i blew the top end out of my 87 lt250r. i had to get it bored out and a bigger piston put in. how and how long do i wear it in? thanks

 

IMHO about as long it it takes to get the engine up to operating temperature. If the machine shop did the job correctly you will be fine to open it up right away.

 

are u sure? cause i have always heard u have to break it in

 

If you ask 15 different people on this issue you'll more than likely get 15 different answers.
Here is my take on this.

I have bought many different two strokes in my life. Most were in the form of little engines, such chainsaws, weedie eaters, blowers ect ect. There is a few two stroke bikes in there as well.
All were boken in the way I described. None has ever blown up or has ever been rebuilt. One chain saw that my dad bought in 1964 is still going strong, and has so much compression it is really hard to pull through. All have many, many, many trouble free hours on them with no problems at all.
Did you ever hear of someone operating a chainsaw at 1/2 throttle for so many hours and then 3/4 throttle for so many more hours...............ect ect? It's not going to happen.
On a chain saw and blower these engines see WOT until the gas tank goes dry. Then I refuel and go at it again for a total of 12 hours a day. Even a quad does not see this kind of punishment. If one could log the WOT time of a quad I bet for the average rider it would be less than 20% of it's life. My chainsaw see's like 80% WOT and my blower see's more like 98% WOT.

Like I said, if it was machined right, you will have no problems. If it was'nt and blows up, it won't be because of going to WOT too soon. It will be because someone did not check the clearances or make them correct in the first place.

If it really makes you nervous go ask the guy who built or machined the engine.

 

thanks for the advice. i didnt mean to affend you by doubting your knowledge, i just dont wanna spend another 500 bucks, you know

 

You don't offend me at all. And neither do people that disagree with me. I know that there are other people that disagree with this type of break-in. People stick with what they know works. I know my technique works; i've done it many time. And in all fairness, I'm sure other peoples techniques works also.
Like I said above; if your nervous about this whole deal then just don't hammer on it too soon. What I would not do is baby it though. In other words, get it up to temp (VERY IMPORTANT) and just ride it normal.

 

this is all very true, my dad and uncle have built alot of motors over the years both for cars, hot rods, motorcycles, and they always say start it up and run it the way you want it to always run, helps seals and rings and other moving parts wear in the way they're always going to be. so if your babying it to break it in the rings aren't going to break in right. and as far as the piston your not breaking it in at all just the piston rings if the machine shop did their job right that is.

 

We need to do a poll on this question.Seems like its usually 50/50

 

Lets think about this for a minute. When a person builds a drag car and spends 15 thousand bucks, the car is not street legal, what does he do? how can he drive it around and "break it in"? He can't. He sticks it to the floor. The only thing I do when i build an engine is get it to operating temp or jus a lil hotter and kill the engine till it stone cold. Its just what i've always done. doubt it makes a difference because i have got too impatient and skipped it and it seemed to make no difference. jus my .02....its either gonna go, or gonna blow!