Engine is from a 86 zx600, according to the specs, it has 81 hp and 39 ft-lb of torque
i first started with the most complete (wiring, coils, carbs, etc.) liquid cooled street bike 4 cylinder engine on craigslist. I found an 86 zx600 (gpz600 in some countries... pre ninja). it was missing some small stuff like covers and cooling outlets. this engine isn't going to be making over 100hp like most newer 600 bikes, so it won't be that fast but it should be respectable. the engine weighs about 120 lb, about double the original engine. some reason the newer models (89, 90...) make about more hp. might be different head/ pistons i see they upped the compression ratio too. I found a front sprocket (JTF512,) that takes the 520 chain (dirt bikes size) and has the same spline. I picked a 17t because the gear ratio with the 50t rear is in between both bikes stock ratios. after that i was looking for a roller. sometimes there are cr500 rollers on craigslist for a good price, but i ended up buying an old bike that came with a parts bike (motor seized, everything in poor condition/ missing). the parts bike became the donor frame/ bike. the bike had drum brakes in the front and rear so i figured i needed to replace it. Kawasaki seemed to run the same size headtube /bearings for a pretty long time so replacement forks are everywhere (96 kx125, 92 kx125, 89 kx250, 81 kdx250 all the same size, cross referenced bearing part numbers as well). I found some forks off an 89 kx250 with a large disc brake and threw them on. After that i did some measurements and figured out how far i had to stretch the frame. i decided on 6 inches to clear the engine/headers/carbs/ etc. while stretching it i also gave the headtube angle a few degrees to make up for the longer forks. i made a cheap "jig" with some 1.75" and 2" square tubing. i welded the frame to it, cut out the old frame, and welded in some new pieces. did some calculations (basic beam stuff) for what size metal to pick. it ended up being a few sizes bigger, 1", and a size thicker (.094) than the stock frame size. i spent a lot of time just grinding the old frame and preparing for welding, old powder coat. the frame was basically cut into the head tube and the rear section for the swingarm and linkage. i welded a new top tube onto the frame and new top bars for the seat. after that i assemble the frame (forks, wheels, swingarm) to check the clearance of the engine. once that was done, i added more metal checking certain clearances. the next step was engine mounts. these are just some pieces of 3/16". lining up the engine with the rear wheel took some patience, but it was finally done. the next step of the build is the down tubes on the bike. i will have to make removable ones since the engine is so heavy and it is a tight fit. also found the carbs were missing a lot of little pieces so i plan on running a mikuni tm38 carb and making a 1 to 4 intake. I need to get a different rear shock, this one is too soft and maybe blown. im looking at the raptor 660 shock. it is a little longer which will raise the engine about an inch, and should also be stiffer, but i could buy a stiffer rear spring if necessary.
so far it is going