Break In Recommendations for New Top End?

I had read a post that related a link for advice on breaking in a new bike. It presented arguments for riding the bike like you plan to ride it from the get go so you would get the best ring seal possible.

It seem logical that this theory would apply to putting in a new piston and rings. What results have y'all had with the tortoise vs hare break in?

Hare. The cylinder pressure will seat the ring properly. If you just cruise around, you'll loose the hatch and the ring wont properly seat. But do what you feel comfortable with. One other thing, it only takes about 30 minutes to seat the ring. If you replaced the piston into the old bore, you can do what you want with it, siezing it really shouldnt be an issue.

once the small window of time is gone,its gone!heres a good link!

break in

Follow the instructions from the piston manufacturer. If you used a Yamaha OEM piston then follow the breakin procedure in the manual. If I remember correctly it mentions top end only breakin procedures (maybe it was the manual for my old bike, anyway it's worth a look). :)

Everyone is always so gung ho to write their own directions, I never have understood how someone can say that the people who designed the motor don't know how to break it in.

Running it hard during break-in seems like stupid advice to me, but I've never really studied the long term effects of break-in on any of my hundreds of engine rebuilds. I have seen machines that were run hard during break-in come back with scored piston skirts though.

Regarding that guy's page about break-in, he says running the motor hard causes more pressure behind the rings. How does he know that?

I don't have the answers, but I believe that avoiding EXTENDED WFO during break-in is never a bad idea.

Page 1-17 in your 2001 YZ 426 manual calls for no more than 1/2 throttle for the first hour of operation. That makes a lot more sense to me than running it hard. Check out Yamaha's recommended break-in here. go to tech articles and there is a 01 YZ manual you can download.

By the way, I'm not calling anyone stupid, I just think that the break-in advice is kinda warped.

I have seen people that know what they are doing assemble top ends dry. They fire them up and run them moderately hard for 30 minutes, the rings should be seated. Change the oil and it's broken in.

Fast break in fast bike as silly as it sounds.

When the rings seat

Yamaben I agree with the 1/2 throttle deal. The problem is with some guys, ya tell them to go out and be easy on the thing for a tank, and they literally idle the thing around. This is a very bad idea. If you run the thing at 60% for a tank, your going to get a great seat on the rings. If you run the thing around at 2500 rpm for a tank, my bet is, you'll get a 20% leak down and an oil burner for life. Running the thing wide open for extended periods is a death sentence for a new piston, I agree. But 3 to 4 heat cycles is all you need to "cure" the piston. But you still have to seat the rings. 6 to 8 3/4 throttle blasts wont hurt the piston, and its what the ring needs to properly seat.

Hell, when I was racing boats, we'd build the new motors with pre broken in cams, just so we could seat the rings on the dyno, then we'd tear them back down and put the new cams in to make sure we could break in the cams with out loosing the hatch for the rings at the same time. That particular class was super sensitive to HP though, and we had to do everything to get every single last fraction of HP. Doing it this way though would usually yield us a leak down of only 3-3.5%. I got 2% on one motor with a soft hone set up once. That was an exceptional deal though, and that soft hone set up was expensive.

bottom line, WFO isnt the idea that Im trying to convey. The idea is that pussyfooting the thing around for a couple of tanks, is far worse than 6-8 blasts around 3/4 throttle all the way through the trans on dry flat ground, not down a sandwash, up hill or anything where an excessive load gets drawn.

Also, change the oil after about 20 minutes of running with a new piston/bore job. The materail that come off the cylinder is akin to grinding compound. Ya wanna get that stuff outa the motor ASAP.

Like I said before, do what your comfortable with, but Ive been racing super high dollar engine for 20+ years, when I say high dollar, Im talkin about a "freshening" that costs 10 grand. Guys that drop that kind of money expect the motor to last a full season or more, and they do.

To each his own though, my YZ has countless hours on it, doesnt burn oil, and has as much compression now as it did just after the ring seated. Leak down is 5.5%. Which aint bad for a mass produced part.

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