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2001 yz 125 break in

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i just rebuilt me 2001 yz 125 and this guy told me to run half a tank of gas through it quarter throttle. then do the same thing but half throttle. then its readly to roll. whats yalls opinion on this

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You can ride it but take it easy for the first few tanks of gas.

do not do this, ride it normal for the reason the above post mentions

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Ride it normal.

However, my YZ250 manual states to start it, warm it up then shut it down and let it completely cool. Then start it warm it up and ride it for about 5 minutes at less than I think 1/2 throttle, shut it down and let it cool. Then warm it up run it at up to 3/4 throttle and occasional full throttle for about 5 minutes. Then warm it up and run it like normal for 5 minutes and let it cool. Then take the cylinder off and inspect and reinstall then it's ready to race. This is all done with 20:1 oil ratio. I am going by memory with all this so if you need the exact wordage, I will get it and repost.

Personally, I skip the 20:1 oil mix because this will lean out the fuel air ratio and second, I would skip the whole take the cylinder off thing too. I guess if you race then it might be worth it, but I seriously doubt most of the riders do this step.

Edited by Mark6299

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Ride it normal.

However, my YZ250 manual states to start it, warm it up then shut it down and let it completely cool. Then start it warm it up and ride it for about 5 minutes at less than I think 1/2 throttle, shut it down and let it cool. Then warm it up run it at up to 3/4 throttle and occasional full throttle for about 5 minutes. Then warm it up and run it like normal for 5 minutes and let it cool. Then take the cylinder off and inspect and reinstall then it's ready to race. This is all done with 20:1 oil ratio. I am going by memory with all this so if you need the exact wordage, I will get it and repost.

Personally, I skip the 20:1 oil mix because this will lean out the fuel air ratio and second, I would skip the whole take the cylinder off thing too. I guess if you race then it might be worth it, but I seriously doubt most of the riders do this step.

Same thing i do. I run my regular ratio and dont do the tear down. No problems yet!

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The best way to state it, it almost doesn't matter what you do so everything everybody has done is going to work. Modern 2-stroke dirt bike engines are not very sensitive to break-in procedure. I can tell you, idling does nothing to break in engines. High speed no load glazes cylinder walls. Lugging is always bad for engines. So basically all that is left is riding it normally for break in.

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Whoa.... what kind of piston did you put in it? Wiseco forged break in is totally different than cast. And you don't run any different pre-mix ration than normal.

Forged needs a longer heat cool down cycle to form the piston to the cylinder moreso than a cast piston.

The above heat/cool down procedure suffices for forged and it should be followed anyway, regardless of cast/forged piston.

Edited by j-bo

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http://mototuneusa.c..._in_secrets.htm

Check out the link, lots of good info.

This is the 2 stroke forum.

"Although the examples shown here are motorcycle engines,

these principles apply to all 4 strokes"

Edited by j-bo

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This is the 2 stroke forum.

"Although the examples shown here are motorcycle engines,

these principles apply to all 4 strokes"

It doesn't say they don't apply to two strokes. I think there are as many opinions on how to break in a rebuild as there are people doing the rebuilds. I was merly giving an accepted example from a guy who is know to have tested many different ways in a scientific approach.

Me personally, I'm one of those guys that I let it idle and warm up, do a final once over to make sure all is ok, then go race it. I believe they never run better than the first 1 to 2 hours of run time.

As far as the forged piston conforming to the cylinder and the cast not so much. If the piston needs to conform to the cylinder you have much bigger issues. The piston should not touch the cylinder in the same manner the rings do. It's the rings that are the subjet of controversy during brake in, not the piston.

Some pistons react differently to time and temp. A forged piston could potentially expand at a much quicker rate than a cast piston and the cylinder and sieze, this is the reason for caution during so called brake in.

The way these engines are made in this erra and the technology used, brake in is a mute point, as long as you rebuild with the same fundamentals used at the factory. If you don't brake it in the old school way and something fails early on, then it was going to fail regardless. Just my opinion from more than 30 years of experience.

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So we don't get in a big pissin match... I'll agree to disagree. :smirk:

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My method:

Warm it up on the stand

Shut it down and let it cool

Give it a once over, radiator clamps, coolant level, head cylinder base nuts, etc.

Just ride it normal

Now, if your "normal" is a dune flogging, I might take it"easy" another 15 or 20 minutes, ie, no 30 seconds of WOT up comp hill or anything. I trail ride / woods race, so a few seconds of WOT is all I can get anyway without wadding myself into an oak tree.

FYI to anyone that's interested -

I've been in about a dozen engine manufacturing plants. Small two strokes are assembled, then fired up at wide open, full load, by pretty much everyone out there. In defense of the "take it easy" guys, this is partially done because of time constraints (some of these plants are trying to push tens of thousands of units thru each day).

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just dont beat the piss out of it, warm it up thoroughly, then go 1/2 to 2/3 throttle for a tank of gas or something. If you go wide open you run the risk of getting a cold-seizure which is no fun

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Whoa.... what kind of piston did you put in it? Wiseco forged break in is totally different than cast. And you don't run any different pre-mix ration than normal.

Forged needs a longer heat cool down cycle to form the piston to the cylinder moreso than a cast piston.

The above heat/cool down procedure suffices for forged and it should be followed anyway, regardless of cast/forged piston.

Remember, you're breaking in the rings, not the piston. Piston material has no effect on break in. Forged and cast pistons both run the same rings in the same cylinder so their break in is the same.

And break in is not a heat thing, it's a pressure thing. Temperature cycling does nothing to break in an engine. You need to make pressure to seat the rings.

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Remember, you're breaking in the rings, not the piston. Piston material has no effect on break in. Forged and cast pistons both run the same rings in the same cylinder so their break in is the same.

And break in is not a heat thing, it's a pressure thing. Temperature cycling does nothing to break in an engine. You need to make pressure to seat the rings.

I thought the piston expanded when it heats up, which means the piston would expand quicker than the cylinder resulting in a cold seize. I literally saw an episode of judge judy where a guy with a 2001 kx125 got a new top end put in by a shop, he flogged it on the first day, it cold siezed, and then the shop had to pay for half of the price to repair it. (because judge judy didnt know shit about engines so she didnt know it was the riders fault)

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Warm it up until the cylinder feels warm by the touch of your hand. Then RIDE IT, load up those rings for the best seal. Get a good heat cycle.

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Remember, you're breaking in the rings, not the piston. Piston material has no effect on break in. Forged and cast pistons both run the same rings in the same cylinder so their break in is the same.

And break in is not a heat thing, it's a pressure thing. Temperature cycling does nothing to break in an engine. You need to make pressure to seat the rings.

To each their own on break in processes. I tend to lean towards what is the more acceptable practice. It doesn't take too much time to do.

But...there is more to it on forged pistons. Or just ask Wiseco or Eric Gorr what they recommend for break-in.

And....a good warm up is necessary/good idea when you're at the track and are warming up to go brraaaaaaaaaaap the crap outta the bike. Cast pistons are more foregiving and you can braaaaaaaap the heck out of it with little to no warm up if you are that much in a hurry.

Cast=rings

Forged=piston/rings

This is from GLM:

break-in and warm up periods are crucial for the forged piston.

An example of the dramatic expansion of forged pistons is the piston skirt clearances in the cylinder. A typical forged piston has a skirt clearance of approximately .0007 to .0009. A cast piston has a skirt clearance of .005 to .007. The forged piston has 10 times more slop in the cylinder. This results in less ring stability against the cylinderical wall, more piston noise and extra blowby.

In all fairness, after the forged piston has reached operating temperature, its dramatic expansion makes up for these extra clearances.

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To each their own on break in processes. I tend to lean towards what is the more acceptable practice. It doesn't take too much time to do.

But...there is more to it on forged pistons. Or just ask Wiseco or Eric Gorr what they recommend for break-in.

And....a good warm up is necessary/good idea when you're at the track and are warming up to go brraaaaaaaaaaap the crap outta the bike. Cast pistons are more foregiving and you can braaaaaaaap the heck out of it with little to no warm up if you are that much in a hurry.

Cast=rings

Forged=piston/rings

This is from GLM:

I have to agree with the hard break-in. The window of opportunity to get the good seal on the rings is VERY small with modern rings and bores.

If it fails on the loaded break-in, then it was going to fail anyways. Just obviously be smart and use common sense. Don't start it and hammer it without at least being to operating temperature and making sure you have no leaks ect., you want to ride it the FIRST time you start it. Be very meticulous to make sure everything is nice and tight, filled with water ect ect so you DON'T have to shut it down, because if you do, you might have lost the ONLY opportunity for the "better" seal. It will prob still run very good, but maybe not as well at it could. I have always done this with all my motors from 2T to supercharged car builds. I have never had one fail, and I always seem to have that "faster" weapon people just think is a fluke. There is science behind it :bonk:

BTW, I asked Eric about breaking in my 295, just to double check on what he does with HIS builds... and he said "warm it up, and RIDE IT"!

The link on post #9 provided by KX450 is a great read.

But as stated above, to each their own. A good break-in, is one that doesn't break. But a better break-in, is the one that gives you that edge :smirk: .

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To each their own on break in processes. I tend to lean towards what is the more acceptable practice. It doesn't take too much time to do.

But...there is more to it on forged pistons. Or just ask Wiseco or Eric Gorr what they recommend for break-in.

And....a good warm up is necessary/good idea when you're at the track and are warming up to go brraaaaaaaaaaap the crap outta the bike. Cast pistons are more foregiving and you can braaaaaaaap the heck out of it with little to no warm up if you are that much in a hurry.

Cast=rings

Forged=piston/rings

This is from GLM:

You're parroting numbers and you don't even know what they mean. You say the forged piston runs .0007-.0009 what (inches or mm?) Cast runs .005-.007. You say forged is 10x looser but your numbers say otherwise. I don't know about 125's but Wiseco specs .0015" for their piston to cylinder clearance in a 250. That is the same for cast pistons. Rings, forged or cast are identical. You can put OE rings on your Wiseco and Wiseco rings on your OE piston.

Ok, forged pistons dolike to run looser in the bore (vs. cast hypereutectic) and do take longer to warm up. That doesn't mean they take longer to break in. The fact is, you're not breaking in the piston, you're breaking in the rings.

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