Sunday, October 23, 2011

300 EXC rebuild

I finally finished the rebuild of my KTM engine. I had to tear it down because of a couple episodes of air filter leaks allowing unfiltered air, dust and sand into the engine. I had hoped that the damage would be limited to the top end, but the connecting rod had some play, so it turned into a complete tear down. I started on a Sunday a few weeks ago, and I had the cylinder off pretty quickly, but I ran out of time to split the cases, so that would have to happen on a Thursday.

Parts were ordered and the cylinder was dropped off at the Crank Shop on Kellog road Essex to be re-chromed. They sent it out and said it would be two weeks, which gave me some time to get the cases split. That job went pretty well considering I had no service manual. The rod took longer to arrive than I had hoped, but when it came in I dropped it off with the crank at the Crank Shop and asked if there was any chance I could get it back in time for the weekend. The nice young lady at the counter laughed and said probably not, but she'd ask. I got a call the next day saying it was ready, which was very cool since that would allow me to get the bottom end back together while waiting on the cylinder. Things went well until I realized that one of the new crank bearings was going to need to be pressed onto the crank, and I lacked the technology to accomplish that. I drove back the the Crank Shop with the crank and new bearing and asked if they could get it on for me. Five minutes later I'm walking out with the job done. LOVE those folks. And better yet, she called me the next day to say the cylinder was back.

Along with the new parts (crankshaft and transmission bearings, full gasket set, new reeds etc.) I ordered a service manual. Service manuals all seem to share a few common traits. They're often indispensable for certain procedures, but just as often they seem to omit critical information about how to actually do stuff. I ran into this with the transmission shift drum and forks. The instructions just said to install the forks on the drum and then install the pivot shafts. No specific reference or index points, but they did have some photos of the assembly. I did what the manual said, but couldn't get the transmission to shift into all the gears, just 1st, 2nd and 3rd. I was convinced I had done something wrong, and I proceeded to take the tranny apart. After several attempts to solve this with no better results, I just gave up and continued putting the engine back together with the hope that it would somehow find 4th and 5th gear once I had it running.

Sure enough, once I put everything back together and tested the bike, I had all 5 gears.

New piston from KTM.

This is my cylinder after the re-chrome job. Lovely.

Engine cases etc. Not exactly a sterile environment.

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