Reuse or Part With the Part

October 12, 2009 07:00 PM
 

Dan Anderson, Farm Journal Columnist

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To reuse parts or not to reuse parts—that's the dilemma. It's a judgement call based on cost, convenience and experience. Here are a few rules of thumb:

 •  Nuts and bolts are OK to reuse if nuts easily thread onto the bolts or if bolts easily thread into the hole. Threading difficulty indicates damaged threads due to corrosion, mechanical damage or stretching from overtorquing. Don't reuse nuts and bolts with damaged threads.

•  Bearings can be reused with considerations. If a bearing is deep inside a machine or requires significant disassembly to access, replace it even if it wasn't the cause of the repair. It's better to replace it now then to repeat the entire process later.

 •  If a sealed bearing is easily accessible and you're willing to replace it at a later date, hold it by the outer race and shake it. Obvious clicking or movement indicates the bearing may have lost its packing of grease and there is excessive free play between the bearings' balls and races. Then, hold the inner race and turn the outer race. Obvious noises or roughness indicate it's time for a new bearing.

•  Roller bearings require close inspection before reuse. Clean them to remove grease, then inspect each roller and the inner faces of the inner and outer races. The surfaces should be smooth and shiny (like a mirror). Replace the bearing if there is pitting, flaking or marring of a roller or either race.

 •  Examine the cage that holds the rollers in place. Look for flared edges between rollers or around the circumference. Roller cage distortion allows free play that will shorten bearing life. 

 •  Always repack roller bearings with grease before reinstallation, unless they will be submerged in lubricant after installation.

 •  Don't use an air nozzle to clean and test roller bearings. Yes, roller bearings make neat siren-like noises when spun with an air nozzle, but running dry at high speeds can cause them to seize and explode in your hand.

•  Bearing flangettes can be reused as long as they tighten around bearings and prevent any movement of the outer bearing race.

•  Bearing housings or bearing blocks should hold their bearing's outer race tight—with no movement. Any bearing housing with obvious scoring marks or metal transfer due to a spun bearing should be replaced.

•  Replace roller chain sprockets if the teeth are hooked or if the rollers of a new chain aren't snug between the teeth of the old sprocket. Roller chains should be replaced when new sprockets are installed. Old chains will quickly wear out new sprockets.

•  Belt pulleys are reusable if paint is still present across the bottom of the groove. Reuse pulleys as long as the belts aren't bottoming out.
nGaskets should never be reused. Gaskets seal by deforming to fill imperfections in the mating surfaces.

•  Hydraulic fittings can generally be reused, but be suspicious of fittings that came apart "hard.” Overtightened fittings may have marred the male or female flare fittings. Inspect both for distortion or metal transfer, and replace if either one is less than smooth.

•  NPT (pipe thread) fittings should initially thread together easily and then become snug. Always use pipe dope or Teflon pipe tape on NPT fittings.

•  In a perfect world, O-rings would always be replaced during repairs. In reality, they can be reused as long as they don't have surface damage. At worst, they'll leak after repairs, and you'll have to disassemble them and install new O-rings.

 •  Reusing parts is a judgement call, and you're the judge, the jury and the one who will suffer the consequences.



Send comments and story suggestions to Dan Anderson at xrdan@netins.net.

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