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Still Not Getting The Urge.

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With winter coming I have come to the crossroads. Rebuild or Not rebuild.

I bought my 01 yz250 used back in late July. It started first kick every time with the owner stating he only rode it a few hours after he rebuilt it. After riding close to every week for 2-3 hours of woods riding, the bike is still kicking over first shot. It doesn't seem to pull as hard since the day I bought it, but I think that's just me finally getting use to it.

Because of the motor doing so well, what do you guys think. I just don't seem to have that urge to send it in for rebuild.

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IMO it takes a fair bit of time, effort, money and patience to split the cases and rebuild it. However if you're riding it every week then I think you will definitely see the benefits, and also make sure you wont get any unexpected surprises next summer - you'd hate to have to rebuild it half way through summer for whatever reason.

Also, I'd say it doesnt pull as well cuz the top end has a fair few hours on it, a fresh piston and I reckon it will pull like you remember it did.

benefits > risks/costs

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learning to split the engine is a very smart move, no one work on your parts as good as you. Splitting the engine is not so difficult and doing a topend is a piece of cake. If you are able to change a tire on your car you should do fine changing pistons.

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Your talking 2.5 months of riding in woods right! If anything i would do rings. You will be able to inspect anything further from there. I agree, it will only take you a couple of hours to do this task if you just take your time and enjoy the wrench time.

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Alright. Looks like I'll be dusting off the manual. I'll buy the whole rebuild kit just incase. Might as well change everything if I have it apart.

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You'll thank yourself for your desicion in the long run. Well worth the minimal time and money put into the top end now compared to if something catastrophic were to happen like a busted skirt. Youre talking $150 compared to $500-1000 or more depending on the amount of damage if the piston choses to let go.

Well worth it in my humble opinion.

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if it were me i would just plan on a ring job. I wouldnt do a whole top end. I know there is others who would though. while doing the rings you will be able to see everything else.

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^If your gonna take the top end apart to replace the rings on a piston with an unknown amount of hours on it why wouldnt you throw a fresh piston in there for peace of mind at a minimum. Guess that just doesnt make much sense to me.

If it were his bike since the top end was installed and he knew how many hours on it he knew how many hours were on the piston I guess I wouldnt disagree so strongly.

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When he initially said rebuild, I assumed splitting the cases and replacing bearings, checking other things out and making sure everything is tight. Now we're just talking about doing rings?!

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Doing only the rings is of questionable value. Yea, it might work. BUT, your piston my look good, but be ready to let go.

Really, do things right and complete a full top end job. If a person cannot spare the extra 100 bucks, shoudl you be riding motorcycles? Especially when the extra 100 has the very real chance of saving you a grand when the piston explodes.

We're talking abotu a used bike. God only knows if the piston was ever replaced.

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When he initially said rebuild, I assumed splitting the cases and replacing bearings, checking other things out and making sure everything is tight. Now we're just talking about doing rings?!

I did too... I dont think it makes much sense to take it apart to inspect internals and not replace the high wear parts such as piston and bearings at a minimum if for nothing more than peace of mind. Throwing a set of rings in there does nothing in terms of reliability.:smashpc:

Dont know where that idea came from...

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Doing only the rings is of questionable value. Yea, it might work. BUT, your piston my look good, but be ready to let go.

Really, do things right and complete a full top end job. If a person cannot spare the extra 100 bucks, shoudl you be riding motorcycles? Especially when the extra 100 has the very real chance of saving you a grand when the piston explodes.

We're talking abotu a used bike. God only knows if the piston was ever replaced.

My thoughts exactly... thats why I questioned the ring idea so strongly!:smashpc:

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Im just saying what i would do. I dont change out pistons on a time schedule. I inspect and replace when needed. I have never had a piston break on me so if it ever happens i may change my tune. Untill then im still sticking with what i do. There are people out there that change pistons every couple of races, I dont get it. The manual says every 5th race. It works for them. Why do they even put inspection criterias and wear limits in the manual anyway. Im not tryin to bust your balls, i really am trying to understand the idea of replacing stuff that is still good. Is there some way that these pistons are damaged and you cant tell? I dont get the idea of a piston "letting go" if its still servicable.

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Im just saying what i would do. I dont change out pistons on a time schedule. I inspect and replace when needed. I have never had a piston break on me so if it ever happens i may change my tune......

Yea I understand everyone's repair/replacement schedule is different and based on personal factors etc.

I guess I and others in this thread read the OP, saw the fact:

- it is a used bike

- not sure how many hours on the piston

- not been in the bottom end to inspect parts and make sure its all tight

- winter is coming up so there is time to take things apart

so suggested common wear parts are replaced - piston, bearing, etc.

If not, there is a risk of the OP starting a new thread halfway through next summer when he could be riding called "piston exploded and scorched cylinder and broke the rod, any one know any good mechanics".

edit: bear in mind a new piston kit, top and bottom end gasket kit and bearings is only about $250, the bike will rip and not gambling on something giving and doing several hundred $$$$ of damage

at the end of the day, its his decision.

Edited by tim512
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Im just saying what i would do. I dont change out pistons on a time schedule. I inspect and replace when needed. I have never had a piston break on me so if it ever happens i may change my tune. Untill then im still sticking with what i do. There are people out there that change pistons every couple of races, I dont get it. The manual says every 5th race. It works for them. Why do they even put inspection criterias and wear limits in the manual anyway. Im not tryin to bust your balls, i really am trying to understand the idea of replacing stuff that is still good. Is there some way that these pistons are damaged and you cant tell? I dont get the idea of a piston "letting go" if its still servicable.

No harm done, but I felt it needed to be questioned as I dont personally know how much experience the OP has with motor internals, and have to base my suggestions assuming he has no mechanical knowledge. Kinda the nature of the beast when it comes to internet forums.

Plain and simple its because they know what the motor parts are designed to withstand within service limits. Running them past those limits is pushing the design of said part/product. I dont think it is necessary to replace the piston every 5 races for the average rider. I run my 250 pistons for 40 hrs then swap them, they get rings at 20 hrs. Usually twice a year on my race bike and once on practice bikes.

The reason you replace it before it fails is because if it would fail your looking at upwards of $1000 to repair something that should have cost you $100. There are so many variables that need to be considered when determining how long your pistons are safe to run its not even funny. If you are a slow trail rider you can get upwards of 100 hrs out of a piston or many more. A guy thats revving the bike out non stop on the track may only get 20 hours out of a piston before it starts to hinder performance and become "unsafe" to run. No hard feelings but I wouldnt feel right not questioning a comment like that to someone asking for help. Cast pistons have a tendancy to show signs of stress fractures when run past service intervals, IMO it is caused by vibration as the piston wears and becomes loose in the bore. Im no engineer but it only makes sense when considering basic physics. Running a piston with any damage what so ever is like riding the bike with a grenade bounding around in your cylinder, as alot of the damage a piston has the possibility of happening cannot/ or is extremely hard to see with the naked eye.

As the saying goes, better safe than sorry. Right? Take what I just said with a grain of salt as Im nothing more than a garage mechanic, but in my experience from things Ive seen, I need to share my humble opinion. However Im sure more experienced mechanics than myself will agree.

But, as Tim said... in the end, ITS YOUR DECISION.

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The pistons have a finite life cycle. I've pulled out shattered cast pistons and still been able to see the machining marks on the sides (after stickign them back together). They would have looked, and measured, new 5 seconds before the blew up.

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Yeah, better safe than sorry. The $200 isn't a big deal during winter break since I'll be riding my 4x4 which is in right now for a winter tune up. The experience of rebuilding won't hurt either.

I was just getting some opinions since the bike is still running like it did when I got it. First kick, minimal smoke, no excessive rattling.

Anyone have links/locations to buy a whole rebuild kit for an 01?

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Wiseco sells one they sell a kit for the top end, and a kit for the bottom end... or you could check out ebay. Always great deals to be had on there. I always keep a couple spare fresh pistons laying around in case something would happen. When I see a good deal I pick it up.

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