Pushrod Length Help

[gadirtracer]

I think I'm needing a set of push-rods that are .100" or so shorter than stock.
Longer seems to be the norm, or at least stock & longer are all over the net for sale.
I realize that there are many different pieces that affect what length is correct, but this is the second engine that is needing shorter push-rods that I've assembled.
Old style SBC block
Pistons .020 in the hole(ya, I know, short block was already assembled.)
40cc sumthin' angle milled heads
ARP screw in studs
Crane(exhaust) & Comp(intake) 1.5 stainless roller rockers
Wondering if I'm checking something wrong. I don't have a checker or an adj. push-rod. I am marking the valve tips,(w/a paint pen, and tried it w/a black marker too) installing rockers and setting the lash. Then turn the engine over by hand several times. Center of "mark" is towards the exhaust ports. At full lift, roller is out towards the edge of valve tip. At the base of cam, roller seems to be centered. Should it not be closer to the intake at base circle?
Thanks for any help...

[mbaker76]

If the heads have been cut that far then when assemlbed everything ends up being closer to the deck and consequently the lifter so a shorter pushrod would be in order.

[stock car driver]

By your description that would need a longer push rod not shorter.

BUT you should buy or borrow a plastic push rod length checker. They are 12-20 bucks from what I remember. You can put a stock length push rod in there and use the checker and see if you need longer or shorter and measure the difference easily. If its short on the push rod end you need longer if its off the valve then you need shorter.



My 360 has been milled every which way and it still uses stock length push rods.

[joedoozer]

I have a checker if you want to borrow it. It slides over the stud, its not the adjustable push rod type.

[parrot69777]

You can easily make your own adjustable pushrod. Just take a stock pushrod.....cut it in half. Then remove about a half inch or so and tap both sections. Take a piece of threaded rod with a jam nut and screw it back together. Usually a 1/4-20 or 1/4-28 works very well.

Never have seen anyone use shorter pushrods....unless it was on a roller cam. Make sure when you go to a longer pushrod to watch where the rocker fulcrum sits on the stud. You want as much of it on the shank of the stud and not on the threads.

[joedoozer]

You can easily make your own adjustable pushrod. Just take a stock pushrod.....cut it in half. Then remove about a half inch or so and tap both sections. Take a piece of threaded rod with a jam nut and screw it back together. Usually a 1/4-20 or 1/4-28 works very well.

I have tried this a few times. Never had much luck drilling a pushrod haha.

[gadirtracer]

I agree, it seems MOST combo's would take a longer push rod...BUT. I have a set of stock length(7.800) and a set of +.100(7.900 Comp). When checking with the +.100 longer rods, my marks on the valve tip moves farther out towards the exhaust side of the head. Stock length moves it in closer to the intake side, but it is still off center to the exhaust side. This is telling me I need a push rod shorter than stock...is it not?

[dynoman14]

Gil,
You have the right idea. The closer you can get the pattern of travel to .000" and in the center of the valve the better off you will be. I try to get most to +/- .050". Much of what you are seeing is from the improper geometry in design of most rockers so you have to get the best compromise with the roller starting about .050" to the exhaust side and then moving in and out to rest somewhere close to the middle.

If you really want to get chronic about it, and I am about pretty much everything you set a dial indicator up with the point on the nose of the rocker and you track it thru its arc and then you can have an actual value to what you are doing, that is if you really want to know. The marker will show you the same thing just not quantitative.

Once you get down to it you will probably see that you will need 8 pushrods for the intake and 8 for the exhaust. Sometime .025"-.050" in length can make all the difference in the world. You will probably want to make sure you are using ARP large base rocker studs as you will cut that movement significantly if you are using other type studs. Also you might want to do your checking with a stud girdle if you are allowed, they help a lot especially when spring pressures are high and the rocker arm is sitting high on the stud.

BTW, how much clearance do you have between the hole in the trunion and the o.d. of the rocker stud, another important factor is to make sure that the rocker trunion does not ride on the threaded part of the rocker stud as it will move another .010-.030" on that.

I know that is a lot of stuff but a couple hundred hours on the spintron will get you looking everywhere to eliminate valvetrain harmonics. In 99% of every race engine out there harmonics are the source of 10-20% power losses at operational speeds of 6500+ RPM. That why most hydraulic lifter engines crap out above that point.

[parrot69777]

I have tried this a few times. Never had much luck drilling a pushrod haha.

Seeing how a SBC pushrod is hollow.....all you have to do is tap it. No drilling required.