ML7 usually came with 0.5hp. But its top speed was only 800rpm. So I should think .25hp is way too low.

Hoover made millions of Sewing Machine motors of the Universal Type which aren't ideal for lathes. The motors run at high RPM off-load, and slow down when asked to do work. Universals are OK for vacuum cleaners and tiny lathes but bigger machine tools prefer motors with high starting torque and fixed speed running: for an ML10 a single or three-phase induction motor delivers a better combination of torque, rpm and power. A ¼HP Universal might stall before it can get up to speed, whereas the extra torque available from a ¼HP induction gets it going.

What you have may be suitable because Hoover made induction motors too. The giveaway is Universal Motors have brushes.

In terms of power, between ⅓HP and 1HP is typical on home workshop machines. ¼HP is on the low side for an ML10 I think. If I owned one I'd go for ½HP or ⅔HP. Ought to say I'm constitutionally against of putting big motors on small machines because doing so risks rapid wear and serious damage if anything goes wrong like crashing the tool-post into the chuck. Others think I'm a wimp!

Myfords were originally fitted with single-phase induction motors because homes rarely had the 3-phase supply needed to power better 3-phase motors. These days 3-phase can be generated electronically with a VFD so I'd almost certainly go that route. Advantages: speed control, improved reliability, more torque (at operating speed), and much less vibration. If nervous of rolling your own you can buy complete packages, for example Newton Tesla.

Dave

Hoovers made lots of induction motors, many more than their universal motors. Might pay to ascertain which type of Hoover motor you have.

Andrew.