After following this post> https://www.camaroz28.com/forums/sho...d.php?t=592005
and it's 200+ replies it was an eye opener to go to the links provided in the latter
part of the post and start reading. Especially the link to Mid-Lift information. >
http://www.mid-lift.com/TECH/TECH-Installed-G1.htm

I have spent literally hours, probably 10-20 hours searching, reading, and thinking about
how to properly select pushrod length, and in the end, still did it wrong. The mid-lift
web site is a very worth while read for anyone that really wants to understand and
properly set up their valve train geometry. I'd be willing to bet that I can reduce the
sweep pattern from .08-.100" (which it is now) to something like .03-.04" by going
back to longer pushrods that move the sweep pattern off-center towards the exhaust
side. What will be really ironic is if the stock length pushrods end up being the
best length. What a laugh, after spending $120 on a set of 7.05" pushrods to
end up right back where I started. I'll post up results when I know more.

Here is a part of the following post that I find very interesting >

http://speedtalk.com/forum/viewtopic...asc&highlight=

"Rocker Geometry is simple: JUST SET THE TRUNNION or SHAFT exact 1/2 of the NET valve lift Below the Roller Pin Axis, measured when the valve is in the closed positioned. It's that simple. Forget looking at foot prints (sweep), because that is a symptom. If you set as I just mentioned, you'll have the exact MID-LIFT geometry, which gets the ULTIMATE least amount of roll across the valve; and the maximum amount of CAM translation through the valve. MISS by only .010" of an inch, and you'll trade of several degrees of CAM information at the valve. So how important is getting ALL of your cam information to the Valve? All THREE dynamics: LIFT, DURATION and VELOCITY. Just because you have accurate "ratio" doesn't mean anything, if you don't set to MID-LIFT and get the other dynamics optimized too."

"Too close is roughly the last 20% of your valve stem diameter. As measured from the OD. If you're running .342" valves, you want the farthest sweep's edge (MID-LIFT) to be no more than .070" from the OD."

The issue of sweep mentioned above is exactly what I have now since I followed
some of the bogus information and set up for a sweep pattern centered on the valve
stem instead of a "minimum sweep" pattern that is off center. As stated above, I'm
going to pull the rocker covers and do some measuring and playing around with
the 7.2" pushrods and see what happens with the sweep. My only concern is that
I'll not have enough turns on the locks to feel comfortable since the rocker arms
will be moving upwards to meet the mid-lift criteria.

 

I find this very interesting too and I am definitely gonna play with my pushrod length checker when I install new springs next week.

 

15 minutes of reading and my head already hurts, i am going to go back over all of this when i get time and pull mine apart.

good post, thanks

 

Some good info there,I actually understand the mid-lift now....I need to go over mine.

 

That is my thread and on page two you can see very clearly(in all those pics) how the valve moves around on the stem with different lengths. And you can notice how the sweep gets less and less with the longer pushrod.

7.300 would give the best sweep, but it was a little TOO close to the edge for me!

 

There's no doubt in my mind!

 

I'm an engineer and quite thorough in everything I do and it frustrates me to no end that
I discover this now. Why did I not run across this in my searches when the damn heads
were off the car and I had tons of room and time to thoroughly look, measure, etc ?????
Not to mention the time and $$ I wasted doing the wrong thing.

Oh well, at least I know now. Your post with all the pictures, besides the awesome job
you did with the pictures, was a total eye-opener!! Thanks for the enlightenment
which showed me the correct path. I hope that others continue to find the right path,
save themselves time and money, and reap the performance gains from a proper setup.

 

 

It almost turned into a photography thread on one page!

Thanks, though!

 

damm I thought all I had to do was use the pushrod checker. Guess I
better start doing more research.I got some new heads coming and I need to figure out what pushrods I need.

 

Geez-o-peez-o! I have been doing pushrod length all wrong, (been trying to get a rocker tip centered on valve tip).
This is a great thread and thank you for it. Mid (valve) lift all makes sense now and the minumum sweep is the goal.
I'm sure the Jesel rocker sets I use have minimized my geometry error, (you have no choice in the geometry with shaft rockers accept for stand height).
But the couple of stud rocker motors I have built in the past might/could have had better geometry.

Keep learning always.

karl ellwein

 

Bingo! Shims.

 

Im installing new afr 227s and bolting on Jessel shaft mounts.From what I understand, it's going to be easier to get the right length, correct??

 

There should be more adjustability with the shaft mounts but from what I have read
shimming of the stands is not recommended. I would imagine it could be done though.

What has me thinking now is the .042" difference in intake vs. exhaust lift on my
baby cam. This is a .021" difference in half lift which means that to really get
things close I may need different length pushrods on the intake vs. the exhaust, or
lash caps on the exhaust valves to make up the difference.

This could be splitting hairs since you have the 1.6:1 translation with the rocker
arm. For my setup it's not worth worrying about, but for the really high HP setups
it could be important. I hope to pop the driver side rocker cover this weekend and
at least take some measurements off the #1 intake and exhaust just to see where I'm
at with the trunion axis to roller axis difference.

 

Maybe I'm missing something here, so please enlighten me. What's wrong with:
1. Install checking springs on the valves in place of the regular springs.
2. Install the adjustable pushrod.
3. Put a light coat of prussian blue on the rocker roller tip and install the rocker.
4. Rotate the engine in the direction of normal rotation and lengthen/shorten the adjustable pushrod until your rocker roller tip sweep is centered on the valve tip, as witnessed by the prussian blue pattern. While your at it check for adequate retainer to rocker arm clearance.
5. Measure the adjustable pushrod length; that is the correct length to be used.
6. Do this on both valves and repeat on a couple of cylinders to double check the results.

That's the way I do it and don't have any problems to date that I know of