Just to clear the air...

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cheap junk parts can also vastly improve & transform a front end, for one

getting a bike humming down the road is one thing, originality concours is another,

all manner of mods are also in abundance
 
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Junk bike + some serviceable and refurbished parts within wear specifications + some new parts = decent every day rider.
sounds like plenty of aviation engines out there, the timed out or worn out junk engines are considered core engines for rebuild
 

grandpaul

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The crank was at standard, pistons & cylinders at .020 (went to .040), valves were good with a light lapping; the engine was nowhere near junk, just filthy & scruffy.
 
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http://flyabonanza.com/Blog/Entries/2012/12/13_Understanding_Engine_Overhauls.html

It is important for the customer to understand when you purchase a FACTORY REBUILT engine, you can either provide your run-out engine to the manufacturer for rebuild or exchange your current engine for an “off the shelf” engine.
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Throughout the world, there are a myriad of reputable shops that specialize in overhauling aircraft engines. An OVERHAULED ENGINE is an engine that has been disassembled, cleaned, inspected, repaired as necessary and tested using FAA approved procedures. The engine may be OVERHAULED to NEW LIMITS or SERVICE LIMITS and still be considered a FAA approved OVERHAUL. NEW LIMITS are the FAA approved fits and tolerances that a new engine is manufactured to. This may be accomplished using standard or approved undersized and oversized tolerances. SERVICE LIMITS are the FAA approved allowable wear fits and tolerances that a new limit part may deteriorate to and still be a useable component. This may also be accomplished using standard and approved undersized and oversized tolerances.
 

grandpaul

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Motorcycle engines don't "time" out. They can, and do, "wear" out to a point that the bike is sold, abandoned, or forgotten in a corner. That does NOT mean that it is worn beyond factory specified service limits listed in the shop manual.

Also, re-boring cylinders to maximum available oversize does NOT mean they are "trashed" if the job is done properly, and decent quality oversize pistons and rings are used. Same goes for crankshafts. Even parts that are well worn, but still within specification range, can still be re-used AS-IS for many more miles as long as the owner takes care to properly maintain and service the bike with good quality lubricants, AND ride it with a reasonable amount of care, not thrashing it mercilessly.

Some engines look quite worn, are dull and faded, maybe even weeping a bit of oil here and there, but will run longer and harder than a shiny engine that hasn't been serviced and maintained, and is abused by it's rider.
 
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It is pretty rare to find a British or American bike which cannot easily be restored to good working condition. Many Japanese bikes are about replacing all the worn or damaged bits with stock parts. With the other, they can usually be welded, machined and other bits adapted to fit.
 
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