Originally 3/4HP, the motor was upgraded to the current 1-1/8HP in the early 1960's.  Despite the increased HP all Mark V units are limited to a range of 700rpm to 5200rpm.  This was fine for the needs of the average DIY woodworker in the 1950's, but if you wanted to drill metal or to use large diameter Forstner bits, 700rpm's was just too fast.  On the other end of the speed range, Shapers run at 10,000rpm's.  The Mark V was promoted as having the ability to be a shaper, but at 5200 it's slow going. 

You'll notice in the drawing that there are two belts in the unit.  One V belt runs from a variable pitch pulley on the motor to a second variable pulley on the lower spindle. A second, smaller fixed-size pulley is also in the lower spindle, and this pulley drives a flat belt which drives a pulley on the top drive spindle.  This arrangement created a high speed lower spindle that turned 1.6 times for every turn of the upper spindle.  Why?  Because the folk who invented the original Mark V back in the 1950's knew that table saw blaces turn at roughly 3000rpm's, but a jointer's cutterhead turns closer to 5000rpms.  So, they made a high speed spindle that turned the jointer at it's proper speed while the saw blade ran at the same time at it's proper speed.  Smart.  In 1954 the flat belt was a toothed Gilmer belt.  This was replaced by a multi-grooved belt called a poly-V when the motor was upgraded to 1-1/8HP. 

Besides the limited speed range, one problem with the mechanical variable speed drive is that as the speed increases, torque decreases.  It’s actual possible to speed-up the table saw blade by slowing the speed down.  This little trick increases torque and prevents loss of power due to belt slippage.

So what’s different about the Power Pro?  Well, the lower drawing is my lame attempt at modifying the original drawing.  It shows a larger motor with a electronic control box mounted piggy-back style.  The V-belt has been replaced by a second, longer poly-v belt, and the entire variable pitch speed control has been removed. The motor is 1-3/4HP when powered by 100volts, but when powered by 220volts it’s a 2hp motor!  And because the speed is controlled electronically there is no loss of torque at high speed!  And speaking of speed, how does 250-10,000rpm grab ya?    Oh yeah!  That means you’ll be able to turn large platters and drill metal with ease.  And at the top end 10,000rpm’s is exactly what we need for shaping. 

Another interesting ability of the Power Pro is the ability to run in reverse.  What good is that?  Well, it means that you’ll be able to reverse your lathe while sanding, which helps to speed-up the sanding/finishing process and creates smoother finishes.  But the real advantage of the reverse drive will be seen by the Mark VII owners who install a new Power Pro headstock on their Mark VII frame.  If you don’t know, the Mark VII not only lifts onto the drill press position, but it flips and lifts in the opposite direction, which puts the headstock under the table; Shaper style!   

So, how do I get one of these bad boys?  From what I hear Shopsmith is looking onto at least four options:

1. You could buy a new headstock that replaces your current headstock.
2. You could buy a newly rebuilt headstock that replaces your current headstock, perhaps with a core exchange.
3. You could ship your headstock to the factory in Dayton, Ohio and have them upgrade it.
   
4. You could buy a kit that allows you to retrofit your current headstock.  This may be a bit more complex than it first appears, because almost all the bearings in the headstock must be replaced with higher duty bearings.  This is because of the higher speeds, which the older style bearings were never designed to endure. 
   

Update June 23, 2010