dirt bike engine in an ATV frame, how do you keep it from ripping apart??

[redrider86]

hello ATVriders,
i have always wondered how you can put Dirt Bike engines in Atv frames and not tear the chassis apart??? Dirt bikes don't have counter balancers and the cases wont accept them. so how do you eliminate vibration on a two-stroke or four-stroke Dirt Bike engine so that you can use it in an ATV chassis???

[modock84]

my 426 has a counter balance

[89trx250r]

i think a lot of people dont understand and they just believe whatever the first person tells them the reason i feel this was is because there is a lot of misconception that the frame will be "torn" apart from an uncounterbalanced motor which is just untrue lol if not the dumbest thing ive ever heard just so you know the 04-08 yfz450's were like 50% counterbalanced at most some even say like 30% and hmm i dont see the forums flooded with omg my motor vibrations tore my frame apart omg omg omg so you should really do as much research on your own as possible....

[atvmxer79]

my crf 450 hybrid is counterbalanced

[redrider86]

how is your CRF or YZ counterbalanced??

[BuB400]

For the 100th time I will ask this question. Why will a dirtbike motor rip a quad frame apart and not rip a dirt bike frame apart? One guy told me its because the front forks on a bike absorb the vibration-ha-ha. If I had the money right now,Iwould be building a hybrid with bike motor.

[atvmxer79]

Im not positive about the yzf motors but the crf 450r, 250r, and the 150r are all counterbalanced from the factory. I knew someone years ago that had PRP build him a trx250r chassis fitted with a yz250r motor and it sucked he would always have problems, the chassis would break mounts and the motor would break down ALL THE TIME! Im not an engineer but i believe that it is because of how much larger an atv is compared to a dirtbike, for whatever reason it cant take the vibration when not counterbalanced, this is why the cr500 motor in trx250r chassis never really worked right either.

[redrider86]

the reason a a non counterbalanced engine doesn't tear a dirt bike chassis apart is because the dirt bike has only two wheels touching the ground, one in the front and one in the back. while a quad has all four wheels planted to the ground.
a non counterbalanced engine is vibrating back and forth which each rotation of the crankshaft, but you can't feel it and it doesn't do any harm to the chassis of dirt bike because the two wheels are in a straight line at the center of the chassis so the vibration from the engine flexs the bike side to side. but on a quad all four wheels are planted so the rolling chassis doesn't flex enough to take up the vibration.

[fearlessfred]

Originally posted by redrider86
the reason a a non counterbalanced engine doesn't tear a dirt bike chassis apart is because the dirt bike has only two wheels touching the ground, one in the front and one in the back. while a quad has all four wheels planted to the ground.
a non counterbalanced engine is vibrating back and forth which each rotation of the crankshaft, but you can't feel it and it doesn't do any harm to the chassis of dirt bike because the two wheels are in a straight line at the center of the chassis so the vibration from the engine flexs the bike side to side. but on a quad all four wheels are planted so the rolling chassis doesn't flex enough to take up the vibration.
i aagree with this explaination, but wanted to add that the atv frame is way more ridged and the 2 wheeler frames up tubes in front of the motor run paralel with the direction of the piston travel ,allowing the suspension to absorb some of the vibration.in the early 90s i built a 250r framed cr 500 quad and it would vibrate the rear grab bar in halve in about an hours time. it was scary fast but couldnt ride for more than 15 mins. with out your arms going numb. i wouldnt recommend this combo to anyone.there is a member on this site that says otherwise. he modded his frame to be more like the two wheeler frame.

[redrider86]

the reason i ask is because i have a 87 250X and would love to put a YZ 250 two-stroike in it. so what about rubber mounting the engine would that work?? i have heard of guys doing that to hybrids and if that is the way to go what type of rubber compound is the best??

[jcs003]

the reason a bike frame can handle the vibrations are due to the frame being thicker and having less connection points. the backbone on a steel framed bike is about 2" in diameter and the rest if the frame is cradling the motor. on an aluminum spar frame the parallel tubes work as the backbone and the lower rails support the engine as a cradle also.

[Fred55]

It should be cleared up that all the 4stroke dirt bike engines that people use for hybrids, KTM, CRF, YZF, etc are counterbalanced already.

[Baileygunns]

If I'm not mistaken the YZ motor should be counter balanced too... Pull the right side case cover off and look. The counter balancer is the gear with a half-moon weight on it.

[fearlessfred]

Originally posted by Fred55
It should be cleared up that all the 4stroke dirt bike engines that people use for hybrids, KTM, CRF, YZF, etc are counterbalanced already. thanks for that info,i did not know that .its a good day ,when u learned something and u know what it is that u learned thanks

[jcs003]

Originally posted by Baileygunns
If I'm not mistaken the YZ motor should be counter balanced too... Pull the right side case cover off and look. The counter balancer is the gear with a half-moon weight on it.

are you meaning the YZ 2-stroke or the YZF 4-stroke?

[Baileygunns]

2 stroke... I just pulled a 96 or a 97 apart a few months back to part out and if I remember correctly it was counter balanced...

[jcs003]

Originally posted by Baileygunns
2 stroke... I just pulled a 96 or a 97 apart a few months back to part out and if I remember correctly it was counter balanced...

i looked in the microfische for the 96-97 yz and wr 250 and didnt see a counterbalancer:confused:

[Baileygunns]

I just looked too... Maybe I'm thinking of the quadracer I parted out. I quess I was mistaken... I know I have a balancer sitting in a box under the bench. lol

Even so, if there was any question with any motor, you can pull the cover off and look.

[brewster426]

im putting a 380 ktm 2 stroke motor in a 400ex..i have heard both ways. im in the process of buiding it. i just ordered a 250r exhaust and i have a yfz radiator on the way. i should know something by monday if it will work or not.