Confused on rocker geometry
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mlrailguy
- Posts: 374
- Joined: Sat Nov 16, 2002 12:01 am
Confused on rocker geometry
Am getting my 2332 together, with the 1.5 ratio rockers. I took a few pics, and posted on here. Have read all the posts, but not sure I'm getting it. Is this what I'm trying to achieve? I don't have calipers, just eyeballing the halfway point of lift on pushrod. Thanks.
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Last edited by mlrailguy on Tue Apr 01, 2014 7:52 pm, edited 1 time in total.
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1432
- Posts: 9
- Joined: Sun Nov 25, 2012 4:56 am
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mlrailguy
- Posts: 374
- Joined: Sat Nov 16, 2002 12:01 am
Re: Confused on rocker geometry
OK, thanks
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r1cpowdercoating
- Posts: 210
- Joined: Wed Dec 08, 2010 9:37 am
Re: Confused on rocker geometry
Hey does anybody make a bolt on 1:25 rocker with out cutting your push rods?
Thanks
Thanks
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jrandy
- Posts: 498
- Joined: Wed Oct 03, 2007 10:39 pm
Re: Confused on rocker geometry
You are trying to split the sweep of the rocker tip across the valve stem.
If the pushrod is too short the rocker will not provide full lift.
If the pushrod is too long the rocker will go way over center. The valve may contact the piston top at full lift and the rocker may not back off enough to allow any lash which would leave the valve open when it should be closed.
The variables are cam lift, valve stem height, lash caps, rocker ratio, rocker block shims and pushrod length.
You must use an adjustable pushrod with light "checker" springs on the valves to check your rocker geometry. So, you need to remove your heavy valve springs and install light springs in place of them. I found some springs at the hardware store and cut them down to fit.
You can create your own adjustable pushrod with cut down stockers using a 1/4 inch tap, threaded rod and jam nuts. I have a few cut to different lengths for stock vs stroker engines that are often very different in overall width.
I usually check the piston deck height first to determine the static compression ratio & whether or not cylinder base shims will be required. Once I know that combination I install empty barrels with whatever barrel shims will be used with the heads and checker springs with no pushrod tubes.
With the barrels and heads in place you can drop in your adjustable pushrod and then install the rockers. You are only checking one valve at first, but once you have that measurement you can check some of the others on both sides of the engine before you start cutting your pushrods to fit.
With flycut heads, barrel shims, head gaskets, etc. as variables you have to use trial and error to figure it all out. It is not hard, but can be a bit confusing at first.
The rocker arm must 'sweep' across the valve stem. If the sweep is not split evenly you will get side loads on the spring and valve that will wear out the guides and may bend the valves.
VW aircooled engines will never be 100% perfect with the rocker geometry. You get it as close as you can.
Other things to check are cam lobe to lifter clearance, valve spring bind and rocker arm to valve cover clearance.
If the pushrod is too short the rocker will not provide full lift.
If the pushrod is too long the rocker will go way over center. The valve may contact the piston top at full lift and the rocker may not back off enough to allow any lash which would leave the valve open when it should be closed.
The variables are cam lift, valve stem height, lash caps, rocker ratio, rocker block shims and pushrod length.
You must use an adjustable pushrod with light "checker" springs on the valves to check your rocker geometry. So, you need to remove your heavy valve springs and install light springs in place of them. I found some springs at the hardware store and cut them down to fit.
You can create your own adjustable pushrod with cut down stockers using a 1/4 inch tap, threaded rod and jam nuts. I have a few cut to different lengths for stock vs stroker engines that are often very different in overall width.
I usually check the piston deck height first to determine the static compression ratio & whether or not cylinder base shims will be required. Once I know that combination I install empty barrels with whatever barrel shims will be used with the heads and checker springs with no pushrod tubes.
With the barrels and heads in place you can drop in your adjustable pushrod and then install the rockers. You are only checking one valve at first, but once you have that measurement you can check some of the others on both sides of the engine before you start cutting your pushrods to fit.
With flycut heads, barrel shims, head gaskets, etc. as variables you have to use trial and error to figure it all out. It is not hard, but can be a bit confusing at first.
The rocker arm must 'sweep' across the valve stem. If the sweep is not split evenly you will get side loads on the spring and valve that will wear out the guides and may bend the valves.
VW aircooled engines will never be 100% perfect with the rocker geometry. You get it as close as you can.
Other things to check are cam lobe to lifter clearance, valve spring bind and rocker arm to valve cover clearance.
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jrandy
- Posts: 498
- Joined: Wed Oct 03, 2007 10:39 pm
Re: Confused on rocker geometry
A 1.25 with stock style adjusters may install using stock length pushrods. However, when you go with the higher ratio rocker you need to use heavy duty pushrods anyway.
Pro builders told me to stay away from the 1.25 stock style rockers, so I did.
I finally got a set in a parts buy and tried using them and they are a pain.
Can't recommend them.
Pro builders told me to stay away from the 1.25 stock style rockers, so I did.
I finally got a set in a parts buy and tried using them and they are a pain.
Can't recommend them.