When people donate things they need to be really clear what they mean. I gave my bikes with no conditions, but the Alford Museum up in Aberdeenshire has a full contract, with proper procedures which cover every eventuality...who insures them, can the Museum take them out, who do they actually belong to, etc etc.
In the old days, "gentlemen's agreements" meant people were a bit fudged about these arrangements. A museum might restore a vehicle at great cost to themselves only to have the owner take it back the next week, or the owner might go looking for his machine only to find it had been sold or worse...scrapped!
Never give anything away unless you mean it...if it's a loan, say so...in writing.