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Realistic Rebuild times and what to do.

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Looking for a little input on rebuild times. Im at 30 hrs on my xcf 450. What all do you replace and when? Do you inspect and then replace or no matter what replace at a set time. Top end rebuild for a 2017 xcf 450 are easy to fine but what are all the parts that get replaced when doing the bottom? I mostly ride trails and single track behind my house. But because i know the trails and ride them often i can really ride pretty hard. On every ride im at places where i have to be in first and second then some places im pinning 5th. Oil and filter at 8-10 hrs moterex 10w50. Air filter every 2 rides (5hrs).

 

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The manual/spec will give you two figures.  One for racing, which basically assumes WOT for the whole time and another one for "recreational" riding.  At 30hrs i doubt you would need to go into the bottom end and probably won't even need to touch the top end.  

 

With rebuilds you need to measure and inspect.  The first wear item that would likely need to be changed internally is the piston rings.  That would/should require new rings and a cylinder hone.  For recreational riding I would "guess" around 100hrs on the top end.

 

Other things you need to keep an eye on would be the valve clearance.  If the numbers are closing up that means its time to have a valve job done.  In the top end there are also plastic guides for the cam chain as well as the chain itself.  Bottom end again you need to inspect and the manual will likely say Inspect and replace as needed.  The big thing is going to be the main bearings, shims behind the main bearings on the crank and the lower end bearing.  Bunch of special tools needed to split the case, hold the crank/clutch, gear stuffers, heated tools to pull the races off etc.  After awhile you might need to change the trans bearings, inspect the oil pump clearance etc.  You will also want to get all rubber parts on the case.  Things like seal for the output shaft since the case will need to go in the oven to install main bearings.

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So cam chain at the same time as piston and rings? Does the cylinder need to be honed even with a new piston? What am i inspecting when i look t OK see what parts need to be replaced? Should the bottom of the valves always look a little black or does that mean i need new valves?

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You need to inspect at 100 hours things like barrel etc , it depends on so many factors

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30hrs at idle is nothing... I've pushed massive hours with nothing more than a valve adjustment. But, I do take care of my stuff. On a 450 I wouldn't even think about touching it till well past 200hrs especially if you're just idling around... 

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Just what I was thinking, not even consider top end until 200 hrs.'16 450 XC. All woods riding for me, mostly midrange RPM. Change oil every 5 hrs and air filter almost every ride.

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8 hours ago, dirtbikedaddy said:

What are things to look for when inspecting?

A service manual will tell you.  The main thing you want to check with it all together is the valve clearance.  Pretty sure the XCF runs Titanium valves on both intake and exhaust.  You want to make sure they are still in spec and that they aren't getting tighter.  I have notebooks for my bikes and write down when i check them, hours etc.  I also do this for suspension settings, carb settings etc.  Its much easier than trying to remember.  

As far as the hone question.  I would say yes.  Anytime you put new rings on you want to hone the cylinder to ensure proper sealing.  You also want to make sure the cylinder is still round(by measuring at various heights and directions).  As far as cam chain, guides and other wear parts.  Those require visual inspection.  If you are tearing it down to the bottom end replace the chain.  I have only had one bike ever that had a chain issue and it sat and had unknown hours when i got it so i have no justification behind that.

 

On the bottom end the crank actually is the same but they separate it and replace the rod and bearing.  The main bearings that the crank rides on are both heated and "pressed" onto the crank with shims behind them and the case is heated and the other side is pressed into the case.

 

Honestly though if you are at 30hrs i think you have plenty of time to worry about other things.  Just keep up to date on the oil changes, clean airfilter, check the valves and braaaap.  

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Thank for the input! Do you guys think as long as it passes a compression test and isnt burning oil its good to go? Ive done the valves once already one intake was right on the limit for being tight the other on the limit for loose and put them both in the middle of spec. Im just trying to get as much info as i can after having catastrophic failure on my last bike.

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What was your last bike? If you aren't a pro racer, and the bike is running great, I wouldn't touch the engine. If the oil coming out looks great and the motor sounds good, leave it alone. I read all the crap about rebuild times on my last bike and replaced two perfect pistons. I'll rideone to two hundred hours unless I see evidence or hear noise.

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I have a 06 450 XC never been apart regular oil changes and carburetor service. I still can pass a leak down test.
These KTM ‘s are a horse of a different color. You pay more in the beginning but simple maintenance they will last. I wish I had bought one years ago

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My last bike was a used crf 450r 08. Crank broke in 5th gear. I just dont want something like that to happen again. I think the leak down sounds like a good way to check up on things without having to buy a 70$ gasket kit. Thanks for the input guys.

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Last week i did a top end rebuild on my 17 450sxf. It has 105hours. Everything looked good, could have went longer. I just replaced the piston, camchain and through a new clutch in it.  The clutch basket had a little bit of play in it but nothing to be concerned about.   All my riding has been intermediate motocross. I ride alot of sand. Air filter every ride and oil every 4-5 hours with filter every second oil change.

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I like the sound of that! Just curious have you been laying the bike on its side and filling the cavities during oil change? I used the reusable oil filters and have just been saturating the filter.

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On 9/24/2017 at 7:01 AM, dirtbikedaddy said:

I like the sound of that! Just curious have you been laying the bike on its side and filling the cavities during oil change? I used the reusable oil filters and have just been saturating the filter.

The shop I had rebuild my crank told me not to use those reusable filters. I had them in my last 3 bikes and now I just use paper filters.  Not worth the risk if a motor shop told me to ditch them.

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