Hi Steve and Grumpy, I tend to believe that this machine is a 20" Rover for 2 reasons...it has a 2 piece rear roller where the SB had a 3 piece segmented unit and all SB 20" machines had an 8 blade cylinder reel; this is a 6 blader. Can we please have a pic of the ID plate that should be affixed to the rear rail and state the Model Number and Serial Number of the machine. This will confirm it as a Rover.
Re the engine, my Scotty 17" 45 had an orange 3HP Briggs fitted to it as new.
Steve's engine may be original because Rover may have inherited a stock of 3HP engines painted orange and black was their choice and well as the solid red and bright green that they used for the chassis. This engine could have been painted black at the Rover factory and the decals replaced at the same time.
The one thing that has me tossed is the deep fuel tank on this engine. In fact, twice as deep as mine. Why? I don't have a clue....maybe this engine was originally intended for a pump?? I guess it will remain a mystery.
Steve, both grumpy and I have given you advice on how to restore this machine to good serviceable condition using best workshop practice....I just hope the person at your local dealership (who will charge you big $$$) will do the same.
Please let us know how you get on.
