Got a little confusion going on for myself regarding pushrod length.

This engine is not fully stock but it does use OE roller lifters.

First off I decided to do the half lift method of finding pushrod length. Cam is on TDC compression stroke with the intake and exhaust valve both on the base circle. The head was set down atop the block sans gasket (can just add the gasket thickness to the length of the pushrod to compensate). The 7/16 studs were screwed down and snuged lightly in place atop the AFR guide plate. I then set the scorpion roller rocker on the rocker arm stud after drawing a line between the center of the roller tip pin and the center of the pivot pin. I adjusted the polynut down till this line was as straight as possible for my eyes in line with the horizontal nature of the top of the valve spring retainer plate. I then did the math for my cam to break 0.520"/0.541" lift to half lift which was 0.260"/0.271" and taking into account of the 7/16" studs and 1 full turn of the polynut equals 0.050" I marked the polynut and turned it 5.2 turns down to set the rocker arm at half lift. I then adjusted my adjustable pushrod out till it took up the slack between the lifter and the rocker arm. The measurement I got out of the 4 times I tried it varying the adjustment for initial level I was getting 6.4875" to 6.50" on the pushrod length.

I noticed the roller tip looked funky so I marked the valve top with a sharpie and wiggled the rocker arm with the 6.50" pushrod length and found that the roller tip in this relaxed position was outboard of the centerline of the valve tip. This is obviously not going to work like that and even accounting for 0.039" - 0.041" headgaskets will not pull the roller tip on the inboard side of centerline.

I looked up the OE length of pushrod which is 6.25" and adjusted the adjustable pushrod to 6.25" and then adjusted the rocker arm down and wiggled on fresh sharpie and the roller mark shows at rest to be inboard of the center line on the valve. I tried it again with 6.35" pushrod length (AFR stated OE length pushrod or 0.100" longer), and it still was inboard of the center line but a little closer.

My problem is why did my half lift method I did multiple times to the tee give me a length of pushrod that put me on the outboard side of the valve tip when it should be on the inboard side?

My other problem is do I go with 6.35 and throw on 0.039" - 0.041" for the headgasket which would force me to run a 6.40" length as there is nothing between 6.35" and 6.40". Or do I take and invest in a machinists edge and keep trying on the half lift method to try and get a different length.

I will be installing the lifters and retainers tomorrow but I cant bolt the heads down as I am seriously contemplating getting the 0.039" headgaskets and not using the recommended 0.041" so I can bump compression up a bit as well as improve quench a little. Im also awaiting for the ARP timing cover/waterpump bolt set to come in as well so I can take some time to triple check this as I want this done right.

 

Where the roller tip runs on the end of the valve makes absolutely no difference as long as it isn't running off of the edge. Inboard, outboard or centered does not matter. What does matter is the motion that the rocker arm produces as the valvetrain actuates. What you want to see is a roller that moves outward, stops and then sweeps back inward as the valve approaches max lift. If it moves out more than it moves in, lengthen the pushrod. If it sweeps in more than it sweeps out, shorten the pushrod. Too short is much better than too long simply because the motion produced happens when the lift and loads are less.

Don't worry about any 1/2 lift stuff. That doesn't make any difference unless you're using a rocker arm that's designed around Jim Miller's Mid Lift Geometry principles. With his design when the rocker arm pivots are at 90 degrees on the valve end the are also at 90 degrees on the pushrod end. One of the ideas being that as the ratio increases on one end it decreases on the other end and the changes in ratio largely cancel each other out. It is interesting but it requires a lot of different rocker arm designs to make it work, sometimes two different designs on the same engine(Big block Ford).

 

I am not sure on the rocker, they are Scorpion 1.6:1 full roller rockers so I am unsure if they use Jim Miller's principles or not. The Lifters are the 302H OE roller lifters so I know there is nothing special there outside of improved valving to stabilize them to 6,500 rpm. I didnt try the contact patch method mainly cause I dont think the hydraulic lifters would be capable even after soaking in oil to overcome the valve spring. I also couldnt simply pull the lifters back and forth with the head on as the lifters I already tried wont come out with the head installed for some reason so I basically just been doing the math aspect at first then I tried the OE length and OE + 0.100" length like mentioned via AFR`s paperwork on my head and both of them put the rest contact point on the inboard side. But from what I have been reading I bet that position will result in a very wide contact pattern through out the lift. Makes me wonder if I should buy a single 6.50" length pushrod and give it a try and see what kind of pattern it produces. It is pretty close to what I am looking at after accounting for headgasket thickness, OE + 0.100 is 6.35" then throw in headgasket thickness of 0.039" which brings it to 6.389" which closest offered is 6.350", 6.375" or 6.400". I guess I could take a gamble on a single 6.50" pushrod for $15 and see if the lifter can open the valve to get me a contact pattern.

This is a photo I took of the sharpie wiped away when I wiggled the rocker arm with 6.25" or 6.35" length pushrod, that 0.100" didnt seem to make a whole lot of difference if any. I already wiped the sharpie mark off I had from the 6.50" but I roughly marked about where it was with a redline, with the blue line representing roughly center of the valve. Honestly with 6.25"/6.35" vs 6.50" the rest position is about the same distance from center of the valve just one is on intake side other is on exhaust side. From the reading I have done it sounds like longer pushrods will result in a narrower contact patch than a shorter pushrod. I also was reading it seems to be a longer pushrod requires less effort than a shorter pushrod to overcome the spring which tells me the shorter rod is changing leverage in the wrong way.



If it really doesnt matter where the contact patch is long as it is narrow and not rolling off the end and from what I have seen with longer pushrods using the half lift method it seems it provides some of the narrower patterns over just setting the rocker arm to be just inboard of the center line. That is why I was concerned cause everything up till now has told me that you want the rocker arm to be inboard at rest, center at half lift and outboard at full lift.

 

That's always a problem a hydraulic valvetrain. The lifter moves around and even with a light checking spring it can be inconsistent. With that said the lifter collapse always makes the valvetrain seem like it has a pushrod that's too short. This makes it seem like the roller only moves outward when the engine is rotated. It'll seem as though it can't even get to the point where the rocker arm starts to sweep back inward even though for the running engine it is just about right.

 

Yep and I really hate to disassemble one of these roller lifters and throw a small washer in to lock it up to make it like a solid lifter, I just dont like the thought of doing that and possibly doing damage when I apply it to full valve spring pressure.

One thing I am thinking of trying tomorrow is doing the 2/3 lift method I was reading and it seems 2/3 lift method is becoming quite popular as it allows for a shorter pushrod.

I really need to go with a shorter one than 6.500" cause I forgot that AFR recommends a .120 wall thickness pushrod and Scorpion recommends the same .120 wall thickness to prevent pushrod deflection with high spring pressure which roller engines do have.

So going with a .120" wall thickness pushrod it limits me to 6.300", 6.350", or 6.400" for Manley Chromoly Swedge end pushrods which is recommended by Scorpion. Even if I remove the Manley brand it still comes up with no 6.500". So it is really making me wonder if I should lean more towards the OE + .100" and let it ride. It is a roller tip and would reduce friction and side loading of the valve but my main thing is lots of magazine articles I came across online mention that with proper geometry using the 1/2 lift method results in valve lift actually being as advertised and not using it can see the valve lift be as much as 0.01" less.

Just seems like there is so much back and forth on this but I am interested in trying the 2/3 lift method and see what length I get for that. With the 1/2 lift I was getting 0.260" with 5.2 turns from horizontal with the 2/3 lift I am looking at 0.346" with 6.92 turns. If I look at exhaust its 0.361 at 7.22 turns so I think I would go for 7 turns even and split the difference and see what length I get then tomorrow.

With what I am looking at I might be over a barrel right now cause stock length is 6.25" I just double checked AFR and their paperwork doesnt state stock or stock plus .100" I could have swore it did, but 6.35" plus 0.039" would put me at 6.40" which I can get a pushrod in with .120" wall thickness and 5/16" outside of that I have no real option unless I try and contact someone that can custom make me a .120" wall thickness 5/16" pushrod in a oddball length. Then I question do I really need to spend the money for custom length push rods in a 306 displacement roller engine that I am building for daily driving with some goodies in it. 6.40" would be essentially what I need including headgasket thickness and would put the contact point on the base circle just inboard towards the intake manifold of center line.

Will have to see what happens tomorrow and what I get measurement wise cause I currently have 0.041" gaskets but I wont be using them as I am leaning towards 0.039" for a bump in compression and improvement in quench since I found out my deck clearance at true tdc when I was degreeing my camshaft is 0.0015". I guess I am doing like the engine builder I know told me about my cam bolt that I am just over thinking this and over complicating this for what is basically a warmed over mild street 302 that I am building.

 

Trend will make anything you want in a pushrod. Would I recommend spending money on fancy pushrods for an engine like this? No. If you did back to back testing on the dyno between an .080 and a .120 wall pushrod in an engine like this you would see no difference in performance. The pushrod is too short, the spring loads, lobe accelerations, and RPM are too low for it to make any difference.

 

Not to hijack the OP thread but concerning pushrods... At one time Trend use to build Trckflow's pushrods. Dave would you happen to know if Trend still builds pushrods for Trickflow?? I see on Summit racing Trend pushrods are more expensive than the Trickflows. Also would you happen to know if Smith Bros pushrods are any good??

​​​​​​https://www.pushrods.net/one-piece-pushrods

 

I don't know for sure if they make them but they used to make them for just about everybody. I've had Smith Brothers pushrods come through one time or another and they were fine.

 

Thats what I was thinking, Scorpion states if its under 8" in length you dont need 0.120" wall pushrods. AFR doesnt make that mention it states 0.120" for even the small block ford heads as well.

I did try a different form today how ever, I did the 2/3 lift method which comes out as 0.346" intake and 0.361" exhaust resulting in 6.92 turns for intake and 7.22 turns for exhaust. I did 7 turns from level just as it is kind of in the middle between the two splitting the difference. With 7 turns on the intake I got on a tape measure 6 5/16" on the adjustable pushrod doing the math for 0.050" per turn came up as 6.3125" length on the pushrod. Once you account for the 0.039" headgasket thickness it puts it to 6.364" length. The pushrod I was looking at was 6.35" which is 0.100" over OE 6.25". Right now I am trying to decide do I want to let it ride at 6.35" or go to 6.40". I honestly dont believe 6.40" would move the base circle contact point on the valve too much further outboard right now with 6.3125" length on my adjustable pushrod I was a little inboard towards intake side of center line. With 6.50" I am a little outboard of the center line to the exhaust side. So with 6.40" I would be basically over the center of the valve.

The upper line is with the 6.3125" length I came up with today at first doing the 2/3 lift method. The lower line towards the exhaust side is 6.50" length. I didnt bother marking with a 6.40" length as it would be right in between the two lines. So I think I could run either the 6.35" or 6.40" length pushrod and be fine both of them have the starting point very close to the center of the valve on the base circle and with 0.520" intake and 0.542" exhaust lift the contact patch should remain fully on the valve.