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how should i break in a 2 stroke top end?

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I'm about to rebuild the whole top end on my RM, and I've a few questions about how to properly break it in. I know I should take it easy for a few rides, but do I need to run a richer fuel to oil mixture like I have seen others doing? Are there any key points I am missing?

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This is my personal view/way- firstly keep the same mixture you have always used! there is nothing to be gained by adding more oil other than actually makeing the fuel mixture weaker

Take a couple of laps at a briskish pace but not to much load, stop have a drink check your fluid levels as it has now cooled off and your ready to go as your not actually running anything in! the only difference is the piston is new and not old, it is going up and down the self same hole as the old one

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You will want to de-glaze the cylinder so your new rings will seat in. I agree , do not alter fuel / oil ratio. Yes, all that is 'breaking' in are the rings , so 20 minutes, let her cool down , good to go .

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I put a drop of oil on the top end bearing, assemble the rest dry. Dut the cyl on and torque it down. Kick it through real quick about 50 times. This dry seats the rings without oil, letting them seat without a fine film to block seating. Finish putting it together and go ride. I do a "briskish" ride not redlining it or holding it wide open just to make sure everything is put together right. I usually do this anyway on a track to check out any changes anyway. After that I just ride as usual. I'v done this on 2 modern 4strokes and a couple vintage bikes.

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I used to use a wet assembly method when I replace the top end, and just recently switched to the dry assembly method a few years back just as stated above... the only thing I lube is the wrist pin bearing with a few drops of 2 stroke oil. I always take it slow for the first lap at the track anyways, rolling all the jumps and seeing what the condition of the track really is. I go back to the truck and let the bike cool down, while I unload the rest of the bikes and get them ready, then go ride the piss out of it. I recommend the same method on any bike I rebuild for my buddies, 2 or 4 stroke. No need to change the ratio to break in the top end.

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i wet assemble everything. but unlike others, i dont use 2 stroke oil. rather i use a high quality motor assembly lube.

all i do to brake in the motor is. let it warm up fully. then let it cool down all the way. re-torqu the base and head nuts. i do this once more.

then, i let it warm up all the way for a third time...jump on it...put it in first and holeshot that bitch. i dont take it easy, more so of a reson of..i dont know how to take it easy. i keep the same ratio.

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A good pair of needle nose pliers really help with circlips if you dont have a circlip tool. Other than that a torque wrench is recommended but is not absolutely neccessary.

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Thanks everyone for your input! Are there any extra special tools such as a torque wrench that I will need in order to assemble the new piston, rings, and bearing?

The most important tool you can have is a service manual. There are a lot of torque values and things that you will need. I hope you have one. It's actually a pretty easy job. I enjoy doing it.

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Not joking what so ever... I have a torque wrench and use it. But there have been instances, in the 14 years I wrenched on my own bikes that I didnt use a torque wrench for anything and never had a single issue that was caused by it.

Thats why I said its a good tool to have but not absolutely necessary. After you wrench on a bike for long enough you can get pretty close to a torque value without a torque wrench. Not to mention a ton of people dont have the money for a good torque wrench, Ive found the cheap ones are complete junk and dont hold accurate torque values for long, if at all!

To each his own I guess... I do agree that a manual is the number one tool on the list IMHO. Just my .02... not trying to give bad advise, just seaking from my own personal experience.

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Not joking what so ever... I have a torque wrench and use it. But there have been instances, in the 14 years I wrenched on my own bikes that I didnt use a torque wrench for anything and never had a single issue that was caused by it.

Thats why I said its a good tool to have but not absolutely necessary. After you wrench on a bike for long enough you can get pretty close to a torque value without a torque wrench. Not to mention a ton of people dont have the money for a good torque wrench, Ive found the cheap ones are complete junk and dont hold accurate torque values for long, if at all!

To each his own I guess... I do agree that a manual is the number one tool on the list IMHO. Just my .02... not trying to give bad advise, just seaking from my own personal experience.

I agree. I didn't have a torque wrench all through high school, and never had a single problem. I picked up a Proto 3/8 still in the box for 20 bucks still in the box!

Plus after you wrench on your bike for a while, your elbow becomes the torque wrench. But for the OP this probably isn't the case.

My break in method. Put some 2T oil on a paper towel and rub the cylinder walls. Then rub with a clean paper towel again and again until the towels come out clean.

Pour a little 2T oil on the main bearings and wrist pin. Start it up and let it run for 5-10 minutes. Shut it off and head to the track. Start it back up at the track letting it warm up for 5-10 minutes.

Then hit the track pretending I just got the holeshot in front of RC!!

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this is how i broke my top end in on my Rm 125: I first let my bike Idle for 10-15 minutes giving very small amounts of throttle periodically then i shut it off let it cool down. touch your cylinder to make sure its cold. once it was cold i took it down the road and to a FSR and i rode it 1/4th throttle for 10 minutes then 1/3 for 10 minutes then about half throttle for 10 minutes. i only went in 1st to 3rd gear. i then rode home and did a oil change and then for my next ride i road semi normal. so not on the pipe all the time and riding hard i just rode. then after like 5 hours i rode how i always do. i'm not at 60 hrs and no problems compression is good 

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this is how i broke my top end in on my Rm 125: I first let my bike Idle for 10-15 minutes giving very small amounts of throttle periodically then i shut it off let it cool down. touch your cylinder to make sure its cold. once it was cold i took it down the road and to a FSR and i rode it 1/4th throttle for 10 minutes then 1/3 for 10 minutes then about half throttle for 10 minutes. i only went in 1st to 3rd gear. i then rode home and did a oil change and then for my next ride i road semi normal. so not on the pipe all the time and riding hard i just rode. then after like 5 hours i rode how i always do. i'm not at 60 hrs and no problems compression is good 

Why change the trans oil, that has nothing to do with a new top end on a two stroke?

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I've done a few two stroke top ends on my own bikes and always had good luck with just riding it like normal.  You usually don't want to keep it at a steady RPM for too long but, thats kind of hard to do on a dirt bike anyhow.  Rebuilt one at a friends house that raced and rebuilt many two strokes and on the first start I idled it for about 30 seconds then he grabbed the throttle and held it WFO multiple times.  Said he did it on all his own and I never noticed any ill effects on that rebuild.  My dad used to always say about first starts, "She's gonna go or she's gonna blow."

 

I tend to agree about the torque wrench, not absolutely necessary if you have mechanical abilities but some people should absolutely never be allowed around any hand tools whatsoever.

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I bought a harbor freight torque wrench for 10 bucks like 4 years ago and it's still going strong. I know it's accurate, maybe I just got a good one.. I squirt some wd40 down in the handle every once in a while and use it regularly.

I personally just feel better torquing everything proper...

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