[Bdk438]

On average how many miles will the motor last before rebuild on a 350 motor?

 

[Goober]

Hard to judge by miles—or even hours—but the longevity of the motor depends a lot on depth and quality of the rebuild and the type of use.

I think the members here who have done complete rebuilds get another lifetime of use out of their quads.

 

[mrbb]

a well cared for and properly maintained and and not abused MOTOR should be good for about 15,000 miles without any major work needed besides basic PM's
this is when you change oil as needed(not just by miles or hours) replace filters, clean and inspect things often and NOT run the crap out of it in HIGH rpm's and extreme conditions
as you run HIGH rpm's more often and in harsh extremes the life span is normally LESS

one of the most important roles in anything lasting long or NOT is in HOW The "X" item is treated and cared for
there really isn;t many things in life that just last no matter what you do or DON"T do to them

so, answering a question like your's is almost impossible, without knowing more on YOU , your PM"S you do, how often and how the atv will be used, where it used also matters a LOT
extreme heat or cold, and or in water or sand, will all decrease life span, just as proper care of it or NOT will

 

[Mjp83]

My new to me 420 has 7,000 miles and 670 hours and was smoking bad. Tore it down, and all looked good inside except head needed bored over .30, new rings and piston. If you can hold a wrench, $110 for machine work and 150 for parts, will get these things rolling again. (I pulled motor as I had trans trouble as well, clutches, timing chain were still in great shape w 7 k miles!).