Thinking about a yz125 dirtbike?

[The motor guy]

Was thinking about either a yz85 or a yz125 dirt bike to use to cruise the backroads, but then I was doing some research and learned that you have to rebuild these things like every 30hrs. Is that true? Same thing with the four strokes. How come I can put 2000hrs on my 2 stroke echo weed eater, but a dirt bike top end doesn't last more than 30hrs.

 

[RhondaHonda]

That 30hrs is in full on motocross wide open use and still probably very conservative.

If you are just cruising dirt backroads and not very tall/heavy a CRF230 is a better choice.

 

[The motor guy]

That 30hrs is in full on motocross wide open use and still probably very conservative.

If you are just cruising dirt backroads and not very tall/heavy a CRF230 is a better choice.

They had a 150 next to it that I sat on and that one was street legal and that thing was too tall and seemed a lot heavier for some reason.

 

[RhondaHonda]

They had a 150 next to it that I sat on and that one was street legal and that thing was too tall and seemed a lot heavier for some reason.

How tall are you?

 

[The motor guy]

How tall are you?

I'm short. 5'5" and only weigh about 125lbs

 

[The motor guy]

I sat on a honda crf125 when I went to the dealer to get a battery for my side by side. I'm more a yamaha guy, but that crf125 was perfect. That was a 4 stroke though, also that dealer didn't sell yamahas

 

[RhondaHonda]

CRF125 would be a great cruising around woods and trails bike I’d think. I have a CR250 2-stroke and my wife has a CRF230 and I prefer the much tamer 230 for cruising around on.

 

[Snagglefoot]

YZ125

 

[joekingcorvette]

Most of those two stroke motorcycles will run almost forever. When we were kids we beat the crap out of two stroke and 4 stroke motorcycles and never wore one out. Just don't forget to use the correct oil and gas ratio for a two stroke and you are good to go. I am sure there are some horror stories about not getting many hours out of one. I bought a brand new Honda Elsinore 125cc dirt bike (approximately a 1970 model) and my brother had a new one at the same time. We beat those things like a rented mule and never had a problem with the engines, clutches, or transmissions. The new ones are much better. I have 1,400 miles on my little 125 Honda Monkey and it's very dependable but I had to replace the battery last year. It's a 2020 model.

 

[Cujet]

The 85 will likely be a shorter life engine than the 125, and a 250 will last longer still.

From experience, and as mentioned above, the 125's and up can last a very long time if well maintained from new, and not abused.

Remember the high quality 1.3HP Echo 26cc engine has a lifespan of 300 hours. The equally high quality 40/25HP 125/80/85cc (crankshaft) motocross bikes make 6 to 9 times more HP per CC.

Two stroke crankshaft lifespan is related to RPM, and oil ratio. The 13,000 RPM 85cc engines do tend to have more rapid con-rod big end failures.

NOTE: Two stroke crankcase oil migration is RPM dependent and oil quantity must be increased markedly as RPM increases. 125cc race Kart engines 24 to 1.

 

[Cujet]

For your size and weight, the 85cc bike will likely be a more comfortable fit.

Or even the Honda CRF150r. Makes a bit more HP and has a wider torque curve.

If you fit well on a 125, and don't mind spending the funds, Husky/KTM sometimes offer two stroke 125/150cc bikes that can (depending on dealership and location) have a tag (license plate) for legal backroad riding. With headlight and tail light.

 

[Astro14]

A two-stroke 125 motocross bike, is the lightest weight and best handling of the full size options. My old RM-125 was so much easier to ride - from a handling and riding perspective - than anything bigger or four stroke.

I have toyed with the idea of another 125 two-stroke. No space in the garage at the moment.

So, I like your idea - and they last a long time if not being raced - particularly with liquid cooing - that keeps the jug and head at a more consistent temperature than the days of air-cooled engines.

Post pictures when you get it!

 

[zrxkawboy]

That 30hrs is in full on motocross wide open use and still probably very conservative.

If you are just cruising dirt backroads and not very tall/heavy a CRF230 is a better choice.

I agree that you should consider a trail bike. I have a Yamaha TTR230, and I'm 5'7", and actually wish the bike sat just a bit higher. I'm told the CRF230 is very similar, and Kawasaki has their KLX230 to consider. If you want shorter/lighter, all of the Big 4 offer 125cc trail bikes. My son has a Suzuki DRZ125, which has been a great bike.

 

[SC Maintenance]

How much have these changed over the years?

In the old days you could pull the cylinder off in minutes. First go around you would lightly hone the cylinder, put a new ring on, and put it back together. The bottom of the cylinder skirt was tapered so you didn't even need a ring compressor.

Next go around you might have to hone a little more, and they would make a piston that was 0.002 oversize. That rebuild was a bit more work, but still not hard.

Are they still this way? Either way they would last a lot more than 30 hours. I would prefer a 2 stroke also if you can make it work.

 

[The motor guy]

The 85 will likely be a shorter life engine than the 125, and a 250 will last longer still.

From experience, and as mentioned above, the 125's and up can last a very long time if well maintained from new, and not abused.

Remember the high quality 1.3HP Echo 26cc engine has a lifespan of 300 hours. The equally high quality 40/25HP 125/80/85cc (crankshaft) motocross bikes make 6 to 9 times more HP per CC.

Two stroke crankshaft lifespan is related to RPM, and oil ratio. The 13,000 RPM 85cc engines do tend to have more rapid con-rod big end failures.

NOTE: Two stroke crankcase oil migration is RPM dependent and oil quantity must be increased markedly as RPM increases. 125cc race Kart engines 24 to 1.

I see. The 300hr rating is an emission compliance period. Usually the el cheapo trimmers at home depot are rated at 50hrs.

 

[Bud_One]

I had an old 93' YZ125 back in 2001 , that I had the engine rebuilt , including nikasil plating the cylinder . I used it for hair scrambles and woods riding. Only rebuilt it once and rode it for two years. Sold it and the guy that bought it from me never rebuilt it . YMMV
I miss that bike, should of never sold it. Replaced it with a 97' Honda XR250R .

 

[IndyIan]

Only the racing 4 strokes need to be rebuilt often. And if you are not wringing their necks on the track, they should last quite a bit longer than the race recommended rebuild interval.
Have your ridden 2 stroke motocross race bikes before? They are fun to rip through the gears, doing wheelies, etc, but have small gas tanks, stiff suspension, tall 1st gears, short top gears, and aren't really meant for relaxed trail cruising. If you go out for a short time they are fine, or have someone bring extra fuel for you.
I have an old 96 race tuned YZ250 and its fun around the farm, but I don't take it anywhere, and really 30 minutes of trying to manage the power is all I need. Even geared down to 55-60mph top speed, 1st is pretty tall.
The YZ125X is a bit more trail oriented but still has the small tank, and they don't widen the gear ratios.
Ktm has the xcw versions of their 2 and 4 strokes which are designed even more for trail riding, with a wide ratio gearbox, slightly bigger tanks, headlight, softer suspension. They are expensive, but a used 125 or 200 xcw is pretty nice. I should sell my YZ and get 200XCW, it would be much better for my usage.

 

[Snagglefoot]

Wasn’t there a low point for two strokes when they almost disappeared ? There seems to be a resurgence. On the other hand, two stroke outboards are toast!

 

[thastinger]

Have an 03 RM100, which is from the Suzuki/Kawasaki collaboration era, those 100s might fit you a bit better and make great little bikes for the type of riding you're describing. They are way bigger than the 85cc frames but not quit 125 size.

 

[The motor guy]

Have an 03 RM100, which is from the Suzuki/Kawasaki collaboration era, those 100s might fit you a bit better and make great little bikes for the type of riding you're describing. They are way bigger than the 85cc frames but not quit 125 size.

How many times have you rebuilt it?