Broken yella terra rocker arm
01-01-2014, 12:23 PM
#23
The thing is I have seen more examples of broken YT rockers here than stock bodies breaking.
You want to BLINDLY dismiss stock as no good because it is stock when the trunnion upgrade on stock rockers has proved to be a SOLID package.
Aftermarket rockers have proven to be harder to control that harder to control might well be the trigger in failures but when the rocker itself is the cause of harder to control well that makes them a hard sell to a reasonable individual, not looking to blindly replace stock parts and brag about what they spent..
You want to BLINDLY dismiss stock as no good because it is stock when the trunnion upgrade on stock rockers has proved to be a SOLID package.
Aftermarket rockers have proven to be harder to control that harder to control might well be the trigger in failures but when the rocker itself is the cause of harder to control well that makes them a hard sell to a reasonable individual, not looking to blindly replace stock parts and brag about what they spent..
01-01-2014, 12:38 PM
#25
The thing is I have seen more examples of broken YT rockers here than stock bodies breaking.
You want to BLINDLY dismiss stock as no good because it is stock when the trunnion upgrade on stock rockers has proved to be a SOLID package.
Aftermarket rockers have proven to be harder to control that harder to control might well be the trigger in failures but when the rocker itself is the cause of harder to control well that makes them a hard sell to a reasonable individual, not looking to blindly replace stock parts and brag about what they spent..
You want to BLINDLY dismiss stock as no good because it is stock when the trunnion upgrade on stock rockers has proved to be a SOLID package.
Aftermarket rockers have proven to be harder to control that harder to control might well be the trigger in failures but when the rocker itself is the cause of harder to control well that makes them a hard sell to a reasonable individual, not looking to blindly replace stock parts and brag about what they spent..
aftermarket rockers solve those problems at the expense of needing more attention to detail when setting them up. they will be harder to control if you don't take the time to match them up with the correct components. you can't just throw them on the engine with your existing parts and expect them to work.
this means checking / shimming all the pedestal pairs for the proper wipe pattern, shimming valve springs appropriately to increase seat pressures, measuring for all your pushrods and getting the preload right on all of your lifters, and avoiding really aggressive lobe shapes.
There are 3 revisions of these arms. The first two experienced failures due to problems with pushrod cup machining and due to cams outgrowing what the rockers were designed to support at the time.
The Rev III's were introduced in 2011. Try if you can to find record of any breakages of the current revision since that time.
Last edited by ckpitt55; 01-01-2014 at 12:46 PM.
01-01-2014, 12:59 PM
#26
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I bought YT rockers back in early 2010 right after they fixed the issues with them breaking and I ran them for an entire season on my TFS235's. That engine saw 7500rpm quite a bit that season racing and never gave me a single problem. I was running what is now BTR's Max Pressure springs. I was also using 3/8 pushrods.
01-01-2014, 01:16 PM
#27
The side loading issue and all of the other pitfalls of the stock rockers are marketing hype to sell roller rockers.
They do not scrub under .630" lift on 1.7:1 ratio rockers and .700" lift on the LS7 1.8.
Roller Rockers require more seat pressure with the same components and cam lobes in order to have even close to the same RPM range of stock rockers per spintron testing done by PAC. In fact, PAC claims the stock rockers out RPM the YTs with LSL lobes by 500RPM even with 35lbs less seat pressure (180lbs vs 145 with the same components).
Point is, you aren't upgrading anything by going to a roller rocker. You are adding more MOI over the valve, which is always a bad thing. You need more spring pressure, which is a bad thing on component life to get equal performance... not better. I would still like to think the friction reduction is worth something. But no one can prove that. On SBC it was worth maybe 5-10HP. But we know the LS rocker is much better than the SBC/LT1 rocker.
You claim the scrubbing is a bad thing. But it's not. Folks don't have issue with it. But folks do have issues with too much spring pressure killing roller rocker arms, damaging lifters, and destroying cams. Yes, their valvetrain is not setup properly in many of those cases, but the roller rockers add more variables than they are worth for the vast majority of users.
I will edit and say that even with aftermarket heads with bronze guides, the issue of guide wear is more of an issue with some heads than others. And it's even prevalent with roller rockers that are not shimmed up for a narrow wipe pattern with bronze guides.
They do not scrub under .630" lift on 1.7:1 ratio rockers and .700" lift on the LS7 1.8.
Roller Rockers require more seat pressure with the same components and cam lobes in order to have even close to the same RPM range of stock rockers per spintron testing done by PAC. In fact, PAC claims the stock rockers out RPM the YTs with LSL lobes by 500RPM even with 35lbs less seat pressure (180lbs vs 145 with the same components).
Point is, you aren't upgrading anything by going to a roller rocker. You are adding more MOI over the valve, which is always a bad thing. You need more spring pressure, which is a bad thing on component life to get equal performance... not better. I would still like to think the friction reduction is worth something. But no one can prove that. On SBC it was worth maybe 5-10HP. But we know the LS rocker is much better than the SBC/LT1 rocker.
You claim the scrubbing is a bad thing. But it's not. Folks don't have issue with it. But folks do have issues with too much spring pressure killing roller rocker arms, damaging lifters, and destroying cams. Yes, their valvetrain is not setup properly in many of those cases, but the roller rockers add more variables than they are worth for the vast majority of users.
I will edit and say that even with aftermarket heads with bronze guides, the issue of guide wear is more of an issue with some heads than others. And it's even prevalent with roller rockers that are not shimmed up for a narrow wipe pattern with bronze guides.
Last edited by JakeFusion; 01-01-2014 at 01:46 PM.
01-01-2014, 02:40 PM
#28
I think you are dead on about the scrubbing at normal lifts, all marketting kind of like the those who swear aftermarket heads are great because they have a thicker deck, but those same folks don't want to hear anything about the 800+hp stock longblock turbo stuff that has become surprisingly common.
Yes scrub can be a problem or head deck thickness can be a problem BUT that doesn't mean they are problems for those of us with reasonable street cars. The point at which an "upgrade" becomes an actual tangible benefit for a particular setup is all too often ignored.
Yes scrub can be a problem or head deck thickness can be a problem BUT that doesn't mean they are problems for those of us with reasonable street cars. The point at which an "upgrade" becomes an actual tangible benefit for a particular setup is all too often ignored.
01-02-2014, 09:19 AM
#29
Stock rockers for me and no problems since. The cons of the YTs outweight the pros. It's either stock rockers or a shaft setup. IMO aluminum rockers make nice paperweights. I didn't like them on my SBCs either which is why I went with Pro Mags and never looked back.
01-02-2014, 12:42 PM
#30
Originally Posted by Brian Tooley
...I would like to include some information that the average customer may not know or understand that is important to long term durability. If it's a race only application that isn't driven on the street, then disregard the information below. If it's driven on the street, then you need to understand this information.
The problem with a stock GM 15 degree rocker (the 12 degree rocker is different) is that over .550" lift the rocker starts to scrub. This "scrub" can damage the valve tips and will cause wear to the bronze guides (powdered metal guides tend to last, but not always) We have seen this on EVERY type of 15 degree head made including AFR, Dart and even GM when bronze guides are installed (stock GM has powdered metal guides).
Most everyone understands how roller rocker geometry should work. As the trunion is raised, the sweep width is decreased, side loading is decreased, lift is increased and life is good. This is called "full arc" type geometry and is what most roller rocker manufacturers who know what they're doing strive for, like Jesel.
As you shim up a GM stock rocker you decrease the sweep pattern, but you INCREASE scrub and increase lift. The increase in lift is a good thing, and is part of the power gain you are seeing. You have to remember that a stock rocker GAINS ratio as it lifts the valve, unlike a roller rocker. As the stock rocker is shimmed up, it gains even more ratio.
The increase in scrub is a disaster waiting to happen. If you remember the problems AFR had when they had some soft valve tips and the valves would get worn down to the locks, this is the same thing you will see long term with shimming up stock rockers, on any head, including the TFS heads.
A stock GM rocker needs to work like a rocking chair works, or like a gear meshes, and is what the stock rocker does well up to about .550" lift, this is called "half arc" geometry. The sweep pattern looks wide, but is simply a function of how a stock rocker must operate. Everything past "half arc" results in the tip of the rocker arm DRAGGING itself across the top of the valve, not good for valve tips or guides.
If you look at WHERE the rocker scroll is contacting the valve at full lift (.600" or so) you will see it's on the VERY TIP END of the rocker scroll with a contact pattern about .010"-.020" wide. This narrow contact patch combined with maximum spring pressure at maximum lift puts the PSI (pounds per square inch) of the contact patch in the stratosphere. (FYI, an LS7 rocker at .650" lift has more contact patch than a LS1 rocker at .600")
Think about having a rocking chair on your wifes new hardwood floor, rock all the way forward to the very tip end of the rails, and then take your feet and push the chair backwards digging the tip of the rails into the floor. This is what a stock rocker does past about .550" or so, the more it's shimmed, the SOONER in the lift cycle this occurs.
The TFS heads come with springs that check at 160 seat 450 open. If you attempt to run stock rockers you need to install powdered metal guides to eliminate the guide wear, and install springs that are no more than 400 open, like the "platinum" springs that TEA sells, they check at 160 seat 400 open. This lesser open pressure makes life easier on the valve tips.
If you are having problems with the stout springs that normally come with the TFS heads then your cam ramp speed may be too high. You might try a little slower lobe, 3/8" pushrods (they drop right in with 1.7 rockers) or you might install some of the springs with less pressure like the "Gold" or "Platinum" and then shim them within .050" of coil bind. Shimming springs within .050” of coil bind takes the “surge” out of them. When the valve train reaches float, power tends to drop like a rock off a cliff, what you may be seeing is spring surge rather than float.
I hope this helps.
The problem with a stock GM 15 degree rocker (the 12 degree rocker is different) is that over .550" lift the rocker starts to scrub. This "scrub" can damage the valve tips and will cause wear to the bronze guides (powdered metal guides tend to last, but not always) We have seen this on EVERY type of 15 degree head made including AFR, Dart and even GM when bronze guides are installed (stock GM has powdered metal guides).
Most everyone understands how roller rocker geometry should work. As the trunion is raised, the sweep width is decreased, side loading is decreased, lift is increased and life is good. This is called "full arc" type geometry and is what most roller rocker manufacturers who know what they're doing strive for, like Jesel.
As you shim up a GM stock rocker you decrease the sweep pattern, but you INCREASE scrub and increase lift. The increase in lift is a good thing, and is part of the power gain you are seeing. You have to remember that a stock rocker GAINS ratio as it lifts the valve, unlike a roller rocker. As the stock rocker is shimmed up, it gains even more ratio.
The increase in scrub is a disaster waiting to happen. If you remember the problems AFR had when they had some soft valve tips and the valves would get worn down to the locks, this is the same thing you will see long term with shimming up stock rockers, on any head, including the TFS heads.
A stock GM rocker needs to work like a rocking chair works, or like a gear meshes, and is what the stock rocker does well up to about .550" lift, this is called "half arc" geometry. The sweep pattern looks wide, but is simply a function of how a stock rocker must operate. Everything past "half arc" results in the tip of the rocker arm DRAGGING itself across the top of the valve, not good for valve tips or guides.
If you look at WHERE the rocker scroll is contacting the valve at full lift (.600" or so) you will see it's on the VERY TIP END of the rocker scroll with a contact pattern about .010"-.020" wide. This narrow contact patch combined with maximum spring pressure at maximum lift puts the PSI (pounds per square inch) of the contact patch in the stratosphere. (FYI, an LS7 rocker at .650" lift has more contact patch than a LS1 rocker at .600")
Think about having a rocking chair on your wifes new hardwood floor, rock all the way forward to the very tip end of the rails, and then take your feet and push the chair backwards digging the tip of the rails into the floor. This is what a stock rocker does past about .550" or so, the more it's shimmed, the SOONER in the lift cycle this occurs.
The TFS heads come with springs that check at 160 seat 450 open. If you attempt to run stock rockers you need to install powdered metal guides to eliminate the guide wear, and install springs that are no more than 400 open, like the "platinum" springs that TEA sells, they check at 160 seat 400 open. This lesser open pressure makes life easier on the valve tips.
If you are having problems with the stout springs that normally come with the TFS heads then your cam ramp speed may be too high. You might try a little slower lobe, 3/8" pushrods (they drop right in with 1.7 rockers) or you might install some of the springs with less pressure like the "Gold" or "Platinum" and then shim them within .050" of coil bind. Shimming springs within .050” of coil bind takes the “surge” out of them. When the valve train reaches float, power tends to drop like a rock off a cliff, what you may be seeing is spring surge rather than float.
I hope this helps.
01-02-2014, 01:09 PM
#31
And here is Brian quoted from another forum:
If you are pushing extreme hydraulic lobes, then breaking parts won't matter. Or if you're looking to turn massive RPM... go with a shaft rocker and solid lifter. The YTs don't fix a problem for the vast majority of well engineered street cars.
If you're running stock rockers in a daily driver, the rocker arm itself becomes a limit if valve tip/rocker tip durability is a concern.
The .62X range is the max I recommend when using stock rockers, which must also be coupled with springs that are under 400 lbs open pressure.
I have pics of valve tips off some LS2 heads that had a complete Comp valve train using .624" lift and 26926 springs. After one year the engine was making noise and the valve tips were chewed up.
The first time I saw this problem was around 2005-2006 when I was involved in durability testing at TFS.
I see heads with chewed up valve tips every other week. It still amazes me at the shops who are selling .650+ lift cams and 450 open pressure springs using stock rockers like it's no problem. On the flip side, it keeps the people who know what's going on busy fixing those problems and selling them the correct parts. Heads with LS7 rockers are not as prone to problems as the 15 degree stuff.
Like I stated before, I keep the lift below .630" and the open spring pressure below 400. The LSL lobes are the most aggressive that I run if I want everything to live, and I always run less exhaust lift than intake. The LXL or Extreme RPM for LS1 are good exhaust lobes.
If it's a track only car, then shove all the lift you want in it and keep everything light with stock rockers. You're not going to put enough miles on it to destroy too much.
Roller rockers require a LOT more spring pressure to keep them in check, then those springs require larger diameter pushrods to prevent them from pole vaulting. Higher pressure springs rob power from the engine, so more lift and spring pressure isn't always the magic answer to more power.
Shaft rockers, big lift solid roller cams, single plane/sheetmetal intakes and big RPM (7500+) work well together.
Stock rockers, conservative cams, long runner intakes and sub 7000 RPM work well together.
The .62X range is the max I recommend when using stock rockers, which must also be coupled with springs that are under 400 lbs open pressure.
I have pics of valve tips off some LS2 heads that had a complete Comp valve train using .624" lift and 26926 springs. After one year the engine was making noise and the valve tips were chewed up.
The first time I saw this problem was around 2005-2006 when I was involved in durability testing at TFS.
I see heads with chewed up valve tips every other week. It still amazes me at the shops who are selling .650+ lift cams and 450 open pressure springs using stock rockers like it's no problem. On the flip side, it keeps the people who know what's going on busy fixing those problems and selling them the correct parts. Heads with LS7 rockers are not as prone to problems as the 15 degree stuff.
Like I stated before, I keep the lift below .630" and the open spring pressure below 400. The LSL lobes are the most aggressive that I run if I want everything to live, and I always run less exhaust lift than intake. The LXL or Extreme RPM for LS1 are good exhaust lobes.
If it's a track only car, then shove all the lift you want in it and keep everything light with stock rockers. You're not going to put enough miles on it to destroy too much.
Roller rockers require a LOT more spring pressure to keep them in check, then those springs require larger diameter pushrods to prevent them from pole vaulting. Higher pressure springs rob power from the engine, so more lift and spring pressure isn't always the magic answer to more power.
Shaft rockers, big lift solid roller cams, single plane/sheetmetal intakes and big RPM (7500+) work well together.
Stock rockers, conservative cams, long runner intakes and sub 7000 RPM work well together.
01-02-2014, 11:25 PM
#32
How can it be said that .620" is the limit when there is documented damage occurring at that lift (annotated in the same post)? That is merely one data point - all that tells you is that .620" is somewhere across the line if you're being intellectually honest. It's not unreasonable to wager that scrubbing starts to occur somewhere south of there, so I'm going to air on the side of caution with a .612/.581 cam (which is not that aggressive, all things considered). Consensus among the aftermarket gods seems to be somewhere in the neighborhood of .550-.600" that this starts occurring.
To offer some data, I ended up needing to shim my rockers ~.125" to center the contact patch due to the nature of the valve job and where the installed heights ended up. To center the contact of the stock rocker with shimming, scrubbing now starts occurring much sooner. Or if I don't shim, all of my wear would now be biased to one side of the valve tip.
How many guys installing stock rockers check the wipe pattern for their individual setup?
I'd contend that they do indeed fix problems. You get less rocker deflection, less fluctuation in lift ratio through travel, less friction / wear of valve tips and guides (especially in bronze). Draw the free body diagrams of valve tip contact if you're so inclined, this stuff is not made up - nor are roller rockers some new fangled concept. If you're looking for hp gains then indeed maybe you should look elsewhere, but reducing friction is a good thing also.
This thread turned out to be a good one for information. https://ls1tech.com/forums/generatio...r-rockers.html
If there's anything the stockers provide that the YT's do not, it's forgiveness. Given that the average guy is not going to check wipe pattern, measure for pushrod length at each individual valve, and be **** about getting their lifter preloads spot on, recommending the trunion upgrade is a pretty good insurance policy.
What guys choose to run is ultimately their business and it doesn't bother me at all - I have no horse in the race. I do, however, like facts. Conjecture and baseless arguments...not so much. If the new arms are a problem, lets see evidence of that. Lets see the reports of failures and valve float issues. Plenty of guys running setups designed by Tony buzzing along at 7k on aggressive lobes that don't seem to be having a problem.
To offer some data, I ended up needing to shim my rockers ~.125" to center the contact patch due to the nature of the valve job and where the installed heights ended up. To center the contact of the stock rocker with shimming, scrubbing now starts occurring much sooner. Or if I don't shim, all of my wear would now be biased to one side of the valve tip.
How many guys installing stock rockers check the wipe pattern for their individual setup?
I'd contend that they do indeed fix problems. You get less rocker deflection, less fluctuation in lift ratio through travel, less friction / wear of valve tips and guides (especially in bronze). Draw the free body diagrams of valve tip contact if you're so inclined, this stuff is not made up - nor are roller rockers some new fangled concept. If you're looking for hp gains then indeed maybe you should look elsewhere, but reducing friction is a good thing also.
This thread turned out to be a good one for information. https://ls1tech.com/forums/generatio...r-rockers.html
If there's anything the stockers provide that the YT's do not, it's forgiveness. Given that the average guy is not going to check wipe pattern, measure for pushrod length at each individual valve, and be **** about getting their lifter preloads spot on, recommending the trunion upgrade is a pretty good insurance policy.
What guys choose to run is ultimately their business and it doesn't bother me at all - I have no horse in the race. I do, however, like facts. Conjecture and baseless arguments...not so much. If the new arms are a problem, lets see evidence of that. Lets see the reports of failures and valve float issues. Plenty of guys running setups designed by Tony buzzing along at 7k on aggressive lobes that don't seem to be having a problem.
Last edited by ckpitt55; 01-02-2014 at 11:35 PM.
01-03-2014, 12:19 AM
#33
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I switched from stock rockers to comp pro magnum 1.75 rollers. I wanted a bit more valve lift, more aggressive ramp rate and a stronger trunnion. I was concerned that they are heavier and would cause valve float though. The roller tips and preload adjustability is nice. Im running pac dual springs with over 30k miles on them and spin the motor to 6600 with no issues. Why aren't people using these more?!
Valve cover spacers required!
Valve cover spacers required!
01-03-2014, 05:18 AM
#34
It is not that critical to center the pattern, it needs to be near center and narrow narrow being more important than dead center.
Those Comps look pretty nice and ProMagnums are what I have used on my LT1s. I would like to see some testing on how much more spring they need vs. stock.
Those Comps look pretty nice and ProMagnums are what I have used on my LT1s. I would like to see some testing on how much more spring they need vs. stock.
01-03-2014, 10:20 AM
#35
It is not that critical to center the pattern, it needs to be near center and narrow narrow being more important than dead center.
Those Comps look pretty nice and ProMagnums are what I have used on my LT1s. I would like to see some testing on how much more spring they need vs. stock.
Those Comps look pretty nice and ProMagnums are what I have used on my LT1s. I would like to see some testing on how much more spring they need vs. stock.
01-03-2014, 10:26 AM
#36
To offer some data, I ended up needing to shim my rockers ~.125" to center the contact patch due to the nature of the valve job and where the installed heights ended up. To center the contact of the stock rocker with shimming, scrubbing now starts occurring much sooner. Or if I don't shim, all of my wear would now be biased to one side of the valve tip.
As as side note, I always considered the YT rockers would need refresh due to the simple fact that aluminum fatigue life is much less than steel and it is only prudent to change out the rockers before they fail rather then wait until they fail. Everyone accepts the need to replace valve springs but not other components. When you start pushing loads beyond their intended design any part has a finite life and it is going to be shorter. However, constant impact loads due to pushrod flex will accelerate part failures.
I think YT was forced to introduce the Gen III as it is being called more due to the extreme spring forces and aggressive ramp rates being run now as compared to when the rockers were first introduced several years ago.
01-03-2014, 12:00 PM
#37
I have Tony's heads as well and ended up with the same shim thickness and narrow wipe pattern. Last check on the guides showed no appreciable wear whereas another head installation with bronze guides and other wide wiping rockers resulted in noticeable guide wear in less than 8K miles.
As as side note, I always considered the YT rockers would need refresh due to the simple fact that aluminum fatigue life is much less than steel and it is only prudent to change out the rockers before they fail rather then wait until they fail. Everyone accepts the need to replace valve springs but not other components. When you start pushing loads beyond their intended design any part has a finite life and it is going to be shorter. However, constant impact loads due to pushrod flex will accelerate part failures.
I think YT was forced to introduce the Gen III as it is being called more due to the extreme spring forces and aggressive ramp rates being run now as compared to when the rockers were first introduced several years ago.
As as side note, I always considered the YT rockers would need refresh due to the simple fact that aluminum fatigue life is much less than steel and it is only prudent to change out the rockers before they fail rather then wait until they fail. Everyone accepts the need to replace valve springs but not other components. When you start pushing loads beyond their intended design any part has a finite life and it is going to be shorter. However, constant impact loads due to pushrod flex will accelerate part failures.
I think YT was forced to introduce the Gen III as it is being called more due to the extreme spring forces and aggressive ramp rates being run now as compared to when the rockers were first introduced several years ago.
I have the same mindset. It's 2024 aircraft grade aluminum, but it's still aluminum. What do you consider to be a reasonable change interval? Tony suggested a refresh of the heads after 45k miles (guides + vj) or so assuming oil changes are kept up with, so maybe then? Probably premature but if I get 5 years out of em I don't think I'll be upset.
Last edited by ckpitt55; 01-03-2014 at 12:10 PM.
01-04-2014, 08:39 AM
#38
Yeah, the cams/springs outgrew what the arms were designed to support.
I have the same mindset. It's 2024 aircraft grade aluminum, but it's still aluminum. What do you consider to be a reasonable change interval? Tony suggested a refresh of the heads after 45k miles (guides + vj) or so assuming oil changes are kept up with, so maybe then? Probably premature but if I get 5 years out of em I don't think I'll be upset.
I have the same mindset. It's 2024 aircraft grade aluminum, but it's still aluminum. What do you consider to be a reasonable change interval? Tony suggested a refresh of the heads after 45k miles (guides + vj) or so assuming oil changes are kept up with, so maybe then? Probably premature but if I get 5 years out of em I don't think I'll be upset.
) I will run the Gen III for a longer time, likely to the 45K miles that Tony mentions although I may not have the car at that point in time. 
12-21-2014, 10:05 PM
#40
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