Wiggle test

[joelster]

Originally Posted by Z28000

Someone up top said there was almost 20 z28 on cargurus for sale I couldn’t find one

That was me. It's easy to find them if you use the "filter" option to select years 14-15, then trim option Z/28. You also have to expand the search to nationwide. The search defaults to a 50 mile radius from your home.

[Z28000]

Originally Posted by joelster

That was me. It's easy to find them if you use the "filter" option to select years 14-15, then trim option Z/28. You also have to expand the search to nationwide. The search defaults to a 50 mile radius from your home.

I found it thank you my friend

[FASTFATBOY]

Give us an update Joelster

[joelster]

Originally Posted by FASTFATBOY

Give us an update Joelster

Update is that they never measured them since I wanted them replaced anyways ugh. Sorry about that as I was interested in the specs. I assumed it was part of the inspection process but it is not if the customer requests them to be replaced.

Heads arrived 4/16. Been slowly putting it together. It's almost there.

Now for the flamesuit stuff! I was talking to a really smart friend of mine that has built several LS7's and has measured a bunch of heads. He swears to me that they aren't machined very well from the factory. He says that sometimes the seats are finished perfectly concentric with the guides. Basically they can be skewed to the side a few thousandths. So every time the valve closes, it side loads the guide. He says that the machining of the seats got a lot better the later the build. Basically the Z/28's are better than the early Z06's from what he's seen.

More flamesuit stuff- Who TF sets these engines up with almost 2 full turns of preload on the lifter? No joke, you set any of the valves to zero lash, then it's literally 1 and 3/4s of a turn to get it to seat. That's roughly .090" of preload. Who would do that on an engine planning to spin to 7000rpm? There's .100" of PTV clearance but if a lifter gets pumped, then you have a c-hair of clearance. I'm running 2 sets of pushrods from BTR, to get the preload into a comfortable zone. I'm also running a full roller rocker from TSP so there's no pushing/pulling on the valve tip.

If I was running a bone-stock LS7, I would spend a few hours and swap the pushrods (stock are 7.800") for a set of BTR 7.775" for $139 just for the extra piece of mind.

Anyways, it should be running this weekend then it's off to get a tune. BTW, the factory CAI is a nightmare to try to get it to fit over a 103mm TB.

[joelster]

Forgot to add, the heads look like jewelry, Lingenfelter did a great job. Total price was $2199, for them to cnc the intake, exhaust, and chambers, set them up with bigger springs, replace the guides, machine the valves and seats, hand sand them, and wrap up all of the stock parts for me. That's including 8 extra lash caps. They want you to run them on the exhaust as well.

[joelster]

Shot a video today. The more I dive into this engine the more I question it lol.

[SIM GhostrdrZ]

Originally Posted by joelster

Update is that they never measured them since I wanted them replaced anyways ugh. Sorry about that as I was interested in the specs. I assumed it was part of the inspection process but it is not if the customer requests them to be replaced.

Heads arrived 4/16. Been slowly putting it together. It's almost there.

Now for the flamesuit stuff! I was talking to a really smart friend of mine that has built several LS7's and has measured a bunch of heads. He swears to me that they aren't machined very well from the factory. He says that sometimes the seats are finished perfectly concentric with the guides. Basically they can be skewed to the side a few thousandths. So every time the valve closes, it side loads the guide. He says that the machining of the seats got a lot better the later the build. Basically the Z/28's are better than the early Z06's from what he's seen.

More flamesuit stuff- Who TF sets these engines up with almost 2 full turns of preload on the lifter? No joke, you set any of the valves to zero lash, then it's literally 1 and 3/4s of a turn to get it to seat. That's roughly .090" of preload. Who would do that on an engine planning to spin to 7000rpm? There's .100" of PTV clearance but if a lifter gets pumped, then you have a c-hair of clearance. I'm running 2 sets of pushrods from BTR, to get the preload into a comfortable zone. I'm also running a full roller rocker from TSP so there's no pushing/pulling on the valve tip.

If I was running a bone-stock LS7, I would spend a few hours and swap the pushrods (stock are 7.800") for a set of BTR 7.775" for $139 just for the extra piece of mind.

Anyways, it should be running this weekend then it's off to get a tune. BTW, the factory CAI is a nightmare to try to get it to fit over a 103mm TB.

Awesome job. Makes me at least put the shorter pushrod and roller rockers on.

[FASTFATBOY]

Originally Posted by joelster

Update is that they never measured them since I wanted them replaced anyways ugh. Sorry about that as I was interested in the specs. I assumed it was part of the inspection process but it is not if the customer requests them to be replaced.

Heads arrived 4/16. Been slowly putting it together. It's almost there.

Now for the flamesuit stuff! I was talking to a really smart friend of mine that has built several LS7's and has measured a bunch of heads. He swears to me that they aren't machined very well from the factory. He says that sometimes the seats are finished perfectly concentric with the guides. Basically they can be skewed to the side a few thousandths. So every time the valve closes, it side loads the guide. He says that the machining of the seats got a lot better the later the build. Basically the Z/28's are better than the early Z06's from what he's seen.

More flamesuit stuff- Who TF sets these engines up with almost 2 full turns of preload on the lifter? No joke, you set any of the valves to zero lash, then it's literally 1 and 3/4s of a turn to get it to seat. That's roughly .090" of preload. Who would do that on an engine planning to spin to 7000rpm? There's .100" of PTV clearance but if a lifter gets pumped, then you have a c-hair of clearance. I'm running 2 sets of pushrods from BTR, to get the preload into a comfortable zone. I'm also running a full roller rocker from TSP so there's no pushing/pulling on the valve tip.

If I was running a bone-stock LS7, I would spend a few hours and swap the pushrods (stock are 7.800") for a set of BTR 7.775" for $139 just for the extra piece of mind.

Anyways, it should be running this weekend then it's off to get a tune. BTW, the factory CAI is a nightmare to try to get it to fit over a 103mm TB.

Your buddy is aligned with the people who I have talked to and what I have read. The seat is not inline-concentric with the guide, the valve head is hitting the seat one side first which eventually pops the head off the valve or unkeys the locks.

A few heads are ok, luck of the draw. The majority are NOT ok, gamble with a $15K engine if ya want.


Glad you decided to get them fixed, good on you and thanks for the update.

[joelster]

Originally Posted by SIM GhostrdrZ

Awesome job. Makes me at least put the shorter pushrod and roller rockers on.

These are what I run on the intake side:


https://www.summitracing.com/parts/btc-pr7775375-16

I run the 7.725" on the exhaust side, but only because I'm running lash caps. If I didn't run the lash caps I would run the same length on intake and exhaust.

[joelster]

Originally Posted by FASTFATBOY

Your buddy is aligned with the people who I have talked to and what I have read. The seat is not inline-concentric with the guide, the valve head is hitting the seat one side first which eventually pops the head off the valve or unkeys the locks.

A few heads are ok, luck of the draw. The majority are NOT ok, gamble with a $15K engine if ya want.


Glad you decided to get them fixed, good on you and thanks for the update.

I don't believe that there's enough force from the valve hitting one side of the seat to pop the locks, or pop the head off. What my friend told me is that they are off by a few thousandths of an inch. I believe the constant hitting of one side, is what causes the guide to wear down. Combine that constant "bind", with a non roller tip rocker that adds a tiny bit of side loading as well, and the guide wear is accelerated. The guides themselves are fine, yet the internet places all of the blame on them lol. I believe that the guide wears down enough that it hangs the valve up a bit on the closing side of the valve event. Once it does that, the lifter can fully pump up, and if you watch my video, they run A TON of preload on the factory stuff. A pumped up lifter and nearly zero piston-to-valve clearance when it's pumped is a bad thing lol.

[FASTFATBOY]

Originally Posted by joelster

I don't believe that there's enough force from the valve hitting one side of the seat to pop the locks, or pop the head off. What my friend told me is that they are off by a few thousandths of an inch. I believe the constant hitting of one side, is what causes the guide to wear down. Combine that constant "bind", with a non roller tip rocker that adds a tiny bit of side loading as well, and the guide wear is accelerated. The guides themselves are fine, yet the internet places all of the blame on them lol. I believe that the guide wears down enough that it hangs the valve up a bit on the closing side of the valve event. Once it does that, the lifter can fully pump up, and if you watch my video, they run A TON of preload on the factory stuff. A pumped up lifter and nearly zero piston-to-valve clearance when it's pumped is a bad thing lol.

The valve rotates a small amount, so "hitting one side" works on the tulip portion of the valve. It actually works on two sides of the valve because it's not contacting the seat at the same time. When motors are torn down after failure most have the heads knocked off the valve where the stem turns up to the face. Many people change the valves also during this preemptive repair because the nitriding process of valves(along with the rods in the LS7) have been shown not to hold up, Del West makes the valves for GM. They also change them to get away from the hollow stem valves.






The guides start off " a few thousandths off" it works on the guide to where the valve is crooked enough to unkey the locks. I have seen more than one picture where the engine was idling and was shut off when the noise was heard and the valve has one lock on it and is about to go into the hole. The valve is bent but didn't kill the block. This action also works on the hole in the retainer. No way to know if the head of the valve came off first or not.

The guides are not fine, they are off center to the seat. .060-.090 is normal for LS lifter preload, this has no bearing. Richard Holdener has proven that the max side of the preload makes more power on the dyno, look him up on YouTube.

A good read, Speed-Talk forum has mostly high end highly experienced machinists and techs in the industry. This post started in 2012 imagine how much more is known now.

https://www.speed-talk.com/forum/vie...d3fc5f01d8b711

But anyway, I proved my point. Glad you got it fixed prior to it coming unwound.

All the naysayers seem to be quiet...

[joelster]

I've seen engines that run on 7 cylinders with bent valves, that hold up for years and 10's of thousands of miles. When I mean bent, I mean you can see a lot of daylight around them when the heads finally come off.

What I meant about the guides are fine, is that they are machined straight and they pass QC. The guides are perfect when they sit in the bin waiting to be pressed into the head. They just happened to be installed off center, but that's not the guides fault, that's the machining of the head that is wrong. The guide is the part that fails the "wiggle test", and is the part that was to blame by GM, but I don't believe that to be the case. The guides are the victim here. The first parts that starts to show abnormal wear, so they take the brunt of the blame.

There is virtually no way for a valve to simply wiggle it's locks loose. Not gonna happen. The only way for it to spit the locks is when a piston smacks a valve and sends it flying with a ton of force. You can show me 100's of pictures of chambers with valve heads snapped off, you're just drawing a different conclusion as to why it broke. Most every LS7 failure still has the springs attached to the top of the valve. Take a cylinder head off, remove a spring and then push the valve down to around .600" lift in the chamber. Now take your hand and move the valve side to side while it is at max lift. You'll be surprised as to how far you can get it to flex when it's in the chamber. They aren't as rigid as you'd think. You can move them side to side quite a bit.

I've watched nearly every Richard Holdener video. They may make more power with max preload, but I'm not running my engine like that. I'll give up 1-2hp for the piece of mind. There's lots of things in an engine that you can do to squeeze the lost bit of power out with disregard to longevity. Everything has to be a balance when you're running an engine like that. The spring needs to be able to properly control the valve and have enough pressure to keep the preload just right, all while working against the oiling system. They can easily control all of this stuff on the dyno in a perfect environment. No different than advancing or retarding the cam. They can move it around to find max power while sacrificing p-to-v clearance, but you'd never want to run an engine with under .030" on the exhaust even if it makes more power. You can run an engine on 3 quarts of oil too, and it will make more power on the dyno. You get the point. Nobody in the world that builds a high-rpm hydraulic roller race engine, regardless of what engine family it's in, would run it with .090" preload. That's why they make short travel lifters, and why tons of engine builders run them.

This is a good read as well: https://www.corvetteactioncenter.com...9XinpytOosh2_Q

Basically a Lockheed engineer bought a Z06, took it apart and did a bunch of measurements. Then made a tool to check the guide centerline in relation to the rocker stud. He found that most of them are off from the factory. Now, with this in mind, a non-roller tip will want to walk off of the valve tip more than a roller tip. At least I think it will. A roller tip won't bind up like a non roller tip will. Again just a theory on my part.

I will read through that speed talk forum post. Thank you for showing me that. Always good to have some positive engagement even if don't agree 100% on something. trying to have a conversation like this on LS1tech, or FB would result in 100 trolls chiming in with nonsense.

Forgot to post this: