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[Z06] Warranty Replacement Heads at 15k mi. Part II - Bore Gauge Measurements
C6 Corvette ZR1 & Z06General info about GM’s Corvette Supercar, LS9 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track
Warranty Replacement Heads at 15k mi. Part II - Bore Gauge Measurements
Finally got the heads disassembled, cleaned up, and measured the guides. Results below.
Nothing we haven't seen before, but it's interesting that while the intake guides were much worse than the exhausts, the intake valves were in better shape than the exhaust valves. Even so, the most wear I found was 0.0006 on a couple of exhausts.
Tools used to take the measurements:
A really bad guide. Anything greater than 0.0037 is too loose.
Hey Jim
When you're taking technical photos you may want to move the can of Silver Bullet out of the way.
So with that Joke out of the way....Do you think that maybe the intake valves are in better shape due to the difference in materials? Intakes are Titanium as opposed to the stainless steel of the exhaust valves???
That makes sense, but I really have no idea. The Ti intake valves have always fared better than the stock exhaust valves, but it seems in the earlier days of the LS7 valve guide saga the exhaust guides typically showed more wear than the intake guides. Lately the intake guides usually show more wear.
The CrN coating on the Ti valves is pretty durable, but let's not forget the core issue - the guides in those heads were out of or close to being out of spec before they were ever installed on an engine, which is why warranty replacement heads are a waste of time.
Last edited by Dan_the_C5_Man; 12-04-2016 at 01:05 AM.
I used to make fun of my "older" machinists with their fancy digital mic's...... Now that going f'ing blind and have cheaters stashed all over the damn place, I'm wishing I had digital tools....
Do you have a roughness tester? I'm curious what the Ra is on those intake stems.
I used to make fun of my "older" machinists with their fancy digital mic's...... Now that going f'ing blind and have cheaters stashed all over the damn place, I'm wishing I had digital tools....
Do you have a roughness tester? I'm curious what the Ra is on those intake stems.
Digital mics are especially nice - fast and accurate w/ no verniers to deal with. The little Mitutoyo in the picture has 0.00005 resolution and certified accuracy of 0.00000 error throughout it's range.
Nope, don't own a roughness tester. It's my understanding the stock intake stem finish is a little on the rough side. That's why some head rebuilders get them polished, and one reason Katech doesn't recommend using them with Bz guides
So the summary is that you found 0.0108" clearance on GM heads that had 15k miles? Were they fully assembled by GM?
That picture was from the first time around when I measured the wear on the original heads at 15k mi, shown this time just for illustration of the measuring process.
But yes, that guide - exhaust I believe - had 0.0108 clearance after a little over 15k miles. These were the original heads so everything was manufactured and installed by Linamar and Chevrolet.
This time around I'm measuring the warranty replacement heads after 15k mi. - Same mileage as when the original heads wore out. The replacements were new GM heads and valves, assembled and checked (allegedly ) by a local machine shop and installed at my Chevrolet dealer. Check out my previous post for more of the back story.
This time I ended up only checking two cylinders on the easy side. #4 & #6 intakes wiggled 0.012, exhausts 0.005 & 0.006. That was all I needed to see so no more wiggling.
This time I ended up only checking two cylinders on the easy side. #4 & #6 intakes wiggled 0.012, exhausts 0.005 & 0.006. That was all I needed to see so no more wiggling.
Too bad we don't have the before numbers, so we could see the actual conditions of the heads when new and then see the actual amount of wear of each guide after 15,000 miles.
Noticed an interesting pattern with the valve guide measurements.
The intakes are all hour glass and the exhaust are all cone shaped(larger at the bottom).
My car is an '09 model built in late '08. The warranty replacement heads are dated '12 and '13. They were installed in July '13.
And before you have to ask:
Yes, all year LS7 heads, '06 - '13, whether they came installed on a new car or came through the parts dept. as service parts, have shown this problem.
This time I ended up only checking two cylinders on the easy side. #4 & #6 intakes wiggled 0.012, exhausts 0.005 & 0.006. That was all I needed to see so no more wiggling.
Wow sorry to hear about your bad luck! Exhaust wiggle isn't terrible and probably would be fine for a while (how long tho?), but that intake wiggle is undeniable.
My car is an '09 model built in late '08. The warranty replacement heads are dated '12 and '13. They were installed in July '13.
And before you have to ask:
Yes, all year LS7 heads, '06 - '13, whether they came installed on a new car or came through the parts dept. as service parts, have shown this problem.
Early build '09 here as well...14/16 guides were out of spec with only 15,000 street miles. Why am I not surprised...
What's your plan of action here...who's doing the rebuild this time around?
This time around the heads will be AHP's moldstar 90 pkg w/ new springs. They were picked up in Harbor City by FedEx about 1/2hr ago, supposed to be here Thurs.
The R&R is being done at VZ Autoworks, a local independent Corvette shop.
I did get some help from GMPP after a bit of "discussion". Basically GMPP agreed to pay R&R labor and materials and the cost of AHP's pkg 4 heads. I'm paying for shipping both ways, the moldstar guides and new springs. Could have been better, but it could have been worse too, so I'm ok with it.
This time around the heads will be AHP's moldstar 90 pkg w/ new springs. They were picked up in Harbor City by FedEx about 1/2hr ago, supposed to be here Thurs.
The R&R is being done at VZ Autoworks, a local independent Corvette shop.
I did get some help from GMPP after a bit of "discussion". Basically GMPP agreed to pay R&R labor and materials and the cost of AHP's pkg 4 heads. I'm paying for shipping both ways, the moldstar guides and new springs. Could have been better, but it could have been worse too, so I'm ok with it.
Same as you...except I was local to AHP for my GMPP claim. I paid for the "upgrades"...MS90 guides, PSI 1511 springs w/Ti retainers, and CHE rocker trunions. I was content with that.
What springs are you getting? Kohle's default spring is typically the BTR duals for his package #4.
I did get some help from GMPP after a bit of "discussion". Basically GMPP agreed to pay R&R labor and materials and the cost of AHP's pkg 4 heads. I'm paying for shipping both ways, the moldstar guides and new springs. Could have been better, but it could have been worse too, so I'm ok with it.
Hell, that's half-way to winning the lottery.. Good result, I am guessing you won't have to do this a 3rd time.
12-03-2016, 10:41 PM
Warranty Replacement Heads at 15k mi. Part II - Bore Gauge Measurements
Early build '09 here as well...14/16 guides were out of spec with only 15,000 street miles. Why am I not surprised... 
