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Quote:
Originally Posted by Joe K
Wear or stretch? Not that it matters, the correction is the same.
Akin possibly to the principle of "pein straightening?"
Interesting concept.
We learned about that at the Nuclear plant. Repeated isolated peining beyond the elastic limit locally deforms the metal creating compression stress which in transferring to the mass of metal causes an overall "reformation."
We pein straightened a shaft about 4 feet long held between balance wheels (you know those wheels you use to find the "heavy side?") The shaft started out visibly bent with a total offset about 0.025 inches over 4 feet.
Using a pneumatic hammer holding a blunt tool (rounded with no sharp edges) one applies the tool to the "low" side of the shaft as it sits, applying it to what is the "concave" side of the bend. This is kind of counter-intuitive to what you might normally expect - a person with a hammer will apply it at the point of greatest displacement hoping to bend "en-masse" and thereby straighten the shaft.
The tool is run back and forth while "rat-tat-tatting" impacting the surface - and this causes the shaft to locally deform. Not even leaving a surface dent. The shaft because of the localized reformation will "straighten." In fact, the instructors direction to us was to continue beyond straight and leave it bent the "other" way. "Walk it an equal distance off center in the 'other' direction - I need to have a demonstration for the NEXT class to correct." he said.
We ended up "walking" the shaft back and forth a couple of times - the process is THAT fast.
Pein straightening even has the advantage of relieving stress - something about the sonic wave transfer within the metal. A stress someone with a hammer can't help but leave and which can cause cracking.
Anyway, one can see how repeated localized roller pressure beyond the elastic limit might cause "belling" of the mouth of the hub.
Joe K
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I've seen piston slap removed in an old motor by using lead shot blasted against the skirts to enlarge them. A set of rings, a hone, a valve job, adjust the bearings and away we go!