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 !

Do a search on my user name and "valvetrain geometry" and you will find a ton of stuff. The concept of centering the pattern on the valve stem is BS.

Feel free to PM me if you would like more.

thanks, sent you a PM.

I just ordered a set of 7.050 length rods last night so i can get it running this weekend...so i hope the centering method isnt that far off.

Gona have to splain that one !
 

Could you elaborate on your statement please?


BTW
http://compcams.com/technical/Catalogs/106-07/264.pdf

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

Agreed. The more sweep there is the less lift there is. As long as the edge of the sweep is more than 20% of the valve diameter you are golden. ;)

I can also vouch for this.

25% is what I was told, but hell, that's only a couple thousandths difference!

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!:D:D 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.

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.

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.

alright ill try that tomorrow. if that was you that called me this evening i apologize, ended up going to a wedding.

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 :confused:

I bet the 3 oddballs have their trunions upside down. They should all have the flat side up.

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.

Yep, that was me. No problem as you seem to be on the right track. Check the speedy comment regarding the trunions too.

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.

well you guys were right about those 3, thanks a bunch i would have probably never noticed that!!

:cz28:

Joelius, i guess im a couple days behind you in the installation, but i feel like im looking at the same motor. did you end up figuring out the correct pr length for yours?