A couple people have expressed interest in Rocinante, my "Seca X" bike, so I thought I'd start a thread about the trials and tribulations of putting an X engine into a 650 Seca frame. I'll start out with a bit of history about how the project came to be, then go into the technical details. It'll probably take several posts to cover it all - I'll start general then get as specific as people want to hear. Feel free to ask questions along the way. I bought my 82 XJ650RJ near-new in 1985. Put a lot of miles on it those first few years, as it was my only vehicle and I had a long daily commute to university. A few years later (1989 +/-) I was considering trading it in for something with a little more power, even though I loved the bike and the riding position fit me perfectly. One day I was in my local Yamaha shop looking at a used Maxim X. Started BS'ing with the salesman about how great the engine was but the cruiser styling wasn't to my taste, and wouldn't it be great to stick the X engine into my Seca? He gave me a funny look and said as a matter of fact, they had an X engine in the basement - an out-of-province rider had crashed his bike, his insurance company paid him out but never bothered to collect the bike. The engine was literally being used to hold the basement door open and most of the other parts were there too - no frame, but boxes of parts they had stripped off including the wiring harness and all the electronic pieces. Following lots of measuring and head scratching (not enough measuring, as it turned out), we made a deal and I was off. With the help of a friend who was a much better mechanic than me, the engine went in and the bike was in rideable (but not pretty) condition within a couple weeks. Fine tuning and improvements have been going on in fits and starts ever since - 24 years later the project still isn't what I'd call finished. It has been ridden regularly that whole time and I don't see that stopping any time soon. So, to start with the FAQ's: 1. Is it possible to put an X engine into a Seca frame? Yes. 2. Is it a quick and easy swap? No. 3. Is it worth it? That depends Longer answer to No. 3: if you like your 650 Seca (or Maxim) but want more power, a far quicker, easier, and probably cheaper route would be to sell the 650 and buy a 900. You won't be disappointed. But if you have access to a complete X engine in good condition and you want something a bit unique, Rocinante is living proof that it is possible. One warning is that if you spend a lot of time in stop-and-go traffic in a hot climate, be prepared for some significant challenges in getting the cooling system to work as effectively as on the stock bike due to frame differences. The project has it's share of challenges but doesn't require any frame surgery or special fabrications. Some of the challenges are obvious (like, how the heck am I going to mount that radiator and run all the cooling system plumbing?) and some sneak up on you but they are all fixable, and overall the swap is a piece of cake compared to some of the builds that people have shared on this forum. Tomorrow I'll start with the technical details.