Hey,
I need some advise. I did a quick mockup last night on my new engine with a head, (brodix IK 180) lifter, rocker and a pushrod. Just to see what the geometry will look like. Brodix recommends a 7.9 pushrod. I started there. It was so long I couldn't even get the rocker to thread on to the stud! Then I got my length checking pushrod. Took it all the way to 6.9 before it started to look ok. Why is it so much shorter?? Its a standard 350 block with pretty standard alum heads. Is it just different geometry with the rocker arm??
Rockers are 1601 comp ultra pro magnum

 

I didn't see you state if it's roller lifter or flat tappet. Roller lifter is going to be near 7.2

 

Yep its roller setup in a roller block. Ive only done flat tappet before this.. Still seems odd that the full roller is .3" shorter. Maybe I will do another mocup and throw a stamped rocker on just to see what t comes out to.

 

well, I just checked again with the magnum rockers and now that are looking good with 7.2 (have not done a full test with marker etc as the heads are just sitting on the surface). Dont know what the hell I was thinking last night! I guess the roller vs flat tappet threw me off plus I was tired 😴 ...

 

Put the head on and went ahead and checked lenght. Looks like 7.150 is going to work for me. this was done adding washers inside my lifter to make it solid at 0 lash. Do I need to add .050 to account for hydraulic lfters and lash?

 

Generally yes. Add whatever preload you put into the lifter.
More importantly, recheck your pattern and adjust the pushrod length (I assume you're using an adjustable pushrod) and see how narrow you can get the sweep.
Width trumps a centred pattern.
Yours doesn't look bad but .030" is attainable.

​​​​​​There are measuring methods that go beyond the simple sweep check.

 

Thanks skinny z. Went at it again and the best I could get for a small pattern was 7.225. So if I do 1/2 turn preload (3/8 stud=.20) I should get 7.4-7.5 ish pushrods?

 

Stud pitch is 3/8-24. So 1 turn is .041".
So, half turn preload is .020".
Your 7.225" best length with the preload added is now 7.245".
Pretty sure you can get a 7.250".
7.3" will advance the pattern towards the exhaust side of the head. 7.2" will pull the pattern towards the intake side.
Folks tend to go longer on the dimension than shorter when stuck between available lengths.

 

Note the change in the pattern as you went longer on the pushrod.
It became narrower which indicates that you're moving the right direction.
And as mentioned, it has started to advance towards the exhaust side.
For experimentation, add another .10-.20" to the pushrod and see where it takes you.
FTR, it's looking like a reasonable result from here.

 

Thanks, had my math wrong there! I did go past 7.225 to 7.5 and it started opening up on me. Right now the pattern is .050 across. smallest I could get it.. I really appreciate the help here.

 

Are you using the running spring for your measurements or a checking spring?
If you've managed to make your hydraulic lifter more or less a solid with the washers you've described, then the running spring is the way to go. Otherwise you have to deal with the error that's induced when using the light weight springs.
Depending on the level of build and the strength of the actual spring, it can be a little or quite a bit.
For a guy like me, it's nothing to sweat over but I use an alternative method to validate geometry and the typical pitfalls that come up with the sweep method aren't a concern.
Still, I think you've got it well dialed in.

 

Im using the running spring. Stacked washers in lifter to make it solid.

 

That's the best way when possible.
For me, I have a link-bar style retrofit lifter. They can't be disassembled like the OEM versions. So I'm stuck using an alternative method.

This may interest you. Long read and some filler at the beginning but there's some good tech that follows.

 

Thats a good article.

 

That's how far the nut moves on the stud.

However, the push rod end of the rocker moves ((1 + ratio) ÷ ratio) times that, since the rocker acts as a lever. 1601 is a 1.52 ratio, if memory serves; so that means that 1 turn on the nut = (2.52 ÷ 1.52) × 1/24, or, about .069". ½ turn is about .035".

Jim's discussion leaves out one EXTREMELY critical point about as-manufactured rocker arms: his little plastic toy makes 2 unfounded assumptions: that ALL rockers have EXACTLY the same geometric relationship among valve stem tip, center of pivot, and push rod cup; AND, that all cam lobes have the same lift. NEITHER of these is true. Therefore while his "point" - which is that when the valve is exactly half open, the rocker should be "level" - is largely true, his application of it (the toy) is NOT.

For an alternative method of "solidifying" a lifter, filling it with some melted TransGel or Vaseline works well. Has the further advantage that you can just slap it into the engine as-is, and within a short time of startup, it will get warm enough to melt and will disappear without a trace or any extra effort.

 

I thought so too.
I use his mid-lift method for my geometry check. It has the advantage of being able to use the full running spring on a hydraulic lifter without the need for stacking it up like a solid. You don't even need the poly locks on the rockers.
Pretty slick really.

 

I can't say I recall Miller using any kind of plastic anything.
It's a simple measurement of the relatives axis' to a common plane. A little math and presto, you have your mid lift method.
No toys.

 

Which of course, is the problem. I personally don't know of any good way to do that, at least, not for yerbasic average home hobbyist. In theory, yes of course; in practice, not so much. It's one of those times where in theory, theory and practice are the same, but in practice, not so much.

As a mathematician, I wouldn't even call that "math", assuming you could obtain those numbers with sufficient accuracy. It's hardly even arithmetic.

https://www.summitracing.com/parts/pro-66789

There's a handful of things like these on the market. Can't recall if Jim ever sold one himself or not, but these are "inspired" by his opinions.

Best way overall for most of us to get accurate and reliable results is to solidify one of the lifters you're actually going to use - since just as all rocker arms aren't the same, all lifters aren't either, especially aftermarket ones that vary from stock-ish replacement such as Sealed Power or whatever - and an adjustable push rod, looking for the narrowest possible sweep on the valve stem, and then selecting a push rod slightly shorter than that (maybe by 1 increment or so) so that the "extra" (wider) sweep ends up at the upper part of the arc where the forces on everything are lowest, and the angle of the rocker tip's motion against the valve stem is more nearly perfect toward full-open when the forces are highest.

 

YES, YES, YES - someone FINALLY explained it correctly!

 

I can't imagine a simpler method for determining if the rocker is 90 degrees to the valve stem at mid lift than Miller's method.
No stack up of lifters. No frozen jello.
None of that.
Lay the rocker in position with the lifter on the base circle and measure.
I made a jig that's sandwiched between the retainer and spring which provided the reference plane. I measure from that to the pivot centres. I've used bar stock or even Allan keys as a measuring aid.




The "jig". Crude but effective. I've since made one out of flat stock cut to fit. I sandwiched this old school Vernier between the retainer and spring. I don't have a flat surface on the top of the retainer so I had to be inventive. If using a traditional retainer with a flat top, that can be used as the reference plane from which to measure.



Measuring from the trunnion axle centre to the reference plane. I've used a know piece of bar stock or in this case, an Allen key.



Measure at the other end. Finding the centre of the roller is easy enough.

No plastic tools involved. No stress on the lifter as you can see there's no poly lock on the stud. And a full running spring can be used although in my illustrations, that's obviously not the case.
Just a little arithmetic. It's handy to be able to work out fractions to decimals though. Does that make it mathematics?
Precision I'll say is fairly tight. Certainly to a couple of decimal places.
I've done a sweep after to verify (with checking springs) but found it wasn't necessary as there's little to no room improvement.
But as always, to each their own.
Please excuse the cat hair.

 

So what do you think of the quality of the heads? Valve job and port casting flash?? I'm thinking of a pair of these for a mild drag only 350...

What cam did you choose to go with them?
Thanks

 

This formula comes from where?
And the relative motion would change with respect to the angle the lever is to the valve stem no? That being maximum plunger travel is at 90° (or midlift if set up that way).

 

Comes from physics. You know, what you had in high school. The rocker arm is a lever. Same "formula" applies to it as any other lever.

 

I don't have my high school text books on hand. Can you represent the "formula" with a drawing?

 

Lever - Wikipedia