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post #31 of 81 (permalink) Old Apr 9th, 19, 6:22 AM
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Gene
 
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Re: comp cams gold

I love these, but there's ALOT to love. $$ https://www.summitracing.com/parts/cro-73605-16

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post #32 of 81 (permalink) Old Apr 9th, 19, 7:03 AM
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Re: comp cams gold

Do you know the history of the engine? What is the piston to valve clearance, vertically and radially. When did the last rocker break?
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post #33 of 81 (permalink) Old Apr 9th, 19, 10:06 AM
 
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Re: comp cams gold

Quote:
Originally Posted by JJ71CHEVELLE View Post
https://www.summitracing.com/parts/cca-7951-1

rocker tips rolls right at the center of the valve
How wide is the sweep? If more than .060" the pushrods are too short.

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post #34 of 81 (permalink) Old Apr 9th, 19, 10:49 AM
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Re: comp cams gold

Quote:
Originally Posted by JJ71CHEVELLE View Post
everything looks fine , but i will check it again
"Looks" or actually is fine?? 700 lift cam is a pretty good size and has some duration, meaning less p/v clearance.

I would guess that retainer to seal should be ok being an aftermarket head. Coil bind could be an issue with 700 as that's what some springs are rated for.

Even if the pushrods were slightly too long or short, I can't see that breaking rockers. Somethings really binding up here.
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post #35 of 81 (permalink) Old Apr 9th, 19, 11:14 AM
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Re: comp cams gold

Quote:
Originally Posted by 427L88 View Post
I love these, but there's ALOT to love. $$ https://www.summitracing.com/parts/cro-73605-16
Hi Gene, yeah Mark likes these too but I had the Comp Cams Hi Tech Stainless ones that look virtually identical to these and broke them. So that's why I went with the Ultra Pro Magnum, they are rated to 850lbs open spring pressure. There is a Comp Cams Ultra Pro Magnum XD that is rated to 1000lbs that may be better for .700 lift for OP.
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post #36 of 81 (permalink) Old Apr 9th, 19, 12:18 PM
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Re: comp cams gold

I ran Crane "energizers" before and decided that the Crowers were the answer. And this with light pressures and only .610" lift. I'm not big on alum bodies.

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post #37 of 81 (permalink) Old Apr 9th, 19, 12:39 PM
 
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Re: comp cams gold

Quote:
Originally Posted by 69-CHVL View Post
"Looks" or actually is fine?? 700 lift cam is a pretty good size and has some duration, meaning less p/v clearance.

I would guess that retainer to seal should be ok being an aftermarket head. Coil bind could be an issue with 700 as that's what some springs are rated for.

Even if the pushrods were slightly too long or short, I can't see that breaking rockers. Somethings really binding up here.
Short pushrod will leave a wide sweep pattern. This will "work" the valve and increase the clearance in the valve guide. Going unchecked this will create added harmonics in the valvetrain.

Pushrod flex, just like a pole vaulters pole, the stored energy the pushrod release on the closing side of the lobe will send harmonics into the valvetrain.

Not saying either one of these is the cause, but can be contributors to a very unhappy valvetrain.

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post #38 of 81 (permalink) Old Apr 9th, 19, 1:28 PM
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Re: comp cams gold

Reading through my old trusty "How to hot rod a big block" book it list aluminum rockers used by professional racers as having a life span of just 6 hours! it may just be metal fatigue.
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post #39 of 81 (permalink) Old Apr 9th, 19, 3:49 PM
 
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Re: comp cams gold

Quote:
Originally Posted by 2cool View Post
Reading through my old trusty "How to hot rod a big block" book it list aluminum rockers used by professional racers as having a life span of just 6 hours! it may just be metal fatigue.
Mercury Marine factory installed Crane Gold on the Blue motors. Ford installed them the factory Cobra Mustangs in the late 80's and 90's.
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post #40 of 81 (permalink) Old Apr 9th, 19, 4:05 PM
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Re: comp cams gold

Quote:
Originally Posted by JJ71CHEVELLE View Post
https://www.summitracing.com/parts/cca-7951-1

rocker tips rolls right at the center of the valve
Javier
These are the AFR heads correct?
If so I can all but guarantee that with the stock Comp rockers if the pattern is in the middle of the valve the pushrods are too short & the geometry is incorrect
In lieu of the backset Crowers The Crane Gold were the better rocker for many years because they had a shorter pivot length
Now the rocker to use is either the custom ones you can get from myself, Chris or direct from AFR for aluminum
Or the backset Crower which I also have but they are not exactly budget friendly
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post #41 of 81 (permalink) Old Apr 9th, 19, 4:42 PM
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Re: comp cams gold

Quote:
Originally Posted by cstraub View Post
Mercury Marine factory installed Crane Gold on the Blue motors. Ford installed them the factory Cobra Mustangs in the late 80's and 90's.

Something tells me these arent the same metallurgy, other than the gold anodized finish.
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post #42 of 81 (permalink) Old Apr 10th, 19, 9:17 AM
 
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Re: comp cams gold

Quote:
Originally Posted by 427L88 View Post
Something tells me these arent the same metallurgy, other than the gold anodized finish.
Same extruded bar as all other Crane rockers, they were the wide body design and had more area.
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post #43 of 81 (permalink) Old Apr 10th, 19, 10:57 AM
 
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Re: comp cams gold

Quote:
Originally Posted by JJ71CHEVELLE View Post
https://www.summitracing.com/parts/cca-7951-1

rocker tips rolls right at the center of the valve
Have you measured the sweep pattern on the tip of the valve?

Chris Straub
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post #44 of 81 (permalink) Old Apr 10th, 19, 12:54 PM
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Re: comp cams gold

For its tensile strength, 6061 (T651 Bare) is listed at 45,000 psi, with a yield point of 40,000 psi. The Brinell hardness is rated at 95. The elongation at break is 12% and shear strength is 31,000 psi. 6061 has a thermal conductivity of 170 W/m-K. And finally, its strength to weight ratio is rated at 115 kN-m/kg.


Spring Rate = (273 – 105) ÷ 0.450
Spring Rate = 168 ÷ 0.450
Spring Rate = 373 lbs./in.*
*Comp Cams lists the spring rate at 370 lbs./in.


To me just pushing the valve too much to the side would result in wearing out the guide more than breaking the rocker, I suspect the rocker is hitting something to cause enough force to break it and it is hitting hard by looking at the break.

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Last edited by 2cool; Apr 10th, 19 at 1:20 PM.
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post #45 of 81 (permalink) Old Apr 10th, 19, 4:28 PM
 
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Re: comp cams gold

Bottom line, this engine is not happy and it needs to come apart. I would say it will be found that there is a combination of issues all contributing to parts failing. It's not the parts fault, its just the weakest link in the system.

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