Help with pushrod lengths
#1
Help with pushrod lengths
Ok here is the situation.
I am setting up a new cam right now with 1.6 NSA rockers. I had my heads milled 20 thousandths and am running impala gaskets. my intake guides were worn, but the exhaust werent, therefore I ALSO had a valve job done on JUST the intake side, which I think made the intake valves seat slightly taller. (probably .025 or so). With my cam kit i ordered 7.150" length pushrods and they are too long.
According to my length checker, 7.050" is optimal on the exhaust side (going by eyeball on the valve stem). No problems here.
Moving to an intake valve, the checker shows 7.050" to be "OK" however 7.000" looks better. The problem is, a 7" pushrod makes the rocker bottom out on the stud just before it makes contact with the pushrod. it is not much at all, its just enough that fingertightening will not drag on the pushrod. I have to tighten about 1/4 turn instead of the normal 1/6 to set the lash.
I need to order new pushrods obviously so what do you guys recommend I do? If the rockers werent bottoming out... is it possible to run two different length pushrods on intake/exhaust?
Would 7.050" all around be alright? what do you guys recommend I do? I want to get this right.
thanks VERY much !
I am setting up a new cam right now with 1.6 NSA rockers. I had my heads milled 20 thousandths and am running impala gaskets. my intake guides were worn, but the exhaust werent, therefore I ALSO had a valve job done on JUST the intake side, which I think made the intake valves seat slightly taller. (probably .025 or so). With my cam kit i ordered 7.150" length pushrods and they are too long.
According to my length checker, 7.050" is optimal on the exhaust side (going by eyeball on the valve stem). No problems here.
Moving to an intake valve, the checker shows 7.050" to be "OK" however 7.000" looks better. The problem is, a 7" pushrod makes the rocker bottom out on the stud just before it makes contact with the pushrod. it is not much at all, its just enough that fingertightening will not drag on the pushrod. I have to tighten about 1/4 turn instead of the normal 1/6 to set the lash.
I need to order new pushrods obviously so what do you guys recommend I do? If the rockers werent bottoming out... is it possible to run two different length pushrods on intake/exhaust?
Would 7.050" all around be alright? what do you guys recommend I do? I want to get this right.
thanks VERY much !
#4
Gona have to splain that one !
Could you elaborate on your statement please?
BTW
http://compcams.com/technical/Catalogs/106-07/264.pdf
BTW
http://compcams.com/technical/Catalogs/106-07/264.pdf
#5
What I have found is that a 7.20" pushrod, which is the stock length, will work for most H/C combos. I use myself as an example since I have heads milled .020", thinner gaskets (Impala), and taller valves. I went through a lot of effort with an adjustable length pushrod, buying different length pushrods, etc., to center the pattern on the valve stem. I ended up buying 7.05" pushrods and had a very wide swipe yet centered pattern on the valve stem.
After reading all the mid lift stuff I realized that it's more important to have the narrowest swipe across the valve stem and the pattern being off center does not matter (within reason). So after spending all the time and money to get to 7.05" pushrods I went and did it all again based on the mid lift criteria. What I ended up with is 7.30" pushrods. In hindsight I could have just run the 7.20" pushrods and called it a day. That's why I refer to it as BS. I'll bet that 95% of the H/C LT1 setups can throw the detailed analysis out the window, run 7.20" pushrods, and be better off in the end.
I don't want to see people waste time and money on this. Put in a 7.20" pushrod and see where the pattern is. If it's .080" or more inside the edge of the valve stem you are golden. In theory, a centered pattern with more swipe will put more side to side load on the valve stem than an off center pattern with less swipe (again, within reason).
Here are some previous posts on the mid lift stuff:
https://www.camaroz28.com/forums/sho...d.php?t=594453
https://www.camaroz28.com/forums/sho...d.php?t=599108
https://www.camaroz28.com/forums/sho...d.php?t=609026
After reading all the mid lift stuff I realized that it's more important to have the narrowest swipe across the valve stem and the pattern being off center does not matter (within reason). So after spending all the time and money to get to 7.05" pushrods I went and did it all again based on the mid lift criteria. What I ended up with is 7.30" pushrods. In hindsight I could have just run the 7.20" pushrods and called it a day. That's why I refer to it as BS. I'll bet that 95% of the H/C LT1 setups can throw the detailed analysis out the window, run 7.20" pushrods, and be better off in the end.
I don't want to see people waste time and money on this. Put in a 7.20" pushrod and see where the pattern is. If it's .080" or more inside the edge of the valve stem you are golden. In theory, a centered pattern with more swipe will put more side to side load on the valve stem than an off center pattern with less swipe (again, within reason).
Here are some previous posts on the mid lift stuff:
https://www.camaroz28.com/forums/sho...d.php?t=594453
https://www.camaroz28.com/forums/sho...d.php?t=599108
https://www.camaroz28.com/forums/sho...d.php?t=609026
#8
Hehe, I ran into truedual's first post about this AFTER I bought the 7.20" rods for my CC503....I thought crap....I may have too short rods because my heads are milled too. Then I saw the follow up posts and saw he went back to 7.20". I then thought whew! I wouldn't mind getting deeper into researching this...but based on his experience(for now) I'm going 7.20" and calling it cool.
Last edited by ACE1252; 07-26-2008 at 03:57 PM.
#9
Well guys I ordered the 7.050" rods and they dont even fit!!!! I end up with slack in the rockers after setting the lash. im at a loss, guess my measurement tool is pulling a fast one on me.
Here is some pictures of my geometry with the 7.150" rods:
intake baseline:
http://www.joeldevriendt.com/files/p...eline_7150.JPG
intake midlift:
http://www.joeldevriendt.com/files/p...dlift_7150.JPG
intake maxlift:
http://www.joeldevriendt.com/files/p...xlift_7150.JPG
exhaust baseline:
http://www.joeldevriendt.com/files/p...eline_7150.JPG
exhaust midlift:
http://www.joeldevriendt.com/files/p...dlift_7150.JPG
exhaust maxlift:
http://www.joeldevriendt.com/files/p...xlift_7150.JPG
I think my intake at max lift is the most questionable. the rest look ok.
Here is some pictures of my geometry with the 7.150" rods:
intake baseline:
http://www.joeldevriendt.com/files/p...eline_7150.JPG
intake midlift:
http://www.joeldevriendt.com/files/p...dlift_7150.JPG
intake maxlift:
http://www.joeldevriendt.com/files/p...xlift_7150.JPG
exhaust baseline:
http://www.joeldevriendt.com/files/p...eline_7150.JPG
exhaust midlift:
http://www.joeldevriendt.com/files/p...dlift_7150.JPG
exhaust maxlift:
http://www.joeldevriendt.com/files/p...xlift_7150.JPG
I think my intake at max lift is the most questionable. the rest look ok.
Last edited by JoeliusZ28; 07-26-2008 at 12:33 PM.
#10
I think you are in the same trap I was in. If you still have your stock length pushrods put them in on #1I and #1E and see what you get. Another item to measure is the number of turns you get on the locks. You want a minimum of 8-9 turns for 7/16-20 studs. This is usually the only downside to longer pushrods because as you lengthen the pushrod you raise the rocker and lessen the number of turns.
#11
I think you are in the same trap I was in. If you still have your stock length pushrods put them in on #1I and #1E and see what you get. Another item to measure is the number of turns you get on the locks. You want a minimum of 8-9 turns for 7/16-20 studs. This is usually the only downside to longer pushrods because as you lengthen the pushrod you raise the rocker and lessen the number of turns.
And funny thing about the locks. 3 of locks on my rockers are sunk deep compared the rest (adjustment bolt is sitting higher) yet the rockers appear to be perfectly in spec
#12
Agreed. Always start with stock and if the pattern is too far off from center, then go with a length checker. In my case stock was right on. As I have read many are. But you saying BS was at first a bit confusing.
#13
The BS relates to the short pushrods (like 7.05") to center the pattern. Like I said, I'll bet that 95% of the time stock length will work better, but the pattern will be off center.