250f Motors, Which holds Together the Best?

[born2ride14]

Ok guys, some of you might know i am putting a 250f motor in my 250x/300ex frame. I had a deal on a crf250r motor, but that fell through. So i am re thinking things, i have heard the the crfs eat up valves like crazy. But i am wondering if i should get and 07 kx250 motor? How do these motors hold up?


Kxrida, you have firsthand experience, have you had to dig into your motor?

Also since there is no dipstick, there is an eyeglass, can you easily see the oil level?

Yz250f motor is out of the question, (Wetsump.... oil tank.... looks crappy....more weight.)


Whats everyones opinion? I think a kxf250 motor would be really different.

[k4f5x0r]

Maybe a 250sxf(KTM) motor?

most power and very reliable. Mine must have some hours on it and all it needs is air filter cleanings and oil changes.

May have to look into their reliability more as i actually am not that aware.

[born2ride14]

Ktm, would be great, to much money if something goes wrong

[jesseweaver]

i would think you couldn't really go wrong with any of the newer 250f motors. i think it was just the 04-05 crfs that had the valve problems.

[eastside 400]

im pretty sure all CRF's have the valve problems, really isnt a big deal, no body is smart enough to fix them the right way, the reason the valves go is that the seats are made from a bad material for Ti, and the OEM Ti valves arent that great, easy fix is to put SS valves and springs meant for the SS valves and do a valve job, faction MX sells kits that have the valves, springs, retainers in one kit.

[SRH]

the yzf is hands down the most durable, dr.d did make a wet sump kit for it too but u gotta change ur oil more often...

ktm parts are expensive ,kawi and suzuki..from my expirience havent held together well but this isnt the newer kawi...all the hondas have valve issues...

[One_Bad_400]

the yzf250 motor is the most reliable....... trust me. the honda isnt :(

[400exrider707]

Seems like any of the 250F motors are just going to tear that 300ex frame apart IMO. Too much motor for the chassis. Why not get a cheap 400ex frame and build it in that? It would be a ton easier, and you would have more room to work with, and I think it would be cheaper. There are far more aftermarket parts readily available for the 400ex frame...

The CRF ate valves because they used Titanium valves. You can always put the stainless valves in and not worry about it. That's what a lot of the desert guys do anyways for those long races.

[beastlywarrior]

because he got the frame for cheap. theres been some sweet 300ex/250f hybrids on here

[KXRida]

Originally posted by born2ride14
Ok guys, some of you might know i am putting a 250f motor in my 250x/300ex frame. I had a deal on a crf250r motor, but that fell through. So i am re thinking things, i have heard the the crfs eat up valves like crazy. But i am wondering if i should get and 07 kx250 motor? How do these motors hold up?


Kxrida, you have firsthand experience, have you had to dig into your motor?

Also since there is no dipstick, there is an eyeglass, can you easily see the oil level?

Yz250f motor is out of the question, (Wetsump.... oil tank.... looks crappy....more weight.)


Whats everyones opinion? I think a kxf250 motor would be really different.

sorry I didn't get to yah sooner. If you can get over the yzf, that's going to be your most reliable hands down in stock form. Any of the newer 250f's are somewhat reliable, but just need to keep on top of the valves and keep them in spec. The kxf is a strong running bike. I really like the power personally over the yzf. The yzf had a nice smooth consistent powerband. The kxf has a considerably harder mid range hit and a lot more over rev than the yzf. Rmz motor pulls pretty close to the same. Crf's are a great overall bike as well, but the older 250f's were down right valve eaters. Newer one's aren't as bad, but the crf would be my last choice unless you get a deal on it.

For the record about the ti valves, the yzf uses factory ti valve and is the most reliable. It's the heads and the seats that are the issues with the crf, not the valves in general. If you have any questions just pm me or reply back.

[SRH]

Originally posted by KXRida
sorry I didn't get to yah sooner. If you can get over the yzf, that's going to be your most reliable hands down in stock form. Any of the newer 250f's are somewhat reliable, but just need to keep on top of the valves and keep them in spec. The kxf is a strong running bike. I really like the power personally over the yzf. The yzf had a nice smooth consistent powerband. The kxf has a considerably harder mid range hit and a lot more over rev than the yzf. Rmz motor pulls pretty close to the same. Crf's are a great overall bike as well, but the older 250f's were down right valve eaters. Newer one's aren't as bad, but the crf would be my last choice unless you get a deal on it.

For the record about the ti valves, the yzf uses factory ti valve and is the most reliable. It's the heads and the seats that are the issues with the crf, not the valves in general. If you have any questions just pm me or reply back.

agreed my buddies have put the ss valves in and still had issues but longer intervals between

the kxf rmz out of the steel frame was AWFUL the newer kxf idk same with the rmz

[300ex_#387]

A few years ago when I raced the youth class locally there were 4 kids with 250f hybrids. All of them were in 400ex frames though. 3 of them were yamahas and the other one was a honda. There is nothing wrong with mounting an oil tank. It was a little easier on the 400ex since it already had one stock. Basically the yamaha is more reliable and it would save you in the long run.

[06 Honda 450R]

One thing you really need to watch out for is abuse, think of this, taking a motor built for a 220 pound bike, and put it in a 390 pound quad that you run the crap out of all the time, there will be alot of wear, you will either have to beef it up some how, or change the oil alot, that might not even work, if you see some of the crf to trx hybrids, the motors have to be beefed up to be able to be used in a quad chasis, i dont think this is a very good idea because even with the bigger motor it has to be beefed up, try riding a smaller motor even harder, you would have to rebuild it alot, which means $$$$$$

[woodsman250r]

Originally posted by born2ride14
Ktm, would be great, to much money if something goes wrong

How is it that everyone always talks about how much money KTM's are? Have you ever compared the prices to Yamaha, Suzuki, Honda, Kawasaki, ect? You people act like it cost a million dollars to repair a KTM engine vs. ten dollars for a Japanese engine?


:confused:

[witech]

Originally posted by woodsman250r
How is it that everyone always talks about how much money KTM's are? Have you ever compared the prices to Yamaha, Suzuki, Honda, Kawasaki, ect? You people act like it cost a million dollars to repair a KTM engine vs. ten dollars for a Japanese engine?


:confused:

Its a lot of asumption and speculation. I went through a couple of KTM's and they were pretty much the same price as anything else for parts.

[06 Honda 450R]

K-MART TRAIL MONSTER!!! :D

[SRH]

K eep T hree M echanics

[KXRida]

Kant Touch Me!

[born2ride14]

I ended up going against my word



































KTM $2000

[k4f5x0r]

Look's just like my 06'. Solid bike overall, i have absolutely no problems on mine, even after dumping it a few times from learning/being too small :p

One thing to check though is the jetting, KTM has them extremely lean from the factory, Mine still is the stock jetting, i just mess with the air screw when i ride. But you really should rejet them.

[born2ride14]

yeah, i am having some jetting problems, only idles on choke

[KXRida]

Originally posted by born2ride14
yeah, i am having some jetting problems, only idles on choke

sounds extremely lean. Rejet your pilot jet and probably your main. If need be you may need to move the needle around as well. Keep in mind, if it's still cold in your area this will contribute too. My bikes will not run in the winter with my summer jets in them.

[k4f5x0r]

ditto, now that i've finally started it after a cold cold winter, mine idles very high and wont stop. Runs great through the range just idles high.

Im gunna clean the air filter and if that doesnt work then clean the carb. If that doesnt work ill get a jet kit, since i needed one before anyway :p

[SRH]

Originally posted by born2ride14
yeah, i am having some jetting problems, only idles on choke

check for airleaks around the intake manifold, could also be a valve issue

[woodsracer144]

Originally posted by 06 Honda 450R
One thing you really need to watch out for is abuse, think of this, taking a motor built for a 220 pound bike, and put it in a 390 pound quad that you run the crap out of all the time, there will be alot of wear, you will either have to beef it up some how, or change the oil alot, that might not even work, if you see some of the crf to trx hybrids, the motors have to be beefed up to be able to be used in a quad chasis, i dont think this is a very good idea because even with the bigger motor it has to be beefed up, try riding a smaller motor even harder, you would have to rebuild it alot, which means $$$$$$

dud that 250f has WAY more Hp then the stock motor that was in the 250x/300ex, that 250f has the same Hp. as a built 250x... i dont think it will have a problem pulling it around, the question is how well the chassis will hold up to it...

any updates?

Originally posted by woodsracer144
dud that 250f has WAY more Hp then the stock motor that was in the 250x/300ex, that 250f has the same Hp. as a built 250x... i dont think it will have a problem pulling it around, the question is how well the chassis will hold up to it...

any updates?

I think he's trying to say, that since the dirt bikes are under less stress because they weigh less, that the gears and crank and actually weaker because they can get away with it.

Same reason they put a different bottom end on the 450's for the quads.