YZ400F maintenance


I've read on the internet (a couple of times) that a YZ400F needs way less maintenance then todays MX bikes and that they're almost 'XR reliable'....

Is this true? Maybe some more info on this....



I don't think that is completely true, they are very reliable, (8 years with a 99 YZ400F and only a clutch failure), but do require a higher level of maint. It really depends on your riding style or how often you ride.

had my 98 for 6 years, and the thing purred day in and day out with only light maintenance(oil, air filter). i miss that thing. they are bullet proof.

My 99 400 is dead reliable. I have only adjusted the valves 2x since I have had it. Just change the oil and re-ring it every so often and it should run for a loooong time.

Ok thanks guys. But how often do I need to change the oil? I hope not like every 500 miles...


It all depends on where you ride it and how hard you ride it that tells you when you need to change the oil. Every 500 Miles is probably too much if you are going to be riding MX, but it probably the max for desert or open trails. 500 miles is about 10-12 hours, you should try for 5-8. Because it is old, even sooner wouldn't hurt.

ok speaking of Yz400 maintenance I have some questions. First of all Ive had my 99 yz400 for 5 seasons now, I am the second owner and have been meticulous with maintaince, oil changes,valce checks etc and I know the previous owner was too. She has been bullet proof for me year after year. I have already replaced the timing chain 2 years ago(preventative maintenance), i have replaced all bearings at some time or another(wheel, swing arm, shock, steering head) as part of maintance I replaced the clutch 2 years ago but that was just preventitive the old one was still ok.

so here is my plan, I was thinking about going for like a new yz450 originally but that would cost me excess of 7grand plus id have to enduroize it like ive done to my yz400(i wouldnt get a WR 450 cuz i don't like them) anyways my new plan is to keep my old reliable 400 that i still love but to give her an overhaul so she feels like i have a new bike(ok i know it won't feel as light but thats ok). I am planning on replacing the piston,rings, not becuase i have any problems but just to freshen it up and prevent a failure in the middle of the year, i figure next season is its 8th season and its original so it can't last forever i got a good deal on a Weiseco piston kit on ebay.

question #1 how many ppl with a yz400 are still on original piston? is it smart to change it now even if all seems fine?

question #2 now ive never had any troubles with my valves, always been in spec, should i replace them with titanium or just new ones while i have it opened up and doing work on it? when replacing valves does that mean replacing the guides, springs and everything else as well, should i do all this cuz im putting a new piston

question #3 boyenseed quick shot accelerator pump? is this a good addition? anyone have one is it worth the 80bucks?

question #4 Im for sure going to an auto decompression cam does it make a difference whether i go with the yz450 stock exhuast cam or should i go with HOTCAM .....further to that is it best to get both intake AND exhaust or is just the exhaust cam ok?

guestion #5 what other things should i do while i am planning all this work?

question #6 I did the timing chain replacement and valve checks my self with no problems, is it that much harder to get down to changing the piston and rings, im contemplating doing this myself what special tools would i need? I am mechanically inclined and have lots of tools already.

question #7 is there any advantage to buying a 2002 yz426 stock carb if i could get a good deal on it?

ps. i ride 99% woods riding, race harescrambles and enduros.

thanx gonna start all the work after xmas........

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