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Re: valve float
[Re: RyanJ]
#513210
11/05/09 11:44 AM
11/05/09 11:44 AM
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Joined: Oct 2007
Posts: 4,213
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,213
New York
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The observed condition (no rotation during normal use) had me a bit puzzled, until I sussed through it.
The spring (let's use only one just for clarity) will tend to rotate as it compresses, since the new height is obtained by reduced the pitch, in fact the amount of rotation is going to be a function of the original pitch angle and more or less distributed among the "active" coils.
Then why doesn't the entire spring rotate on the head?
The coefficients of friction of the spring's seated coil and the head surface are "gritty" enough that the traction resists movement.
If they were lapped in to a mirror polish, they might move. It's a happy coincidence that for normal spring design this relationship works.
Boffin Emeritus
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Re: valve float
[Re: dusturbd340W5]
#513211
11/05/09 11:55 AM
11/05/09 11:55 AM
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Joined: Oct 2003
Posts: 11,688
W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,688
W. Kentucky
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Quote:
what would the valve stem look like if I where getting into valve float
When Ryan freshened my Edelbrocks he found some valves that had seen severe float. The stems, where the top of the locks had been riding were beat up pretty bad. I don't have the valves anymore or I'd take a photo for you.
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Re: valve float
[Re: S/ST 3040]
#513212
11/05/09 01:48 PM
11/05/09 01:48 PM
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Joined: Jan 2003
Posts: 8,547
State College, PA
RyanJ
moparts member
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moparts member
Joined: Jan 2003
Posts: 8,547
State College, PA
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Quote:
I understand offset rockers undergo extreme side loading themselves
but, don't see any possible way a pushrod/rocker arm can transfer
any side load to the valve stem.
Prolonged intervals in tear-downs might result in stem wear perpendicular
to the rocker shaft but, I can't envision the side loading.
Well based on my real world experience, generally I only see extreme stem wear on intakes that are being ran with offset rockers... Rarely ever see it on exhausts that run with little to no, offset.
You can see the unusal wear patterns on almost anything that is going to be loaded unevenly..... look @ inside of a non bushed heavily offset intake rocker arm sometime after prolonged use, you will see the rocker is wearing unevenly side to side, it's being cocked on the shaft, which gets worse as it wears & it is putting uneven load on tip of valve side to side...
Non roller bearing rockers (bored alum rocker that just is riding on shaft) seem to do it worse since the rocker wears more than a NB style rocker like a T&D/Jesel/HS, but even a NB style rocker can do it with time....
Just look at wear on a roller cam that is being run with offset lifters, you will see taper in the wear pattern on the lobes, even with a needle bearing roller lifter riding on it that "should" be distributing load evenly across roller wheel, it does'nt.
Thinking/theorizing about things like this is fine, but sometimes actually measuring/looking at used parts to find out what is actually going on in the real world is often better. 
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Re: valve float
[Re: justinp61]
#513213
11/05/09 01:54 PM
11/05/09 01:54 PM
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Joined: Jan 2003
Posts: 8,547
State College, PA
RyanJ
moparts member
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moparts member
Joined: Jan 2003
Posts: 8,547
State College, PA
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Quote:
Quote:
what would the valve stem look like if I where getting into valve float
When Ryan freshened my Edelbrocks he found some valves that had seen severe float. The stems, where the top of the locks had been riding were beat up pretty bad. I don't have the valves anymore or I'd take a photo for you.
& yes getting back to original question, easy way to ID float is to look at valve tips around lock groove for vertical scratches that are caused by locks "scratching" the stems, also look for metal transfer on backside of locks, during float the locks will move around in the retainers & transfer material (similar to cap walk material transfer) & sometimes the lock Ridge/ridges on the locks themselves will start to wear badly.
When set of heads has been into bad float & valves are usually scored up @ tip, you have to file the lock grooves down back to round to get valves out of guides.
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Re: valve float
[Re: RyanJ]
#513215
11/08/09 07:45 PM
11/08/09 07:45 PM
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Joined: Oct 2007
Posts: 4,213
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,213
New York
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But... what exactly is moving?
If the rocker is taking up the clearance in opposite directions at each end, the mis-align is limited to a trig function of the clearance and the length of the rocker on the shaft axis from the roller to the pushrod.
Senior moment and I don't have the actual rocker dims, but this looks like the clearance ÷ body length = arctan of the mis-align angle.
If the clearance is .002" and the body is 1" long (on the shaft axis), the angle is only .11° (about 1/10th of a degree).
That should be detected at all. If the rocker is longer than that, the angle is even less.
Even if the bushing is toast (.010"), this is still only .57° (1/2 of a degree).
The only other answer ICTO is that the lever is bending away from the center, and introducing a 3rd axis to the roller tip.
If it really bends that much, there isn't enough cross-section in the stressed area - this is a design problem.
Boffin Emeritus
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