What causes 250f 4 stroke to explode?

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12/26/2017 5:25 PM

I am thinking of buying a used yz250f 2009.

The bike looks very clean and well maintained. $2000 USD.

However, many people online have made me a bit hesitant in buying a used 250f.
Everyone seems to think they are ticking timebombs.

What exactly would cause a 4 stroke to have a complete failure?
How would you prevent that.

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12/26/2017 5:30 PM

Yamahas are pretty tough.
Typically lack of maintenance and beating the shit out of them.

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12/26/2017 5:35 PM

Lots of moving parts and very high RPM's......like very high. I think these newer 250F's are way more bullet proof compared to what they were just 5 - 6 years ago. Definitely a lot more durable then what they were 10 years ago. Seen a lot of 2004-2009's blow the living shit out of themselves over the years.

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And there goes Jeffro. One of God's own prototypes. A super high-powered mutant of some kind never even considered for mass production. Too weird to live, and too rare to die.

Pimpin' Ho's , Rollin' fatty's......drinkin' beers , beers , beers!! ~ Ja

12/26/2017 5:44 PM

The main issue with the 250F's is lack of normal maintenance. These little engines turn a lot of rpms and are a full on race configured engine that is not built for a long life, but rather a very high output of power vs size. This means they require regular maintenance and for the most part there are a lot of them on the market that just did not have that.
The biggest failure rate comes from broken valves. This is due to not replacing them when they start to grow and closing up the valve clearances. The valve breaks and then that in turn takes out the piston, head, rod, crank and the cases.

If you should elect to get one used, then if you have starting problems and find the valves need to be re-shimmed, then it's time to have the head reworked with new valves , springs, retainers, clips and have the valve seats cut or replaced as well as replacing the cam chain.
Also don't forget to replace the crank on as regular maintenance as well.

Paw Paw

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12/26/2017 5:48 PM

Paw Paw 271 wrote:

The main issue with the 250F's is lack of normal maintenance. These little engines turn a lot of rpms and are a full on race configured engine that is not built for a long life, but rather a very high output of power vs size. This means they require regular maintenance and for the most part there are a lot of them on the market that just did not have that.
The biggest failure rate comes from broken valves. This is due to not replacing them when they start to grow and closing up the valve clearances. The valve breaks and then that in turn takes out the piston, head, rod, crank and the cases.

If you should elect to get one used, then if you have starting problems and find the valves need to be re-shimmed, then it's time to have the head reworked with new valves , springs, retainers, clips and have the valve seats cut or replaced as well as replacing the cam chain.
Also don't forget to replace the crank on as regular maintenance as well.

Paw Paw

How much would all of that cost?

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12/26/2017 5:49 PM
Edited Date/Time: 12/26/2017 6:01 PM

Frog8fly wrote:

I am thinking of buying a used yz250f 2009.

The bike looks very clean and well maintained. $2000 USD.

However, many people online have made me a bit hesitant in buying a used 250f.
Everyone seems to think they are ticking timebombs.

What exactly would cause a 4 stroke to have a complete failure?
How would you prevent that.

USD? Are there other types of currency in Montana?

Oh, and welcome, I see you just signed up. Interesting to see what perpetual circle you will take the users on that think this is real.


Much ty

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much ty. How to spot a paid forum poster/artificial forum traffic producer (see list of actions/phrases below):

Copius pattern amounts of phrases like “Anyone have”..., “Anybody know?”.... and their variations.

Thoughts?
Any help is appreciated!
Thanks in advance!





12/26/2017 5:58 PM

A used bike is ALWAYS a gamble, these aren't used cars so service history/hour meters are very little use.
The general condition of the bike is your best gauge of how its been looked after and rode. If I was going for a used 250f my biggest concern would roughly how many hours on the crank/if its ever been changed. Other stuff like valves and pistons can be checked/changed much easier.

Take advise online with a pinch of salt, different brand loyal guys will slag off other brands, and 2 stroke guys will slag off 4 strokes. Reality is there are no basket case brands, they are all fairly solid with good maintenance, and a 4 stroke won't grenade itself as soon as you kick it over.

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12/26/2017 6:06 PM

If you're slow and you change the oil it will be fine. Just don't rev the piss out of it.

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12/26/2017 6:23 PM

i had a hand me down motor from leighton lillie in my 08 crf250 and i rode that thing for like 200 hours, not including him practicing on it all year. and it finally let go, rod broke. if you check your valves and cam/cam chain every few months, itl go for a long time

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12/26/2017 6:40 PM

Only one person in this thread has the correct answer.

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12/26/2017 6:51 PM
Edited Date/Time: 12/26/2017 6:51 PM

Frog8fly wrote:

I am thinking of buying a used yz250f 2009.

The bike looks very clean and well maintained. $2000 USD.

However, many people online have made me a bit hesitant in buying a used 250f.
Everyone seems to think they are ticking timebombs.

What exactly would cause a 4 stroke to have a complete failure?
How would you prevent that.

kzizok wrote:

USD? Are there other types of currency in Montana?

Oh, and welcome, I see you just signed up. Interesting to see what perpetual circle you will take the users on that think this is real.


Much ty

What was the point of your comment?
How could me asking about dirt bikes not be real?

I said USD because I'm very international. Even though I am from Montana, I'm currently living in South America.

Stop being a troll.

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12/26/2017 6:51 PM

slipdog wrote:

Only one person in this thread has the correct answer.

Who might that be?

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12/26/2017 7:04 PM

2 strokes never blow up. Oil

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12/26/2017 8:29 PM

You cant tell how well it's been maintained by looking at.

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12/26/2017 8:45 PM

if theres a bomb in the bike it'll blow up know what im saying?

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12/27/2017 12:33 AM

slipdog wrote:

Only one person in this thread has the correct answer.

Much ty

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12/27/2017 12:38 AM

Photo

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12/27/2017 12:42 AM

It has two more strokes...

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12/27/2017 12:50 AM

nytsmaC wrote:

Much ty

Dude I guess I caught the very tail end of this one can you or someone please give me a brief synopsis on the “much ty” ..... this is all i know at the moment

Photo

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12/27/2017 1:37 AM

Lightning78 wrote:

Dude I guess I caught the very tail end of this one can you or someone please give me a brief synopsis on the “much ty” ..... this is all i know at the moment

Photo

http://vitalmx.com/forums/Moto-Related,20/KTM-SXF-250-2017-opinion-guys,1319490

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#1
KX125

12/27/2017 1:55 AM

Frog8fly wrote:

I am thinking of buying a used yz250f 2009.

The bike looks very clean and well maintained. $2000 USD.

However, many people online have made me a bit hesitant in buying a used 250f.
Everyone seems to think they are ticking timebombs.

What exactly would cause a 4 stroke to have a complete failure?
How would you prevent that.

250fs are high rpm motors. the upper bearing and piston take the most abuse.

correct jetting, and regular oil. really its just simple maintenance

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"If you feel in control, you're not going fast enough" ~Mario Andretti

12/27/2017 2:18 AM

Maintenence. When you buy any used 4 stroke the first few things to do is check the bottom end for play, replace the piston, replace the timing chain, make sure the valves are sealing, and check valve clearance.

Never believe the previous owner about any work being done. People will lie abou anything when theres thousands of dollars waved in their face.

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2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600

12/27/2017 4:29 AM

Just buy a 2 stroke. I wouldn't own a 4 stroke (especially a 250f) if I was concerned about keeping up with the required maintenance and fixing it should anything unfortunately let go.

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12/27/2017 6:31 AM

Put in new bearings, cam chain, rod, piston, rings, valves and stem seals... change your oil every serious ride and the oil filter every third oil change, check your valve clearance as per manufacture specs and keep your air filter clean, don’t over oil as that will make starting harder. Use good quality engine oil (not nessasarily brand named) Don’t be scared just look after it.

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12/27/2017 6:34 AM

Sprocket bolts! Yes....im now one of you

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12/27/2017 8:20 AM

Because they don't have a factory ecu

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12/27/2017 8:26 AM
Edited Date/Time: 12/27/2017 8:26 AM

The only reason it should completely explode is if there are explosives planted directly on the bike. If set of your bomb near the bike it should only partially explode. The only other thing that would do it is if you have the purple power band YZ's. They're literally a ticking time bomb.

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12/27/2017 8:37 AM
Edited Date/Time: 12/27/2017 8:39 AM

Sidecar wrote:

Put in new bearings, cam chain, rod, piston, rings, valves and stem seals... change your oil every serious ride and the oil filter every third oil change, check your valve clearance as per manufacture specs and keep your air filter clean, don’t over oil as that will make starting harder. Use good quality engine oil (not nessasarily brand named) Don’t be scared just look after it.

X2, seems like part of the fun would be replacing and/ or rebuilding the motor. I’m sure there’s plenty of up to date manuals for this one.

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12/27/2017 9:00 AM

smashingpumpkins167 wrote:

If you're slow and you change the oil it will be fine. Just don't rev the piss out of it.

This guy knows what's up. I bought an 09 YZ250f for my first small modern four stroke. I replaced the top end when I got it. I like to go through my bikes when I get them. I have a ton of stock parts left over if you need a replacement part or something.

I'd try to get the bike for $1500-1800. Check the footpegs and shifter for excess wear, wiggle the chassis and see if anything is moving that shouldn't, and look at all of the wear items like chain and sprockets, tires, and brakes.

Those older Yamaha 250f motors are bulletproof. No one wants them anymore so you can buy parts on ebay for nothing. Mine is trick, and I love it. I'm very competitive on it in local hare scrambles against much newer and more expensive bikes.

GOOD LUCK!

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12/27/2017 11:35 AM

Paw Paw 271 wrote:

The main issue with the 250F's is lack of normal maintenance. These little engines turn a lot of rpms and are a full on race configured engine that is not built for a long life, but rather a very high output of power vs size. This means they require regular maintenance and for the most part there are a lot of them on the market that just did not have that.
The biggest failure rate comes from broken valves. This is due to not replacing them when they start to grow and closing up the valve clearances. The valve breaks and then that in turn takes out the piston, head, rod, crank and the cases.

If you should elect to get one used, then if you have starting problems and find the valves need to be re-shimmed, then it's time to have the head reworked with new valves , springs, retainers, clips and have the valve seats cut or replaced as well as replacing the cam chain.
Also don't forget to replace the crank on as regular maintenance as well.

Paw Paw

When you were referring to the valves, you said. " this is due to not replacing them when they start to grow and closing up the valve clearances "
By " grow " do you mean that the valve stem itself is stretching leading to lack of clearance?
I always thought that loss of clearance was due to wear on the valve seating face and the valve seat, effectively allowing the valve to be pulled deeper into the seat, closing up the clearance until proper valve sealing is lost resulting in burned exhaust valves and hard starting.
I always thought that the valves themselves broke due to metal fatigue or from hitting the piston when a keeper failed causing the spring to be released or the timing chain being too loose and jumping the timing gears?
Are these modern titanium valves stretching then fracturing? I've never considered that or heard of it before?

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2020 YZ450F
2006 YZ125
2013 YZ 250F special edition
2017 YZ 250
2015 YZ 250f soecial edition
2019 KTM 85 big wheel