How do you figure pushrod length using cam base circle
Safety Car
Joined: Sep 2003
Posts: 3,558
Likes: 2
From: Cape Coral FL
One thing I'd like to comment on which I think is a common misconception is that 'aftermarket' cams have a .030" smaller base circle. I believe this has come about because that is the difference between the base circle on an LS1 and LS6. The fact is that 2 aftermarket cams with identical specs can have different cam base circles. This can be due to extra 'clean up' during grinding due to inconsistencies in the stock. One cam of say 224/224 .568"/.568" can have a base circle of 1.480" and another 1.475". the extra .005" has been taken off to make the smaller one clean. You can't just say that because a cam is larger than stock the grinder made it -.030". You have to measure.
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Also, due to diffeences in deck height and rocker boss height the ONLY way to be certain of the correct PR length is as vettenuts has been saying, "measure'. It will be differnt for each engine and more importantly each combination of components. Buy a dial gauge - $50 with a stand from Summit, the PR length checker $20 from Comp, measure, do the calc to gauge length, add the preload, order the pushrods, sleep easy.
--------------------------------------------------------------
Also, due to diffeences in deck height and rocker boss height the ONLY way to be certain of the correct PR length is as vettenuts has been saying, "measure'. It will be differnt for each engine and more importantly each combination of components. Buy a dial gauge - $50 with a stand from Summit, the PR length checker $20 from Comp, measure, do the calc to gauge length, add the preload, order the pushrods, sleep easy.
Pro
Joined: Nov 2003
Posts: 503
Likes: 1
From: Greensboro NC
One thing I'd like to comment on which I think is a common misconception is that 'aftermarket' cams have a .030" smaller base circle. I believe this has come about because that is the difference between the base circle on an LS1 and LS6. The fact is that 2 aftermarket cams with identical specs can have different cam base circles. This can be due to extra 'clean up' during grinding due to inconsistencies in the stock. One cam of say 224/224 .568"/.568" can have a base circle of 1.480" and another 1.475". the extra .005" has been taken off to make the smaller one clean. You can't just say that because a cam is larger than stock the grinder made it -.030". You have to measure.
--------------------------------------------------------------
Also, due to diffeences in deck height and rocker boss height the ONLY way to be certain of the correct PR length is as vettenuts has been saying, "measure'. It will be differnt for each engine and more importantly each combination of components. Buy a dial gauge - $50 with a stand from Summit, the PR length checker $20 from Comp, measure, do the calc to gauge length, add the preload, order the pushrods, sleep easy.
--------------------------------------------------------------
Also, due to diffeences in deck height and rocker boss height the ONLY way to be certain of the correct PR length is as vettenuts has been saying, "measure'. It will be differnt for each engine and more importantly each combination of components. Buy a dial gauge - $50 with a stand from Summit, the PR length checker $20 from Comp, measure, do the calc to gauge length, add the preload, order the pushrods, sleep easy.
Great explanation.
Thanks
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Yes, but with 0.100" preload that puts you at 7.400. With your current pushrods, you would be at 0.125" preload.
When you checked it was the lifter on the cam base circle?
Did you tighten the rocker (no need to 22 lb-ft, but maybe 10 or so)?
What is the base length of the adjustable, 6.8"?
The pushrod should be turned until the up and down slop is taken out, not side to side, so if you gently lift the tip of the rocker the tick tick will just go away.
When you checked it was the lifter on the cam base circle?
Did you tighten the rocker (no need to 22 lb-ft, but maybe 10 or so)?
What is the base length of the adjustable, 6.8"?
The pushrod should be turned until the up and down slop is taken out, not side to side, so if you gently lift the tip of the rocker the tick tick will just go away.
Last edited by vettenuts; Jan 7, 2007 at 05:16 PM.
Thread Starter
Melting Slicks
Joined: May 2005
Posts: 3,394
Likes: 12
From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
This is how I did it, I had the engine so one valve is open and the other is closed. I checked the one that is closed. I put the checker in and just snugged the bolt. Then turned the adjustable checker out till it was seated against the cup in the lifter and the cup in the rocker. After that I could not move the rocker up or down but it would move side to side. I assume that since one valve is down "open" the other would be in the correct place to check it. Am I wrong?
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
No, that sounds OK as long as the other is really open so you are not in the overlap of the cam. Based on you trying both the 7.400 and the 7.425, don't think its really an issue with the pushrods. You may want to hold onto the 7.400's until you are happy or sort this out just in case.
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Safety Car
Joined: Jan 2001
Posts: 3,879
Likes: 3
From: Hobart, WI
Just make sure the the lifter is on the absolute low point of the cam or directly opposite the lobe. You then test for the 0 lash measurement, then lock the checker. At this point a 8" caliper is the best tool so you can measure the length of the checker compared to a known length push rod (like a stock one). This accounts for the measured length vs actual. Once you establish the length of the push rod tool compared to a known push rod + or -, add your desired preload (say .060?) and you have the new push rod length.
Thread Starter
Melting Slicks
Joined: May 2005
Posts: 3,394
Likes: 12
From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
it has 57k on it now. It was quiet before I put the cam in it. There was one time that after I ran it kinda hard that it made a funny tick. It done it at idle but the next day it was fine. Put the cam in and it started sounding like crap. Yesterday when i took it to northern Iowa to a funeral I noticed when i got there I backed up beside a car and I could hear it ticking. "sound reflecting off the other car". Then when I got home it didn't sound that bad. It had the sewing machine sound but it didn't really tick. This damn thing has me worn down. I'm about ready to just pull the heads and replace the lifters.
Thread Starter
Melting Slicks
Joined: May 2005
Posts: 3,394
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From: Leon Iowa
St. Jude Donor '06-'07-'08-'09
Burning Brakes
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From: Goose Creek SC
Hammer
