Banana groove small block rocker shafts

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Agree looks like fretting where the hold down is. I still do not see oil holes [ plural ] where the scuffing can be seen caused by the rockers. The one oil hole that I can see looks like to have clean metal around, maybe where the separating spring or spacer sits.
 
15 years and 1000’s of runs and 60,000+ street miles. They are the original rockers. I will look at the new shafts, when I check them. The rocker has a full groove in the middle where that hole is. That is the cast iron pedestal side.

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There is some on the hood down side. I will definitely keep an eye on them. Already checked them once after installing new rockers and shafts. Took a press to get the rocker off.

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furrystump said:
There is some on the hood down side. I will definitely keep an eye on them. Already checked them once after installing new rockers and shafts. Took a press to get the rocker off.
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I don't know how long ago that was, but for sure those shafts were loose. The fretting is a dead give away that the shaft wasn't being held tightly in the head and was dancing around. That movement plays hell on parts and could have contributed or been the cause of the initial failure. Did you replace the bolts/hold downs after that failure?
 
No, reused the bolts and hold downs. The reason it failed is that generation rocker wasn’t bushed and is a steel rocker and they have had a very hard life. It started to gall and away it went. Might put studs in the shafts. It was still rocking turning it over with the starter, I think it grabbed, the valve got tagged and broke it loose.
 
That all might be true, but the hold downs were loose for a bit, you don't get fretting without time.

A loose shaft could cause the rocker to bind on the shaft as the shaft moves.
 
I do not see how a loose shaft could cause the rocker to bind on the shaft. An overtightened shaft, yes, because it is no longer round, but oval shaped.
A loose shaft, if loose enough, would leak oil pressure & may starve the rockers.
The pic in post #22 tells the story....
 
Bewy said:
I do not see how a loose shaft could cause the rocker to bind on the shaft. An overtightened shaft, yes, because it is no longer round, but oval shaped.
A loose shaft, if loose enough, would leak oil pressure & may starve the rockers.
The pic in post #22 tells the story....
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If you can see how an over tight shaft can cause a bind, you can see how a loose one would.

A loose shaft will deflect before it starts to convert the linear motion of the cam into rotational, and it's happening at 8 different points along the shaft at at 8 different loads as valves open and close. The rigidity of the shaft requires it to be held down firmly.

Could the shaft have been loose enough to lose oil lubrication to the rockers? Sure. Could be a combination of multiple factors.
 
No, do not agree that a loose shaft would cause binding. Maybe if the shaft was 1/16" wall thickness, but it is muuuuch thicker than that.....
 
Bewy said:
No, do not agree that a loose shaft would cause binding. Maybe if the shaft was 1/16" wall thickness, but it is muuuuch thicker than that.....
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A loose shaft can't be distorted by load from the lifters and springs, but can be distorted by over tightening of the hold downs?

Ok
 
Turbo,
Using your logic: the side of the rocker closest to the spacers separating the rockers would bind because that area is between the shaft hold downs & is unsupported.
 
Bewy said:
Turbo,
Using your logic: the side of the rocker closest to the spacers separating the rockers would bind because that area is between the shaft hold downs & is unsupported.
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There's a difference between a seated stationary shaft and one loose enough to move. That rocker shaft was loose, and was loose for more than a few seconds or minutes as those rockers destroyed themselves.

You've got a shaft that would be moving around, with counteracting forces all along it. We're not talking about those forces located on a stationary section 3" long with only two rockers on it, but potentiality the whole length of shaft with all eight.

How much does it take in that situation to make the shaft deflect and close up the .001 clearance?


Again, all of that, and no chance but you think a 3/8 bolt and a stamped hold down can?

Ok.
 
'A shaft moving around'......
Not for long. The bolts will back out & there would be quite a bit of valvetrain noise requiring the engine to be stopped to investigate.....
 
Bewy said:
'A shaft moving around'......
Not for long. The bolts will back out & there would be quite a bit of valvetrain noise requiring the engine to be stopped to investigate.....
Click to expand...

And yet it went on long enough for fretting to occur. Fretting is cyclical, it requires repetitive movement between closely mated surfaces.

To summarize, 3/8 bolts can distort the shaft, but not bending from the increased moment of the loose shaft, and a loose shaft would increase noise to the point that immediate action would be taken, but also occur for so long to cause fretting in multiple locations on the shaft?
 
The stocker r/shaft bolts are never really tight. They are a 3/8" coarse thread bolt, same as used to bolt the intake to the heads, recommended tq for these is 45ft/lb.
The r/shaft bolt is 25 ft/lb because a hollow shaft is involved; excessive tq would distort make it. Because it is hollow, it is going to have some 'spring' in it & can never be fully tightened like the above int bolt. So I can see how fretting could occur because there could be movement.
 
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