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RM 125 advice needed

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Hi everyone I just joined and I was looking to get advice on a bike I just bought. It is a 93 rm 125 I got for $100. Im looking to build a spare bike for my friends to ride with me as I already have a kx 250. The bike is completely stock and seems to be in pretty good condition minus the bars. The only problem is that the engine is real tight. The previous owner said he put in a new piston and compression seems good only problem is its very hard to kick like the engine is tight. I know its impossible to diagnose without breaking the cases but I wanted advice as to if this bike is worth putting money into. Thanks

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That looks like a great find to me. I would take the cylinder off and see what is tight. I probably won't cost that much to fix.

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I havent had a chance yet to pull it apart. Are replacement parts hard to find for a 1993? I cant seem to find much for a 93-95, do any companies make a bottom end kit

I tried to take off the jug but couldnt find my 12mm wrench. I managed to get the head off, the cylinder wall look pretty good but the piston had about 1/2mm of play. Is that normal?

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Edited by kev70ss

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1st Welcome

2nd great bike.We have three 90's RM's -My 95 250 rips as hard as my bubbies new KTM.

Hot Rods makes crank kit. Im sure you can find a link here.

Try this first. Give it nice and warm putt up the street n back.

Drain your crankcase oil.check-out the condition of the oil i.e any shavings.or weird colors of fluid. I run gear saver,650m of 10/40 will work. give it a ride. see if it improves. Nice fresh 32-1,plug,Clean filter-=Rip!

Let's see it.-Im up here in Orangevale,CA-If you need part's-hit me up.

Again-Welcome.

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Just saw your pic's -Normal.When you kick it by hand is it still tight ?

Yeah its pretty tight still even with the head off. Its still pretty hard when i try kicking it by hand. I guess I'll know better this weekend when i break open the case. Im hoping its some kind of bearing that went bad.

Nice RM's!!!

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How does your oil look ?Any flakes ? I Anti-freeze in Sons-125-It made Mud.-Hard to kick over. Have you rode this yet ?-last ditch effort before splitting the cases.--night.

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I got the top end off tonight and everything seems good except the bearing where the connecting rod attaches to the crank. The crank spins freely but the connecting rod doesnt want to move unless you kinda force it. Would a hotrod crank kit be a fix for this?

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From your description, you need a new crank (Hot Rods are OK). The bearing that is tight is commonly called either the "big end" bearing or the "rod bearing". Get the crank, a gasket set (pick a brand - OEM Suzuki, Athena, Cometic to name a few), and put a new ring on the piston. You should strongly consider main bearings and seals too (cheap insurance).

These motors are EASY to disassemble / reassemble. Plenty of info available here and at least a few willing to help to boot.

Cosmetically, the bike is in remarkably good shape. If it were mine, I would have no qualms about the $100 plus the additional parts to make it run.

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Thanks guys

I just got out the crank tonight and the rod bearing is seized. Everything else looks pretty clean. I found a guy who can change the rod for $35, is that good or should I attempt it myself. I haven't found any literature on how thats done so I have no idea, my guess you need a press. I took a picture of the crank. You can see some heat discoloration bu the crank, I guess that where the bearing went bad. IMAG0006.jpg

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It takes a certain amount of skill to redo a crank, the main concern with the job is getting the alignment correct. It needs to be within .003 runout or else it will vibrate and take out the main bearings.

$35 is a fair price but get some background on the shop doing it. Make sure they do it right.

For sure replace the mains and check the rest of the transmission bearings while your in there. Also inspect your clutch, 125's get abused :lol:

RMC has a good video on bottom end rebuilding and other things,

http://www.youtube.com/user/RockyMountainATVMC#p/c/A14890CE79ACFAAC/18/kYX-bOG9vR4

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Thanks guys!!

Im getting the crank rebuilt now and it will be ready on Monday. While I have the engine out, does anyone know if there is an off the shelf paint close to the stock gray frame color?

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thanks, I get the rotating assembly back tomorrow. The machinist said my piston was done, so I need a new one. The cylinder walls look perfect and I just measured with a micrometer and got 53.89mm. Do I get a standard 54mm piston kit?

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thanks, I get the rotating assembly back tomorrow. The machinist said my piston was done, so I need a new one. The cylinder walls look perfect and I just measured with a micrometer and got 53.89mm. Do I get a standard 54mm piston kit?

did you use a micrometer or dial calipers? dial calipers arent nearly as accurate, just keep that in mind, and no the cylinder should measure roughly .002" or .051mm above whatever piston size you get, because the piston will be exactly what it says it is, so if it says 54mm it will be 54.000+/- .001

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I would take the cylinder to the machinist and have them measure it. It's easy to measure it wrong and you don't want to get the wrong piston. The blue color on the crank is normal. they have to heat the crank to get the pin in. If it was blue on the bottom of the conn rod, that would indicate too much heat at the rod. The pin doesn't spin so it doesn't generate any heat.

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