Craftsman 42", 18.5 lawn tractor: blades are hitting in the mower deck. Blades are new and deck is balanced. Is it wear on the Mandrel - Shaft? Mandrel bearing?

you will need to replace the bearing mandrel

Even new blades can be out of balance, but my guess would be either the other blade spindle, or the tensioner pulley bearing.

Sounds to me like you bent a spindle. Turn the mower off and get under it and see if you can spin the blades. The blades whould spin and not be wobbly. If either one of the blades are wobbly then you'll need to replace the spindle.

Also check to make the blade belt hasn't come off or is not destroyed.

Good luck!

just click this link and check with them,, http://www.searspartsdirect.com/partsdirect/index.action

Here's a link I found Doug on your belts. https://www.shopyourway.com/questions/1126482

Hi, you might want to pull the blades off and check the blades and adapters for cracks or breakage or wear. if not the spindle assemblies could have the excessive wear to them. You did not say how old the unit was so hope this helps

when you put the new blades on did you notice if they were even with each other? the 42" decks have a tendency to "warp" inward on the left side. this causes the left blade to ride at an angle to the right blade - there is a tool to correct this, but not all shops have it - sometimes you can remove the deck, flip it over and wallop the inside edge of the left mandrel until the blades are even - a 2 lb. sledge works well for this

there was a problem with the lighter gauge decks [thinner steel], and the deck would actually bend inward on the left side. this would tilt the mandrel inward making the blade cut at a slight angle to the right blade - there is tool to straighten the deck [the left mandrel housing usually breaks, though] - some shops have this tool, others have never heard of such a thing - most sears l&g field techs have this tool in their trucks - i have the tool in my shop, but i have had luck with turning the deck over and whapping it a couple of times on the inside edge of the left mandrel until the blades line up

put your mower on level ground. Concrete or pavement. Check to make sure deck is setting level. If not, adjust deck. NEXT. Make sure mandrel or shaft isn't bent or broken. (this is what you bolt your blades onto and top side is where the belt runs.) If you have hit a root or rock. These will bend and break. If so, Remove and replace with good used or new one. You can purchase the housing for somewhere around 25 to 35 dollars

Are you sure the spindle is not bent and also are you balancing the blades when sharpening. Other then that make sure bolts are tight on the mandrel. With the deck off and standing up spin the blades and watch center of balde to see if something is bent. Also watch pulley on the other side to see if its bent.