[Z06] Have any "fixed heads" failed ?
08-21-2015, 08:29 PM
#41
Le Mans Master
Not an engineering flaw. It is a production flaw. However, all of that stuff could just be a red herring. If you check the actual engine failures reported on the forum since 2010 dropped exhaust valves are the ones that are most prevalent. Dropped intake valves are approximately 10% of the total. If you look at the reports of guides out of spec the ratio between worn intake and exhaust guides is much closer to 50%.
We we are actually looking for what causes valve heads to break off and drop into the cylinder and comparing those two sets of data indicates there is a problem with the assumption that worn guides are the main cause of dropped valves. Otherwise, the number of intake and exhaust valve drops would correlate closely with the out of spec guide data.
Bill
We we are actually looking for what causes valve heads to break off and drop into the cylinder and comparing those two sets of data indicates there is a problem with the assumption that worn guides are the main cause of dropped valves. Otherwise, the number of intake and exhaust valve drops would correlate closely with the out of spec guide data.
Bill
Now, if GM said surface finish should be "X" smooth, and the parts were shipped with "Y" smoothness, then THAT is a QA issue / production flaw. If you have evidence to the contrary, I will retract my statement.
And we've been down this road before - You simply can not in good faith, make an apples-to-apples comparison or correlation between worn out intake guides / valves and exhaust guides / valves, in relation to valve stem failures - the two valves couldn't be any more different in design, materials and application.
Last edited by Dan_the_C5_Man; 08-21-2015 at 08:40 PM.
08-21-2015, 08:36 PM
#42
Le Mans Master
You're welcome.
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Keep in mind that if you do go with this set, and wish to use OE heads, they will require machine work as the rocker pedestals get milled down. Depending on total valve lift, the amount of milling will vary. After milling, the fastener holes will need to be drilled out further and re-tapped. The fastener locations over the intake runners will most likely punch through, into the intake runner, so you will need to use a thread sealant or Loctite on those fasteners. The rockers also take up more space under the covers, so you will need to either use a valve cover spacer, or taller valve covers. I only mention these things to you, and anyone else who may stumble onto this, to be aware that there are other costs and considerations that need to be accounted for when using a rail system. Those additional costs can easily exceed $1000. The Crower system also has a roller tip option, that’s about $100. The upgrade gives you needle bearings, verse a pin at the tip roller.
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Keep in mind that if you do go with this set, and wish to use OE heads, they will require machine work as the rocker pedestals get milled down. Depending on total valve lift, the amount of milling will vary. After milling, the fastener holes will need to be drilled out further and re-tapped. The fastener locations over the intake runners will most likely punch through, into the intake runner, so you will need to use a thread sealant or Loctite on those fasteners. The rockers also take up more space under the covers, so you will need to either use a valve cover spacer, or taller valve covers. I only mention these things to you, and anyone else who may stumble onto this, to be aware that there are other costs and considerations that need to be accounted for when using a rail system. Those additional costs can easily exceed $1000. The Crower system also has a roller tip option, that’s about $100. The upgrade gives you needle bearings, verse a pin at the tip roller.
).I think the message is (for me anyway), if you want the ultimate, go with the Crowers or similar, especially if you are running an aftermarket cam and / or higher spring pressures. But if you are simply trying to negate the valve scrubbing of the stock rockers (and other issues like slop, odd wear patterns, needle bearings coming apart, etc.), the YT's can fit the bill nicely.
08-23-2015, 01:36 PM
#43
Team Owner
I have 21,000 miles on them.
08-23-2015, 04:54 PM
#44
Le Mans Master
08-23-2015, 08:53 PM
#45
Melting Slicks
08-23-2015, 08:57 PM
#46
Did mine once, after so many miles of nothing but WOT runs along with road trips, I had mine checked and refreshened. It's like anything else, thing will wear, but I'm still on the same valve guides if that says anything. Just had it all redone, more headwork, milling, etc, etc. I've got Manley SS valves with oversized bronze valve guides from TSP. You gotta open em up so the valves will fit in em, but there's more meat. Running a 660 lift cam, heads are milled, port and polished by LWA and I had already port matched em before hand. So far so good. Also running N20 and meth inj.
Everything looked fine last time and in another year or so, I'll have em checked and re done again if need be. Cars almost paid off, so it'll be time for a TT build with the MTI 6 shooter setup
Everything looked fine last time and in another year or so, I'll have em checked and re done again if need be. Cars almost paid off, so it'll be time for a TT build with the MTI 6 shooter setup
08-24-2015, 08:10 AM
#47
Team Owner
I lucked out as it wasn't loosing the coolant internally as I first thought. Just a sloppy installation job of my new heads by a local shop and the plugs at the rear of the heads were leaking. Took it to LG Motorsports in Plano, and they did a super job of locating the problem and fixing it and they also fixed a vacuum leak that the other shop couldn't locate (and then tried to tune around it).
LG tuned my car(to fix the screwed up tune done by the other shop) and it's running great and it's not loosing coolant.
LG tuned my car(to fix the screwed up tune done by the other shop) and it's running great and it's not loosing coolant.
Last edited by JoesC5; 08-24-2015 at 08:30 AM.
08-24-2015, 08:18 AM
#48
Team Owner
I see on TFS's website that those heads require headers as they will not work with the stock exhaust manifolds. I also could not find, from their website, if the intake valves are Ti. Since they are about $500 cheaper for a pair than the PRC265 heads(with Ti intakes), it makes me wonder.
Are the TFS castings GM 6 bolt castings or new TFS castings? I ask as they have powered metal guides.
I didn't want to go with headers.
EDIT: I see where TFS has a 4 bolt LS7 head that will allow the use of the factory exhaust manifolds. The PRC265 heads are 6 bolt and allow for the use of the factory exhaust manifolds.
Are the TFS castings GM 6 bolt castings or new TFS castings? I ask as they have powered metal guides.
I didn't want to go with headers.
EDIT: I see where TFS has a 4 bolt LS7 head that will allow the use of the factory exhaust manifolds. The PRC265 heads are 6 bolt and allow for the use of the factory exhaust manifolds.
Last edited by JoesC5; 08-24-2015 at 12:37 PM.
08-24-2015, 11:43 PM
#49
Le Mans Master
I lucked out as it wasn't loosing the coolant internally as I first thought. Just a sloppy installation job of my new heads by a local shop and the plugs at the rear of the heads were leaking. Took it to LG Motorsports in Plano, and they did a super job of locating the problem and fixing it and they also fixed a vacuum leak that the other shop couldn't locate (and then tried to tune around it).
LG tuned my car(to fix the screwed up tune done by the other shop) and it's running great and it's not loosing coolant.
LG tuned my car(to fix the screwed up tune done by the other shop) and it's running great and it's not loosing coolant.
08-25-2015, 09:40 AM
#50
Safety Car
I see on TFS's website that those heads require headers as they will not work with the stock exhaust manifolds. I also could not find, from their website, if the intake valves are Ti. Since they are about $500 cheaper for a pair than the PRC265 heads(with Ti intakes), it makes me wonder.
Are the TFS castings GM 6 bolt castings or new TFS castings? I ask as they have powered metal guides.
I didn't want to go with headers.
EDIT: I see where TFS has a 4 bolt LS7 head that will allow the use of the factory exhaust manifolds. The PRC265 heads are 6 bolt and allow for the use of the factory exhaust manifolds.
Are the TFS castings GM 6 bolt castings or new TFS castings? I ask as they have powered metal guides.
I didn't want to go with headers.
EDIT: I see where TFS has a 4 bolt LS7 head that will allow the use of the factory exhaust manifolds. The PRC265 heads are 6 bolt and allow for the use of the factory exhaust manifolds.
08-25-2015, 12:01 PM
#51
Tech Contributor
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Respectfully, by definition it is a design issue - the original deign specification for the surface finish on the Ti valves was insufficient to prevent accelerated wear of the guides.
Now, if GM said surface finish should be "X" smooth, and the parts were shipped with "Y" smoothness, then THAT is a QA issue / production flaw. If you have evidence to the contrary, I will retract my statement.
And we've been down this road before - You simply can not in good faith, make an apples-to-apples comparison or correlation between worn out intake guides / valves and exhaust guides / valves, in relation to valve stem failures - the two valves couldn't be any more different in design, materials and application.
Now, if GM said surface finish should be "X" smooth, and the parts were shipped with "Y" smoothness, then THAT is a QA issue / production flaw. If you have evidence to the contrary, I will retract my statement.
And we've been down this road before - You simply can not in good faith, make an apples-to-apples comparison or correlation between worn out intake guides / valves and exhaust guides / valves, in relation to valve stem failures - the two valves couldn't be any more different in design, materials and application.
Jason, has said he thinks the problem is due to the guides and the valve seats not being concentric with the guides and a production valve guide clearance tolerance which is too wide to begin with. That theory fits closer to the data than anything else I have heard. The lack of adequate concentricity puts stress on both valves, on top of that loose guide tolerances may permit more movement and stress. Those two conditions may have more impact on the exhaust valve stem than the solid intake valve stem and would sort of explain why exhaust stems break more often than intake stems.
Bill
08-25-2015, 12:18 PM
#52
Le Mans Master
I won't argue over where the so called mistake was made or if it was actually made since it doesn't matter. You are proposing a theory of why valve heads drop but your theory doesn't account for the majority of incidents. It is highly doubtful there are two separate failure modes taking place here. Since both intake and exhaust valve heads have been known to break off the theory has to address why they both have the same failure mechanism and why the percentage of failures isn't close to 50%. Worrying about GM's supposed specification issue with the intake valve coatings doesn't get us there and does nothing to advance the ball forward.
Jason, has said he thinks the problem is due to the guides and the valve seats not being concentric with the guides and a production valve guide clearance tolerance which is too wide to begin with. That theory fits closer to the data than anything else I have heard. The lack of adequate concentricity puts stress on both valves, on top of that loose guide tolerances may permit more movement and stress. Those two conditions may have more impact on the exhaust valve stem than the solid intake valve stem and would sort of explain why exhaust stems break more often than intake stems.
Bill
Jason, has said he thinks the problem is due to the guides and the valve seats not being concentric with the guides and a production valve guide clearance tolerance which is too wide to begin with. That theory fits closer to the data than anything else I have heard. The lack of adequate concentricity puts stress on both valves, on top of that loose guide tolerances may permit more movement and stress. Those two conditions may have more impact on the exhaust valve stem than the solid intake valve stem and would sort of explain why exhaust stems break more often than intake stems.
Bill
You just stated what I, Katech and everyone else believes - intake stems have a poor finish, contributing to accelerated guide wear. Bad machining of heads contribute to accelerated guide wear. Excessive guide clearance creates stress on the stem from the head slamming shut at an angle. Exhaust stems are hollow, coupled with heat and it causes fractures and failures.
PLEASE show us all of the failed exhaust valve heads with in-spec guides..
Simple.
You keep going on about all of these "intake valve failures..", as an argument against excessive guide clearances being responsible for exhaust valve failures.. Just how many intake failures have we had, exactly, and what percentage vs. exhaust failures??
I know you are trying to be helpful, but common sense needs to prevail in these situations, or we will "never move the ball forward".
Last edited by Dan_the_C5_Man; 08-25-2015 at 12:20 PM.
08-25-2015, 12:41 PM
#53
Safety Car
I fail to see how we are in disagreement.
You just stated what I, Katech and everyone else believes - intake stems have a poor finish, contributing to accelerated guide wear. Bad machining of heads contribute to accelerated guide wear. Excessive guide clearance creates stress on the stem from the head slamming shut at an angle. Exhaust stems are hollow, coupled with heat and it causes fractures and failures.
PLEASE show us all of the failed exhaust valve heads with in-spec guides..
Simple.
You keep going on about all of these "intake valve failures..", as an argument against excessive guide clearances being responsible for exhaust valve failures.. Just how many intake failures have we had, exactly, and what percentage vs. exhaust failures??
I know you are trying to be helpful, but common sense needs to prevail in these situations, or we will "never move the ball forward".
You just stated what I, Katech and everyone else believes - intake stems have a poor finish, contributing to accelerated guide wear. Bad machining of heads contribute to accelerated guide wear. Excessive guide clearance creates stress on the stem from the head slamming shut at an angle. Exhaust stems are hollow, coupled with heat and it causes fractures and failures.
PLEASE show us all of the failed exhaust valve heads with in-spec guides..
Simple.
You keep going on about all of these "intake valve failures..", as an argument against excessive guide clearances being responsible for exhaust valve failures.. Just how many intake failures have we had, exactly, and what percentage vs. exhaust failures??
I know you are trying to be helpful, but common sense needs to prevail in these situations, or we will "never move the ball forward".
Sometimes I read your posts and you come across as the kinda guy who just likes to hear himself talk.
Last edited by Tech; 08-25-2015 at 01:18 PM. Reason: typo
08-25-2015, 12:51 PM
#54
Team Owner
08-25-2015, 01:03 PM
#55
Team Owner
08-25-2015, 01:16 PM
#56
Safety Car
With that being said, I'm not suggesting that TFS is a better choice than PRC265. I'm just pointing out that just because they are stainless valves, doesn't mean the heads won't work well.
08-25-2015, 02:19 PM
#57
Le Mans Master
Can't seem to figure out your point. Everything Bill has said is consistent with common sense. He said improperly machined guides is likely a contributing factor (by agreeing with Katech). He said that exhaust valve failures rates are higher, perhaps, because they are weaker valves.
Sometimes I read your posts and you come across as the kinda guy who just likes to hear himself talk.
Sometimes I read your posts and you come across as the kinda guy who just likes to hear himself talk.
It is clear people "choose sides" in this debate - you can choose any side you wish, and believe whatever you wish.
I re-read my post, seems pretty clear - Bill is the one arguing that the correlation between loose valve guides and exhaust valve / stem failures is dubious, not I. You want to join his side of this discussion, have at it.
08-25-2015, 02:25 PM
#58
I fail to see how we are in disagreement.
You just stated what I, Katech and everyone else believes - intake stems have a poor finish, contributing to accelerated guide wear. Bad machining of heads contribute to accelerated guide wear. Excessive guide clearance creates stress on the stem from the head slamming shut at an angle. Exhaust stems are hollow, coupled with heat and it causes fractures and failures.
PLEASE show us all of the failed exhaust valve heads with in-spec guides..
Simple.
You keep going on about all of these "intake valve failures..", as an argument against excessive guide clearances being responsible for exhaust valve failures.. Just how many intake failures have we had, exactly, and what percentage vs. exhaust failures??
I know you are trying to be helpful, but common sense needs to prevail in these situations, or we will "never move the ball forward".
You just stated what I, Katech and everyone else believes - intake stems have a poor finish, contributing to accelerated guide wear. Bad machining of heads contribute to accelerated guide wear. Excessive guide clearance creates stress on the stem from the head slamming shut at an angle. Exhaust stems are hollow, coupled with heat and it causes fractures and failures.
PLEASE show us all of the failed exhaust valve heads with in-spec guides..
Simple.
You keep going on about all of these "intake valve failures..", as an argument against excessive guide clearances being responsible for exhaust valve failures.. Just how many intake failures have we had, exactly, and what percentage vs. exhaust failures??
I know you are trying to be helpful, but common sense needs to prevail in these situations, or we will "never move the ball forward".
There's is no winning with this guy he gives poor advice Katech says this so he thinks its more substantial Darin Morgan says in my posts explains it perfect why we have this issue so Bill did you read Darins posts or is he not good enough information for your theory's since you obviously know more than anyone here, it amazes me how people still think and play the guessing game. Chad even showed tests on here and got banned for basically showing the problem with the heat and gauling what happened there?
Bill you checking your guides again after you put about 25k miles on your car or are just going to assume there fixed. Please show us proof Bill please please.
08-25-2015, 02:31 PM
#59
ME?!?! I think you have me confused with that other guy.. Do a word count on my posts and compare; that should keep you busy for a bit.
It is clear people "choose sides" in this debate - you can choose any side you wish, and believe whatever you wish.
I re-read my post, seems pretty clear - Bill is the one arguing that the correlation between loose valve guides and exhaust valve / stem failures is dubious, not I. You want to join his side of this discussion, have at it.
It is clear people "choose sides" in this debate - you can choose any side you wish, and believe whatever you wish.
I re-read my post, seems pretty clear - Bill is the one arguing that the correlation between loose valve guides and exhaust valve / stem failures is dubious, not I. You want to join his side of this discussion, have at it.
Bill always has argument or a theory on things correct he try's to help ok but given poor advice and saying wrong statements on this forum is not being helpful just likes to argue I bealive last time he told someone drive your car till it makes noise then check your guides really I rest my case....Darin Morgans posts are still on my thread I wonder why Bill never asked Darin the Question he will be honored to answer.
08-25-2015, 02:49 PM
#60
Anyone who quotes blanket statements such as this does there self a grave disservice. Statements like, “you can't control a SS valves" or " dual springs are bad" should come with qualifying statements regarding combination and application specificity! These, "blanket statements" drive me absolutely insane. Dual springs are fine in the majority of cases and disastrous in others just as single coil springs are. The spring design used for a particular head will depend on many variables such as valve weight, cam profile, engine speed, engines intended purpose, driving style and much much more. You can’t just say dual springs are bad. When buying springs its best to consult a professional.
As far as not being able to control SS valves? You can control ANY valve right up to the point where you can’t anymore. Overly simplistic answer I know but I just wanted to point out the absurdity of the statement . For steal valves in an LS engine you can’t "adequately" control the valve bounce past 6800rpm BUT that does not mean the valve train is out of control! Valves bounce is just a fact of physics and it happens in all engines at high engine speeds. It’s a situation you try and minimize but ALL valves bounce. When valves start bouncing more than two times and start bouncing high enough to bleed off intake charge back up the intake tract, power can be substantially decreased. Our bottom line here at Reher Morrison is this. If you plan on operating your engine under or just up to 7000rpm then steal valves can be used but exceed that and it’s time for Titanium valves, period!
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As far as not being able to control SS valves? You can control ANY valve right up to the point where you can’t anymore. Overly simplistic answer I know but I just wanted to point out the absurdity of the statement . For steal valves in an LS engine you can’t "adequately" control the valve bounce past 6800rpm BUT that does not mean the valve train is out of control! Valves bounce is just a fact of physics and it happens in all engines at high engine speeds. It’s a situation you try and minimize but ALL valves bounce. When valves start bouncing more than two times and start bouncing high enough to bleed off intake charge back up the intake tract, power can be substantially decreased. Our bottom line here at Reher Morrison is this. If you plan on operating your engine under or just up to 7000rpm then steal valves can be used but exceed that and it’s time for Titanium valves, period!
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