What could cause the vavle stem tip to get 'beat up'?
11-21-2009, 03:22 PM
#31
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Jim responded...
Well, I had to look up 'spalling'...
Here it is...
Then I had to look up high point loading...
http://books.google.com/books?id=Ulv...0valve&f=false
>Dave:
The tips were not mushroomed. Some showed signs of spalling, others actually shelled out. High point loading?
Jim P.
I mentioned this in passing to some of my Z28 friends and it's spawned a
> very contentious discussion but it keeps coming back to "how were they
> beat up?" or "What did they look like?".
>
> Can you tell me what you mean? Were the tips mushroomed or deformed
> and scored or ???
The tips were not mushroomed. Some showed signs of spalling, others actually shelled out. High point loading?
Jim P.
I mentioned this in passing to some of my Z28 friends and it's spawned a
> very contentious discussion but it keeps coming back to "how were they
> beat up?" or "What did they look like?".
>
> Can you tell me what you mean? Were the tips mushroomed or deformed
> and scored or ???
Here it is...
Mechanical spalling
Mechanical spalling occurs at high stress contact points, for example, in a ball bearing. Spalling occurs in preference to brinelling where the maximal shear stress occurs not at the surface, but just below, shearing the spall off.
One of the simplest forms of mechanical spalling is the plate impact, there are two waves of compression that are reflected on the free-surfaces of the plates, and then, they interact to generate a region of high tension stress inside one of the plates.
Mechanical spalling occurs at high stress contact points, for example, in a ball bearing. Spalling occurs in preference to brinelling where the maximal shear stress occurs not at the surface, but just below, shearing the spall off.
One of the simplest forms of mechanical spalling is the plate impact, there are two waves of compression that are reflected on the free-surfaces of the plates, and then, they interact to generate a region of high tension stress inside one of the plates.
http://books.google.com/books?id=Ulv...0valve&f=false
Last edited by DirtyDaveW; 11-21-2009 at 03:30 PM.
11-21-2009, 06:52 PM
#32
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Location: MI
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Typical features of a Hertzian metal fatigue failure. Also ref... Shigley "Mechanical Engineering Design." Full roller contact @ the valve tappet is key to preventing this failure mode. Also a typical failure in roller bearings under high load. B.
11-21-2009, 10:03 PM
#33
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11-23-2009, 01:06 PM
#35
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Yes, I've had it. Crane gold RR's SA type. Hertzian fatigue cracks on the valve tappets (AFR heads). Upon further study of the failure, I traced the root cause problem to point loading @ roller due to angular misalignment caused by stud movement. I fixed with ProMag RR's. Used 7/16" studs (with red loc_tite) and the large ProMag rocker trunion bearings, and, custom fit PR guide plates for full roller valve tappet engagement. I did not grind the valve tappets. Still running today. There is alot of stress @ the valve tappet due to the difference in radius of the roller and valve tappet flat (zero radius). I lov my copy of Shigley. Just throwing it out there. B.
11-25-2009, 10:57 AM
#36
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Just ordered some Scorpion 1.7 ratio, 7/16" stud, .150 offset Roller rockers(SCP1034). I thought I'd punt on my old rockers. I have had these CC ProMags (1.6, 7/16" ratio) on there since 2007 when I went to the solid roller cam. I don't know for sure they're at fault, I just thought I'd make sure and get some new ones. Plus, with these .150 offset Canfields, I would feel better with the rockers matching. This 1.7 ratio in conjunction with my current cam will move my I/E lifts to .607/.602
12-03-2009, 12:19 PM
#37
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They just arrived...
Huh? Oh.. packing. Never seen this style before...
Now this is more like it...
Pretty....
So I went out to the shop and thought I'd do a quick 'trial' fit using the in-place Iskys. Ugh.. nope. Let me try the stock GM guideplates. Ugh.. nope. Back to the Iskys. Looks like I'll have to do more trimming/grinding on the ISKY's to get them to line up correctly.
Huh? Oh.. packing. Never seen this style before...
Now this is more like it...
Pretty....
So I went out to the shop and thought I'd do a quick 'trial' fit using the in-place Iskys. Ugh.. nope. Let me try the stock GM guideplates. Ugh.. nope. Back to the Iskys. Looks like I'll have to do more trimming/grinding on the ISKY's to get them to line up correctly.
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