maintainance

[joshpendry]

I have a 2000 model RM125 that I've had 3 years. I have not rebuilt the bike yet but the manual says I should have by now. I talked to the dealership I bought it from and they said not to bother with it until it loses a great deal of power. It has not lost much power at all but I can tell a very small difference. I have noticed that it runs poorly at high rpm's but I've change the pipe, silencer, and sprockets. When I do rebuild my bike, I want to bore it out. How much do I bore it? I want to get some more low end power for hill climbing because I do a lot of it. Would boring my bike out give me more power for hill climbing or is it a waste? And would it still lug down halfway up the hill if I bored it?

Thanks
Josh

 

[Sawblade]

Josh,
Welcome to DRN! You have all ready answered your own question. If you have noticed a lose of power it's time to do a top end job. Don't wait as your local shop suggest as the end result of blowing up your motor could be much more expensive then the top end job.

If you are wanting to go the big bore route, now would be the time since you will be tearing down the top end. Eric Gorr does some of the best work in the country and supports DRN as well.

Check out Forward Motion at:

http://www.eric-gorr.com/

If you have never done a top end job, look through you owners manual. It should guide you through most of the basics. If you don't have a owners manual, drop some dollars to get one. Finally, take your time and learn!

 

[bclapham]

josh:

i have just finished building a big bore rm144. as sawblade says, eric gorr is the person to work with. yes, you will get much more power.

however, if your engine has three years on, it will probably need new bearings and seals in the bottom end- it will definately need them if you are going with a powerhouse 144 bigbore.

also note, the big bore uses a 58mm piston vs the 54mm stock. you will have to slightly file/grind down the cases to make room for the new piston- it is best to do this when you have the bottom end apart, so youve got a good excuse to change them bearings!

either way, if its never had a new piston in three years, put one in before you ride the bike again- its probably worn to the point of blowing up!

 

[joshpendry]

Thanks for all the help. Also, What would be the most that I could bore it? And how can I get more low end? I know nothing about it really.....I know how to tear one down and rebuilt it stock but besides that......I'm lost. And also how much would this cost to bore it to the max. Thanks again

Josh

 

[motometal]

i'm not against overbores, but you may want to consider other (cheaper) options.

compression and low end power are directly related, so just replacing piston and rings will help in this area.  Or, you could have the cylinder and/or head modified for more compression and more low end.  If the compression is boosted, you should run race fuel if you aren't already (at least a 50/50 mix if not 100%).  Depends on your budget too, if the bike hasn't been run too hard you may be able to get by with the existing lower end (bearings) if you don't overbore. 

Have you tried gearing the bike down?  That alone could help tremendously on the hills!

 

[joshpendry]

Yes I have changed the front and rear sprockets, put a FMF fatty pipe and FMF Shorty silencer on the bike.....which gave me quite a bit of low end.....but its still lugging down about halfway up a hill (NOTE: I climb or at least try to climb very steep hills....lol) But as a I said earlier, I've had the bike 3 years and havent even torn it apart to look at the piston to see what kind of shape its in. Do you think a big bore is in order or should I just go back with the stock Piston and Rings? I can tell a big difference riding this year than the year I got it. But its still got a lot of power. And everyone tells me that since I replaced the stock pipe that I should Re-Jet my carb which I havent done. Could this have some kind of effect to why its lugging down when other bikes are leaving me in the dust? Which I ride with YZ 426's and DR250's and they climb a lot better. Any replies are appreciated.

Thanks again
Josh

 

[motometal]

I think you are mixing two issues here, replacing the piston and rings (and possibly lightly honing the stock bore) to bring the bike back to stock power, or enlarging the bore.  Modern bore coatings are very hard, and there is a good chance that the bore is still well within spec.

You don't automatically have to change jetting with a different pipe, each bike and combination is different.  Some pipes come with a slip of paper stating recommended jetting; in my opinion that's a bogus generalization.