TheSamba.com :: View topic - Understanding 1.4 slipper foot rocker geo. Not elephant foot.

Mon Sep 03, 2018 6:39 pm

This thread is for 1.4:1 slipper foot rocker geometry, only!
If you have questions on elephant foot rockers.
There are plenty of threads on that subject.

So I have an AA 1.4:1 slipper foot rocker arm geo issue on my hands. That I'm having a hard time understanding.

The rockers slip over the valve stem at a rather low ratio. In my opinion, that causes the rocker (ATM) to pull the valve stem toward the rocker shaft. Causing premature valve guide wear.

So let's look at what I have currently.

The rocker at "0" lift.

The rocker at 1/2 lift,

And finally, full lift.

The above pics were without any shims under the rocker arm supports.
I'm under the impression that the "0" lift and the full lift should be at the same point on the valve stem.

I have a set of Scat rockers on order that should be here this week.
I will compare them to the AA rockers once they arrive.

So am I way off on the geo on the valve stem side of the rocker?

I'll work out the PR end once I get the valve side of things figured out.

Any help would be helpful.

Mon Sep 03, 2018 6:55 pm

I would layout dye the foot of the rocker and mark the center of it with a sharp scribe and do the same on your lash cap. Move the valve to 50% lift. Then shim the rocker stands till the marks line up or as close as you can reasonably get to it.

I thought with the use of lash caps, the shims are a given.

Wed Sep 05, 2018 1:05 pm

Put your indicator on, and get things at 1/2 lift.

Then make your marks.

Cycle thru the open/closed of the valve, looking carefully at full open and full closed valve.
They should both be an equal number of degrees away from your 1/2 lift mark.

Said another way,
Your adjuster screw should sight straight down the pushrod at 1/2 lift..

It's hard to tell these things sometimes from a pic vs. looking in real life.

Wed Sep 05, 2018 1:34 pm

it will probebly be perfect if you mill .040~.050" off the rocker blocks. be sure to do them square. also check to be sure the rocker tips are square to the rocker shafts. but no the rocker will not end up in the same place it is a foot and what do foots do? walk. but you do not want it to walk off the top edge at all.Ive not seen a 1.34 or 1.3 rocker that did not need at least .040" lowering to get them right .( execption some of the needel bearing real nice looking rockers need to go oh so much lower than that to work right)
if you leave it to high it will kill guides in most cases especialy with a high lift cam. a .320" cam may be fine.
I did a 1.4 rocker with a hyd cam , it was low lift lobes and it still ended up being .040 lower to get the geo right. I think when all that stuff was figured nobody took the thickness of the lash cap into account...go figure they were after all... just engineers that know everything. ( I had a run in with a engineer at the post office today...hard headed, it has to be done like this or the world will....but thats another story)

Wed Sep 05, 2018 4:57 pm

Do you want to know how things are, or how they should be?
We've been through this so many times.
With some topics practice does improve how easily it can be explained, but this might be an exception.

The short list is-
-Top of lash cap to rocker shaft center should be 90 degrees at 1/3-1/2 lift
-contact patch starts low and climbs high at 90, but past 90 can stay near centered if tips are ground to a good curve.
-SINCE the contact past 90 does not fall, the valve side ratio is increasing as it goes past 90, to counter act this the pushrod pivot is moved to hit 90 much later, so the decreasing ratio on the pushrod side counter acts the increasing ratio on the valve side. however this is not a perfect relationship, as a result this isn't a constant ratio design. the ratio will change as you shim the rocker shaft or change the pushrod cup adjustment.
-is milling or shimming the rockers the right way to change the wipe pattern? not necessarily.
does fudgeing wone thing to fix another sometimes work ok? sure, but be aware the ratio will change. If you already have the springs shimmed for a certain lift then, oops, or, that would be a consideration far as what part needs 'fixing" if any. i can't think of any other explanation. it's one of those things.... makes you think other people know something you don't, but sometimes that isn't the case. it's a lever. IMo if the tips aren't right then they should be re-ground, and if the contact is wrong the rockers should be moved up or down, not outward or inward. there is a lot of fudge things a long way but if you go too far the ratio will become WAY higher and/or angles more extreme.

Wed Sep 05, 2018 6:15 pm

Rugblaster, clatter, Mark Tucker, modok,
Thank you all for the advice.

Rugblaster, I tried to scribe a mark across the lash cap (successful) and the side of the rocker foot (unsuccessful). The AA rocker foot is too hard to make a clean scribe mark on. But then I have old tired eyes that makes it difficult to see the fine line, I'm trying to scribe.

Clatter, Thank you for the simple explanation and guidance. I'll have another look and see if I can get it straightened out.

Mark Tucker, if I machine off 40-50 thou off the rocker stands. That will place the "0" lift further toward the heel of the rocker foot. In my mind, that will cause the rocker to pull the valve stem toward the rocker arm shaft. I'm likely wrong on this. But I cannot take the chance of loosing another head do to my possible setup error.

modok, I'm not looking for sugar coating. I want to do this right and have an engine that will last many thousands of fun miles.
Do you want to know how things are, or how they should be? My answer to this question is yes. How things should be.

I read almost all of what you all post and have respect for your incite and wisdom. You guy's are some smart, talented, craftsmen.

Based on all of your advice. I now believe I have a path forward and can get this geo problem worked out.

The whole reason for this thread is, That most all of the threads that I read over the weekend blended the rocker adjuster over the valve stem and the rocker adjuster over the PR. But that became confusing when trying to separate the wheat from the chaff.

Adjuster over the valve stem. Pretty straight forward.
Adjuster over the PR not so straight forward.
Hence this thread.
Maybe someone can glean good information from this in the future and not have to post stupid questions like this again.

Thank you! You guy's rock.

Wed Sep 05, 2018 9:26 pm

In all your pictures your not at the actual high point of the rocker. That’s where the problem is. I can see shortening or shimming fixing it to some point. But your pushrods will need to change length. Hopefully they haven’t been cut yet.

Thu Sep 06, 2018 1:54 am

what about flipping the rocker stands upside down? might make it worse but trying it is free

Thu Sep 06, 2018 12:07 pm

the rocker does more walking at low lift than pulling, infact it is going the other way at low lift thus the walking., also less pressure so sliding is eazer than at full lift. at full lift if the rocker is high it does inface pull the stem tward the shaft killing guides. it is also common practice with very expensive rocker systems( T$D and Jessel) when the cam lob lift get so high the rocker pivot is lowered so the gep will be right at full lift where the max pressure is at. and dont ferget if you mill .050 off the rocker blocks do them square to the shaft and all the same, then if you dont like what you think you see you can shimm it back. good luck. I only have about 135000 miles on these guides in my heads, they seem fine.but I only have .420 lobe lift. x ratio=

Thu Sep 06, 2018 6:49 pm

Mark, Do you have Scat rockers? I ask because I received my Scat rockers today and when checking them out. I now understand what you are talking about.

At "0" lift the PR end is just about 90° to the adjuster on the rocker. So lowering the rocker bases makes sense with these new rockers. At half lift, the Scat rockers over the PR are way far from the ideal 90° at the adjuster.

The AA rockers were the opposite. At "0" lift the rocker was at an angle. At half lift the AA rocker adjusters were almost perfect to the ideal 90° over the PR.

All that said. The Scat rockers are better at the valve stem end. Well really just better overall quality wise.
The foot slides over the lash cap properly. If the rocker blocks are machined down .050" the adjuster end should be ideal at half lift as well as the valve stem end being at the proper angle at half lift.

Thank you all again for your help getting me to understand just how to get there slipper foot 1.4:1 rockers sorted.

Have a great evening.

Thu Sep 06, 2018 7:15 pm

Maximum FORCE on the adjuster screw will be at the opening and closing ramps, so if it was going to break that is where it would happen, at high rpms.
It's can be argued either way, taht the adjusting screw should be straight near closed or straight at half lift, both make sense, as long as the pushrod joint is not binding, both should work.
I don't think the scats need correcting.

Thu Sep 06, 2018 9:58 pm

Oh, man, there is just too much to this subject at times;
So many different combinations of parts from different places..

There are many respected (VW) builders who pontificate the benefits of rocker-shaft-center-90’-to-top-of-lash-cap at 1/2 lift out there.
Said another way; plane of lash cap top cuts rocker shaft thru the middle at 1/2 lift.
And we can all agree the benefits of this in theory;
The thrust loads generated against the stem/guide are likely to be most minimal if we deviate from 90’ as little as possible.
Therefore, if we are exactly 90’ at half lift, thrust angle is split/similar between full lift, and closed valve.

Having deciphered :) what mark is saying, I can fully understand his reasoning for having 90’ come after 1/2 lift.
Especially considering the difference in loads of initial/low, vs. full/upper lift..
V8 world does this; try to re-read what he says about these things, and it can make sense.
It also shows why he is a fan of milling rocker blocks..

Next time I do a serious motor, I think i’ll err a bit on the side of 90’ after half lift..
If (when) there’s some inevitable error in your setup, have it be that way.
Sometimes you can’t see your error, so if you can, put it for certain on the right side of the theoretical towards the other guy’s theory..! :wink:

Also mark your lash cap with some blue;
That can give you yet another reassurance that you’re on the right track.
Having the wipe mark go across the center of the lash cap feels good.

-but-

If this all becomes gibberish,
Adjuster screw sighted straight down the push rod at 1/2 lift will get you set right..

Fri Sep 07, 2018 1:25 pm

the pushrod has nothing to do with the rocker to valve geo. the pushrod has a ball joint. you are setting the rocker to valve geo.if you break adjusters you have interfearance issues.or the adjuster is hung way too farr outt
if what modock says is right..... when you turn off the engine and a valve is at full lift the adjuster has less pressure than the valve that is closed......dont wory about the pushrod end.execpt for pushrod to tube clearance. of coarse modocks thinking/theroy may work in austraila..

Fri Sep 07, 2018 4:56 pm

mark tucker wrote: the pushrod has nothing to do with the rocker to valve geo. the pushrod has a ball joint. you are setting the rocker to valve geo.if you break adjusters you have interfearance issues.or the adjuster is hung way too farr outt
if what modock says is right..... when you turn off the engine and a valve is at full lift the adjuster has less pressure than the valve that is closed......dont wory about the pushrod end.execpt for pushrod to tube clearance. of coarse modocks thinking/theroy may work in austraila..

It’s all a system. So while I agree you don’t need to worry about the ends of the pushrods, you still need to worry about their length. Having to mill the rocker stands seems like an unlikely necessity unless you’re doing something one off.
But, I probably don’t know what I’m talking about

Fri Sep 07, 2018 5:48 pm

Every motor is one off. Getting the rockers lower brings the swipe closer to the rocker side. If you need to go that way, that’s your option.

Sun Sep 09, 2018 6:07 pm

Ok, so here's where I ended up.
"0" lift,

Half lift,

Full lift,

This is with a .060" shim under the rocker stand.

While the "0" and half lift look pretty good.
The full lift is severe.

Interesting that I can feel the pressure fade away as the rocker reaches full lift.

What ya'll think?

Sun Sep 09, 2018 6:30 pm

Interesting. The valve end of things looks fine from here but as I said before I can't really see the contact.

Why the .060 shims?

Sun Sep 09, 2018 6:44 pm

modok wrote: Interesting. The valve end of things looks fine from here but as I said before I can't really see the contact.

Why the .060 shims?
The center line of the rocker shaft didn't line up with the valve stem/lash cap. When I installed the rockers without shims.
Hence the .060" shim.

Since I'm in the build phase of things. I can post a pic of the rocker shaft without the shim. To give you a better idea of what I'm dealing with.

Please define the contact that you are asking about? Do you mean the alignment with the lash cap to the rocker foot?

Sun Sep 09, 2018 6:56 pm

Use a sharpie on the lash caps. Where is your swipe pattern. Looks to me the shims need to go bye bye.

Sun Sep 09, 2018 7:40 pm

You have to get the pushrods out of the equation. At least at the start. Photo 1, at least to me, looks like the right geometry at half lift not 0.....I would try to imagine a 90-degree angle from the CENTER of the rocker shaft to the midpoint of the rocker foot and the other leg of the angle being the center line of the valve stem. Can you see in the first photo how the pushrod appears in the same line as the adjuster screw? That is the way you want it to look at half lift. All you may have to do is shorten the pushrods.

Prop the valve open at half lift and get the rocker foot looking like photo 1.....however you have to do it....remember the 90-degree deal at half lift.

Then, after that step is done, using an adjustable pushrod, measure how long your pushrod needs to be. Folks get these steps in reverse order. To my way of thinking, doing it any other way is silly.

Like has been said, it is desirable to have the wear pattern to be in the center, meaning equal distance, top and bottom across the face of the lash cap. given the inadjustability, up and down, of the rocker shaft, this may be difficult to obtain.