Rhoads V-PROs - mid-lift rocker geometry - push rods measurement
 

I've been corresponding with Jack Rhoads about measuring for new push rods with the Rhoads V-PRO lifters. In an email he wrote, "Bottom out plunger when determining pushrod length and ADD about 0.020” to the pushrod." No explanation why you add it or what it does. I didn't really think anything of it until I started to really think about it. So I called him and got even more confused. He did mention that the V-PROs plunger travel is 50 - 60 thou. So I got more intrigued about why he wants to ADD 20 thou to the initial rod measurement. I've concluded that I really don't know so I sent him another email today with more questions.

If you have the rocker pinned in the sweet spot using mid-lift or the old witness mark method, why would you add another 20 thou and move the intake side of the rocker up more and not take into account rounding to the nearest 50 thou for the rod, or the additional bump you get when adjusting the lifters? I would think you 'd subtract some length, perhaps the plunger travel from low to high RPM so you can keep the rocker as close to mid-lift as possible when it's running at the higher RPMs...some constant that works with however you setup the lifter for you engine.

If you have any thoughts on this feel free to share.

So I spent some time last night writing a detailed email explaining my understanding and asked some specific questions. His reply was, "I think you should use any method that feels right to you. It can get complicated". So he didn't answer one question or provide any detail on why you ADD length to the measured pushrod. Not sure what you call that, but it's not tech help.

Let’s get some basics nailed down that can’t be disputed..

1)
Your lifters as you have posted have about .050” of adjustment range that they will work in just fine without noise if there made right.

2)
as any motor heats up any dimension that was a clearance will close up some and other will open up.
3)
As valve seats bed in and ware over time and valve stem tips and rocker arm tips ware what might have been a no gap / clearance condition will develop a gap.
4)
Aluminum heads will typically grow about .005” to .008” when up to normal operating temp, and iron heads will grow about 1/2 that amount.

Basically all you are doing when adjusting a hydraulic lifter is providing enough room for dimensions like above to change while maintaining a no clearance condition and also keeping the plunger from coming up against the clip ( be it round or flat C type) to hold the plunger from exiting the body of the lifter.

So basically you have been told in your corespondence that if you have a given push rod length that gives you good geometry at half lift then a push rod .020” longer will have the plunger compressed .020” out of that .050” you have to work with .
This is fine and as dimensions change when the motor is hot and things ware some you should never hear a clacking lifter or rocker.

I would subtract the .020” for the correct pushrod length with a VPro.

I agree with everything about wear and heat expansion. The V-Pros are adjusted from the bottom up using a feeler gauge at the valve to loosen or tighten the reduction in valve lift, duration, and velocity vs. from the top down to set a pre-load. So that's the conflict. Adding length if you're setup starts at the top of plunger travel makes sense, but all the published tech info at Rhoads emphasizes the bottom up procedure. Adding length to a rod that's already bottomed out seems counter-intuitive.

what do the instructions that came with the lifters say?

I've read past posts from you about V-Pros and it looks like you've used them a number of times. Thanks for your input. I would also lean toward subtracting 0.020" from the initial measurement that has the rod bottomed out and the rocker at a good spot, perhaps slightly more to move the rocker to mid-lift in the upper RPM (above 3500) range. Maybe that's getting too picky. My setup will use 0.020" lifter adjustment once the new rod is in place. That'll get the plunger just off the bottom of the lifter. 0.013" - 0.014" approximately, then as RPM increases the plunger will move up to provide full valve lift, duration, and velocity. At least that's the theory.

There are instructions on adjusting the lifter (assuming you have the push rods already in), but they don't have anything published on the website or with the parts about measuring for rods given good and proper rocker geometry.

You buy new lifters, rockers, and a cam, you clearly need new push rods, so not providing instructions for that procedure is a miss in my opinion.

I'm sure there are experienced engine builders that can read the lifter adjustment instructions and then figure out how to determine proper rod length, but for us guys that rarely go deep into these things, it's good to have some assurance on how it's done by the company selling the parts.

I don’t think any lifter instructions provide information on pushrod length. Once you get your pattern, you can determine length based on the amount of preload specified.

https://www.rhoadslifters.com/Pages/Installation.html

I should have posted I did not have time to do that could have made things clearer.

He should have said that the more change you want in duration between idle conditions and and rpm’s above 3500, then the more you should adjust the lifter as he recommends that being starting with the lifter nearly bottomed out.

I've read that sheet several times now and the one they supply with the parts is similar, but different.

There's no mystery on how to get the rod length with solid and std HFT lifters. I think what threw me off was the anti-pump feature and how the plunger changes position as RPM increases.

Many decades ago Rhoads adjusting instructions told you to bottom the lifter plunger and back it out a full turn. It has changed a few times since.

We usually round up when determining pushrod length for applications using Rhoads.

Valve train geometry is a bit complicated to explain. It gets trickier when folks double check their notes with others on the Internet. I believe that deters manufacturers from wanting to get deeply involved with advice. I have seen Jesel several times refer folks to their instruction sheet which is different than the "mid lift" theory. I've seen Jesel many times state the it's up to the end user if they want to follow their recommendations or set them up with the "mid lift" theory".

I had an issue with setting Rhoads from zero then tightening down. Spin the motor around then to see if I forgot one they had bled down(like they are supposed to) and the pushrod was loose!

Thank you Paul for your comments on this. I agree that the geometry can get tricky to understand. Round up? Yes. Better to be long than short. I suppose there’s a risk to mfrs if they put too much information out there about other parts they didn’t sell.

After all this overthinking, I can see how I’ll set the rod length. Easier to visualize now. Hold the rocker geometry as close as you can and make sure the lifter setup procedure can be done exactly as the directions indicate. The unknowns are how the rocker changes geometry as the lifter achieves full valve lift. A guy could subtract another 0.010” on top of the 0.020” initial deduction. A little bit of guessing but not really. I can only estimate the plunger lifts maybe 10 -15 thou between idle and high RPM.

Measured for pushrods last night. We attempted to setup with midlift. It didn’t work as expected. Once setup the rocker sat on the exhaust side of the valve tip. So the witness mark method was done and the initial rod length was reduced by 1/4”! My guess is the rocker arms are not designed to be setup exactly with mid-lift geometry. They’re designed to fit Pontiac. That’s all. Find a rod length to ride the roller as close to the center of the valve tip and be done.

I tried the mid lift scheme when it became the new rage marking the side of a roller rocker and it took me in a wrong direction... Not all rockers are the same meaning the relationship of the cup and top of the valve tip vertically speaking from the rocker fulcrum they are not just about inboard / outboard points of interest so some brands of engine family's might work, In spirit mid lift is correct to give the smallest sweep on valve tip but you can observe the tip markings to get there is easier for me > on a Pontiac <

Jay, didn't you build a 455 recently with V-Pro's? Could you tell us about how and why you set up your V-Pro's on that engine?
THanks
Jeff

From everything I’ve read, the narrowest pattern is preferred over the pattern closest to center of the valve tip. In some cases, the narrowest is in the center.

Narrowest pattern is preffered and if that happens to close to edge of valve stem then the brand of aftermarket rockers becomes suspect and if all else fails going .050 different length pushrod to get off the edge shouldn't effect sweep all that much........ Longer than oem valve lengths can alter where the pattern will center because physically the top of the valve stem is closer to the stud (rocker fulcrum) due to intersecting angles

When starting from a pushrod that is a set length, adding .020” (as Rhaod’s said) to the length then checking the pattern with a pushrod checker is correct. If you’re starting out using a pushrod checker with no idea what the length may be, to get the actual pushrod length you subtract the .020” from the pushrod checker length. What Rhaods was suggesting was not wrong, they were just starting from a set pushrod length, versus starting with a checking tool. In other words, for finding what the operating contact pattern of the rockers with V series Rhoad's, one way you add lash to the length, the other way you subtract it.

Vpro’s have an extra shim in them to raise the plunger so they can be set with less lash than a Vmax. If you follow the instructions for Vpro and Vmax with their corresponding recommended lash settings the plungers operate at the same height for both the Vmax and the Vpro. With the combination of the shim under the plungers and adding the .020” lash on a Vpro the position of the plunger is pretty close to the same as a regular standard lifter with 1 turn from zero preload. In other words the pushrod length for a Vmax or a Vpro is the same as standard lifter. I never seen that a different length pushrod was required on a Vpro versus a standard regular lifter. A Vmax running a ton of lash to pass a vacuum rule of a racing class might take a different length pushrod than a stock lifter, but for most street stuff the pushrod lengths will not change from a standard lifter. You can switch to V series lifter and use all the same valve terrain parts as regular lifters use.