| Author | Message | ||
     Runt13 |
I would like to pass along some information. There seems to be a lot of misinformation about pushrods. We are all programmed to think lighter is better, not so! Don't get me wrong i was programed that way too! And that's why i am sharing this information with you. What you need is a pushrod strong enough for your application, or stronger. trust me you will not be sorry. So here it goes. The OEM pushrods that are not adjustable are better then any screw type adjustable pushrod out there. A matter of fact if at all possible never use a screw type adjustable pushrod in a performance application. A stiff non adjustable pushrod is the right choice, and don't worry about how heavy the pushrod is, it makes no difference, you will ever notice! How do i know this and why should you trust me? Good question! I work for the V-twin division of JESEL VALVETRAIN INNOVATION. We have over 35 years of valvetrain knowledge. We also have two spintrons, a superflow dyno, and countless other machines and people that make us one of the worlds leading valvetrain companies. I am also the guy who makes all of our pushrods! Here is an example, Mike Lozano who runs a pro-gas 4 cam V-twin in AHDRA. Runs a complete JVT valvetrain system. The pushrods we use in this engine are a 9/16 x 5/8 x 9/16 double taper pushrod that has a .095 wall, the are almost 14 inches long. We spin this engine close to 10,000 rpms, With a lift at the valve of 1 1/8". This means the installed spring pressure needs to be #425 and the open pressure is well over #1000. We couldn't achieve this without the BIG pushrods. There is no reason all you Buellers out there, should put flimsy, light or silly screw type pushrods in your engines. It just don't make sense! This is not a sales pitch, there are many companies that sell quality pushrods. So don't take the easy way out...do it right! jim miller JVT [Jesel V-Twin] www.jeselvtwin.com 732-901-9101 8am to 4 pm eastern time | ||
| Blake |
The dragster specs are interesting. That is a lot of spring pressure! What is a stock Buell running, something around 140 LBs spring pressure? I'm not sure I accept your characterization that adjustable pushrods are problematic and something to be avoided. Plenty of folks have been running adjustable pushrods with never a problem, me included. Material strength is probably not the main hurdle for achieving acceptable pushrod structural integrity. Bending stiffness which imbues the pushrod with the ability to resist buckling is probably the primary concern in defening against pushrod structural failure. The actual stresses within a pushrod are likely not severe, not anywhere near the actual yield strength of the material (steel alloy). But as with any long thin member, buckling is a major concern. We can defend against bucking failure via five approaches: We can add lateral bracing, reduce the compression loading, add fixity (clamping) at either or both ends, increase the stiffness, and/or decrease the length of the compression member (the pushrod). Neither bracing at midspan or thereabouts nor adding fixity (clamping) at either end is feasible due to the lateral movement and angular deflections of the pushrod as it's top end moves with the rocker arm. If anything, the loads will be increased with higher performance cams and valvesprings, so we cannot reduce the loading. The length is what it is so we cannot shorten the pushrods either, at least not without a new engine design/configuration. So that leaves increasing stiffness as our only viable option for improving the structural integrity of a pushrod. We can increase bending stiffness three ways: We can add material (increase wall thickness), increase effectiveness of the bending cross section via increased diameter (but thinner wall), or use a stiffer material (higher elastic modulus). Steel is very difficult to beat for stiffness; it is three times as stiff as aluminum alloys and twice as stiff as titanium alloys. Super high grade carbon fiber, graphite really, or some kind of metal matrix composite would be about the only material systems that could significantly improve upon the stiffness of a steel pushrod. Someday maybe those kinds of pushrods will be commonplace. Until then, we have steel. Steel is good.  Yes, I know there are aluminum pushrods too. They are larger diameter. The little screw adjuster end in adjustable pushrods are located at the extreme top end of the pushrod. If they were in the middle of the pushrod, it would be problematic, in effect acting like an elastic hinge in the middle of a column subject to buckling. A hinge in the middle of a column is not good. In fact it is a guaranteed disaster, but at one of the ends, it is of little consequence, obviously, since so many are in service and performing just fine. It is critical that the threaded end be well tightened and of high quality (close tolerance/straight and on axis) to handle the loading. A good high quality adjustable pushrod end doesn't significantly degrade the column buckling strength of the pushrod. There's more too it of course, some lateral loading and of course the dynamic loading due to the mass of the pushrod itself. Maybe you can talk a little bit about which components of the pushrod loading govern its design. Spring pressure for sure is an obvious major load. Anyway, that's all I know; I'm no pushrod expert, just a structural analyst. | ||
| Runt13 |
Very good response! And you are correct in allot of what you have posted. Your post is the starting point of it all. As we go further and farther into valvetrain dynamics, things change. As with the introduction of harmonics, valve float, and lifter loft. Once the system is put on the spintron you would be surprised at what actually go's on at different rpm's here's my point! Most people that ride Buells are of the technical sort. They may not be an engine builder or even a regular mechanic, but they are always in the quest of the next technical toy. And I respect that! What I have found is that if you stay with the same base circle cam and do not move your valvetrain components locations, your OEM pushrods are all that you need! If you go further, say, different ratio rockers, different base circle, or a valve/ spring pack change. Find a good non- adjustable pushrod company and take the time to order and install them. You will not be disappointed. They are usually less expensive and once you have the lengths, less time consuming to install. Once there in you have one less thing to worry about. I have built well over 100 performance engines, from everyday street riders, et bikes, national champion road race bikes, to all out drag race machines. I could not have done this without the help and knowledge of other people, so when I learn something , i share it! | ||
| Panic |
"What I have found is that if you stay with the same base circle cam and do not move your valvetrain components locations, your OEM pushrods are all that you need!" Errr... no. To maintain the same geometry, the pushrod length must be reduced by 1/2 of lobe height increase. | ||
| Justin_case |
Use an adjustable pushrod to determine the overall length of your custom made pushrods. | ||
| Djkaplan |
Pushrod weight is important on street applications where we can't use valvesprings with 425lbs of seat pressure. Valve-float is always a concern with Harley engines that spin fast. I agree that adjustable pushrods aren't needed if there is no need for them (isn't everything like that?) but you are incorrect about pushrod weight in street applications. Not just pushrods, too. Everything that moves in the valvetrain should be light (but strong enough, of course). Look at the new 'beehive' valvesprings. Ever wonder why they were like that? Remember; all the stuff that the cam moves has to be moved back by the valvespring. Too much weight reciprocating back and forth is going play havoc with valve-float. I have a lot of respect for Jesel components from my car racing days... don't screw that up now. | ||
| Panic |
(Message edited by panic on March 16, 2007) | ||
| Panic |
(Message edited by panic on March 16, 2007) | ||
| Djkaplan |
"IMHO jim miller's emphasis was that a weight saving MUST NOT be at the expense of reduction in stiffness." That's not the impression I got from what he said. It was this cavalier statement that prompted my response, "...and don't worry about how heavy the pushrod is, it makes no difference, you will ever notice!" I still disagree. "A 3/4” OD with .048” wall gives about the same weight as a 3/8” at .083”, and still over 7 times as stiff (600% more)." The math works and it looks good on paper... but you are forgetting that pushrods are fed lubricating oil for rocker arms. Fill your 3/4" diameter pushrod with oil and weigh it. As a point of reference... the rocker arms, pushrods, and lifters on a Harley engine are heavier than their counterparts in a Chevy small-block V-8. | ||
| Panic |
Have a nice day. (Message edited by panic on March 16, 2007) | ||
| Djkaplan |
That's a bit apples vs. oranges; there are reasons for the weight difference. It was just a point of reference to show how heavy these components are already. You seem to be agreeing with my statement (and my only point, really) that weight is important when it comes to valvetrain compenents..."Everything that moves in the valvetrain should be light (but strong enough, of course)."... so I'm not sure what point you are trying to make (at this point). You did touch on a subject I find fascinating though; harmonics. Not just spring harmonics, but the harmonics in the system as a whole. I read an article by Kevin Cameron last year (in his TDC column) that explained how a heavier flywheel could create more peak horsepower by damping some of the instability in valvetrain motion(or something to that effect). Clearly, there is more to it than a cam pushing stuff and and a spring pushing the stuff back (much more than I'll understand), but there is still the tenet that lighter is better when it comes to moving stuff backwards and forwards, over and over again. | ||
| Djkaplan |
I just called Jesel... Jim Miller doesn't even work there anymore. | ||
| Djkaplan |
I was enjoying the push-rod talk with you Panic, but the enjoyment must have been one-sided. Sometimes, I guess, no matter what you say... someone's just going to hit you with a fish...  . |
