So I rebuilt the top end of my 300 last season. Although it wasn't because it got damaged, it was just regular maintenance at 40k miles. I was mostly in there to inspect everything, but also replace the piston rings, hone the cylinders, clean the cyl head, all new upper gaskets, full new set of water piping, and a full clean out of the coolant and oil channels and lines.
Link to the thread I made back then, continue reading here for the TLDR essentially. I think I even described the emotional toll doing that work had on me in the thread, it was scary working on my only bike as a college kid. I don't have the cash for a new bike, lol. But I had an idea for what I was undertaking, and it couldn't have come out better IMO.
Hey fellas! Figured I'd start a thread for this, move it if needed. My '14 N300 with 40k+ miles, a lot of commuting, hard riding, track days, and some people learning on it needs some real love and care. It runs pretty good, it shifts a little crunchy, a bit of lash has developed in the...
www.kawasakininja300.com
Had to take the motor completely out, and it lived on my bedroom table for about 2 months to do that. The work cost me about $400 in parts IIRC, but the cost was mostly time and effort. My story was a success story, it still runs beautifully to this day with mid 50,000 miles on it, and it's gonna be out on the track in the spring time for sure.
That said, I agree with Ghostt's sentiment to buy just a used motor. If you haven't undertaken similar projects in terms of time, space, cost, effort, or complexity, then I don't recommend it be your first. My 'simple' top end rebuild took up my entire house. I am not kidding, every room (including the kitchen) had bike parts everywhere. It took about 2 months of constant hand work. Things almost always break during maintenance, and you have to wait for parts in the mail. Everything was laid out in the orders/directions they came out of the bike. I hand washed
every single part that came out and went into the motor, including the outside of the whole engine.
Not to discourage you if you want to learn. By all means, if you are prepared to undertake that level of work, I absolutely think you should, and we on the forums here can empower you with experiences and knowledge along the way. Just make certain you won't be the probably 95% of people who undertake an engine rebuild just to find out half way in that it's extremely complicated and detail oriented.
Here's the kicker. All that stress and strain and time and money was just for routine maintenance, not even a repair. My advice to you is that if you open it, and find transmission or crankshaft related failures, I wouldn't even try the repair, and just go for a used motor. Especially those problems, but obviously a ruined cylinder head is gonna be a costly fix as well. So unless you really want to learn and don't care about the time and money, and you find those serious problems, I wouldn't undertake the work.
But again, if you are here to learn and experience, I think there is priceless knowledge to be learned pulling apart any motor, especially one that might be unrecoverable. And in that same frame of mind, myself or anyone else here with the experience would be happy to guide you.
Good luck. Doesn't hurt to just get the motor out of the bike first. Follow the shop manual, it's free online if you haven't found it yet. Also, check oil and coolant reservoir EVERY time you fire up the bike, and you will avoid almost all serious engine problems!
-Mike
