and he said they were in pretty good shape when comparing to GM specs and tolerances. The intake valve guides were worse than the exhausts with the exhausts all being within spec.
The worst intake guide was out of spec by .0001 at the bottom but in spec in the middle and the top. Valves were pretty much straight with nothing but normal wear variance in valves. All valve lengths were within .0001 of each other. Almost no variance at all. He will be sending me the measurements in an email latter today.
The engine has about 15K miles on it since it was installed in Oct. 2011.
I will post the measurements when I have them. All I have to do is decide what I want to tell him to do. It looks like the exhaust valves and guides are all in good shape. I was hoping for a black and white situation where either everything was in good shape or things were pretty bad. Now it looks like it is more of a gray area with doing nothing a viable alternative.
I think from a wiggle test standpoint the engine would probably have passed if subjected to a properly conducted test. It is hard for me to imagine the one intake valve wiggling a lot with only the bottom of the guide being out of tolerance.
UPDATE: This engine is a warranty replacement for the original which dropped a valve three plus years ago. The engine is completely stock and this is the first time it has ever been opened up.
UPDATE: Valve Guide Clearances (These were all determined using a valve guide bore gauge and valve stem measurements)
UPDATE: I added the Valve Stem Measurements and GM Specs to the Chart.
One thing the shop owner showed me on my old heads was an overheat type of mark that went from the spark plug location into the exhaust ports. Not all of the combustion chambers had the mark but most did. It was a dark streak through the normal combustion byproducts.
Update 4/29: Got my car back Monday afternoon. The new heads from GM had guide clearances between .0016 and .0026. That fits right in their production specs. The shop installed bronze guides with Ti/Mo intake and exhaust valves with all of the guides set at .0016. Traded the old heads to the shop to cover their labor. With GMPP paying for the new heads and trading the old heads for guide installation/fit, valve job, ARP head bolts and new valve seals I got out of this for about $2800 (the cost of the valves/guides) and roughly 5 weeks down time on the car. Gibbon's Motorsports in Mooresville, NC did the work. They can do all of the work in house.
The results of the check indicate that I would have gotten lots more service out of the heads but once they were apart it didn't make sense not to address the out of spec guides. GMPP obviously agreed. Since I still plan on tracking the car quite a bit I decided the best thing to do was to upgrade the new heads with Ti/Mo intake and exhaust which were recommended by both Katech and Gibbon's Motorsports. Peter Gibbons set the new guide/valve clearances at .0016.
A couple of things I think are noteworthy out of this experience with the valve guide issue is most of this started 3 years ago when people were searching for the cause of exhaust valve heads dropping. Poor exhaust valve manufacturing was an original theory but debunked by Katech, then loose guides became the hot theory. The only problem with loose guides as the cause of the valve drops is the data shows quite a few intake valve guides being out of GM's service spec Vs exhaust valve guides being out of spec. However, the vast majority of valve drops were exhaust valves. The numbers don't add up. If bad guides were causing the problem it seems like there would be substantially more engine failures due to dropped intake valves.
Bill
Last edited by Bill Dearborn; 04-29-2015 at 03:34 AM.
I think I would put it back together and check again in another 10-12k miles, assuming these are not factory valves and guides... What are the specs on the heads and cam?
I finally decided to get my guides checked at a Motor Sports Shop in Mooresville, NC. Dropped the car off yesterday afternoon and the owner called me to let me know what they found. Heads were removed from the car and he said they were in pretty good shape when comparing to GM specs and tolerances. The intake valve guides were worse than the exhausts with the exhausts all being within spec.
The worst intake guide was out of spec by .0001 at the bottom but in spec in the middle and the top. Valves were pretty much straight with nothing but normal wear variance in valves. All valve lengths were within .0001 of each other. Almost no variance at all. He will be sending me the measurements in an email latter today.
The engine has about 14K miles on it since it was installed in Oct. 2011.
I will post the measurements when I have them. All I have to do is decide what I want to tell him to do. It looks like the exhaust valves and guides are all in good shape. I was hoping for a black and white situation where either everything was in good shape or things were pretty bad. Now it looks like it is more of a gray area with doing nothing a viable alternative.
I think from a wiggle test standpoint the engine would probably have passed if subjected to a properly conducted test. It is hard for me to imagine the one intake valve wiggling a lot with only the bottom of the guide being out of tolerance.
Bill
If these heads are assembled with O.E. exhaust valves we would recommend changing those out before re-assembly for some extra peace of mind.
Last edited by Livernois Motorsports; 03-18-2015 at 09:29 AM.
I finally decided to get my guides checked at a Motor Sports Shop in Mooresville, NC. Dropped the car off yesterday afternoon and the owner called me to let me know what they found. Heads were removed from the car and he said they were in pretty good shape when comparing to GM specs and tolerances. The intake valve guides were worse than the exhausts with the exhausts all being within spec.
The worst intake guide was out of spec by .0001 at the bottom but in spec in the middle and the top. Valves were pretty much straight with nothing but normal wear variance in valves. All valve lengths were within .0001 of each other. Almost no variance at all. He will be sending me the measurements in an email latter today.
The engine has about 14K miles on it since it was installed in Oct. 2011.
I will post the measurements when I have them. All I have to do is decide what I want to tell him to do. It looks like the exhaust valves and guides are all in good shape. I was hoping for a black and white situation where either everything was in good shape or things were pretty bad. Now it looks like it is more of a gray area with doing nothing a viable alternative.
I think from a wiggle test standpoint the engine would probably have passed if subjected to a properly conducted test. It is hard for me to imagine the one intake valve wiggling a lot with only the bottom of the guide being out of tolerance.
UPDATE: This engine is a warranty replacement for the original which dropped a valve three plus years ago. The engine is completely stock and this is the first time it has ever been opened up.
Bill
Well I would rework the heads since you have them off and likely exhausts are close to limit. Lets see those numbers.
Well I would rework the heads since you have them off and likely exhausts are close to limit. Lets see those numbers.
DH
Waiting for them. He said the exhausts were not close to the limit and the valve stems checked out fine with what he considered as normal wear for 15K miles.
I'd clean up/inspect the valves and have some new guides installed since you're already half way there.
Valves have all been cleaned and inspected/measured. They are all in good shape with no issues. Both intake and exhaust.
Still waiting for him to email the valve guide measurement sheets. At least one intake guide should be replaced since it is a hair out of tolerance. I need to make a decision on how I want to proceed tomorrow as I have an event on 4/24, 4/25 and 4/26 and need the car back to prep it. If I decide to get fancy with Ti/Mo intake and exhaust valves the parts delivery time could become a factor along with putting a big hole in my wallet.
I finally decided to get my guides checked at a Motor Sports Shop in Mooresville, NC. Dropped the car off yesterday afternoon and the owner called me to let me know what they found. Heads were removed from the car and he said they were in pretty good shape when comparing to GM specs and tolerances. The intake valve guides were worse than the exhausts with the exhausts all being within spec.
The worst intake guide was out of spec by .0001 at the bottom but in spec in the middle and the top. Valves were pretty much straight with nothing but normal wear variance in valves. All valve lengths were within .0001 of each other. Almost no variance at all. He will be sending me the measurements in an email latter today.
The engine has about 15K miles on it since it was installed in Oct. 2011.
I will post the measurements when I have them. All I have to do is decide what I want to tell him to do. It looks like the exhaust valves and guides are all in good shape. I was hoping for a black and white situation where either everything was in good shape or things were pretty bad. Now it looks like it is more of a gray area with doing nothing a viable alternative.
I think from a wiggle test standpoint the engine would probably have passed if subjected to a properly conducted test. It is hard for me to imagine the one intake valve wiggling a lot with only the bottom of the guide being out of tolerance.
UPDATE: This engine is a warranty replacement for the original which dropped a valve three plus years ago. The engine is completely stock and this is the first time it has ever been opened up.
Bill
How many track miles/sessions you figure you have on this completely stock engine and heads?
So not all the guides were in spec one is off correct. I would replace everything since your already there good luck with your decision.
Yes, I have been seriously considering doing all the guides just because we are in there and using stock valves. He is recommending aftermarket valve springs due to the high revs/temps the motor sees during track days.
I was in a similar position at 15k when I had my heads sent to WCCH. All exhaust were fine, but my intakes were approaching the service limit. I did have a cam and mods all that time too.
My logic was, everything is ok now, but what if this is right where things start to snowball? I reworked my heads with new guides, new OEM exhaust valves, katech ti mo intake valves, port and polish plus a mill job of .030. Car has been strong since, another 15k with drag, track, street miles and dyno pulls at 546rwhp. You may want to at least run new guides and maybe just a newer set of OEM exhaust valves since they are only a few hundred bucks.
Yes, I have been seriously considering doing all the guides just because we are in there and using stock valves. He is recommending aftermarket valve springs due to the high revs/temps the motor sees during track days.
Bill
I question the necessity for aftermarket springs. I am not aware of there being any issue with OEM springs, including in track use. Unless of course a bigger cam is installed. Which is not your plan. From a metal fatigue perspective I suppose one might consider fresh springs, but I see no reason not to use OEM ones.
Of course, this is just the opinion of a simple staple salesman.
I question the necessity for aftermarket springs. I am not aware of there being any issue with OEM springs, including in track use. Unless of course a bigger cam is installed. Which is not your plan. From a metal fatigue perspective I suppose one might consider fresh springs, but I see no reason not to use OEM ones.
Of course, this is just the opinion of a simple staple salesman.
He has built a lot of race engines with a fair number of them being road race engines. He says the big issue is keeping good valve springs on the engine and that aftermarket springs can provide more durability. He believes the worst valve train abuse comes on down shifts since the engine reacts differently to mechanical acceleration.
He sounds like he is more in Jason's camp when it comes to valve train bounce and the problems that can cause.
I would have the heads worked. You are at the outer range of acceptable clearance. One thing that happens with the oe pm guides, is rapid wear once it starts. I would send the intakes to Del West for re-coat and polish. On the exh side, you have options. I would also look to the PSI beehives with ti retainers. Good luck.
I would have the heads worked. You are at the outer range of acceptable clearance. One thing that happens with the oe pm guides, is rapid wear once it starts. I would send the intakes to Del West for re-coat and polish. On the exh side, you have options. I would also look to the PSI beehives with ti retainers. Good luck.
GMPP sent a rep to the shop today and asked the shop to send them a quote. They may cover some or all of the cost. Waiting to hear their determination.
I finally decided to get my guides checked at a Motor Sports Shop in Mooresville, NC. Dropped the car off yesterday afternoon and the owner called me to let me know what they found. Heads were removed from the car and he said they were in pretty good shape when comparing to GM specs and tolerances. The intake valve guides were worse than the exhausts with the exhausts all being within spec.
The worst intake guide was out of spec by .0001 at the bottom but in spec in the middle and the top. Valves were pretty much straight with nothing but normal wear variance in valves. All valve lengths were within .0001 of each other. Almost no variance at all. He will be sending me the measurements in an email latter today.
The engine has about 15K miles on it since it was installed in Oct. 2011.
I will post the measurements when I have them. All I have to do is decide what I want to tell him to do. It looks like the exhaust valves and guides are all in good shape. I was hoping for a black and white situation where either everything was in good shape or things were pretty bad. Now it looks like it is more of a gray area with doing nothing a viable alternative.
I think from a wiggle test standpoint the engine would probably have passed if subjected to a properly conducted test. It is hard for me to imagine the one intake valve wiggling a lot with only the bottom of the guide being out of tolerance.
UPDATE: This engine is a warranty replacement for the original which dropped a valve three plus years ago. The engine is completely stock and this is the first time it has ever been opened up.
UPDATE: Valve Guide Clearances (These were all determined using a valve guide bore gauge and valve stem measurements)
UPDATE: I added the Valve Stem Measurements and GM Specs to the Chart.
Bill
Did your car by any chance make any type of ticking noise on idle all the time?
03-17-2015, 05:52 PM
LS7 Valve Guide Check
I'd clean up/inspect the valves and have some new guides installed since you're already half way there.
