Honda C70 Engine

Nothing!! I am currently upgrading my engine with a larger cylinder head. I have always been worried about overheating these motors (especially since I got the bore up kit). I have never ran my engine hot (or hard enough) to overheat it, yet! Having extra cooling, better porting and flow from this new head always helps!! Check out the arrows in the pictures showing the larger fins compared to a stock 72cc head. This head is pretty cool! Its brand new made by Honda and is designed to be used in JDM Honda Cub 90 motors. If you got a ZB50 with a bore up kit and are still using that stock head or a standard roller bearing 72cc head, this upgrade is a must!!! I do have an extra one of these new heads available forsale if you are interested. They are $230 each and includes new intake & exhaust valves. All you have to do is swap all the head guts from your stock ZB head (valve springs, rockers, cam, etc) and put them into this head. They will fit. Your piston will be happy and reward you with more power!. :-)

Here are some pictures of the engine during it's testing stages. I hope to purchase a cam cover heatsink in the near future. On the picture of the right side of the engine, I custom CNC machined the "HONDA MADE IN JAPAN."  Click on pics for full size pictures.

The engine for my Project ZB50 came out of a 1983 C70 72cc 3 speed automatic Passport. The original ZB50 engine was in really good shape and had nothing wrong with it. I could of used the factory engine as the foundation for my build up, but I decided to use a 1983 Honda Passport engine instead as it has a electric starter. With the electric starter, I could be just like the full size sportbikes and start the engine with a push of the button!! You can call me lazy.  :-)

I wanted a lot of power out of this ZB50. The factory 50cc 3 speed automatic engine did not have enough power. The Honda Passport engine was 72cc and also had a 3 speed automatic transmission. In stock form, the C70 engine would probably provided me with enough power for general cruising, but I seem to always want more! As you have probably remember, my goal is to keep up or beat the 2 stroke YSR50 and NSR50! I started this project by completly taking apart the Passport engine. First on the list of things to do was to swap out the 3 speed semi-automatic trans for a 4 speed manual clutch transmission out of a CT70 H model. The swap was fairly straight forward, but requred some minor machine work on the Passport engine cases. With a 4 speed transmission, the gear ratios are much closer together, meaning that you can keep the engine RPM near it's powerband longer. This will equal more power and no need to wait for the engine to rev up (such as with a 3 speed). At the same time I also installed a high volume Takeagwa oil pump kit. I also had the crankshaft modified for a longer stroke. After that, I put the lower part of the engine back together with a manual style clutch cover. A 88cc big bore piston kit was also installed. Piston skirt and squish band was also modified. Now with a stroked crankshaft and big bore kit, I am sure the total displacment for this engine is over 88cc now. Unfortunately, I have not had the time to calculate the total displacement on this engine.

The cylinder head was also ported and a set of oversized valves installed to help the engine breath better. The cam is a Kitaco special high lift racing cam.

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