Rodrigo Alvarez

Tinkering as a way of life

K75 Restoration: Bike rebuild

Once all the parts were ready to be assembled, I managed to trick a Gonzalo (The same Gonzalo from the kite foil) to help me carry the assembled engine and gearbox from a fourth floor to the garage. Frankly, I started the day thinking the bike wouldn’t start. There could be a thousand other things that could go wrong, and remember, up to now, I haven’t seen this bike running.

Gonzalo, resting before lowering the engine down four sets of stairs

As I don’t have the engine mount tool, we bolted the gearbox and final drive on to the engine, then the center stand and then the back wheel. This way the engine can be “dressed” from the top.

This is how it looked before installing the frame

I would say that the hardest part is to re-connect the choke and the throttle cables as they have to be guided between the filter and the airbox. The rest of the build, though long, is pretty simple. Every unplugged cable was re-connected (there is no chance of getting it wrong) and every tube re-fitted. Once we were done, we filled up with coolant and checked for leaks, then we did the same for the oil circuit.

Finally we fitted the fuel tank and reconnected the lines. Filled with around 2L of fuel. Turned the key and….nothing…. wait a minute, this was worse than when I started….


Ok, so, I knew for a fact that the battery had charge, as I had checked the previous night, but for some reason, the bike wasn’t being powered. Doing the easiest thing first, of course, I checked the battery was properly connected, and that the fuses were not blown… Voila! For some reason there was a blown fuse. We reached into my car and pulled one of the spares. Turned the key and the dash came on. Good! Brake lights? Good! Flashers? Good!.

Moment of truth, the bike started cranking but wouldn’t start. This was expectable up to a certain point as there was no fuel in the fuel lines. So, we tried again, and again, and aga… wait a minute, it should have already started and that fuel pump was doing a weird noise. I offered Gonzalo to leave if he had something else to do, but in his own words; “I’m not leaving if this bike isn’t running”. Thats the spirit.

Let’s get back to basics; fuel, air, compression and spark. New sparkplugs should take care of the spark. Clean airbox and throttle bodies should have taken care of the air, and new piston rings and valves should have taken care of the compression. It all points to the fuel delivery or a miskate in the engine re-assembly.

This was actually recorded before dismantling the engine, same failure mode, different root cause

How do we know fuel is reaching the cylinder? We proceeded to pull out the fuel injectors to check they were spitting fuel, and indeed, they weren’t! Doing the easiest thing first (as always) a trip to the petrol station and 8L of fuel later, we tried again, this time, the fuel pump noise was normal and after two cranks the injector started spitting. Injectors assembled and let’s try again then. Not even a full crank later, we had a running motorcycle! Though it still needs to burn all the excess oil, and it looks like we didn’t fit the exhaust properly, I am very happy! It also sounds really smooth, nearly turbine like!

Big shout out to Gonzalo for helping with this part!