I am just about to finish up the top end rebuild on my motor, so ive started thinking about how im going to break it in. the service manual i have just says run the bike below 1/2 throttle for the first hour, and below 3/4 for the second hour. the regular premix is 32:1 should i change that for breaking in a new top end? anything else i should do besides what my manual says? ill check coolant levels often during the break in, ill check all the most bolts, especially those on the motor after 1/2hr, 1hr. and 2 hr, as well as my plug to make sure im not running too lean. any other suggestions?
how should i break in a rebuilt motor?
- Thread starter tank_tech
- Start date
longtime coming
Member
- Mar 18, 2006
- 265
- 0
Warm it up good. Then just take it for a short ride (15 minutes or so). Ride it on hard ground, not deep sand or dirt. Work it hard to 1/2 throttle, vary the throttle position constantly. Doing short figure 8's would be perfect (1st, 2nd, 3rd gear up and down). Let it cool, check for leaks, check the headbolts and anything else you loosened. Then just ride it. The engine usually lets you know how it feels. Don't make it struggle, but don't coast around either. It doesn't take very long to break in the rings. And if you're too easy on it, they don't seal as well as if you ride it with authority, but only to about 1/2 throttle for the first 20 minutes or so. After about an hour or less, it should take whatever you want to give it. If the jetting was good when you tore it down, it should be good when it's back together. But watch the plug and make sure it is blowing blue smoke while it is warming up.
works for me.
works for me.
scottiedawg66
Member
- Sep 26, 2006
- 75
- 0
i usually just get it up to temperature, revit (not pin it, just rev it up and down) up to full operating temperature let cool and repeat three times (three heat cycles). then wheelie time!
- Jul 20, 2009
- 417
- 0
Didn't someone cover all this a couple of months ago on here, or maybe in Canadian Dave's KDX forum. I think someone posted a very good article about running the motor in quite hard and not nursing it. It was excellent reading with lots of studies done.
2strokerfun
Member
- May 19, 2006
- 1,500
- 1
Probably. This question comes up pretty regularly. Not as often as jetting or oil/gas ratio.Joburble said:
- Aug 29, 2004
- 2,958
- 0
scottiedawg66
Member
- Sep 26, 2006
- 75
- 0
^ that is how i break in my 4 strokes (lots of engine de compression as well). really not much different the heat cycles if you ask me.
The difference between that and heat cycling the engine is having pressure to force the rings against the cylinder walls. When the bike is on the stand, no matter how much you're varying the RPM, there is no load on the engine. There is not enough force to mate the rings to the cylinder wall. 3 heat cycles could be 30 minutes or more of running the engine with no load. According to Mototune's theory, this is plenty of time to create an oil glaze on the cylinder walls. If he's right, and that does happen, the rings will never seat properly afterward. It all makes sense to me. I still do at least one proper heat cycle when using a forged piston. With an OEM or aftermarket cast piston, I don't worry about it. Crank it up, warm it up, and ride it like hell.
2strokerfun
Member
- May 19, 2006
- 1,500
- 1
I, and a lot of others, do a couple of heat cycles by riding the bike. Slow first time, medium second time, pretty fast third time. But there was nothing scientific about why I started doing it that way. I just had a freaking brand-new engine I rebuilt myself and couldn't stand not to get on the bike and ride it !!
