mabye time for a rebuild?

G

gabe19

Member
Jul 13, 2008
13
0
bike is a '03 rm 125. From what I can tell the motor is all stock, has stock pipe and all that crap. I put in a twin air air filter but I think thats the only thing that has ever been put on the bike. It has a couple of little after-market accessories like renthal bars, excel rims, and asv brake away levers. It starts up fairly easy except for when it occasionally stalls out during tight woods riding, it runs pretty cool, and the spark plug is a nice tanish brown so I'm guessing the jetting is ok. It has some clutch drag, enough where when I lock up the back brake in gear it dies out if I don't rev the motor. But the thing I was wondering about is if i need to get it rebuilt. When I put my hand over the exhaust when the bike is at idle it seems like there isn't much pressure at all. the bike runs really strong and usually starts up first kick. what do you guys think? Oh by the way the previous owner is pretty stupid he told me it was a '92 but when i got it home and ran the vin it was a '03 so i don't think he was ever smart enough to get any work done on the bike.
 
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RM85rider123

Member
Oct 28, 2007
681
0
It most likely needs a top end. The most easiest compression test(and the fastest, but may not be too accurate) is to push down on the kick starter. How hard is it to push it down with your arm?



the best thing to use is a compression tester though.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Merrillville,Indiana
The best thing to do is, get a manual and top end gasket set. Take it apart, measure and inspect. Then you know. And inspect the clutch while your at it.
 
C

Cabot

Member
Sep 3, 2007
158
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Whens the last time you changed the oil?
(yeah, two strokes have oil too)
 
G

gabe19

Member
Jul 13, 2008
13
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I change the oil after every couple of rides, I've been switching back and forth from atf type-f and 10-30 and I think I'm going to stay with 10-30 because atf seems to make the clutches extremely grabby (plus I can't find it for cheap near me and I can get oil for free from a friend at a lube shop). I don't believe the previous owner really did any maintenance to the bike because tho because when I got it the air filter was really really dirty and the oil looked pretty craptastic.

I tried a compression tester that i rented from autozone but the stupid thing only said 60 and that was after I kicked it over a couple of times.

I can push the kick start down with my arm yes but I'm a big guy so I don't know how hard it is supposed to be. when I push it down by hand there is some reasonable force behind it.

so is the low flow coming out of the exhaust at idle normal?
 

IndyMX

Crash Test Dummy
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Jul 18, 2006
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When you used the autozone compression tester, did you hold the throttle wide open?

If so, and you got 60, you need a top end. Bad.
 
J

_JOE_

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May 10, 2007
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For the hundred bucks it costs to rebuild it, I wouldn't take the chance. If that's the original piston you're flirting with disaster. A compression test will only tell you how good the ring seal is. You need to measure the piston skirt to have any idea if it's serviceable. As cheap as a 125 piston kit is, you might as well just replace it while it's apart anyway. I wouldn't trust a piston in that thing longer than 20 hours.
 
G

gabe19

Member
Jul 13, 2008
13
0
no I didn't hold the throttle wide open, I've never heard of that before. I don't know if it's the origional piston or not in it. it looks like at some point the bike was raced, the suspension looks as thought it's been revalved (atleast the shock anyway). So the motor might have been gone through or not but I have no information on that.....

Joe, 20 hours? you've got to be kidding me right? thats like 2 weeks of riding.
 
C

Chili

Lifetime Sponsor - Photog Moderator
Apr 9, 2002
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In our 03 we changed the top end usually when compression dropped to around 140 psi. These bikes won't have the same blast coming out the silencer like the current 4 strokes do.

Joe's not kidding, if you check the manual Suzuki specs to change the piston at 10 hours.
 
R

RM85rider123

Member
Oct 28, 2007
681
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I thought if you raced you're supposed to change it every 10 hours? Because the manufacturers suppose you are going to race it , then they put 10 hours in the manual..... Right?
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
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Merrillville,Indiana
RM85rider123 said:
I thought if you raced you're supposed to change it every 10 hours? Because the manufacturers suppose you are going to race it , then they put 10 hours in the manual..... Right?
Click to expand...
The rings will safely last 10 hours in that race bike. That would be a good point to see how your engine is wearing, take it apart and measure. The CR's life is even shorter. Modded and higher compression, shorter yet.
 
J

_JOE_

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May 10, 2007
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gabe19 said:
That really sucks. 10 hours and then time for a rebuild is a joke.
Click to expand...
Go get an XR. A race bike isn't for you.
 
G

gabe19

Member
Jul 13, 2008
13
0
Go get an XR. A race bike isn't for you.
Click to expand...

I don't think so. I like to go to fast for a strictly trail bike. I eventually want to start racing anyway once I get enough practice and can afford the traveling.

You know one of my neighbors has 2 cr 500's, he rides one and wants to sell the other but buying my rm was alot cheaper than what he wanted to sell his other bike for.
 
C

CarnageZ28

Member
Mar 25, 2008
109
0
That RM500 will make you it's bitch ...

Your going from a 30 horsepower 125 to a 60 horsepower beast of a motocrosser, that is 30-40 lbs heavier, made for a large dude to ride, etc.

If your not racing/running a 125 hard, you can go 30-40 hours on a piston.

My 250, I do the piston and rings once a year. I usually put on 40-50 hours on it. They always look like I can run them longer, no real wear but I replace it anyways.

My 125, same deal. If you ride in the woods, where your not WOT all the time, you can get more hours out of it. I ride some TIGHT woods, and some open areas. I like to go fast, but I do not abuse the motor either.

Its generally accepted that if your not racing it, you can get 40 hours out of it. But only with proper maintenence. Mix your premix precisely, make sure your jetting is dead nuts on, gap your plug right, and CLEAN YOUR AIR FILTER! Ive seen some kids who race (Very well mind you, top of B class MX) and still get a summer out of a piston, where they are riding 2-3 times a week a couple hours at a time.

Keep an eye on things, measure compression, and peal at piston to cylinder wall clearance at around 20-30 hours, depending on conditions.
 
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