Z/28 Head swap DIY!!!

[The_Raging_Bull]

Great write-up, only thing I would have added was t use stud mounted roller rockers..AHP charges extra $$$ for those, but they eliminate any chance of side loading of the valve stem and guide concentricity. I'm getting this done on my Z06 head from AHP this year. Kohle's comments were that stud mounted roller rockers.will be the most durable - and if the if the heads were dissembled at 75,000 miles, there would be no issues.Basically its the $2800 extra fix to make their LS7 heads bullet proof.
Great write up though--thanks!

[BJJKRIS]

Originally Posted by The_Raging_Bull

Great write-up, only thing I would have added was t use stud mounted roller rockers..AHP charges extra $$$ for those, but they eliminate any chance of side loading of the valve stem and guide concentricity. I'm getting this done on my Z06 head from AHP this year. Kohle's comments were that stud mounted roller rockers.will be the most durable - and if the if the heads were dissembled at 75,000 miles, there would be no issues.Basically its the $2800 extra fix to make their LS7 heads bullet proof.
Great write up though--thanks!

Honestly didn’t even know they offered the service. I used the Michigan grade 12 bolts since ARP doesn’t offer a solution. I’ve checked mine once and will check the torque on them again this weekend to see if they’re still good. I’m sure I’m just being paranoid but every bit of ticking I hear, I have this terrible image of rockers slipped off the valve stems in my head. Although the new heads are much quieter than what I took off.


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[j o n]

Originally Posted by The_Raging_Bull

Great write-up, only thing I would have added was t use stud mounted roller rockers..AHP charges extra $$$ for those, but they eliminate any chance of side loading of the valve stem and guide concentricity. I'm getting this done on my Z06 head from AHP this year. Kohle's comments were that stud mounted roller rockers.will be the most durable - and if the if the heads were dissembled at 75,000 miles, there would be no issues.Basically its the $2800 extra fix to make their LS7 heads bullet proof.
Great write up though--thanks!

Does your Z06 have the stock cam? Or aftermarket?

Originally Posted by BJJKRIS

Honestly didn’t even know they offered the service. I used the Michigan grade 12 bolts since ARP doesn’t offer a solution. I’ve checked mine once and will check the torque on them again this weekend to see if they’re still good. I’m sure I’m just being paranoid but every bit of ticking I hear, I have this terrible image of rockers slipped off the valve stems in my head. Although the new heads are much quieter than what I took off.


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You're running the stock cam. I too have communicated with Kohle. Your setup is what he recommends with the stock cam.

[BJJKRIS]

Originally Posted by j o n

Does your Z06 have the stock cam? Or aftermarket?







You're running the stock cam. I too have communicated with Kohle. Your setup is what he recommends with the stock cam.

Stock cam for me. But Jake at AHP has informed me that with my psi1511 springs I will be able to upgrade to the 116 cam later without changing springs if I’d like. Honestly not sure I ever will. I’m fine with the power it makes now.


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[The_Raging_Bull]

Originally Posted by BJJKRIS

Honestly didn’t even know they offered the service. I used the Michigan grade 12 bolts since ARP doesn’t offer a solution. I’ve checked mine once and will check the torque on them again this weekend to see if they’re still good. I’m sure I’m just being paranoid but every bit of ticking I hear, I have this terrible image of rockers slipped off the valve stems in my head. Although the new heads are much quieter than what I took off.

I'm with you, basically follow Kohle's advice on breaking your repaired heads with his specific break-in oil... I don't remember what he told me - a premium grade with higher zinc on break-in I'd think..but I don't remember.
On stud mounted roller rockers...I was talking to him about how to make the heads bullet proof and mentioned what another engine builder had told me on using stud mounted RR to help prevent side loading. The thing is stud mounted will make sure your contact point is in perfect alignment, as its a long reach in the LS7 heads. The same setup though..Moldstar 90 guides -> they're from F1 and wont gall even under low lubrication moments...something we all strive to avoid.

[BJJKRIS]

Kohle from AHP got back to me about wiggle test results on my heads. And let’s just say I’m glad I did this swap when I did. I drove this car to Miami from Jacksonville and then to gulf coast of Mississippi with a few guides that were .015!!! .008 is the limit on play, anything over is considered out of spec. So if there was any question on whether or not the LS7 heads were fixed with the z/28... more evidence that they were not.


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[Sakudog]

The root of the issue is GM used valve train parts for the LS7 that had lower RPM limits than went into production. This was never resolved.

[BJJKRIS]

Originally Posted by Sakudog

The root of the issue is GM used valve train parts for the LS7 that had lower RPM limits than went into production. This was never resolved.

I thought it was due to machining errors? I’ve also heard that it’s due to the offset rockers. And then that the exhaust valves don’t have enough heat pulled away from then due to the powdered metal guides...

Do you think it was specifically the guides that weren’t up to the higher RPM’s? Or the exhaust valves themselves?


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[Palutz]

Excellent write up! You got some balls

[Sakudog]

Originally Posted by BJJKRIS

I thought it was due to machining errors? I’ve also heard that it’s due to the offset rockers. And then that the exhaust valves don’t have enough heat pulled away from then due to the powdered metal guides...

Do you think it was specifically the guides that weren’t up to the higher RPM’s? Or the exhaust valves themselves?


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I won't claim that I'm 100% correct and I'm also not sure it matters why, but the fix is here. I wrote the original LS7 headswap that this write up was modeled on. I worked closely with powertrain engineers at GM and was asked to participate in the class action lawsuit about this issue. The facts are there, but sealed. I'll say I've been told that the cause was not a single thing but a few errors aligning into a perfect storm. "99% of our customers will never track their cars.." and that is true if you've ever met a Baby Boomer Corvette owner.

If your tracking your Z28, you must do this fix or your asking for a bigger bill when you drop a valve on track.

[BJJKRIS]

Originally Posted by Sakudog

I won't claim that I'm 100% correct and I'm also not sure it matters why, but the fix is here. I wrote the original LS7 headswap that this write up was modeled on. I worked closely with powertrain engineers at GM and was asked to participate in the class action lawsuit about this issue. The facts are there, but sealed. I'll say I've been told that the cause was not a single thing but a few errors aligning into a perfect storm. "99% of our customers will never track their cars.." and that is true if you've ever met a Baby Boomer Corvette owner.

If your tracking your Z28, you must do this fix or your asking for a bigger bill when you drop a valve on track.

Very interesting. I’ve always thought it was more than just one specific thing causing issues. The theory that it’s more of a perfect storm of faults causing failures is usually the case with the most catastrophic failures I’ve seen in my line of work as well (weapons/radars).

Just got the full print out of results.

1 int: .016"
1exh: .006"
3 int: .018"
3exh: .006"
5 int: .013"
5exh: .006"
7 int: .011"
7exh: .006"

2 int: .009"
2exh: .006"
4 int: .013"
4exh: .006"
6 int: .009"
6exh: .006"
8 int: .010"
8exh: .006"

.018 HOLY SHIT!!!

Glad I took care of this when I did.



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[j o n]

Originally Posted by BJJKRIS

Very interesting. I’ve always thought it was more than just one specific thing causing issues. The theory that it’s more of a perfect storm of faults causing failures is usually the case with the most catastrophic failures I’ve seen in my line of work as well (weapons/radars).

Just got the full print out of results.

1 int: .016"
1exh: .006"
3 int: .018"
3exh: .006"
5 int: .013"
5exh: .006"
7 int: .011"
7exh: .006"

2 int: .009"
2exh: .006"
4 int: .013"
4exh: .006"
6 int: .009"
6exh: .006"
8 int: .010"
8exh: .006"

.018 HOLY SHIT!!!

Glad I took care of this when I did.



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The expense to do so hurts a lot less now I bet

[Gbland60]

Thank you BJJKRIS for the info Glad you done the work yourself. Atleast YOU know about every bolt that was touched. My biggest fear is someone pulling threads on block. Gotta be a wonderful feeling having that peace of mind now. �� Good catch !

[Zslash28]

Excellent write up and big thank you for the follow up on the specs. Have to save up some money now to get this done. And might as well add a cam.