Different ratio rocker arms have almost zero effect on pushrod length.

Jebby

 

Rocker stud pad height has ZERO effect on pushrod length requirement. The camshaft lift and base circle are the drivers of pushrod length requirements. The actual geometry of the head is a smaller factor.

Think about it this way.....if you have perfect rocker arm geometry.....then you add a thick washer under the rocker stud.....the stud will ride higher BUT the rocker arm and adjusting nut stay in the same place in space. The nut will be screwed further down the length of the threads because you added a washer but the rocker arm geometry did not change. If you go the other way..... remove the washer from under the stud then machine the pad down by a quarter inch, the geometry still does not change. The rocker does not change its location in space....it can not go up or down....the valve stem never moved....the pushrod never moved....and the nut stayed in place BUT now less stud threads are left exposed. The stud height or length never affects geometry.

Camshaft base circle size is the BOTTOM of the valvetrain travel. The top of the cam lobe is the TOP of the valvetrain travel. When you ADD LIFT OR REDUCE the base circle diameter, you are CHANGING the rocker geometry.

Stock length pushrods work well for a stock or close to stock cams. If you change the lift of the cam (or diameter of the base circle) you need to check to see how far off you are on rocker arm geometry.

Typically we want to add lift when we do a camshaft change. In order to get proper valvetrain geometry back after we install a higher lift cam, it usually requires a somewhat taller pushrod to get the rocker back into proper geometry. The "sweet spot" in the middle of the total valvetrain travel is "higher" now. The rocker arm tip should be at a perfect 90 degrees to the valve stem when the lift of the valvetrain is positioned in the middle of lift travel.

You can assemble an engine and ignore the valvetrain geometry. It might run. It might break parts. It might wear out the valve guides faster. It might loose some RPM. It will at the minimum be down on power. It is not hard to check with a cheap adjustable length checking pushrod. Maybe $15? Custom length quality pushrods if required are less than $100. Not a whole lot more than the bottom of the barrel, stock length, less reliable replacements.

 

This is correct.....only the cam base-circle, lifter height and valve stem length/installed height have an effect on pushrod length on a stud mount rocker system.
It is always good practice to check the length no matter what the setup is......

Jebby

 

The rocker stud pad height has zero to do with pushrod length?

Are you really going to stick with that story? I am referring to the difference in GM iron head stud pad height compared to aluminum aftermarket pad height. The distance from cam to stud pad is higher.

Then, why did I need 0.100 longer pushrods by changing to aluminum heads to get a perfect valve-stem wear pattern? (nothing else was changed)
Then why does an extra thick head gasket change the wear pattern?
Even the thickness of using guide plates under the stud will change the pushrod length.

Something tells me someone is not checking the valve-stem wear marks.

 

Pad height has Zero effect and that's a big ZERO ,
Aluminum heads are not a direct copy of the original heads but a improved version that is engineered for the head and requires a longer valve
Head gasket raises everything up thus requiring longer pushrods ... true
Dead center wear spot does not mean perfect rocker geometry at all just so you know, Miller mid lift theory does and wear the tip rides where it rides if mid lift is correct

 

The only time that stud pad height affects pushrod length is on a shaft mounted rocker arm system.....as the rocker is rigidly bolted to the pad itself. On a stud mount rocker....the rocker trunion can slide up and down the stud freely.....lifting the stud height does nothing to affect it.
Heads U.P. , you most likely need a .100 longer pushrod because the installed height of your springs are 1.800 as opposed to 1.700 stock....this is very common......and is what is considered the ".650 lift" combination.....the ".550 lift" combo is 1.700.

Jebby

 

Exactly! Very few people know this.

 

Many running around with bad geometry wrong springs and dont even know it.
Chi com heads are well known to have locations "off",good lucking getting that right,.
One reason why they are cheap.
Even with Z28 or basic springs, buy good ones guys, the cheap stuff will give issues sooner or later. Not the place to skimp

 

This quote is directly from Manton Pushrod Companies web site.
(Word for word, I did not alter)

Rocker arm Geometry and proper pushrod length.

Many variables directly affect determining the proper pushrod length.
Pushrod length is affected by all of variables listed below:

Block Deck height
Head Deck Ht
Cam Base Circle
Rocker arm design
Lifter Receiver Cup Ht
Valve-stem Ht
Head Stud Boss Ht
Rocker arm Stand Mounting Pad.

I'm sorry. Could you repeat the last one again?
( I don't make this **** up. Its all right there in black & white)

 

Like this one on a Buick.

That refers to a rocker arm that bolts the trunion to the head. Chevrolet did not use those on the small block/big blocks. We use adjustable rocker arms.

 

Yeah, rocker arm stand mounting pad if using shaft mounted rockers….which I am sure is what they mean…..or a non adjustable as in the pic above where rocker height is solely dictated by the stand.
If you look at the side view of an adjustable setup….the fulcrum is the rocker trunion but the stop is the bottom of the poly-loc….so the geometry is dictated by raising or lowering the poly-loc….while the rocker just slides either up or down the stud….
How high the stud pad is has nothing to do with it.

Jebby

 

Let me explain in "for instance mode". Try to get a visual of this scenario.

Lets say you just installed a crazy looking aluminum head. The rocker stud pad is 4" higher than stock location. It so high that no valvecover will fit.
So, will the stock length pushrods work? Of course not.

Lets say the rocker stud pad is 2" higher. Will the stock pushrods work? Of course not!

Lets say the pad is a half inch higher. Stock pushrods still work? Of course not.

Lets say the pad is a quarter of an inch higher than stock. Need longer pushrods? I am betting yes.
That was just a made up scenario way out of proportion. But you get the idea.

I understand that a mounted rocker "shaft" containing 8 rockers arms is going to be all the same height across the head. And its a fixed height without adjustment.
But by the same token all 8 rocker arms sitting on rocker studs will be at the same height also. They ride on rocker bottom, stud.and pad.
So if all 8 rocker stud pads are higher, then an adjustment must be made. And that is done through longer pushrods (or shorter).

 

No. The pad height makes no difference.

If you put in a 6" long piece of ready rod and a jam nut at the bottom against the head it makes no difference in the rocker ratio. You can simulate a higher pad by putting shims under the jam nut all day long but in the end....the rocker arm is always located at one end by the valve stem tip and at the other end by the pushrod. Changing the height of the pad only moves the stud threads up or down. The rocker arm does not go up or down with it.

 

Again, I am not talking about the ratio, the geometry and such.

I am saying that if the aluminum head rocker pad is higher than stock, you must make up the difference of that new dimension with a longer pushrod.
If you don't believe that, take an old junk SBC pushrod and cut off about a quarter inch. Which would be the equivalent of a quarter inch new heads higher pad.
See how that works out.

 

But that’s not how a fulcrum works on an adjustable system….the bottom of the poly-loc resting on the rocker trunion is the “stand”….if the rocker stand was a 1/4” higher or lower makes no difference as the geometry is dictated by the valve stem height and the cup in the lifter….you pick the pushrod length to accommodate the geometry, not the other way around. The poly-loc is adjusted to hold the geometry in position…..
Now in some cases…I have seen the rocker too low on the stud and it rubs on the radius….but that is not the stand being too high….it is the valve stem or pushrod being too short….or the whole thing doesn’t work due to poor parts choice….
But if I went out right now on my Dart 200’s and milled 1/4” off the stand….the pushrod length doesn’t change….the rocker will just ride higher on the stud….

Jebby

 

Just a quick note,to all who cares,There has been a debate on whether my stock length pushrods would work with these heads and after talking to Summit and to another person that I know,which is very familiar with Chevy and has worked on a lot of race cars,and they all say that my length pushrods are fine,and could even go to a 1.6 rocker arm.

 

And as a person who has built over 200 engines….I am going to say you need to check geometry regardless….it might come back at 7.800….but it might not….but unless you check, it is not “fine”.

Jebby

 

Yea,just to be safe,it will be a few days till I get the checker,you can’t even order one through auto zone.

 

If running an aftermarket cam with stiffer springs I would step up to a stronger 1 piece pushrod anyways. Not the cheap ones with ***** on the end.
They flex as that spring compresses fwiw. Dont wanna bend/break one. Easy way not to lose power, valve control which can save your valve job, tips etc
I learned that one the hard way.

 

Fella's..........

Look'n at those dish pistons.
Take off '010 off the shiny new aluminum heads deck will make you 10:1 maybe.

Don't forget to do the intake runner flanges to match up.

ramair in california.
ready to slide into the pacific.....