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If you can believe the below, I borrowed from another tech site, your valve train geometry being off has more effect on side loading of valve stem than cam lift.

Looks like reguardless of lift, valve train geometry being off is biggest factor in side loading and not cam lift. But maybe the higher the lift the more side load pressure applied so it becomes more important to run RRs if valvetrain geometry isn't corrected.


"A well designed and lightweight roller rocker can be of benefit in a high performance engine. With that said, and to answer your question, when is a roller rocker *necessary*? Well, the true answer is that there is no lift value, ramp style, or lobe shape that absolutely requires a roller rocker. If the valve geometry is set correctly, a non-roller rocker can be used for all but the highest of lifts and lobes that will normally be found in street application cams. Rollers are often used to reduce side loads with medium aggressive street cams simply because the builder is too lazy or doesn't know how to check and correct the valve geometry, in those cases the roller can help, but if the geometry is way off there will still be excessive side loads applied to the valve stems and guides.
The illustrations below show the basic contact patch that should be looked for when checking valve geometry. Some engine builders will look for a pattern that gets no closer than 0.050" to 0.060" to the edge of the stem, others, like myself, look for a pattern that is centered and has a *maximum width* of 0.050" to 0.060". A well centered and minimal contact patch will give the best valve train wear and performance. On a higher lift cam (for HD's and street use I consider this to be lifts exceeding 0.580") the combination of a roller rocker *and* correct geometry will usually result in maximum valve train longevity. How much longer than a non-roller setup? It's still a crap shoot, IMO. I've seen non-roller setups that have less guide wear than a roller setup with the same cam and vice-versa for a given mileage. In many cases I use them simply because the owner either demands them or is expecting them as part of a high dollar, high performance build. On a pure racing, no holds barred, maximum effort engine a lightweight, *stiff*, roller setup would be my choice for any pushrod motor. On the street? I tend not to go with super high lift, aggressive lobe profile cams so rollers are not usually necessary. I do have them in my own personal motor, but I could just as well have done without them. The choice is yours, I can build a motor with or without roller rockers that will likely last you a long time. If having roller rockers gives you a warm, fuzzy feeling, then by all means go for it. The difference between the two setups with respect to top end overhaul frequency will be negligable as long as the valve geometry is set correctly."




Play nice now.
 

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Right ON!
In a V8 we just change the pushrod length. Depends on how the cam manufacturer acomplished the added lift of the performance cam. Base circle, or added lobe? If distributed evenly the geometry would not be effected. Seldom is the case.
Sweating the details has rewards
 

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It is very true about valve geometry. Problem is there is only one porter I know who does set up the valve length to match the cams your running. When the Geometry is set correct the rocker should be 90* to the valve stem at 50% of the valve lift....if it isn't the valve stem has to be raised or rocker arm modified. Dan Basiley sets up the geometry on the heads he does for you, attached is a picture of his work I had done for a TW9B woods cam. Stock valve stems are even with the spring collar.The rocker arms where modified also, they are Dans roller rockers which he takes your stock rocker and installs his roller on it at the correct angle needed for placment on the valve stem. A bit more work but thats what is involved in setting up the Geometry. Notice the f i on the rocker...that rocker is fitted for the front intake only...it is FINGER PRINTED to the build.
Since most porters don't do this work builders play it safe by installing roller rockers at .550 lift and larger. The market today with off the shelf heads that are avaliable to you don't have the correct valve geometry set because the Mgr doesn't know what cam your going to use, so its a good practics to install the roller rockers with the higher lift cams. Setting up the geometry also insures you tha cam will open the valve to the correct height and timing. Now once a head has had the geometry set up for the cam used it wouldn't be advising to change cams in that build....the Geometry will be way off.
 

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Discussion Starter #4
Doc,

Would be interesting to see the pics, but I know the rule, "If your Moniker an't RED then attachments are dead".

If you think other Black listed members would be interested then PM and I will be glad to host them on my picture site.
 

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nw_guy4_fun said:
Just an FYI T-man Performance and John Sachs are a few of the many that are very aware of geometry and do correct it.
Thats good to hear and good to know....it is just one of those things that take time but does benifit in extra power and life of the valve.
 

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Discussion Starter #7
hdmd88 said:
It is very true about valve geometry. Problem is there is only one porter I know who does set up the valve length to match the cams your running. When the Geometry is set correct the rocker should be 90* to the valve stem at 50% of the valve lift....if it isn't the valve stem has to be raised or rocker arm modified. Dan Basiley sets up the geometry on the heads he does for you, attached is a picture of his work I had done for a TW9B woods cam. Stock valve stems are even with the spring collar.The rocker arms where modified also, they are Dans roller rockers which he takes your stock rocker and installs his roller on it at the correct angle needed for placment on the valve stem. A bit more work but thats what is involved in setting up the Geometry. Notice the f i on the rocker...that rocker is fitted for the front intake only...it is FINGER PRINTED to the build.
Since most porters don't do this work builders play it safe by installing roller rockers at .550 lift and larger. The market today with off the shelf heads that are avaliable to you don't have the correct valve geometry set because the Mgr doesn't know what cam your going to use, so its a good practics to install the roller rockers with the higher lift cams. Setting up the geometry also insures you tha cam will open the valve to the correct height and timing. Now once a head has had the geometry set up for the cam used it wouldn't be advising to change cams in that build....the Geometry will be way off.
For those that can't view Doc 's attachments, here what you see.



 

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I'm trying to learn about valve geometry. If someone can share these pic's I would appreciate it!!!!! Thanks

PS: if anyone knows a good link to info on valve geometry, shimming rockers to set geometry please send it to me!! ;-)
 

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quoted from Baisley Website..
When using our corrected geometry rocker arms the valve stem end will form a right angle (90 degree) to the centerline of the rocker shaft at half lift. At the same time the center of the pushrod ball, at half lift, will also form a right angle to the center of the rocker shaft. This gives equal arc motions above and below the center of the rocker arm shaft for both the pushrod ball travel and the valve stem travel.

Using corrected geometries provides control and stability of the valve train at high RPMs. Resulting in a more constant power curve as the RPM limits are raised.

Question: When do we recommend applying corrected geometry to your rocker arms?
Ans: A noticeable improvement in control and reliability will be found when corrected geometry rocker arms are used on cams with .625" lift and up. The greater the lift of the cam the more important it will become to use corrected geometry rocker arms.

Bottom line
The geometry is fine if the porter knows where to set the protrusion under .625" lift
Also what is not told, full lift is not achieved when the geometry is not optimized on those .650+" lift combinations
 

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Just an FYI T-man Performance and John Sachs are a few of the many that are very aware of geometry and do correct it.

nw_guy4 did my corrected set up with Baisely rollers, the 120 is very quiet top end and almost hit 25K miles on this set up. LOL tearing the motor top end off today and going to refreshed it along with new lifters.

heads and cyl. are going back up to Don,
 
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