Question about 2-stroke engines ...

[Flyingpony]

I've learnt from reading various posts on KB that the piston of a 2-stroke needs to be replace some 500 operating hours or what ever. This I find to be a some what interesting defect for a 2-stroke engine but kind of understand that it's probably due to their stressful operating conditions they have such a short life.

What has really taken me by surprise is the number of 2-stroke engines suffering crank shaft (bottom end) failures and people thinking it's normal. Or the frequency of crank shaft rebuilds.

The reasoning from my point of view is, a crank shaft is designed to last the life of the engine.

So what is it about 2-stroke engine that causes their cranks to suffer such a short life?

[Mooch]

So what is it about 2-stroke engine that causes their cranks to suffer such a short life?

I think it's a combo of things. If you think about performance 2 strokes the NSR/TZR/KR1/RGV's were making 220 - 250 + hp per litre. That's lots of power per cylinder and is similar power ratio to the current Motogp four strokes.

For me it was using constant higher RPM using the 7,500- 11,000 range more, using HP rather than Torque to move the bike along.

Owning a two stroke is a bit like being possessed. Once the evil grin starts your eyes gaze over and you just want to trash the living daylights out of one. They become a very rewarding bike to ride. Unfortunately they won't last as long as a result.

[Racey Rider]

Sounds to me you've been reading about GP125's.
These two stroke GP racers are built to be light and as fast as they can. With the expectation they will be striped frequently and parts renewed to keep them at there peak performance.

Other two strokes like the RG150 are built for road riding. The motors could last 50 000km with care, but a piston kit at 30 000km is the norm.

Dirt two strokes are in a worse riding environment often, so can ingest dust if not looked after properly causing wear.

Two stroke lawn mowers often are neglected as far as air filters go. But still they run! Just not at peak performance.

It's about the type of two stroke you run, and what is expected from it.

[Motu]

You need to compare apples to oranges - 4 stroke dirt bikes now need far more maintanence than 2 strokes,they need pistons more often than 2 strokes,valves....the works.
And an ER 185 will run forever.....

Depends on the use,and the performance level of the engine.My DT230 has done over 25,000km,most of that in lower gears with wheelspin - I think a 40hp XT225 would need a rebuild every 1000km.

[Ixion]

I've learnt from reading various posts on KB that the piston of a 2-stroke needs to be replace some 500 operating hours or what ever. This I find to be a some what interesting defect for a 2-stroke engine but kind of understand that it's probably due to their stressful operating conditions they have such a short life.

What has really taken me by surprise is the number of 2-stroke engines suffering crank shaft (bottom end) failures and people thinking it's normal. Or the frequency of crank shaft rebuilds.

The reasoning from my point of view is, a crank shaft is designed to last the life of the engine.

So what is it about 2-stroke engine that causes their cranks to suffer such a short life?

Shit . Why didn't anyone tell me about this. That means that Phoebe's pistons are about 25 years overdue for replacement! Dunno about short life, 30 years doesn't seem too bad.

[Mr. Peanut]

Owning a two stroke is a bit like being possessed. Once the evil grin starts your eyes gaze over and you just want to trash the living daylights out of one. They become a very rewarding bike to ride. Unfortunately they won't last as long as a result.

Tell me about it...

[slydesigns]

yeah, but aint it fun while they DO work ok... other than always riding it like an MX bike with one finger hovering over the clutch lever ready to pull it in if... sorry I mean WHEN... something finally lets go.

[Coyote]

My brother's KX125 needs a new piston every 14 hours. My friends CRF250 which he races at the highest junior level needs a new piston every 4 hours. I replaced the RGs when the clock read 32000km. Quite a contrast

[Madmax]

My H1 has a set of pistons that are 30 years old

[cowpoos]

My friends CRF250 which he races at the highest junior level needs a new piston every 4 hours.

40+hrs more like it.....

[Coyote]

40+hrs more like it.....

Nope, it's 4 alright. Then again the piston are in pretty decent nick when they come out, just since he's a hard out racer needing top performance out of his bike he replaces them regulary. He can afford it