I'll give you some good detailed information, not because I'm trying to be better them anyone else or anything I just like to be as detailed as possible and educate any if I can.
The 04 and 05's are great for sure a nice jump in power from the 400ex, yes I would do it if I were you. The 450's are peppy and responsive and relatively fast but who cares bout top speed in my opinion unless you're trying to win drags and stuff lol. The 04 and 05 TRX's are not as fast as the 2nd Gen TRX450R's (06 and newer) but they're good bikes they're kick start only as well... Now the 06 ad up is electric with a kick start option any many changes to the engine.
Yes as Duke said, they have Crank Failure issues. Just change you oil after ever 3 or 4 big rides to watch out for metal shavings because usually before the crank fails you start finding silver "Glitter" in the oil filter changing the oil more often will give you more of a chance to catch the crank failure before it destroys the cases.
Now If you do have one that has a rebuilt bottom end ask who rebuilt, ask what crank crank and bearings were installed. it a lot of guys will say they rebuilt their selfs it which is sometimes scary to me personally because if you're inexperienced in working on the 04 and 05's and use Hot Rods bearings or install a new OEM bearing into a worn out left case then you'll have crank failure in no time. Hot Rods cranks are okay but their bearings are total garbage any one with experience will tell you that as well.
The 04 and 05's have an Updated crank design though that helps already prevent the crank from failing, when you buy a new OEM (or Hot Rods crank) they come with a collar that needs to be heated up to be pulled off and Heated to be re installed after the main collar is installed, supposedly what it does its keeps the crank from moving side to side by keeping that collar in place rather then moving thus causing the crank to "walk" to the right then they have an over sized seal that comes with if you decide to use the updated collar. It's optional.
Me in my opinion if you happen to get a crank failure at some point (if it's an un touched stock bottom end still) I just think of it as that is when you can build a better engine for more power and learn more about them.
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