KZ400 Diesel - Rebuilding A Wrecked Engine

During the construction of my KZ400 diesel motorcycle, many people had asked about the reliability and longevity of the Yanmar L70 clone engine. I had supercharged it, boosted the horsepower and max RPM, and taken it to the absolute limit numerous times.

Now, I have an answer for that. After 7 years of development, as well as:

-4 certified land speed records
-2500 miles of riding.
-Disabled speed governor
-Supercharged to 5psi
-Upgraded valve springs

...the crankcase split in half directly below the cylinder, nearly blowing the top end clear off...

 

 After careful examination, I was confident that the guts of the engine were fine, and the damage was limited to the crankcase. So, rather than simply swap engines, I registered an account with AliExpress and purchased a replacement crankcase to transplant as much as possible out of the blown motor.

 

After working through my backlog of projects, I put the bike back on the bench. The first step was to disassemble the drivetrain, clean the frame, and improve some of the mounting hardware and wiring.

I finished stripping the engine, and was able to examine the inner assembly for the first time. Overall, the components were in excellent condition, the only major issues being excessive carbon buildup in the combustion chamber, and wear on the output-side plain bearing.

I also inspected the camshaft, and found no evidence that the stronger valve springs had caused any damage to the lobes.

Next, I refurbished the original engine internals, deburred the new crankcase, and installed everything with fresh bearings, gaskets, and seals.

Finally, I brewed up some caffeine and locked myself in the garage for a marathon reassembly session!