Just want to get more educated about this. I'm rebuilding my 07 YZ250F head soon. I have heard from some that valve springs wound at the same diameter will not fully extend and cause valve float due to vibrations caused at different rpms. They argue that this is the reason for accelerated valve wear. The solution to this problem is said to be conical valve springs while still running titanium valves(stock or aftermarket I believe) Others say that extending the life of your valve train is best done by using stainless steel valves and heavier duty valves springs. What are your opinions concerning the one mod versus the other? How does the added stress of heavier steel valves and springs affect the engine's performance or durability in different areas(especially timing chain). Has anyone run the conical springs, if so, what has your experience with them been like? I hope I don't sound like an idiot, just want to educate myself more before I decide on one or the other.
Conical valve springs vs. Stainless valves
- Thread starter taloolamx
- Start date
The short answer is:
run stock valves and the stock springs and change the springs when they start to lose pressure (1 to 3 times per season depending on use)
or
for a bulletproof but more costly solution use a full Kibblewhite kit consisting of their stainless steel valves and spring package. This is the best solution I have found.
The longer WHY take this approach is explained (hopefully) below. I wrote this a while back when the subject of conical (sometimes called beehive) springs came up.
The spring is the "softest" part of the valvetrain and has the lowest natural frequencies and tends to be the most heavily scrutinized part of the system. But to build a reliable valvetrain the entire valve acceleration curve has to be looked at as a series of harmonic accelerations that include the cam profile, and the rest of hard parts that are part of the motion of the valve. Each harmonic acceleration has an amplitude sometimes referred to as it's resonance factor and there is an intricate relationship between engine rpm, system harmonics, component resonance factors as well as spring surge frequency. Some designers use second derivative valve acceleration rates to try and understand these relationships, others use a third derivative based on the cam's jerk values. That's just one of many relationships that have to be considered to cope with 13,000 rpm valve gear. The point being there is a lot more going on here than just picking up the Petersen Spring catalog and saying, gimme 100 of part # 123-R3, and there isn't 100% agreement even at the OEM level on the best way to cope with these complex relationships.
It's possible that any one of us could mix and match parts and come up with a combination that works, but the chances are better that we'd break a bunch of parts before we stumbled onto the combination that works. Ultra high rpm valvetrains like these can be an expensive place to do cut and try experiments.
I'm well aware of the characteristics of conical springs and the difficulty in applying straight rate spring thinking to their design. I've been following published research on conical springs since the 70's and I think it's a pretty interesting technology. Comp Cams has certainly shown their value in automotive circles, and KTM has shown us how bad they can be if the technology is not applied correctly. Despite what some folks might believe, conical springs are not the generic prescription for every valve train design issue.
For those who aren't bored to death at this point let's back up a bit.
All springs including conicals have a resonant frequency. Straight rate springs tend to have a fixed natural frequency while the resonant frequency of a conical spring varies as the spring shape changes during compression. Both straight rate and conical springs still have a surge point based on their resonant frequency but if designed properly for the application both types of springs will surge at a point well outside the peak rpm range. The difference being IF designed correctly the conical spring should be able to do this with a lighter smaller spring. I have no doubt that under the correct circumstances conical springs will be a huge step forward from the 80 cent springs Suzuki and some of the other OEMs put in the bikes.
The problem is, KTM didn't get it right the first time they used conical springs so the average racer reading this stuff has even less chance of hitting a cut and try homer. I have yet to see a motorcycle solution using conical springs that has proven to be better than well designed standard coil springs.
As is so common in the motorcycle business, there a a few less than scrupulous companies that have been telling people on internet forums that their conical springs completely eliminate harmonics and it just isn't true. WMR racing was famous for this. ;)
I hope this helps. :cool:
run stock valves and the stock springs and change the springs when they start to lose pressure (1 to 3 times per season depending on use)
or
for a bulletproof but more costly solution use a full Kibblewhite kit consisting of their stainless steel valves and spring package. This is the best solution I have found.
The longer WHY take this approach is explained (hopefully) below. I wrote this a while back when the subject of conical (sometimes called beehive) springs came up.
The spring is the "softest" part of the valvetrain and has the lowest natural frequencies and tends to be the most heavily scrutinized part of the system. But to build a reliable valvetrain the entire valve acceleration curve has to be looked at as a series of harmonic accelerations that include the cam profile, and the rest of hard parts that are part of the motion of the valve. Each harmonic acceleration has an amplitude sometimes referred to as it's resonance factor and there is an intricate relationship between engine rpm, system harmonics, component resonance factors as well as spring surge frequency. Some designers use second derivative valve acceleration rates to try and understand these relationships, others use a third derivative based on the cam's jerk values. That's just one of many relationships that have to be considered to cope with 13,000 rpm valve gear. The point being there is a lot more going on here than just picking up the Petersen Spring catalog and saying, gimme 100 of part # 123-R3, and there isn't 100% agreement even at the OEM level on the best way to cope with these complex relationships.
It's possible that any one of us could mix and match parts and come up with a combination that works, but the chances are better that we'd break a bunch of parts before we stumbled onto the combination that works. Ultra high rpm valvetrains like these can be an expensive place to do cut and try experiments.
I'm well aware of the characteristics of conical springs and the difficulty in applying straight rate spring thinking to their design. I've been following published research on conical springs since the 70's and I think it's a pretty interesting technology. Comp Cams has certainly shown their value in automotive circles, and KTM has shown us how bad they can be if the technology is not applied correctly. Despite what some folks might believe, conical springs are not the generic prescription for every valve train design issue.
For those who aren't bored to death at this point let's back up a bit.
All springs including conicals have a resonant frequency. Straight rate springs tend to have a fixed natural frequency while the resonant frequency of a conical spring varies as the spring shape changes during compression. Both straight rate and conical springs still have a surge point based on their resonant frequency but if designed properly for the application both types of springs will surge at a point well outside the peak rpm range. The difference being IF designed correctly the conical spring should be able to do this with a lighter smaller spring. I have no doubt that under the correct circumstances conical springs will be a huge step forward from the 80 cent springs Suzuki and some of the other OEMs put in the bikes.
The problem is, KTM didn't get it right the first time they used conical springs so the average racer reading this stuff has even less chance of hitting a cut and try homer. I have yet to see a motorcycle solution using conical springs that has proven to be better than well designed standard coil springs.
As is so common in the motorcycle business, there a a few less than scrupulous companies that have been telling people on internet forums that their conical springs completely eliminate harmonics and it just isn't true. WMR racing was famous for this. ;)
I hope this helps. :cool:
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