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RM 125 top end rebuild (newbie warning)

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This is my first dirt bike (2001 RM 125), first 2 stroke I've owned, and first time cracking open any motorcycle engine. I got this bike 6 months ago but I've only gotten to take it out a handful of times. The previous owner had the top end done, rode it a few times then got a new bike and this sat for 2 years. When I did take it out it spooged like crazy and it had a little sluggish throttle response, other than that it ran fine and fast, so I decided to just do the top end again and open up the carb and put everything back to stock if it wasn't already.

I just wanted to run a couple pics by you guys to make sure I'm all good. Any input is greatly appreciated. :)

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My bike as it sits now

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Top of the piston and cylinder wall

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Piston removed

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scary gouge I found in my spinny thing... its about as long as the width of my pinky fingernail and not too deep. :lol:

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another cylinder shot, super smooth

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Do my reeds look ok? Don't know what I should look for

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Cylinder looks worn. I would have a shop look at it if it needs re-plate or just new cross hatching. Plus the scratches by the exhaust ports. Crank should be ok as long as whatever caused the gouge isn't still in the bottom of the engine. (split engine to see?) If the previous owner didn't change the main bearings, they may be due. Reeds look good. Check that they sit tight against the frame at the top ( in the pic) and no cracks (on the other side). Check the sticky at the top of the forum for info on setting the jetting when you're ready for that. OH yea, a manual is priceless!

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Cylinder looks worn. I would have a shop look at it if it needs re-plate or just new cross hatching. Plus the scratches by the exhaust ports. Crank should be ok as long as whatever caused the gouge isn't still in the bottom of the engine. (split engine to see?) If the previous owner didn't change the main bearings, they may be due. Reeds look good. Check that they sit tight against the frame at the top ( in the pic) and no cracks (on the other side). Check the sticky at the top of the forum for info on setting the jetting when you're ready for that. OH yea, a manual is priceless!

Thanks, I'll have it looked at. Yea I wouldn't have had the confidence to do this without the manual.

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That crank looks like someone smacked it with a claw hammer while trying to true it after a rod rebuild. As long as the bike did not vibrate really bad before you tore it down I wouldn't worry about it if the big end rod bearing is good. If you had a lot of vibration, then the crank was rebuilt wrong and is out of true. Turn the reed box over and hold it up to the light, if you see a gap then replace them or if they are chipped on the corners or cracked. The cylinder needs to be deglazed and check to see if it is out of round (egg shaped and out of round in the middle of the cylinder). Or you could send it off for a re-plate jog (about 200 - 250 with shipping).

Edited by Padgett

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A good peice of advice i can give you is that when you get your new piston ring check the ring gap in the cylinder with fealer gauges to check it that the gaps are not too small or too big, if you are not sure what i mean take it to your loacle bike garage and ask them to check it for you or some one else on here will be able to help you more, as im not good at explaning but better at ilastrting rather. and one other good tip put a clean rag in the crank case to stop any dirt droping in and when you install the rist pin retaining clips they wont fall into the crank case if you drop them. Good Luck

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UPDATE!!!

I just wanted to say thanks for all the advice you all gave. My RM is running like a champ, after I finished the top end I only took it on one ride. Then I decided it was time for a carb rebuild and some new plastics as the old ones were beat. Here's the pics..

The day I brought it home. I paid 0$, I traded my non running 99 R6 straight accross for it.

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NEW PLASTICS!!! (after the top end and carb build)

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New seat cover

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Left side complete w/ new grips and gas vent hose

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All done!

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I took it out to Divide Peak in the hills above Santa Barbara last weekend - epic clouds

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It was a pretty good day.

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:bonk:

Thanks again guys!!

Still deciding on what kind of graphics I'm going to do. Hmmmmm....

Edited by bam0

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