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my 1st 4-stroke - 08 kx450f

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So just recently set my 98 kx250 aside in the garage and got myself an 08 kx450f. Took it out for a couple small rides and realized real quick that I needed a new chain a sprocket and new chain guide. Haven't had the time to go through the entire bike yet but wanted to see if I can get some input on what things I should definitely be checking out. New to the 4-stroke world so other than the routine maintenance stuff not sure if there are some particular things on these bikes that are susceptible to wear and tear I should be putting an eye on now.

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Search TT, there are a lot of good threads on maint. of the 08 hear. I would check the primary oil pump screen for debris. Check all grease-able bearings and even the ones that are not grease-able. Check spokes, all nuts and bolts for torque, including the rear sprocket. Check valve adjustment. Change the oil often, the more often you change it the longer it will last. Every 2 to 5 hours is not uncommon. If it has never been rebuilt (top and bottom) it is probably ready if it shows many hours of ride time. Check to see if it has had the accelerator pump and leak jet mod, if not do it, you'll like it. Check throttle cables for wear at both ends. They frey more often than the two strokes.

Let me know how you like it compared to the 2 stroke. I am thinking about going back to one.

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As kx450f63 wrote, there is more to go wrong generally with it being a dirt bike, than worrying much about your 08 4 stroke engine. You sound like your good on the usual maintenance tasks.

As far as 4 stroke specifics go, with your 08, if you are not sure of the age of the timing chain, then put a new one on. It's not expensive, easy to do, and re-installing the tensioner is impossible to get wrong assuming you wind it back and reset it. Valves can wear and it'll get hard to start before anything else happens. But if the timing chain goes wrong then it's often ugly.

If you are feeling paranoid, then install a new Wiseco 12:1 piston kit. Forged "bridge box", stronger wrist pin, and it's lighter all up than stock too. I did about 200 hrs on one. Done about 70 on the current Wiseco. However my stock 06 pin came out badly galled after just 35 hrs. Lucky me!

I think a key to longer service intervals is keeping the revs down and stay off the rev limiter. I read some words by an experienced pro team mechanic who said the life span of a typical 250F is reduced by half for every 10% increase in peak RPM. Do some numbers and that means a huge variation in wear according to rider habits.

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I would check the valve clearance right away... Then grease all the bearings, like swingarm, shock linkage, steering stem.

I would also check the sag? have you set that? Its very important. What condition is the suspension in? and how old is the piston? Being an '08 it needs a suspension rebuild and new piston, unless this stuff has already been done. Fresh suspension makes a ton of difference.

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Thanks for all the input. This will get me going in the right direction. I'll have to look into the timing chain and the valves. The bike runs awesome and the suspensions feels good. I actually just redid the suspension on my 2-stroke and coming to the 4-stroke, the suspension felt just right for me. The front forks always seem to have some oil streaks on it. Don't know if this is normal or if there is a small leak.

Is there a way to lower/loosen/pitch forward the rear brake pedal? when my foot sits on the peg it applies pressure onto the brake so I always have to be conscious about it.

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Thanks for all the input. This will get me going in the right direction. I'll have to look into the timing chain and the valves. The bike runs awesome and the suspensions feels good. I actually just redid the suspension on my 2-stroke and coming to the 4-stroke, the suspension felt just right for me. The front forks always seem to have some oil streaks on it. Don't know if this is normal or if there is a small leak.

Is there a way to lower/loosen/pitch forward the rear brake pedal? when my foot sits on the peg it applies pressure onto the brake so I always have to be conscious about it.

Just adjust the nut/shaft behind the pedal.

If you are seeing oil streaks, check the wipers for dirt and debris the might be holding the seals open.

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To lower the rear brake pedal enough, sometimes you need to grind a couple of mm off the end of the threaded push shaft.

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To lower the pedal you need to loosen the jam nut, then remove the pin that goes through the rear of the pedal. Pull the clevis away from the pedal and turn it clockwise a turn or two at a time then reinstalling to recheck height. Then reverse steps to reinstall.

The fork seals can be cleaned with a very thin plastic (like picture negative, there is a tool sold to do this) first you will need to lower the dust wipers and clean the area with soap and water so you don't push new dirt in. Conform the plastic to the fork leg, then gently slide into the seal and work around the entire diameter of the seal. You may see a small amount of oil escape while doing this, don't be alarmed. In my experiences fork seals can be cleaned like this many times extending their life many years.

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