Pushrod Length Check..WTF am i doing wrong?

Ok, i think i've read every tutorial out there on how to do this and it doesn't seem like rocket science but my results are not adding up. Here's what I've done:
Place engine at TDC, install lifter (hydraulic flat tappet Comp Magnum) in #1 lifter galley, install adjustable pushrod (stock length to start), add dyecam to valve stem tip, bolt down stock rocker arms, adjust pushrod length to the point where pushrod spins but doesn't go up and down.

I rotate the engine two full cycles and take off the rocker to observe the wear. Now, since these are stock rockers i know its not going to be some clean mark right in the middle but the wear pattern goes from the pushrod side of the stem to about 3/4 towards the header side.

SO, here's the kicker. I know the deck height is shorter than stock and the heads have only been milled flat. With those two factors one would ASSUME that i would need shorter pushrods. However, after doing this check about 5 times the pushrod was actually LONGER than stock. I need some help!!!

 

I will be watching for a expert reply . From what you mention a shorter deck and head I would assume you would need a longer than stock push rod. uzzled:

 

This is a Buick? With a stock-type rocker shaft assembly?

The geometry you're looking for is BUILT-INTO the shaft rocker assembly and the valve stem tip height. The pushrod length does NOTHING except give you proper lifter preload.

If you had independent-adjustable rockers like a Chevy--or the Edelbrock heads that have Chevy-style stud-mounted lifters--then pushrod length affects valvetrain geometry. (but rocker geometry and valve stem tip height ALSO affects valvetrain geometry, so everything still has to work "together".)

 

Also don't forget when sizing pushrods with hydraulic lifters, you have to take the preload distance of the lifter into consideration. That's .030.

 

How would i need longer pushrods if i've shortened the distance between the rocker arm and lifter?

So how do i measure the preload on the lifter? Its not something you can just eyeball. Also, does the wear pattern not matter with the stock rocker arms?

 

With stock rocker arms, there is nothing you can do to change the point where the rocker contacts the valve tip. You have to change the pivot point, which is fixed by the shaft.

You can shim the shafts, if your way out of wack.. measure your valve tip height, Ideal is 2.050- 2.090 acceptable is 2.090 to 2.125

Much beyond that, and you start to get "over center" issues with the valvetrain. this can lead to the inability to rpm properly, due to hyd lifter failure.

At that point the best fix is to put in shorter valves.. I have used 409 Chev valves, with the intake turned to the proper size, to fix tip height issues in iron heads.

JW

 

Preload on most hydraulic lifters is usually between .020 to .060. Any less than .020 will result in noisy valve train and more than .060 preload will result in excessive pump-up. So if you are using an ajustable pushrod, with lifter on heel of cam, spin the pushrod with your fingers and extend it until the pushrod just stops spining. At that point you can take the pushrod out and measure it. Then just add .030 to the length and that will be the pushrod length you need.
Just curious if anyone uses lash caps to add length to make up for too short of a valve stem?

Larry

 

A person with strong hands will extend the pushrod until the lifter plunger is bottomed, and the valve is starting to open before the pushrod won't spin any more.

Better to check for lengthwise movement rather than spinning movement of the pushrod.

BEST is to remove the intake manifold and LOOK at the lifter plunger. Sometimes you can see the plunger through openings in the head. Other engine families have head castings that don't permit seeing the lifters very well.

Once you have your adjustable pushrod set to the appropriate length, you need to figure out which of the (at least) three different ways to measure a pushrod your supplier uses, so you and the supplier are measuring the same way.

Anything can happen, but the usual issue is that the valve stem is too long. Re-cutting the seats will raise the valve tip, as does refacing the valve.

I suppose a new, larger-head valve on a freshly-cut seat (using "virgin" parent metal, or using a seat insert) could make the valve tip low.

 

Post a pic of the wear pattern. Those magnum lifters require. 002"-.004" preload. An adj. valvetrain is required if using them. However good for checking for required pushrod length. Very stiff plunger. Did you use light checking springs or regular valvesprings?
Are all the valve stem tips the same height?

 

No need to go through all that. Just use a little common sense and you will be fine. It may take a minute or two to get "the feel" of it. I don't know of anyone with enough "Vulcan Grip" that could start a valve to open with an automotive valve spring.
Also, if those lifters are the "Pro Magnum" lifters then RG67BEAST would be correct at .002 to .004. The part# for those is 865-16.
Larry

 

You can run enough pre-load on the 865 pro magnum lifters to keep them quiet, the .002-.004 setting is for max rpm, typically above 6500.

I have run .030 preload and run those lifters to 6000 rpm in many engines.

JW

 

Good to know, I'll have to print and save that info. Since you have used those 865's, do they have the hardened base like the Delphi? A few of the images on line show them to but not sure if those images are just generic.

Larry

 

Here is the wear pattern. Again, this is with the adjustable pushrod adjusted to where it just starts to spin and with no vertical movement. it's only slightly longer than the stock pushrod at this point so when I get home today ill throw the stockers in there and do the same thing.



All the stem heights are the same ante vale springs are TA Stage One Plus.

 

What compressed thickness head gaskets are you using? I believe the early 455 years were the .020 steel gaskets, so if you have lets say, Fel Pro Blues in there now, they normally measure .038 compressed. Technically that would require an .018 longer pushrod. Again it also depends on how much material was removed from the deck and head surfaces. Bottom line is to check it with your adjustable push rod to zero lash, add your desired lifter preload to that length and order them up. Also that pattern looks ok to me.

Larry

 

They're .040 compressed. So, can I assume that if the wear pattern is good, that the pushrod length is as well? Do i still need to account for preload?

 

You may need a longer push rod because the base circle on your camshaft is probably smaller than what you had. This is necessary to get more lift.

 

You're back to thinking it's a Chevy. Pushrod length does NOTHING for the wear-pattern at the rocker tip. Pushrod length sets the lifter preload. Yes, you must get close enough with the required length to provide some lifter preload. Pushrods are shelf-stock in 0.050 increments, so if you measure more-accurately than that, round to the nearest .050 that provides at least your minimum preload--unless you insist on lifter preload set to the thousandth. I think that would be a waste of time and effort. Some lifters have plunger travel of more than 0.250, so it's not like you have to be dead-nuts accurate with those. Other lifters have restricted travel of just a few thousandth...and you would have to be perfectly accurate. I'd never advise using that style lifter in a shaft-rocker engine unless each rocker had some adjustment.

Again, you ALSO need to verify HOW your pushrod supplier measures their pushrods, so you can measure yours the same way.

 

Thanks. I measured total plunger depth at .13" and preload with stock pushrods was .1". So, i am assuming i can order pushrods that are .07 shorter than stock and that would give me .03 of preload. Yes?

 

The cheapest solution is to shim the shafts. The pattern is not that far off so first just use .010"-.015" and use a different valve to compare how far the pattern moves. If it is acceptable shim all the pedestals the same. To get an accurate pattern the plunger must not move.
Ray

 

I'm looking at the available pushrods from TA and they offer a 9.275 and 9.30. If I go with the 9.275 I should have roughly .025 of preload and with 9.3 it would be .05 of preload. Is it better to be on the low or high end of the clearance?