what's the cause of this problem?

Refresh my memory, please: on a big twin blade mower, what is the problem when there is an uncut strip in the middle of the deck as the mower goes along.
Seems like it has to be either one or both blades shorter than it/they should be.
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Could be. If you have any common sense you can determine from clearance considerations the proper blade diameter(s).
OR it could be that the deck was knocked about so that the forward blade was knocked backwards and the rear blade knocked forward.

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May need new blades. One is in front of the other so they can overlap a bit but eventually they may need to be replaced.

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wrote:

Dull blades. If the tips aren't cutting you get the ridge.
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