Craftsman lawn mower scalps lawn- need advice

My guess is that one mandrel assembly is out of alignment on my one year old craftsman 20hp 42" model 917.27682.
It was scalping the lawn when going over bumps at low heights. I thought it was a bent blade but did the same with a new blade.
I removed the deck and did some tests. One blade is at the same depth when rotated 360 (so works fine) while the other is low on one blade tip and high on the other. It is slightly beyond the edge of the bottom of the deck, so obviously will scalp the lawn if the deck bottoms out.
If the blade is removed and replaced about 180, the low/high reverses.
If the blades are swapped, the low/high is still about the same on the same mandrel.
I noticed that there are four bolts around the pulley/blade drive assembly and wonder if the alignment can be corrected?
I know I can probably shim it at the blade to get it into alignment, but is there another fix?
Or is it beyond repair? I am reluctant to replace the pulley assembly in case the deck itself has an alignment problem.
Unfortunately, the machine did not come with a IPB of the mower deck, only the tractor, so I cannot figure out just what is involved in the pulley/blade drive assembly.
Any help appreciated.
GA

low tire??
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snipped-for-privacy@webtv.net wrote:
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Nope. That was the first thing I did, check tire pressure. The blade actually comes down about 1/8" below the bottom of the deck. I thought it was a bent blade, but if I shift the blade 180 but fix the pulley, the blade is still beyond the bottom and at the same place. So the blade is fine but the pulley assembly or the mandrel is off.
GA

George Abbot wrote: ...
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The last two statements are contradictory -- if the high/low position interchanges when the blade is rotated 180 degrees on the spindle, that would indicate a bent blade as any tilt or bend in the shaft would be the same and the location of the low spot moved w/ the blade.
OTOH, if swapping blades doesn't change the symptoms, the blade isn't bent (or the even more unlikely that they're both bent exactly the same way).
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There would likely be a parts diagram on the Sears web site for the deck as well I would think...
First check to see if the shaft of the offending spindle is bent. If you have a dial indicator, that's the most direct way, but you can improvise w/ any tool you can position at the side of the shaft where the blade mounts and rotate it slowly to see if the distance between the shaft and the tool point changes. If it does, that indicates the shaft is bent which would provide the symptoms (other than the dichotomy noted above). It would have to be replace as it will be treated.
It is also possible the deck where the mandrel mounts got bent if hit something or that there's a combination of both bent spindle and deck. It would seem unlikely the mounting itself would be able to cause a camber as the castings are likely just bolted directly to the deck so a movement there would simply be lateral, not angular--but, that would need a picture to see clearly.
I'm guess the most likely is the shaft is bent...
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On a lot of brands, you can just press out the shaft and replace that but on my Craftsman, I found that the pulley is welded to the shaft so Sears gets to sell you a complete mandrel assembly...in my case it was about $70.
Tom G.

Tom G wrote:
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That'd be a bummer...have had nothing but Deere for nearly 20 years now, so don't run into those type of corner-cutting issues.
Another thought for OP -- check that the blade flange is square to the shaft--if it is a press fit or similar it might be cockeyed or bent so blade is cocked wrt to shaft centerline.
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dpb wrote:
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My error. Got a bit confused. the high stays the same.

on 5/26/2008 8:26 AM George Abbot said the following:
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Are they tight? Perhaps some came loose causing the belt to pull the pulley to one side.
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Thanks to all for the help in identifying my problem with my craftsman 20hp 42" model 917.27682.
It is a bent mandrel. I ordered the complete assembly as I did not want to try and force the shaft out since it did not want to leave.
I got it down to the shaft, ball bearing unit, and the collar still together as a unit. I gave the shaft a few wacks with hammer and a piece of wood cushioning the blow to see if the shaft would come out. It did not move.
So how do you get the mandrel and ball bearing unit out of the collar so only the mandrel needs to be replaced? Be nice to have a spare.
GA

George Abbot wrote: ...
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Best would be to see a picture so can tell how it's put together. W/O seeing, no great ideas other than it possibly will require a press.
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dpb wrote:
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Thanks for the reply.
The IPB shows the mandel, collar and bearing assembly so the mandrel goes into the collar and the bearing assembly is at the top of the shaft in the collar. Fairly simple so it probably is a press issue. I do not see any clips, keys or anything else to keep the shaft of the mandrel in the collar.
GA

George Abbot wrote:
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What shape is the shaft in? Shine it up so don't have extra crap to put thru the bearing and use some good penetrating oil--something other than WD40 that will actually have a chance of getting wicked in.
Then, if you don't care about possibly wiping the bearings, a bigger hammer is the tool if don't have press or can't cobble up something out of the scrap pile to use w/ a hand jack or don't want to take it to a machine shop.
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dpb wrote: ...
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One last note -- depending on the shape, it is sometimes possible to pull the bearing off a shaft instead of pressing driving the shaft out of the bearing if you can somehow find a way to get a purchase w/ the puller legs and press against the shaft end from the right direction.
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dpb wrote:
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Thanks for the help.
GA

George Abbot wrote:
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No problem...of course, if you choose this route, remember the hardwood or brass block, not the hammer directly on the shaft. Of course, this shaft is toast anyway, but in general...
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