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  #16 (permalink)  
Old 10-19-2012, 01:44 PM
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when brown did that the photo tech wasn't really there to "see" the roller moving
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Old 10-19-2012, 01:57 PM
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It will be a problem when using stock or roller tip rocker arms if your engine has restricted lifter oiling and/or high valve spring pressure. Marginal rocker arm oiling will burn up and seize the rocker balls (metal sliding on metal). That is one reason why full roller rocker arms were introduced by Harland Sharp for 1965 FI Corvettes using a 30-30 cam and restricted oiling edge orifice solid lifters.

If you are using short or reduced travel lifters with restricted valve train oiling, do not use stock or roller tip rocker arms.
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Old 10-19-2012, 03:21 PM
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You mentioned just using aluminum rockers, what is the max spring pressure recomended. i have seen anywhere from 350-800 . i have also heard of people highly disliking them because of strength issues.
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Old 10-19-2012, 03:48 PM
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Quote:
Originally Posted by birkey View Post
You mentioned just using aluminum rockers, what is the max spring pressure recomended. i have seen anywhere from 350-800 . i have also heard of people highly disliking them because of strength issues.
The manufacturer's specs on a particular will tell you the seat and open spec.

If in doubt, there are always the $tainle$$ steel versions to consider.

Dave W
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Old 10-19-2012, 04:08 PM
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Originally Posted by birkey View Post
You mentioned just using aluminum rockers, what is the max spring pressure recomended. i have seen anywhere from 350-800 . i have also heard of people highly disliking them because of strength issues.
Use just a little more than your cam calls for thats it. If it says 100 lbs seat then you wont need anymore than that on a normal build. Behive springs can even lower the seat pressure a little more.

350 is alot for street use should cover most cams that are considered street able. Anything to much more than that and the valve seats will need to be freshened up every 10K miles or round abouts. Its better to go with lighter valves and retainers than it is to use heavier springs.
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Old 10-19-2012, 04:35 PM
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I realize that there are many threads concerning this topic but i want to hear some opinions now. Do they actually help with friction? Is there an actual hp gain? Or is this all hype??
Where they really help is the fulcrum. The ball and socket is very highly loaded and becomes a problem to lubricate and cool as the amount of lift and the frequency (RPM) go up. These things in a competition engine will fry themselves to death, the steel of the socket will blue than burn black and if you persist crack and fail around the ball, you can guess what happens next.

The roller tip somewhat less apparent, I suppose, as a friction reducer, it certainly makes it easier to see where the tip is actaully pushing on the valve stem tip compared to the sliding shoe of a conventional lifter. There is a small amount of tunablility here for a couple percent of lift depending on whether you center the contact point at mid lift or full lift.

Regardless of the engines end use once lift starts getting into the range .5 inch, I just install roller rockers as a matter of course unless class rule prohibit it.

Bogie
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Old 10-19-2012, 06:06 PM
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Is there a big difference in life expectancy between aluminum and stainless?
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Old 10-19-2012, 07:34 PM
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Is there a big difference in life expectancy between aluminum and stainless?
Yes, the problem with aluminum is fatigue the constant load changes finally gets to them although they start with a material that has about the same strength as stainless it just tires faster as it laod cycles.

Stainless also offers the benefit of being narrower which is a problem with center bolt covers and aluminum rockers, sometimes there just isn't enough space for both. While you can and I have kissed the sides of the rockers for clearance you can see that it doesn't improve the fatigue issue.

I have run a set of Jim Millers aluminum PVS's on the street now for nearly 10 years and a about 350,000 miles, but he doesn't make them any more. They are sturdy pieces, but do make for a crowd under the rocker cover, hard to even get a breather baffle in there.

Bogie
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Old 10-20-2012, 06:44 AM
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Is there a big difference in life expectancy between aluminum and stainless?
If you take a bar of aluminum that take 100 lbs to brake and start pulling on it with 10 pounds over and over again it will snap at some point. Steel will not fail in the same manor. It will take its full force over and over again.

That being said. The ones that i have seen fail. Its always the little steel wheel that craps out. It gets chipped or burned up and once it starts to fail it goes fast. As others have said may be because lack of oil and it takes the most abuse. For the most part good name brand rockers should last you a long time. I would focus my worries on getting them installed and adjust properly. That is what causes most rockers steel to titanium to fail. The wheel not lined up so it rolls off the edge of the valve stem. All rollers only work if the wheel glides across the top of the stem and never rolls down the edge. They can fail very quickly if the stem is not under the wheel at max lift. Its not ok for them to roll over the edge of the valve stem.

Hope that make since. In the real world buy the ones your cam manufacture recommends or sells. Mostly for the reason of support during install and warranty. If your entire vavle train is comp then comp can help you set everything up and will stay on the phone as long as it takes to work any issues that come up. If it all a bunch of mixed up stuff they will help but its not there products so they have no information on them and how they work together. Get the good stuff from a top manufacture they will know how to fix it and whats not going to work togther before you pull out the credit card.
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Old 10-20-2012, 11:44 AM
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I am using Scorpion narrow body, self-aligning, 1.5 aluminum roller rockers. I used more expensive Manley SS valves with a .290" tip in lieu Ferrea SS valves that have a .250" tip. The longer valve tip put the rocker arm self-aligning roller in the center of the valve stem throughout it's arc. The extended tip also allowed for an extra .040" rocker to valve lock clearance for the self aligning rocker rails. Valves with longer valve tips must be a consideration when using self-aligning rockers.

The stock GM valves used on the 1996-up Vortec V8/V6 engines have valves with 8 mm (.314") stems and .289" tips for self aligning rockers. Using aftermarket 11/32" (.343") locks, 11/32" retainers with GM valves will cause valve spring failures.
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  #26 (permalink)  
Old 10-20-2012, 01:06 PM
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Quote:
Originally Posted by techinspector1 View Post
When roller rockers first came out, Racer Brown (camshaft manufacturer) set up a high speed camera and filmed the action at speed. He found that the roller tip roller was too small in diameter to make a mechanical couple with the valve stem tip and that the rollers just skidded across the valve tip.

The roller trunnion, on the other hand has shown to reduce friction and oil temps.

Therefore, if I could find a roller trunnion with a stamped tip, that would seem to be the ideal unit.
Exactly like Chevy does on the LSx engines.

[img]https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTmXOLw3qCwfL85Oke
phpe1b-UwSSJN6U-AYgFsrzBOBZmdyImb[/img]

Quote:
The longer valve tip put the rocker arm self-aligning roller in the center of the valve stem throughout it's arc.
That's a pretty good trick.
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  #27 (permalink)  
Old 10-20-2012, 05:57 PM
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Originally Posted by cobalt327 View Post
Exactly like Chevy does on the LSx engines.

[img]https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTmXOLw3qCwfL85Oke
phpe1b-UwSSJN6U-AYgFsrzBOBZmdyImb[/img]

That's a pretty good trick.
X2, people don't seem to realize the rocker is cutting a cosine not a tangent on the valve stem which means it's making an arc across a fixed straight line which means the foot print from start to end is a smudge of some width not a spot.

Bogie
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  #28 (permalink)  
Old 10-20-2012, 09:17 PM
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Thank you for the explanation, bogie.

My post above had the image munged. An image of the Gen 3/4 rocker arms is below.

Quote:
Originally Posted by cobalt327 View Post
Exactly like Chevy does on the LSx engines.



Quote:
The longer valve tip put the rocker arm self-aligning roller in the center of the valve stem throughout it's arc.
That's a pretty good trick.
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