The Yamaha XT600 and XT660 on/off motorcycles easily get 35,000 miles before needing a rebuild but you don,t hear of 600 Grizzlys and 660 Grizzlys with the same motor getting close to that before they need motor work.
I know the Motorbikes have easier road miles but still even at 50% less the ATVs should get 15.000 miles.

 

IMO it's dirt in the motor. Off road use get's tons more dirt in.
So you say "but I have a good filter and I maint it".. Me too and my piston wore..FAST.
So I took it to the Wiseco booth at the race and they said "dirt". So not wanting to think they knew, I asked 2 more top name builders..Dirt was the answer.
They say that off road dirt is pounded into so small of particle that it goes thru the filter.
Thinking further, The skirt was dull. That means dirt they say. So if dirt is going past the rings, makes sence to me that dirt is getting into the bottom of the motor.
That's my 2 cents.

 

Yup, dirt, dust, mud all take a toll. The air cooled motors have looser tolerances and can handle a little more wear too. The dirtbikes ridden mostly offroad have to be rebuilt at ABOUT the same intervals. The fender coverage and smaller tires really help keeping the crud out somewhat though.

 

Another reason is off road machines run at max output. Highway machines, after initial acceleration, rarely run faster than 2500 rpm.

 

All this depends on how well you take care of the machine! IMHO you CANNOT do enough maintenance on any off road machine! As with anything dirt and heat will kill a motor!

 

Maybe its because the Grizlly motor has to carry around 2-3 time's the weight the motorcycle engine does?

 

Come on now I know I'm a little bit over weight but I think it more like 2.5 times....ok

 

never be the one to ride last in the pack. :P try to ride near the front of the pack, less dirt will be kicked up, less engine wear. lol or dont ride in extremely dusty areas.

 

I would say because ATVs weigh more, are in harsh conditions more often usually, ridden for longer periods at a time...usually, and sometimes it seems that bikes have a little better engineering with things than atvs.

 

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The motors would be built at the same place,what the bolt them into is anyone guess. I doubt the 660 motor for the ATV is of less quality then the on one that goes into the motorcycle.