Pushrod lenght
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 3,010
Likes: 1
From: Sweden/Stockholm
Pushrod lenght
This is what I ben toldon how to set up the correct pushrod lenght.
Set rocker arm at zero lash, spin the engine over by hand 2-3 times. You want it to be riding in the dead center. If the rocker is favoring the rocker stud side of the valve tip, your pushrod is too short. If it favors the opposite side, your pushrod is too long...
But now im reading this aswell.
What is your feedback on this?
"Pushrod Length- Incorrect pushrod length can be detrimental to valve guide wear. Most sources say that centering the rocker contact patch on the valve stem centerline at mid valve lift is the correct method for determining the optimum pushrod length. This method is wrong and can actually cause more harm than good. The method only applies when the valvetrain geometry is correct. This means that the rocker arm lengths and stud placement and valve tip heights are all perfect. This is rarely the case. To illustrate this, think of the valve angle and the rocker stud angle. They are usually not the same. If a longer or shorter valve is installed, then the relationship of the valve tip to the rocker stud centerline has changed. Heads that have had multiple valve jobs can also see this relationship change. Note, the rocker length (pivot to tip) remains unchanged, so the rocker contact patch will have to move off the valve centerline some particular distance for optimum geometry to be maintained.
The optimum length, for component longevity, is the length that will give the least rocker arm contact area on the valve stem. In other words the narrowest wear pattern. This assures that the relationship is optimized and the rocker is positioned at the correct angle. This means that the optimum rocker tip contact point does not necessarily coincide with the valve stem centerline, and probably will not. What is the acceptable limit for being offset from the valve stem centerline? That will depend on the set-up. A safe margin to strive for is about +/-.080" of the centerline of an 11/32 diameter valve stem. This means that no part of the wear pattern should be outside of this .160" wide envelope. As the pushrod length is changed, the pattern will change noticeably. As the geometry becomes closer to optimum, the pattern will get narrowest. If the narrowest pattern is too far from the valvestem centerline, then the valve to rocker relationship has to be changed. In this case, valve stem length will need to change. "
Set rocker arm at zero lash, spin the engine over by hand 2-3 times. You want it to be riding in the dead center. If the rocker is favoring the rocker stud side of the valve tip, your pushrod is too short. If it favors the opposite side, your pushrod is too long...
But now im reading this aswell.
What is your feedback on this?
"Pushrod Length- Incorrect pushrod length can be detrimental to valve guide wear. Most sources say that centering the rocker contact patch on the valve stem centerline at mid valve lift is the correct method for determining the optimum pushrod length. This method is wrong and can actually cause more harm than good. The method only applies when the valvetrain geometry is correct. This means that the rocker arm lengths and stud placement and valve tip heights are all perfect. This is rarely the case. To illustrate this, think of the valve angle and the rocker stud angle. They are usually not the same. If a longer or shorter valve is installed, then the relationship of the valve tip to the rocker stud centerline has changed. Heads that have had multiple valve jobs can also see this relationship change. Note, the rocker length (pivot to tip) remains unchanged, so the rocker contact patch will have to move off the valve centerline some particular distance for optimum geometry to be maintained.
The optimum length, for component longevity, is the length that will give the least rocker arm contact area on the valve stem. In other words the narrowest wear pattern. This assures that the relationship is optimized and the rocker is positioned at the correct angle. This means that the optimum rocker tip contact point does not necessarily coincide with the valve stem centerline, and probably will not. What is the acceptable limit for being offset from the valve stem centerline? That will depend on the set-up. A safe margin to strive for is about +/-.080" of the centerline of an 11/32 diameter valve stem. This means that no part of the wear pattern should be outside of this .160" wide envelope. As the pushrod length is changed, the pattern will change noticeably. As the geometry becomes closer to optimum, the pattern will get narrowest. If the narrowest pattern is too far from the valvestem centerline, then the valve to rocker relationship has to be changed. In this case, valve stem length will need to change. "
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Those two methods may be in effect saying the same thing, though I've not seen the second one before this.
If the valve length and the push rod length are both right it seems that the rocker pivot point must be correct too.
Maybe drawing a little model would help with clearing up this idea to see how the rocker tip moves across the valve tip throughout the range of motion for various push rod lengths.
If the valve length and the push rod length are both right it seems that the rocker pivot point must be correct too.
Maybe drawing a little model would help with clearing up this idea to see how the rocker tip moves across the valve tip throughout the range of motion for various push rod lengths.
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 3,010
Likes: 1
From: Sweden/Stockholm
Originally Posted by 65Z01
Those two methods may be in effect saying the same thing, though I've not seen the second one before this.
If the valve length and the push rod length are both right it seems that the rocker pivot point must be correct too.
Maybe drawing a little model would help with clearing up this idea to see how the rocker tip moves across the valve tip throughout the range of motion for various push rod lengths.
If the valve length and the push rod length are both right it seems that the rocker pivot point must be correct too.
Maybe drawing a little model would help with clearing up this idea to see how the rocker tip moves across the valve tip throughout the range of motion for various push rod lengths.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
LOL, LOL.
Just another example: Take any given subject on our cars and ask ten people and you'll get 11 different versions of what you should do.
Save yourself a lot of aggravation trying to understand the convoluted thinking of others. Just go with the recommended procedure the major cam companies print. Companies like CompCams and Crane.
Jake
Just another example: Take any given subject on our cars and ask ten people and you'll get 11 different versions of what you should do.
Save yourself a lot of aggravation trying to understand the convoluted thinking of others. Just go with the recommended procedure the major cam companies print. Companies like CompCams and Crane.
Jake
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 3,010
Likes: 1
From: Sweden/Stockholm
Originally Posted by JAKE
LOL, LOL.
Just another example: Take any given subject on our cars and ask ten people and you'll get 11 different versions of what you should do.
Save yourself a lot of aggravation trying to understand the convoluted thinking of others. Just go with the recommended procedure the major cam companies print. Companies like CompCams and Crane.
Jake
Just another example: Take any given subject on our cars and ask ten people and you'll get 11 different versions of what you should do.
Save yourself a lot of aggravation trying to understand the convoluted thinking of others. Just go with the recommended procedure the major cam companies print. Companies like CompCams and Crane.
Jake
