[grivera]

When using the half lift method, does the cam need to be rotated so the lifter is at the half lift point on the cam?

[Kenth]

I may be wrong, but "half lift" is lobe lift times rocker arm ratio divided in two is X.
Place rocker 90° to the valve stem.
Adjust the rocker nut half the amount of X.
Adjust the push rod for zero play.
(With hydraulic lifter add .050" to the final length of the pushrod)

To check, turn the crank, take measurement at valve tip for X and the rocker will be 90° to the valve stem.

Jobs done!

[HWYSTR455]

Originally Posted by grivera

When using the half lift method, does the cam need to be rotated so the lifter is at the half lift point on the cam?

No, the cam should be on the base of the lobe.

One does not account for the preload/valve adjustment when calculating pushrod length using the half lift method.

Watch the video all the way through to understand it:

https://www.youtube.com/watch?v=o5is9BsH5OU

If one is unsure if the lifter plunger isn't full at top of (HYD) lifter, you can shine a light down there and actually see it. It should be seated against the snap ring.

If you can't see it, use a cheap borescope, like one of these:

https://www.amazon.com/gp/aw/d/B0DK9...9-da0da9323246



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[HWYSTR455]

Originally Posted by grivera

It needs a light spring cause he’s opening the valve to half lift and checking for 90 degrees at that point. He used a light spring in the video.

He specifically says the lifter is on the base circle. He never moves the crank/cam.

The valve is completely seated.


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[HWYSTR455]

Originally Posted by steve25

I know this is not the race section so this info might not matter much to some, but here is why patterns produced by the same ratio rockers can be different with the same length push rods being used.

These charts were made by David Vizard using BBC rockers.

Note in particular how the initial ratio can be by very different even though the advertised rocker ratio is the same!

This is also why some motors running the same ratio rockers can be down or up by 8 to 10 hp.

Some rocker ratios are different, but what this is showing is that the tolerances of the rockers are all over the place. They can vary from rocker to rocker in the same set even.

Some manufacturers choose to manipulate the rocker ratio in diff ways, like as an example, one may choose to move the cup, some may choose to move the tip roller centerline. This can change the initial ratio. Or better to think as 'the arc' of the rate.

Variance for TDC valve lift seems to be kind of low, like in the .001-.004 range.

'Advertised' rocker ratio is basically only to the .1 range. Like a 1.7 advertised rocker can vary from 1.700-1.799 .

So a better test would be to compare all the rockers of a SET of the same. That would show you the variance of tolerance across the same rockers.

If all the rockers in a set are the same ratio, or even varying .001-.004, the amount of performance difference will be very minor.

Not sure how this applies to the OP of 'pattern vs half-lift methods', but still interesting.


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[HWYSTR455]

Can someone post a link to the Dave V. test?


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[HWYSTR455]

In this pic from the vid, you can see the valve is not compressed at all:


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[steve25]

If your asking about what I posted up it was out of his second book on Big Block Chevys, so there no link to post.

[1975ta]

Hey guys,

Thanks for all the responses as they have been helpful. I decided to try a different set of rocker arms instead of my comp cams ultra gold. I am going to return them and I already have a set of Harland Sharpes on the way. I will post updates when they get here but I theorize that I will get some different results. I most likely will need different pushrods but we will see. They are the same ratio, that being 1.5.

[grivera]

Originally Posted by HWYSTR455

In this pic from the vid, you can see the valve is not compressed at all:


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Near the 7:09 mark, he rotates the poly-lock 7.1 turns, which moves the rocker off the established 90 degrees. At 8:04, he says you lower (unseat) the valve to re-establish 90 degrees. I believe the point of the light spring is so you can verify your measurements as he does at end of the video when he rotates the cam to the half lift point to illustrate the rocker is at 90 degrees to the valve.

[chuckies76ta]

I realize this might be over kill to some of you who are much better at this than me, but years ago Cliff had suggested to buy one extra set of the lifters, I would be using. Cut off the link bar and remove internals and stack washers to fill in the void and make the lifter solid for measuring push-rod length. At the time I was and still am a novice at all this stuff. Using the solid helped me verify my work with the springs installed on the engine. I did mostly everything in the guys video, then tried it with a checking spring and then I finished with the springs installed to check my work. I only run solids now, so I only deal with setting lash.

[steve25]

Yes, for solids be it roller or flat tappet that’s the way to do it.

With a hydro be it roller or flat tappet you run a very light checking spring so that the plunger does not compress.

Then once you find the length push rod needed you add .050” to that unless you plan on running near zero lash.

[HWYSTR455]

Originally Posted by grivera

Near the 7:09 mark, he rotates the poly-lock 7.1 turns, which moves the rocker off the established 90 degrees. At 8:04, he says you lower (unseat) the valve to re-establish 90 degrees. I believe the point of the light spring is so you can verify your measurements as he does at end of the video when he rotates the cam to the half lift point to illustrate the rocker is at 90 degrees to the valve.

Yeah I guess you could verify your measurements with a dial gauge on the rocker and move it to half lift with the adj pushrod in place if you want to be double sure. But the fraction you might be off by turning the poly lock is so small, it's not going to make a difference. And pushrods generally come in .050 increments as he mentions, so it's not going to be dead-nuts on regardless.

Usually pushrods are measured during an initial assembly, along with a number of other measurements. And think that's why in that particular video there's a checker spring on there. Like when you go to degree the cam and you still have it setup with the spring and pushrod in place. That gives you an op to verify open/close events, and determine true half lift of the cam/lobe.

If you want to get real technical, you would have to have the head gasket on there too when you measure (does not appear to be the case with the example vid). Or you can account for it when ordering pushrods. Like if you plan on using a .039 thick head gasket, you can add that to the length of pushrod you plan to order.

I've measured for pushrods when an engine is all together and in the car. I remove the locking nut from the adjuster pushrod so it doesn't hang up on the guide plate, and mark a line across the upper & lower halves. Can also wrap a piece of tape on it to keep it from moving when handling during removal.

Obviously you can't do the after check when you do it that way unless you have solid lifters, just be as accurate as you can when measuring.

Many people have a machine shop or builder assemble the heads, so it's a pain to have to swap over to a checker spring. So skipping the double-check usually occurs. Same for people who swap cams, lifters, and/or rockers, not doing the double-check.


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[HWYSTR455]

Originally Posted by steve25

...Then once you find the length push rod needed you add .050” to that unless you plan on running near zero lash.

Again, you never add/subtract lash when calculating pushrod length, because the lifter will pump up. Even for solid lifters you don't add/subtract. Solid lash is to account for thermal expansion/contraction/deflection. (possibly other factors too)

If you question it, contact a high-end builder and ask, someone who uses half-lift method.


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[grivera]

Originally Posted by HWYSTR455

He specifically says the lifter is on the base circle.

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Makes sense that it would be on base circle but I can't find where he says it in the video. https://www.youtube.com/watch?v=o5is9BsH5OU

[chiphead]

Originally Posted by steve25

Yes, for solids be it roller or flat tappet that’s the way to do it.

With a hydro be it roller or flat tappet you run a very light checking spring so that the plunger does not compress.

Then once you find the length push rod needed you add .050” to that unless you plan on running near zero lash.

This is the challenge, the lifter cup WILL compress with checking springs. I used the Straub video when I did my 434. I got a pushrod length with the Straub process. Then I tried to verify that length by rolling the motor through and verifying the pattern. Imagine my surprise when the pattern was off. Well, the Hyd Roller lifter was compressing when I was rolling it through, invalidating the pattern.

I also discovered something that was mentioned, the size of the roller wheel. Draw the line not to the center of the wheel, but to the tangent that actually touches the valvestem. This will yield a slightly shorter pushrod. Then add the desired preload and you're done.

You can't roll it through to check the pattern, unless you can approximate preload AND keep the lifter cup from compressing as you roll it through.

[67Lemons]

Originally Posted by grivera

Makes sense that it would be on base circle but I can't find where he says it in the video. https://www.youtube.com/watch?v=o5is9BsH5OU

This method seems almost too easy, better than any other method that I’ve seen. If it works then I guess it’s right?

[chiphead]

Originally Posted by HWYSTR455

Again, you never add/subtract lash when calculating pushrod length, because the lifter will pump up. Even for solid lifters you don't add/subtract. Solid lash is to account for thermal expansion/contraction/deflection. (possibly other factors too)

If you question it, contact a high-end builder and ask, someone who uses half-lift method.


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They never show the lifter in the BBC used as an example in that video. If it was a solid roller, then you don't have to worry about preload or lash to get the pushrod length right. But in a hyd lifter engine, the amount of desired preload will increase the pushrod length. If you wanted to run a deep preload like Cliff recommends, you'd have to add the amount of preload required to put the hyc lifter cup near the bottom of its travel.

[grivera]

I did like Cliff does, and then the math on the back end to come up with length.

[Formulas]

Originally Posted by 1975ta

Hey guys,

Thanks for all the responses as they have been helpful. I decided to try a different set of rocker arms instead of my comp cams ultra gold. I am going to return them and I already have a set of Harland Sharpes on the way. I will post updates when they get here but I theorize that I will get some different results. I most likely will need different pushrods but we will see. They are the same ratio, that being 1.5.

You will end up with different results those ultra Comp golds, ..... Have a dimension problem somewhere that makes them a bit whacky on a Pontiac

I have a set... I mocked them up on a iron 67-70 4bbl head with RA-IV valves and they looked much better in that situation because the valve tip ends up a bit closer to the rocker stud