I don't think the stars are meant to actually shear. My experience has been that they don't. 3 bolt spindles break long before and 4 bolt ones will tweak first. Normally, this is an installation issue- much of the time the blade isn't squarely mounted on the star and secured well. You can replace the manderl shaft kits only. I think the 3 bolts come w/ both bearings and nut and the kits for the 4 has just the lower bearing now. I would get new bottom hardware regardless.

Well, you had best "bite the bullet" and go buy 2 new mandrell housings and shafts! The stars, as you describe them, are used for turning the blade, and cannot be replaced, except by buying the new shafts.
That said, it might be in your best interests to just spend the extra money and buy two mandrel assemblies, with the shafts included in them. While you are at it, better check the blades for bends and cracks, twisting, nicks, and other things. If any of those things are found, buy new blades, too.
And---buy a spray can of bright red paint, and go paint that rock, so it can't hide in the weeds and long grasses!
A piece of pipe, with a signal flag on it, driven into the ground near the rock will be of help, too!
A good weed whacker would save a lot of time and money, too. HTH: Rusty Jones, The Mower Man.

I agree with the above usually an installation problem with the stars being worn away. Few things come to mind, first as suggested above did you align up the blade with the star, hold it and tighten the bolt? second did you clean off all the dirt from the star and mandral shaft and blade contact area on both sides?, and last did you get the blade mount bolt tight enough to hold torque and not loosen causing the blade to eat up the star on the mandral shaft? Usually the blades will make a clunking sound when the blade mount bolt loosens (unusual sound that's not normal during operation). And last the rock could of caused the blade to stop breaking the toque on the bolt and splattering the star teeth, then you would have a loose fit and in a short time the clanking effect would cause the star to be destroyed.

In the future I would make sure the blade and star contact points are clean, install the blade and feel the blade slot into the star on the shaft, hold the blade till the bolt is ran all the way up so there is no dought it's still engaged. Torque the bolt to spec's using torque wrench. Inch pound torque wrench is better, but any torque wrench is better than guessing what tight is if you not acustom to tighting fastners. It's also a good idea to check the blades every month during the mowing season. I think you owners manual will have an hourly check on them could be as little as 10 hours, 25 hours, or 50 hours of use?

Thanks for the replies -

When I replaced the OEM mandrels this spring, and after noticing the damaged stars on the old ones, I took extra caution to be sure the stars on the mandrel and blades aligned perfectly, then tightened them to the specs in the owner's manual. I even flipped the mower deck over when I did the mandrel R&R work, just to assure the blades were nice and flat against the mandrels.

One thing I'm wondering - the mandrels were aftermarket (Oregon) - anyone have opinions on original equipment (Sears, in this case) vs. aftermarket? I've gotten away from ordering from Sears, as their shipping rates and delivery time has turned me off. Does anyone have a favorite source of parts to suggest?

My lawn area is about two acres + or - , somewhat irregular terrain, and even after being here 15 years a mowing hazard will pop up. Often after the winter freeze, rocks will appear that were previously covered.

I'll replace the bad mandrel shafts, and keep a few on hand - just in case.

I'm wondering if the blade might have been a wee bit loose, and hitting that rock was enough to let it tear up the star.

*sigh*

IMO nothing wrong with aftermarket oregon products. the rock probably done all the damage and running it after the rock knocked it loose may of been the results of the hammering effect on the star or it could of just happened all at once. Alot of force in action when blade suddenly stops or slows down for half second or less, something got to give, luckily it was the mandrel housing. Get you some new parts and don't worry about it, seems you know what your doing just doughting what the rock can or could of done thinking if may of been something you done wrong? I don't think you done anything wrong except ran into the rock!

This is an old message, but just in case anyone is reading, I've sheared off or severely damaged the mandrel 'star' by not having the blade tight enough and when I did hit something, it just ground down the star. I have a craftsman 42" lawn tractor and a 57" garden tractor and have become very good at replacing mandrels and/or mandrels-housings.

I have had lots of problems with the spindle quills on AYP tractors (Craftsman, Husqvarna, etc.). The spindle housing is way too fragile to put on a large horsepower, wide cut mower. AYP certainly should have done a better job of engineering. It makes one think that maybe these things are designed this way so they can sell more of them...profit...profit...profit. I have also noticed that some aftermarket brand blades are thinner than OEM blades and will not tighten up like they should and will leave "play" on the star shaft. Additionally, the bolt washer is concaved to create a bit of a cone (spring washer) to add compression to the blade body. If the washer is turned the wrong way, the blade will slip and damage the star pattern. I also do not use the self-tapping bolts that come with the mandrel housing (I have had the bolt to break off the mounting ear while being tightened). I drill through the mounting tab and use a Grade 8 bolt and nut (with a drop of thread lock compound)to mount the housing to the deck more securely. This has worked better for me and the spindle housing is removeable later if need be.

I have one that is only 2 years old at 18 months I had to replace the mandrel on both sides one was totally shot as if the service men from sears who delivered it never tightened the thing up right the second side was lose but not totally shot of course since the one side was ruined and the second side looked half baked I replaced both sides and tightened them up myself real good or so i thought I parked it away for the winter used it this summer and now i have a sound that appears to be a repeat of the same issue is this defective manufacturing maybe? I will be taking it apart to investigate and hope I don't have to keep purchasing this every season to keep the darn thing running.. companies are getting so cheap with the manufacturing of products these days I am disgusted with sears lately..I would love to hear more of these stories to know if i need to look elsewhere for a tractor.

I think that overall these spindles hold up quite well. I would think that there is an issue with tightening the top nut if there are regular bearing issues. 60 foot pounds is the suggested torque for Husqvarna machines plus if you are reusing the nuts, feel free to dress w/ blue locktite. If you would like more help, I'd suggest starting a new thread with the model number from below the seat.