HO Durango & Silverton #493 - connecting rod

[LoveAllGauges]

During normal operation of the locomotive something happens to the left side connecting rod causing it to jam causing the wheels to lock and an abrupt stop. I was able to get it working again however this has happened twice in the 2 months I've owned it. Seems to me the stroke of rod causes the piston shaft to come all the way out consequently causing everything to bind. The first time it caused the locomotive to derail, topple over breaking the plastic coupler pin on the tender.

Over the last 35 years I've used Bachmann train products but never had a malfunction such as this. I would appreciate your help in finding a remedy to this issue.