Chatter lately about rocker shim plates?

[fairlaniac]

Lately I seen a few conversations about the use of, making of and production of rocker shim plates. A lot of this is new to me, not that I am a seasoned engine builder. So when are these required? I get the rocker to valve tip alignment but what causes the situation to use the plates?

Thanks,

[blykins]

When the geometry of the rocker arm is off in relation to the valve tip.  Sometimes we need to move the rockers up to get the pattern/geometry correct.  Sometimes we have to move them down, which obviously doesn't require shims but mill work.

In the rocker stud world, such as SBF's, you use the pushrod length to get the geometry correct.   With rocker stand engines, like the FE, you have to move the whole assembly up and down. 

[fairlaniac]

When the geometry of the rocker arm is off in relation to the valve tip.  Sometimes we need to move the rockers up to get the pattern/geometry correct.  Sometimes we have to move them down, which obviously doesn't require shims but mill work.

In the rocker stud world, such as SBF's, you use the pushrod length to get the geometry correct.   With rocker stand engines, like the FE, you have to move the whole assembly up and down.

So when does the need come in? On the only two FE's I ever played around with in the valve train I ordered custom length push rods to get my geometry to work.

I am asking because I am currently building my 427. I have not gotten to the valve train geometry yet but I wonder if I will encounter this issue? Hence my question, "how do you get to the point of needing a shim plate?"

thanks,

[blykins]

Custom pushrod lengths don't affect rocker arm geometry.

Rocker arm geometry is how the rocker arm interfaces with the valve tips.  Changing pushrod length on an FE doesn't affect rocker arm geometry, but for whatever stand height (which does affect geometry) you settle on, then the pushrods have to obviously work between the rockers and the lifters.

Simply put, rocker arm geometry is based on what kind of pattern you get on the valve tips, plus how much lift you gain/lose because of the geometry you end up with.  If the rocker arm tip rides the intake side of the valve hard, or the exhaust side of the valve hard, then you can get increased valve guide wear and reduced net lift.   Also, if you have a wide pattern, you're losing lift because the rocker arm tip is spending too much time moving across the valve tip instead of translating motion in making the valves go down. 

All in all, you want to try to have as narrow of a pattern as you can, somewhere near the center of the valve tip.

[fairlaniac]

Custom pushrod lengths don't affect rocker arm geometry.

Rocker arm geometry is how the rocker arm interfaces with the valve tips.  Changing pushrod length on an FE doesn't affect rocker arm geometry, but for whatever stand height (which does affect geometry) you settle on, then the pushrods have to obviously work between the rockers and the lifters.

Simply put, rocker arm geometry is based on what kind of pattern you get on the valve tips, plus how much lift you gain/lose because of the geometry you end up with.  If the rocker arm tip rides the intake side of the valve hard, or the exhaust side of the valve hard, then you can get increased valve guide wear and reduced net lift.   Also, if you have a wide pattern, you're losing lift because the rocker arm tip is spending too much time moving across the valve tip instead of translating motion in making the valves go down. 

All in all, you want to try to have as narrow of a pattern as you can, somewhere near the center of the valve tip.

That makes sense. I did have my contact pattern a little off center on my 390 that I built a few years ago. I put the .040" thk. drain back tins under my rocker stands to get the geometry I needed. I never knew some situations would require 1/8" or more.

Thanks for the explanation.

[e philpott]

Doug here's a good read for you http://www.crankshaftcoalition.com/wiki/images/a/ad/MILLER_ROCKER_HISTORY_MID_LIFT.pdf

Brent , doesn't having the adjuster " in " with longer pushrods have more lift than a adjuster turned way out to compensate for slightly shorter pushrods ?? I know we're splitting hairs and it's not quite the same as geometry with shims

[blykins]

Doug here's a good read for you http://www.crankshaftcoalition.com/wiki/images/a/ad/MILLER_ROCKER_HISTORY_MID_LIFT.pdf

Brent , doesn't having the adjuster " in " with longer pushrods have more lift than a adjuster turned way out to compensate for slightly shorter pushrods ?? I know we're splitting hairs and it's not quite the same as geometry with shims

Absolutely.  The adjuster way out makes the pushrod "walk" without translating to movement that opens the valve.  I like seeing the adjuster up into the rocker body as much as I can make it go.

[Joe-JDC]

This adjuster all the way in, depends on if the stand height is correct.  The stand height will affect this as well as the stand placement.  If you move one or the other, then the actual valve lift may not change, or change negatively.  I have proven this by moving the stands around, the height up or down, and the adjuster travel with a dial indicator on the retainer with the run springs in place.  You CAN manipulate the lift somewhat by using all these to your advantage.  A checker spring will give false readings if using aluminum rocker arms.  They deflect with the run springs.  You will lose ~ .020-.025" lift with a strong run spring and aluminum rocker arms.  The more correct the geometry is, the less affect the adjuster will have on valve lift.  Joe-JDC

[blykins]

This adjuster all the way in, depends on if the stand height is correct.  The stand height will affect this as well as the stand placement.  If you move one or the other, then the actual valve lift may not change, or change negatively.  I have proven this by moving the stands around, the height up or down, and the adjuster travel with a dial indicator on the retainer with the run springs in place.  You CAN manipulate the lift somewhat by using all these to your advantage.  A checker spring will give false readings if using aluminum rocker arms.  They deflect with the run springs.  You will lose ~ .020-.025" lift with a strong run spring and aluminum rocker arms.  The more correct the geometry is, the less affect the adjuster will have on valve lift.  Joe-JDC

Joe, as you say, most rocker arms have engineered deflection built into them.  If you use a checking spring, then you will see a goofy amount of lift, as in way too much.  They are made with "over" ratio so that when you apply a real spring load, you don't lose so much lift. 

With a 400 lb valve spring, my non-adjustable rockers will lose about .010" lift when dialed in correctly, usually with about a .040-.050" pattern on the stem. 

[cammerfe]

Custom pushrod lengths don't affect rocker arm geometry.

Rocker arm geometry is how the rocker arm interfaces with the valve tips.  Changing pushrod length on an FE doesn't affect rocker arm geometry, but for whatever stand height (which does affect geometry) you settle on, then the pushrods have to obviously work between the rockers and the lifters.

Simply put, rocker arm geometry is based on what kind of pattern you get on the valve tips, plus how much lift you gain/lose because of the geometry you end up with.  If the rocker arm tip rides the intake side of the valve hard, or the exhaust side of the valve hard, then you can get increased valve guide wear and reduced net lift.   Also, if you have a wide pattern, you're losing lift because the rocker arm tip is spending too much time moving across the valve tip instead of translating motion in making the valves go down. 

All in all, you want to try to have as narrow of a pattern as you can, somewhere near the center of the valve tip.

That last sentence virtually says it all!!

KS

[blykins]

Trick Flow head with .200" whacked off the bottoms of some T&D street rocker stands:



CJ head with my non-adjustable roller rockers:



Profiler BBF head with Jesel rockers:



I spend a lot of time getting the geometry nailed down.  As you can see, the mark doesn't have to perfectly centered, but you have to balance the width and the location. 

[447 Stroker]

Gah, Needed a good set of shims about 3 months ago. 

[Cobrajet2]

Custom pushrod lengths don't affect rocker arm geometry.

Rocker arm geometry is how the rocker arm interfaces with the valve tips.  Changing pushrod length on an FE doesn't affect rocker arm geometry, but for whatever stand height (which does affect geometry) you settle on, then the pushrods have to obviously work between the rockers and the lifters.

Simply put, rocker arm geometry is based on what kind of pattern you get on the valve tips, plus how much lift you gain/lose because of the geometry you end up with.  If the rocker arm tip rides the intake side of the valve hard, or the exhaust side of the valve hard, then you can get increased valve guide wear and reduced net lift.   Also, if you have a wide pattern, you're losing lift because the rocker arm tip is spending too much time moving across the valve tip instead of translating motion in making the valves go down. 

All in all, you want to try to have as narrow of a pattern as you can, somewhere near the center of the valve tip.

At what point does the width of your valve tip pattern warrant messing with raising or lowering your stand heights? I have read 12% to 15% of your pattern width to your cam lift. Would everyone here agree? I am at about 16-17%, worth messing with on a street motor?

Mike

[blykins]

Custom pushrod lengths don't affect rocker arm geometry.

Rocker arm geometry is how the rocker arm interfaces with the valve tips.  Changing pushrod length on an FE doesn't affect rocker arm geometry, but for whatever stand height (which does affect geometry) you settle on, then the pushrods have to obviously work between the rockers and the lifters.

Simply put, rocker arm geometry is based on what kind of pattern you get on the valve tips, plus how much lift you gain/lose because of the geometry you end up with.  If the rocker arm tip rides the intake side of the valve hard, or the exhaust side of the valve hard, then you can get increased valve guide wear and reduced net lift.   Also, if you have a wide pattern, you're losing lift because the rocker arm tip is spending too much time moving across the valve tip instead of translating motion in making the valves go down. 

All in all, you want to try to have as narrow of a pattern as you can, somewhere near the center of the valve tip.

At what point does the width of your valve tip pattern warrant messing with raising or lowering your stand heights? I have read 12% to 15% of your pattern width to your cam lift. Would everyone here agree? I am at about 16-17%, worth messing with on a street motor?

Mike

I don't think that 12-15% rule is too applicable.   The BBF up above has .950" net lift.  The CJ headed engine above has .630" lift.  A 12% pattern of .630" lift is .075", and to me, that's unacceptable with a roller tip rocker in most cases.  If it were a shoe style rocker, I'd probably reconsider that statement. 

IMO, you have nothing to lose if you try to make it better.  I've seen gains of .020-.030" lift by correcting the valvetrain geometry, which can be substantial in some applications, even some street applications.  Just imagine a situation where you have a camshaft with .350" lobe lift.  In a perfect scenario with a 1.76" rocker ratio, you should get .616" of lift at the valve.  However, you're gonna lose probably .010" to pushrod deflection.   If the geometry isn't right, you can potentially lose .030" of lift, or possibly even more.  So now, instead of .616" lift, you're looking at .576".   That can make a difference.