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If it's just a chain and sprocket that are broken, I wouldn't think it would be that involved or costly to repair. I would price out the parts and go from there as you can decide if it's worth fixing or not. Perhaps you could even find these parts used somewhere and get an even better price.
If you are somewhat mechanically inclined, I'm sure it's something that you could tackle.
Here is a link with some microfiches of your machine: Parts and Diagrams for Toro Consumer 56170, 11-32 Professional Rear Engine Rider, 1987 (SN 7000001-7999999))
If it's just a chain and sprocket that are broken, I wouldn't think it would be that involved or costly to repair. I would price out the parts and go from there as you can decide if it's worth fixing or not. Perhaps you could even find these parts used somewhere and get an even better price.
If you are somewhat mechanically inclined, I'm sure it's something that you could tackle.
Here is a link with some microfiches of your machine: Parts and Diagrams for Toro Consumer 56170, 11-32 Professional Rear Engine Rider, 1987 (SN 7000001-7999999))
