Question about rocker geometry/ lash
09-12-2012, 05:16 PM
#1
Question about rocker geometry/ lash After researching geometry and zero lash, I've only got one question. When checking push rod length, its correct when the roller tip stays centered on the spring?? If so, is this not the same thing as having zero lash? I hope I'm on the right Track, if not maybe someone can point me straight.
09-12-2012, 05:50 PM
#2
If the rocker tip is touching your spring, you have big problems.
It should swipe across the top of the valve stem, with the pattern centered on the stem tip as the rocker moves across its full range of motion driven by the cam lobe.
This has zero to do with lash, which is set after the rocker geometry is established.
It should swipe across the top of the valve stem, with the pattern centered on the stem tip as the rocker moves across its full range of motion driven by the cam lobe.
This has zero to do with lash, which is set after the rocker geometry is established.
09-12-2012, 05:56 PM
#3
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Not sure the question...but..
Zero lash is the point at which there is no free movement of the pushrod between the lifter and the under-side of the rocker when the rocker tip is firmly against the valve tip, and the lifter is on the base of the cam lobe.
Correct geometry (in it's simplest form) means that you have the tip of the rocker "centered" on the valve tip as much as possible throughout the entire range of lift.
I usually use a dial micrometer to measure at the valve...zero lift, to max lift (lobe lift x1.7) with the rocker on.....using a marking compound on the valve tip, and verify a correct "swipe" pattern of the rocker on the valve tip. Then, measure required pushrod length....add for desired preload....and order pushrods.
Hope this helps.
Edit:Crain...ya beat me to it! lol
Zero lash is the point at which there is no free movement of the pushrod between the lifter and the under-side of the rocker when the rocker tip is firmly against the valve tip, and the lifter is on the base of the cam lobe.
Correct geometry (in it's simplest form) means that you have the tip of the rocker "centered" on the valve tip as much as possible throughout the entire range of lift.
I usually use a dial micrometer to measure at the valve...zero lift, to max lift (lobe lift x1.7) with the rocker on.....using a marking compound on the valve tip, and verify a correct "swipe" pattern of the rocker on the valve tip. Then, measure required pushrod length....add for desired preload....and order pushrods.
Hope this helps.
Edit:Crain...ya beat me to it! lol
09-12-2012, 07:16 PM
#6
I'm not able to figure out what you're saying, but the next step you should take is getting & thoroughly reading a book on Engine Blueprinting.
The fundamentals you're asking are covered in most decent $20-and-less books, and it's a great investment if you want to assemble a reliable engine the first time around.
The fundamentals you're asking are covered in most decent $20-and-less books, and it's a great investment if you want to assemble a reliable engine the first time around.
09-13-2012, 07:49 AM
#7
I've got the most part of it figured out I believe. It just confuses me how when your wipe pattern is correct how you can still have play in the push rod.. how do you adjust the rocker for zero lash when the roller tip is already centered on valve tip?
My push rod checker and rest of my parts haven't got here yet. I'm a visual person so I think one I see it, I'll get a better grasp on it.
My push rod checker and rest of my parts haven't got here yet. I'm a visual person so I think one I see it, I'll get a better grasp on it.
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09-13-2012, 08:13 AM
#8
When your valvetrain is in action your rocker tip will start on one side of the valve tip and sweep across to the opppsite side. The roller tip will not stay centered on the valve tip the entire time.
To measure pr length you need to have the lifter all the way down on the cam lobe with the valve fully closed. Most aftermarket cams have a smaller base circle than stock.
To measure pr length you need to have the lifter all the way down on the cam lobe with the valve fully closed. Most aftermarket cams have a smaller base circle than stock.
09-13-2012, 08:49 AM
#9
Sweeping across the valve tip is what I thought comp cams didn't want in their video?? It shows them checking it with a dry erase marker and once the center was "wiped" clean of the marker, they said that was correct.
But, as long as the valve is closed, I should be on the lobe base of the cam, correct??
But, as long as the valve is closed, I should be on the lobe base of the cam, correct??
09-13-2012, 08:22 PM
#10
You should be yes. Normally the base circle of aftermarket cams are smaller than stock. So unless your heads are milled and using a stock gasket, chances are you will either need 7.4 or longer
Edit heres a link you should check out. Brian tooleys last comment on the thread will be helpful for you and the entire thing is worth a read. It really helps you understand whats going on a making sure a critical part of your valvetrain is how it should be.
https://ls1tech.com/forums/generatio...gs-theory.html
Edit heres a link you should check out. Brian tooleys last comment on the thread will be helpful for you and the entire thing is worth a read. It really helps you understand whats going on a making sure a critical part of your valvetrain is how it should be.
https://ls1tech.com/forums/generatio...gs-theory.html
Last edited by Tainted; 09-13-2012 at 08:41 PM.
09-13-2012, 08:38 PM
#11
It didn't bring up a link.. the heads that are going on the car are stage 2 patriot 243s milled to 59cc. Using factory gm head gaskets to help with clearance. The push rod checker, lifters, and all gaskets came today, I'm ready to go back with it. 
