A DC motor just change over the brush wires, done it on a two brush set ups on generators and quite a few old motors and often found wrong rotation for a engine so saving to have a crossed belt often just changed the rotation. A good way to check rotation is just using a 12v battery, even one of the high DC 400+ voltage motors or generators will motor on the 12volt and the direction it turns is its also the way it generates, and old generators often need a flash of voltage if have had long period of inactivity. My old 1953 generator is direct DC Dyno-Start and if hand started is reluctant to generate, if its really big it can take a few minutes to come on load so never leave a dc generator with a open circuit running not connected to a load. I once thought it odd a generator would motor but no voltage just standing looking at it to then see it show a few volts, in a spit second went sky high even with a load on and not thinking broke the connection there was a good two plus inch ark, voltage metre maxed out at 2,000 volts, luckily the insolation was good and I had my wooly hat on as a bit hair razing to say the least. Biggest reversing DC motor I saw working near me was a 50HP planer motor would brake stop and change direction that a small car would fit on the planers bed, road was closed the other day so done a short cut through the village and recognised one of the last workers I think still alive that used to work there so I stopped a had a good chat.
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