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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By Zack Ailing
      hey guys just picked up a new project bike. Its a 2008 Yz450f with a big bore kit and a stroker crank. The total cc of the engine is now 499. It runs on race gas and will be an absolute monster when shes ready to rip. I will continue to make more videos on the bike so stay tuned Link to the video: 
    • By High On Octane
      2005 YZ450F, Athena Big Bore, Power Bomb, Q4.
      Ok.  Last fall after a decently hot day at the track, I noticed coolant leaking from the weep hole on my water pump after pulling into the pits.  Ordered an Athena re-seal kit, put it all back together and didn't really get a chance to ride it.  3 weeks ago, went out to the track, and after about 20 laps, it started leaking again.  Kept filling it with water to get thru the day, never ran anywhere close to dry or empty, jut a cup or 2 low.  Ordered a Hot Rods re-seal kit with bearing and also ordered a new w/p shaft.  Did it all again and got it back together, ran it, and as soon as it got to temp, it was leaking out of the weep hole again.
      So, what the heck am I missing?  I'm totally stumped on this one.  Is something wrong with my case cover?  Do I need to replace the w/p itself?  I'm feeling like I should've just ponied up for the Boysen in the first place, and now it's biting me in the butt.  Any help or suggestions is greatly appreciated.  Thanks!
    • By Awheeler25u
      Alright guys, my 04 YZ450f runs fine minus some slight backfires when decelerating (need to adjust fuel screw). The other day when I was done checking my valve clearances I changed the oil and filter and put the bike back on the stand, kicked it a few times without the ignition coil in to get some oil flowing got off and noticed a little drip spot on the ground, it was no bigger than a dime so I thought nothing of it. Started the bike with no issues took it for a quick 10-15 min ride, came back to the garage to find out my whole case was soaked with oil and it started pooling in the low spots on the clutch basket side. I cleaned all the oil off and took it out again for 5 mins to try and see where it was coming from, here are my three possible places but nothing directly leads me to believe it’s any of the three either.
      1. Decompression plug area
      2.  Valve cover gasket leak (not really sure because the amount of oil leaking Looks to be a large amount
      3. Oil tank (bad weld or cracked weld somewhere
      what are you guys thinking?
    • By bofar
      Hey guys. I could really use your help diagnosing an issue that came up riding today. Bike is a 2013 YZ450F. Well maintained and haven't had any issues until now. Both the oil and coolant are new and levels are to spec. 
      After riding for about an hour in the sand dunes, I noticed a grinding going on on the right side of the bottom end (from what I could tell). When I looked to see what was going on my kickstarter was vibrating and grinding really loud. This was a different sound than if you engaged the kickstarter while running. It sounded less "clanky" and more "vibrating/grinding" if that makes sense. Grabbing the kickstarter and moving it didn't help the issue.
      When I noticed it, I shut the bike off and gave it a second. Being a few miles deep into the dunes, I had to get it out of there so I started it back up and it seemed fine- no grinding. I headed back to the car and after a few minutes, it came back so I shut it off again, started it back up and nothing. That process happened one or two more times before I made it back to the truck. Seemed to run fine otherwise. 
      Once I got it back to the truck I started it up and tried to pay more attention to what was going on but it wasn't doing it. I did seem to have more of a metal on metal noise coming from the motor. I started and stopped the bike a few times and after the motor stopped there was a distinct metal clank/grinding noise that happened right after the motor shut of for maybe half a second. This doesn't happen every time. 
      I tried doing some research and have seen things that make me think it could be the spring that connects to the kickstarter, or the kickstarter stopper plate- but really I have no idea.
      Seems strange that the issue is off and on.
      Thanks for the help!
    • By Goof331
      Does anyone know if there is any differences between the 2 radiators? Will the yz450fx radiator bolt on a yz450f? What I am wanting to do is wire up a fan to my 2016 yz450f. I know how I am going to do it I just don’t want to use a “universal” fan kit. What I would like to do is get a 450fx radiator and the direct bolt on Trail Tech fan for that radiator to have a good clean look.