Need To Determine Correct Push Rod Length
Thread Starter
Pro
Joined: Jan 2004
Posts: 503
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From: Forney Texas
Need To Determine Correct Push Rod Length
I am gearing up to install a Comp Cam p/n 12-404-4 with a .464" lift on both the intake and exhaust. I currently run 1.6 Roller Rockers and use the stock 7.80" length but hardened push rods. I need to know how to be sure the push rod length is correct for a my given application. I have seen push rod checkers advertised but have never used one. I did question Comp Cams and the tech told me the stock rod length would be fine. I know when I installed the RR's the tech at Trickflow (push rods) or at Harland & Sharp (RR's) could not give me a length. I figured since the RR's would give around .040" more lift there would be enough room for a little error. I am not so sure on this go round.
Point me in a direction, please.
Thanks,
90Indy
Point me in a direction, please.
Thanks,
90Indy
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
If rocker arm geometry is correct the rocker tip will sweep a path across the valve stem tip that stops equal distant from either side of the valve stem. Also the rocker tip would then be exactly in the center of the valve stem tip when the valve is 1/2 open.
To check the rocker arm geometry, install one rocker and rotate the crank by hand as you note the rocker tip path across the valve stem tip. If the geometry is very close, stop here.
To determine the push rod length required to establish correct rocker arm geometry install the adjustable push rod and the special test spring and very push rod length till rocker arm geometry is observed to be correct.
To aid in measuring rocker tip path across the valve stem tip some guys use a felt tip marker pen on the valve stem tip.
To check the rocker arm geometry, install one rocker and rotate the crank by hand as you note the rocker tip path across the valve stem tip. If the geometry is very close, stop here.
To determine the push rod length required to establish correct rocker arm geometry install the adjustable push rod and the special test spring and very push rod length till rocker arm geometry is observed to be correct.
To aid in measuring rocker tip path across the valve stem tip some guys use a felt tip marker pen on the valve stem tip.
Pro
Joined: Dec 2002
Posts: 603
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From: 84 383 XFire Chandler, AZ
This may help.
http://www.compcams.com/information/Products/Pushrods/
I will also be installing the same cam in my 84 (heads too) and the lift calculates to .494. Lobe lift X Rocker Ratio (0.309 x 1.6). My 84 has flat top pistons (no valve reliefs) so I will be checking things out multiple times. Just to make sure.
CS 268AH-14
http://www.compcams.com/information/Products/Pushrods/
I will also be installing the same cam in my 84 (heads too) and the lift calculates to .494. Lobe lift X Rocker Ratio (0.309 x 1.6). My 84 has flat top pistons (no valve reliefs) so I will be checking things out multiple times. Just to make sure.
CS 268AH-14
Thread Starter
Pro
Joined: Jan 2004
Posts: 503
Likes: 0
From: Forney Texas
Thanks for the info. The link left by Elkabong was very informative. Sounds like I need to take my time when setting up the valve train. At least now I know what to look for.
Thanks again.
90Indy
Thanks again.
90Indy
