Posts
4
Joined
11/2/2020
Location
East Aurora, NY
US
Hi guys, just got around to making my first post!!! I know that the answer to this question can vary greatly, but what is the lifespan of your average motocross bike?i bought a pristine 2010 yz125 in may and have since put 118 hours on it. My maintence schedule is as follows:
-Top end every 35 hours(after that the compression drops fast)
- trani oil wvery 10 hours(motorex 15-50)
-gas mixed at 32:1 (motul 800)
-stock jetting
- bearings regreased every top end change(they always look good)
My concern is more with big ticket items wearing out, like the frame developing cracks, transmission failing, stuff like that.at the rate im racking up hours ill be at 500 with 2 years. Are these bikes made to last that long?
By the way, i ride 50/50 motocross and trail and am moving up to novice next season
-Top end every 35 hours(after that the compression drops fast)
- trani oil wvery 10 hours(motorex 15-50)
-gas mixed at 32:1 (motul 800)
-stock jetting
- bearings regreased every top end change(they always look good)
My concern is more with big ticket items wearing out, like the frame developing cracks, transmission failing, stuff like that.at the rate im racking up hours ill be at 500 with 2 years. Are these bikes made to last that long?
By the way, i ride 50/50 motocross and trail and am moving up to novice next season
Structural Components:
Frame/Swingarm: IF and ONLY IF you aren't a member of the wheelie boys and send your YZ125 into a parked car, your frame is designed to last many years without failure. Normal riding conditions will fatigue a frame (minor dimensional changes) but a failure is unlikely. Depending on climate (dry vs. damp etc), greasing the chassis bearings will have the biggest effect on how the chassis holds up. If a linkage bearing goes dry, you can stress the linkage/frame causing a failure. If you live in a damp region and ride a lot of mud, grease the chassis every 10 hrs at least.
Chassis wear items: some components are consumables and will wear with normal riding. These consist of:
-chain block, chain slider, chain rollers, all cables, brake pads a rotors. These need to be inspected at regular intervals and replaced as needed.
Engine: This is the biggest unknown. I have seen people ruin an engine in the first few hours of running. It seems like your maintenance schedule is legit but here are the most important things to get the most life out of an engine:
-air filter: clean airfilter every ride or when dirty. A two stroke needs a clean airfilter at all times. if you suck any dirt, it's game over. The piston and cylinder take a beating and the crank/rod does as well. You can never be too careful.
-piston/rings: Wear is inevitable. Change at regular intervals and have everything measured by a reputable machine shop. Record wear rates so you can see how things are wearing out over time
Crank: Replace the crank every 100hrs. Some will say this is too long of a service interval, while some will say they can go 250hrs on a 125 crank. I don't like to gamble. 100hrs is a lot of run time on a needle bearing (lower rod bearing). Replace with all OEM parts and have a known, good mechanic do the work. At this time it is also advised to put all new bearing and seals in
Transmission: Since you will be replacing the crank, it's a good time to inspect the transmission as well. All gears and forks should be inspected for wear. Gear dogs should be inspected for signs of wear which will develop axial thrust resulting in mis-shifts, false neutrals and creates a tremendous load on the engine cases. Have them inspected and replaced as necessary. I will catch some shit for saying this, but Yamaha gear boxes are soft and need to be watched. If it were me, I would replaced the most commonly used gears every 100-150hrs (2nd, 3rd, 4th drive and driven gears. I would also replace the shift forks and inspect shift drum and shift mechanism
Known YZ125 issues: The powervalve actuation pins (pins pressed into actual powervalves) will wear and fall out causing the powervalve system to be non-effective. Replace with roll pins, or thread powervalves to accept a set screw to hold the pins in.
My estimate is that with a good maintenance schedule and normal riding, a frame can go 700-800 hours before I'd be concerned about a catastrophic failure. Same with the swing arm. Engine cases I estimate have a life span of 400-500hrs before they thermally and mechanically fatigue. Again, these are just my opinions based on working on bikes for the past 30yrs and really focusing on life span of the components used by average guys and pros. Inspecting the components is crucial to catching a failure before it happens.
The Shop
I like to run a magnetic drain plug, it has saved me a few times in the past. You see a chunk of steel stuck to that thing, it's time to replace some gears in the trans.
Post a reply to: Longevity of yz125(or any mx bike for that matter)