[Tim Corcoran]

I admit I'm a little confused about getting the correct length pushrod. With a solid valve lifter it's pretty straight forward. With a hydraulic lifter is where I need some insight.

I have the comp cams evolution lifters and preload travel is .125"

I bottom out the travel making the lifter act like a solid lifter.

With an adjustable checking pushrod I find the best pattern towards the center of the valve with the shortest sweep.

Since the lifter was bottomed out when checking now I need to add or subtract a certain amount to make up for bottoming out the lifter. This is where I get confused. Do I add or subtract for the correct pushrod length and by how much?

Also is it better to have the pattern more towards the exhaust side or the intake side?

Thanks for any guidance on this

[Formulas]

Subtract from adjustable pushrod length because the depressed plunger is adding length / increasing distance

[Tim Corcoran]

I talked to the comp cams tech guy. He said the preload travel is actually .150 and not .125 as the instruction sheet says. He also said when adjusting the valves the preload should be .100. And he said to subtract .050 to get the correct pushrod length using the method I am using. As far as the pattern on the valve tip some say you want it in the middle of the valve and some say you want to smallest sweep pattern even if it's not in the middle. I noticed that when the pattern is in the middle of the valve and then I adjust the checking push rod longer in .050 intervals the pattern gets narrower as the pattern moves out towards the exhaust side of the engine. Just curious how some of you professionals do it. I suppose I could put a .050 feeler gage between the valve and the rocker and that would be the same thing and I wouldn't need to subtract .050.

[HWYSTR455]

Use the half lift method, don't bother shooting for a good pattern, the pattern is technically a result of the correct length pushrod.

https://www.youtube.com/watch?app=de...s9BsH5OU&t=12s

If I'm understanding you correctly, total travel of the plunger is .150, and the preload recommended is .100?

Just use the Straub method, measure, and then subtract .50 from the pushrod length you come up with. No need to overthink it. Whatever the pattern is when using the correct pushrod length is the best pattern you can get.


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[steve25]

Some other facts .
As you preload the lifter the geometry acts like you have a shorter push rod in place.

Lifter preload is done really for just two reasons.

1) is to maintain a noiseless valve train over a lot of miles as the valvetrain wares and valves recede.

2) so if the valves ever float the plunger clip ( if it’s a round wire type ) is not be forced out .

Longer push rods can make the rocker tip contact pattern move more and more to the exh port side of the head, shorter ones will do the opposite and might create rocker body to retainer clearance issues.

For the least amount of leverage action on the valve you want the narrowest patten on the stem top , if you can not achieve this, but end up .020” to .035” on one side or the other I would not consider having such a deal breaker for running that push rod length, and especially if a roller tip is riding on the top of the stem.

Also note as you play around from the stock push rod length of 9.145” that you will gain or loose lift so you really should be using a very light checking spring so as to not overwhelm the spring under the lifter plunger when rolling the cam around.

Also consider that when in use even at only 5000 rpm the valvetrain will deflect about .010” to .012” and that amount of lift will be lost.

If your lucky and play around a lot with push rod length you can compensate for this loss and enjoy all the power you can was meant to provide.

[grivera]

I went through this deal here:

https://forums.maxperformanceinc.com...lution+lifters

[HWYSTR455]

Yeah Ken in that thread also commented, if you have correct mid-lift geometry, you will have the tightest sweep.

That's why I say all the time, do the geometry right, and you will have the best sweep.

If you go by the sweep only, you can be there for hours, and in actual running, may find it's still not right. Not sure why so many still use the sweep method, it's a waste of time.



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[grivera]

I did both methods on mine. The bulkiness of the 1.65 HS rockers made it tricky to draw the line with the sharpie.

[HWYSTR455]

Yeah, my Crower rockers w the narrow nose made it a little tricky too, but doable.



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[Skip Fix]

The problem with shooting for the perfect mid lift is different rockers have different diameter roller wheels, different pushrod cup depth in relation to the centerline of the trunnion. So getting the perfect mid lift, smallest pattern and a fairly centered on the valve tip or a lash cap is a challenge unless you are designing your own rocker!

[HWYSTR455]

Originally Posted by Skip Fix

The problem with shooting for the perfect mid lift is different rockers have different diameter roller wheels, different pushrod cup depth in relation to the centerline of the trunnion. So getting the perfect mid lift, smallest pattern and a fairly centered on the valve tip or a lash cap is a challenge unless you are designing your own rocker!

It doesn't matter, the key points are the axis of the body & nose bushing/bearing, not all three including the pushrod cup.

If the nose roller is larger in diameter, the cup will change, not the ratio. If you burry the cup into the body, it will contact thru the arc range. Manufacturers of rocker arms know the key points and arc of travel, and design the rocker to be rigid in that range. If you change the body, it will improperly stress the body, just makes no sense.

Even if valve lift is over 1", by design, the rocker would have to be able to tolerate x load thru the arc. The rocker would have to be longer and custom, but the design remains the same, it has to be structurally the same, just longer. Not to mention the head would also have to be designed to accommodate that range of travel.

Once you go past a certain angle the pushrod would deflect, and the action of motion wouldn't be pushing the lifter in the direction it needs to travel. The pushrod would be going more laterally that vertically past a certain range of the arc.

Not sure if I explained that right, but think you know what I'm trying to say.

For Pontiac heads, and the off the shelf cams & rockers that are available, the method is still the most effective 99.999% of cases. Anything else and you would actually need a true 'rocket scientist' so to speak.

Try it. Take every available rocker & cam combo and see how the tip pattern ends up using the mid- lift method. That will end the debate. F1 engine builders use the same method, and that's the most technically advanced piston engines on the planet.


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[Tim Corcoran]

I've tried the straub method in the past. I found it difficult to see the line between the two axles being 90 degrees to the valve accurately. People have been using the sweep method for many years with good success. I ended up with the sweep a little towards the exhaust side with a small sweep area. It might not be perfect but I am happy with it. Ended up with a 9.050 length.

[grivera]

Looks great

[Dragncar]

Mine are about in the same place, all is good.

[Skip Fix]

Try it. Take every available rocker & cam combo and see how the tip pattern ends up using the mid- lift method. That will end the debate. F1 engine builders use the same method, and that's the most technically advanced piston engines on the planet.

But they have rockers designed for that engine also. Most all of ours Pontiac, Chevy etc are a ball park estimation of the manufacturer they just change cup to trunnion distance for ratio changes.

Ive tried it on a couple even seeing the angle is tough with valve cover rails even on end cylinders!

[HWYSTR455]

I get it, and it is easier with the aluminum body rockers.

I have a 6" steel ruler that I use, makes it pretty easy, though you do have to look hard at it to be sure.

I don't think you can use a ruler with the large nose body on some rockers, and with some types of retainers, but it's not impossible.

I use a fine tip sharpie too, sometimes when a sharpie tip is boogered it makes it tough to visualize.

Most pushrod manufacturers offer increments in .050, so there is a little 'fudge factor' too.



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[Skip Fix]

And then using a shaft system and their set up tool you wonder how it is too

[ta man]

Originally Posted by HWYSTR455

It doesn't matter, the key points are the axis of the body & nose bushing/bearing, not all three including the pushrod cup.

If the nose roller is larger in diameter, the cup will change, not the ratio. If you burry the cup into the body, it will contact thru the arc range. Manufacturers of rocker arms know the key points and arc of travel, and design the rocker to be rigid in that range. If you change the body, it will improperly stress the body, just makes no sense.

Even if valve lift is over 1", by design, the rocker would have to be able to tolerate x load thru the arc. The rocker would have to be longer and custom, but the design remains the same, it has to be structurally the same, just longer. Not to mention the head would also have to be designed to accommodate that range of travel.

Once you go past a certain angle the pushrod would deflect, and the action of motion wouldn't be pushing the lifter in the direction it needs to travel. The pushrod would be going more laterally that vertically past a certain range of the arc.

Not sure if I explained that right, but think you know what I'm trying to say.

For Pontiac heads, and the off the shelf cams & rockers that are available, the method is still the most effective 99.999% of cases. Anything else and you would actually need a true 'rocket scientist' so to speak.

Try it. Take every available rocker & cam combo and see how the tip pattern ends up using the mid- lift method. That will end the debate. F1 engine builders use the same method, and that's the most technically advanced piston engines on the planet.


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There hasn't been a Formula One pushrod engine in 60 years..you must know some old F1 mechanics?

[HWYSTR455]

Yes, the term comes from engine design & engineering training dating back to even before F1, and is still taught to this day. It just happens a guy in the 60s-early 70s coined the phrase mid-lift, do the homework.

UTi and other schools also teach mid-lift tech.

If you're interested, tons of stuff out there, here's just a couple:

https://www.eliminatorproducts.com/u...VzRGRrdz0=.pdf

https://www.hotrod.com/articles/ctrp...train-geometry

https://www.crankshaftcoalition.com/...Y_MID_LIFT.pdf

https://www.ijirset.com/upload/april/36_ROCKER.pdf



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