Hi all,

Was reading an article on rocker geometry the other day, and a point was made that seemed to make sense to me but condradicts other opinions.

Why do we want to see the pushrod perpendicular to the rocker arm cup at half lift?( I understand the valve side doing this.) wouldn`t we want the pushrod perpendicular at full lift when the springs see`s maximum pressure.

The guy that wrote the article had build 100`s of engines this way, and basically said don`t get caught up with the pushrod 1/2 lift-perpendicular thing as it doesn`t make engineering sense.

What do you think?

Regards, Keith.

If you had it perpendicular at full lift then your pushrod ball end would be on a dramatic angle compared to the cup at no lift..........and that makes less sense from an engineering point of view !

Maximum pressure created by the valve springs is not going to change the "load" by much on the pushrod if its perpendicular or not.

alot of work on one side of the cup

The load will change Craig, as the distance from center line of the rocker shaft is decreased so effective load on the push rod will be more than it was when geometry is set conventionally

You can effectively change the ratio of the rocker arm by using a pushrod that is a little on the long side

As the rocker moves past centre the ratio increases

no that would only change lift characteristics not ratio. I always thought maximum load was when its ramping not at max lift position.

Kind of like "it takes more effort to lift something than it take to keep it up after being lifted". Also like riding up a hill on a bike. hardest part is half way and moving up. then its easy once on top.

So the half lift geometry is correct in my view.

you contradict yourself there

When i was first setting my geometry i started out almost perpendicular at full lift and yes, the angle at zero lift was pretty wild. I had to relocate the studs to get it right at both ends.

Not saying i agree with the fellows view, just thought it would make good discussion and maybe learn something along the way.

Regards, Keith

The reaon for saying "pushrod perpendicular at half lift" is just used to simplify the geometry process.

The priority for stem and guide life,
is to have minimum and central, and smallest, sweep of the rocker arm on the valve tip.
(up and down, not left to right)

The pushrod angle, being nice, is second most important.

The other thing to note is: what do you want?
The above requirement is for long (hopefully) stem and guide life.

If you want maximum lift, and are prepared to suffer the cosequences,
then poor geometry CAN add lift and the power that comes with it.

morning dave, the voice of reason!!!!

Bloody DB, correct again, primary concern ic valve guide side loads for head longevety. Certainly the ratio does change with this wierd method, I believe the f vee guys do something similar to get crazy lift for the same cam profile.

Dave,

Do they use pushrod perpendicular at 1/2 lift reasoning because this then means the valve side geometry will be right?

I assume by not having the pushrod go thru centre up to full lift, that this then changes the ratio by giving more lift.

Could one set the valve side geometry perfect, whilst having the pushrod side favour the "one side" of perpendicuar to give more lift than the rocker should.?

Cheers, Keith.

less friction .more power.
i quess there is going to be more strain on the valve train,unwanted strain for little gain's,and were his test's done on pushrod's that had a straight angle from lifter to rocker's.this would also make adifference in loads on the valve train.
2 cent's is up.
cya.
zoom mag issue150,what a great mag.hint hint.

Hi

Sorry to drag up an old post.

I attempted to fit a set of 1.4 rockers to my sons motor, the photos tell the story. It looks like the rocker post stud would need to be shifted to make the pushrod have a better angle.

Steve

Hi Steve, you need to shim the rocker gear to improve the angle, then get appropriate pushrods and set the length to suit. The lower pic looks to be at full lift, that is the angle of pushrod to adjusting screw angle (in line) your looking for at 1/2 lift, so the angle should be equal at zero and full lift each side of straight at 1/2 lift !!
Set the rocker height to get the angles you need, then get the pushrod length sorted.
Is the cam for 1.4 rockers.....it MUST be compatible.

Hope that helps.

Hi Matt

Its an AP2 cam. I didn't want to go to wild for a P plate driver, its a great cam but I now wished I had gone up a little in specs. I've used 1.4s on a stock WBX cam and Berg equivalent Engel 100 without any issues.

I had an adjustable pushrod in there, I tried all sorts adjsuter screw positions, shims and pushrod length combinations and I couldn't get it any better, you can only go so far out with shims as the angle of the valves and the rocker studs converge.

I have no idea what brand rockers they are, I bought them at a swapmeet cheap.

Steve

They are Sig Erson rockers, and are most likely 1.5s.
They made 1.5s ad 1.65s from memory.
Those are not the original adjusters that they came with,
so make sure the oil path is still flowing to the shaft.

Moving the stud hole can help the pushrod angle, but hurt the valve side,
which is your primary reason for doing the geometry in the first place.
For future reference, you can offset the hole using a timesert designed for 10mm threads.
(what I use for a case saver when increasing head stud size).

I would like to see less adjuster hanging out ,
(one turn from bottomed on the underside of the arm, while makng sure oil can still flow to the shaft).
With the adjuster closer to the underside of the arm, you may be getting a better comprimise.
The small shim may get the adjuster on less angle at zero lift,
but winding the adjuster closer to the arm's underside will be a better scenario if that will work.

What you have now will work, being that the tip sweep is priority,
but I would like to see it a little nicer on the pushrod side too.

So... more thread out past the nut, and a longer pushrod.
Make sure the rocker covers still fit too!

Hi

Thanks for the help & replies.

I had another fiddle and I got it a lot better as far as the pushrod angle to adjuster goes. My major concern now is how close the pushrod is to the pushrod tube. I will try these suggestions.

I thought Berg always said to about 1 3/4 threads poking out of the adjusting nut.

I'm going to build up a 2442 oxy boxer down the track but I just wanted to get a little more pep out of this one.

Steve

are the sig erson rockers any good? how reliable are
they?

They are OK for what they cost,
and made from cast iron.
I have seen a few sets with worn out pads, but only one broken one that was abused.

By comparison, I have seen every other brand break from various causes
so these things are OK in my book.

The original adjusters were a male shape rather than the conventional cup style,(likeChrysler V8s),
which, while it is a good set up, it is unconventional.(so requires the correct push rod end),
so most people change to a more easily avaiable style of adjuster.

Hi

I measured the location of the oil holes in the rocker to the adjuster screw, they need the adjuster screw roughly where I had it in the above photos.

I'm not happy with pushrod angle so I might not fit these now.

Steve

Ive got the same old sig erson rockers on the stock cam in my 1600. Ratio came out a little under 1.4 from memory, using shortened stock pushrods and setup in the usual 1/2 lift lash adjuster in line with the pushrod. I need to re shim mine when I pull the motor apart again, they use a slightly different size shaft I couldn't find the right shims for at the time, although it's setup ok it could be a little better I think. What side clearance do people run on their rockers?

Hi Steve,

i found lash caps have different thickness on their heads and used a few different sets to help sort the angles.

Daimo