Rebuilding a Blown Engine - Part 1

This has not been a great year for Honda engines in my garage, which I suppose is to be expected when you race 40+ year old junkyard bikes. Two of the motors, the original mill from the 1968 CL450 and the engine from my friend's 1970 CB had both suffered...fairly catastrophic failures.

Thats not so bad...

OH GOD

The CL450 engine developed an air leak through a worn out carburetor and burned a hole in the left piston. As for the CB450 engine? That is the result of running low on oil at freeway speeds. kaboom. 

I had already recommissioned a CB500T engine for use in my CL racer, so I decided to combine the remains of the two engines into one runner, to get my buddy's CB back on the road. Obviously the original CB engine was toast (what with half a piston floating in the case, and the piston pin welded to the conrod), so we pulled apart the CL engine with the holed piston and began cleaning.

Not TOO terrible

Luckily, most of the debris from the piston had gone out through the exhaust before the hole broke through the piston crown. What little had gotten inside had been deposited on the top of the conrod, which cleaned up easily. We swapped the good side covers, sprockets, and electrical bits from the CB to the CL, and will recondition to head for installation later. The CB head is a later model with thicker castings and stronger studs, so it is the better choice.

For the guts of the engine, we tracked down some NOS pistons, aftermarket pins and clips, and rehoned the cylinders to clean up the minor scuffing and glazing. After that, the parts went together smoothly.