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Well, I am thinking about picking up a 2004 YFZ 450 here in the next couple of weeks. It has a DuraBlue axle, Houser a-arms, and Douglas rims with Holeshot tires. I have been told the motor is stock, which is my main concern since I have heard about many 04-06 YFZ's having engine problems. I am not really sure about how many hours the quad has on it, with the way it looks I would say not many at all but looks can be deceiving.
Anyways, from what I have heard/read the culprit for many of the engine problems that the 04-06 YFZ's have seems to be be related to poor lubrication. Insufficient lubrication causing excessive wear to the piston/rod/crank/cylinder causing hundreds to thousands in damage. Looking around online I have read about many people sending their 04-06 clutch covers out to be retrofitted with the 07 YFZ 450 oil nozzle as well as installing a redesigned higher volume oil pump to solve this issue. I was looking into sending it here YAMAHA YFZ450 OIL UPGRADE
As I stated above, I do not own the YFZ yet, I have an individual that wants to trade me a 2004 YFZ 450 and probably some cash for my 2000 Yamaha R1 streetbike. The only reason I am hesitant to do this is because I have heard quite a bit about the lubrication issue that the 04-06 YFZ's have. Have any of you gotten away without doing the oil mod? Has anyone done the oil mod? If so what are your thoughts on it? Was it worth the money? Were you able to do it yourself? Also, are there any other common problems that I should look out for on this bike?
I have an '04 and '05, neither with the oil mod at the moment. The reality is, you may get 100 hours before it rears its head, or 10. No one knows. If you don't ride the rev limiter constantly and keep fresh oil/filter in it I would still get it done but it wouldn't keep me from riding in the meantime.
Otherwise maintenance is key. You NEED to keep the air filter clean/oiled, fresh oil, and stay on top of valve adjustments(not to hard, maybe a 15 minute job once you have doen it a few times.) The motors really are pretty durable.
A few known issues: There is a plug in the top of the motor on the '04 that is rubber and can blow out if you overfill the oil. Replace it with a metal one if it hasn't been done already.
'05+ already have a metal one in place.
The charging system doesn't run full time on that model year as well. Running with the lights on makes the machine constantly charge the batt and solves the issue. If you don't have lights, Yamaha has a resistor kit that likewise solves the issue.
I hate the chain adjuster on the '04/5 as well. It is functional, but the '06+ style is WAY better. I switched mine out, but it can be spendy. You basically need the swingarm, brake, brake plate, shock and linkage to make it work. I bought everything off a guy doing
a part out.