1992 Honda CT70/110cc Engine

I bought this 1992 CT70 from the original owner who had put over 30,000 miles on it. He used it as his main source of transportation everyday to work and back. He said that it ran fine until one day coming back from work, the engine suddenly made some knocking noises and died. He took the top end off and found that the problem was the ball bearing on the right side of the cam siezed up, which  ruined the camshaft and also the head. He then advertised it in the classifeds as a parts bike. With the exception of the engine not running, the bike was almost in mint condition except for a little wear and tear. I got it home and started to dissasemble the engine and found out that the oil drain plug hole was replaced with a copper sleeve since the original threads on the aluminum case were worn out and stripped (due to too many oil changes-Remeber this bike has over 30,000 miles!!!!). He probably took it to an inexperienced Honda mechanic who drilled out the worn threads, replaced it with a pressed in copper sleeve with internal threads. The mechanic did not remove all the aluminum shavings from the engine case when he drilled the case. The shavings found its way through the oil screen into the oil pump, locked up the oil pump, oil pump cam chain driven sproket and also clogged the oil jet in the engine case which resulted in a blown cam bearing. Luckily the crankshaft suffered no problems. The mechanic should of fixed it the right way by removing the clutch cover and clutch, which exposed the oil pump/screen and then drill it out to the next larger size and re-tap the hole with a larger drain plug.

CT70 with the Passport engine bolted on. The original carburator had to be used since the electric starter was in the way.

I had finally found a low mileage 1983 Honda Passport engine with electric start. I mounted it on, did some wiring and it ran great. I was not satisfied with the top end speed with the Passport gearing so I swapped a 4 speed manual clutch gearbox from a 1970 Honda CT70 H model engine. Then one day me and my dad went trail riding.  My dad rode his 1969 Honda CT70 with 3 speed automatic and it had lots of power going up hills while I was riding the 1992 CT70 and I had to keep slipping the clutch to go up the hill. I was very unsatifisfied with the performance of this engine. It was excellent on street but had no power off road. I later dissasembled this engine to modifiy it for my Project ZB50 and found out that it was way too restricted. The size of the valves on the head were the same diameter as the ones from a 50cc engine! Imagine a 72cc piston breathing through 50cc valves!