2-Stroke Top-end Rebuild Break-in/Run-in Procedure

[Imho]

I have recently completed a top-end rebuild on my son's 1992 YZ125 and went searching for a break-in/run-in procedure. It seems that there are many and varied opinions ranging from the Yamaha "pull the head off a few times and check this and that" approach to the "just get on the thing and ride" approach. I am after some kind of consensus on the procedure (I expect there isn't one) or at least what NOT to do. This is what I have so far:

1. Use the normal ratio of premix as more premix equates to a leaner mixture and therefore hotter running.
2. Two warm-up/cool-down cycles at or near idle.
3. A ten minute run at no more than 1/4 throttle with minimal load on the engine, followed by a cool-down.
4. A ten minute run at no more that 1/2 throttle with varying but moderate load on the engine, followed by a cool-down.
5. Now go for it!

Any help would be appreciated.

 

[georgieboy]

do a search on break in, you will find some threads.
the procedure yr telling sound good.
Some take two full tanks easy on the new topend, some go banging right away.

 

[bclapham]

dont forget, if you put in a forged piston (weiseco etc.) the break in should be more stringent- i read here that if you dont heat cycle weiseco pistons properly its very esy to seize the engine! do a search on a OEM vs Wiseco piston thread (assuming you bought one!)

cheers

 

[RM_guy]

Your break in method is good even for a Weisco (forged) piston. I usually do three heatup/cool down cycles though. Instead of using time (10 minutes of running), run it until the cylinder gets hot to the touch. Make sure that the engine is dead cold before doing the next cycle.

Good luck:)

 

[Senior KX Rider]

Your routine is what I have done with my bikes for years. Works for me:)

 

[Imho]

Thanks for the advice everyone, the procedure I listed seems to have worked well, so far :) .

 

[yzeater]

I did 5 heat cycles until the cylinder was hot. Worked for me. Unfortunately a minute into my first ride I got stuck in 2 feet of mud. Had to rev the engine out more than I felt comfortable doing.

 

[Jaybird]

Heat-n-cool, heat-n-cool, heat-n-cool, ride-n-roost.