2000 Posts and climbing!!!
Join Date: Apr 2016
Re: 1980 Troy Bilt Horse tiller with Kohler K161T 7hp
Yes, you should get a flywheel with all the fan blades (what I believe you were calling fins). Missing fins means it isn't blowing as much air over the engine, which is what keeps it from overheating. The engine will still run, at least for awhile, but it is likely to eventually overheat if you don't replace it.
You also want to reinstall that shroud (I believe you called it a shield plate) and replace any other missing shrouds, as they keep the air being blown by the fan on the flywheel flowing around the engine. If they are not there, the air doesn't flow around the engine, and it winds up overheating.
I would also suggest changing the engine oil, as the fan blades may have been missing for awhile when the machine was still being used. I don't know what the correct oil for your engine is.
Don't know why they would be busted, maybe someone just fooling around not knowing what they were for, or done maliciously (you said the business failed suddenly), or using them to hold the flywheel stationary while working on the engine. But it doesn't really matter, it's done.