the TF, TH, TE, TFD, THD, are all 2 cyl wisconsin engines with both pistons going up and down together, they can be had with both magnetos or distributers, with these engines it does not mater which spark plug you put your plug wire on, both wires spark together due to the fact both wires are conected directly to the coil.... the main differences between them are the bore and stroke combination as well as compression ratio, governed RPM, and thus hp, along with a few other things such as aluminum heads etc. These engines have a very distinctive sound and the latest THD's were produced to about 1976
the TJD is the more modern engine at a higher 18 HP output and came out in 1968 they have a piston which go up and down at opposite times. they to came out with magnetos or distributers, however magneto engines use a mag with a distributer built in (they have a rotor) your engine which I can see has a distributer has the leads exit the distributer cap 180* apart, this tells me that you have a TJD engine as no other engine has this setup.
these are great fully rebuildable engines with a piston oil pump, forged rods and crank, automotive style rod bearings and taper roller main bearings. the lifters are adjustable and actuate valve rotators. TJD, THD, and TFD engines also have hardened replaceable valve seats. Many of the wisconsin engines I have dug into also had replaceable valveguids as well i noticed... the carburetors are simple and durable,keep the fuel clean and you cant ask for a better carb IMHO. havent had many magneto problems eather, good stuff.
great engines, I have running examples of wisconsin 2 cylinders from handstart engines of the 1940's to electric start of the 1970's.
-Leo-