how to know if i need a new top end

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rm1125er01

Member
Jun 16, 2010
14
0
hey, im new to this site and dirt bikes in general.. i just picked up a '93 rm 125. ran good till i took it to walker valley and fliped it on the trails.. when i picked it up it had a bit of anitfreeze that came out of the head and i fouled a plug. i limped it back to the truck and took it home. i took the head off and cleaned everything, got a new plug and new gas. after i finished putting it back together i took it around the block a few times.. but no powerband.??? someone told me i needed a new top end but i thought id ask a few of the experts on here b4 i start ordering parts lol. any feed-back is greatly appreciated!!!
 
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julien_d

Member
Oct 28, 2008
1,788
1
If you just bought a used 2 stroke, it needs a new top end ;). While you're in there, you can check the powervalves and such as they might need attention as well.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
A used bike is unlike a new bike. The new one you have a better chance everything is in spec, to safely get you to your finish line. A used bike should be completely taken apart and checked. Fixing the motor is cheap compared to the rest of the bike. Inspect and measure. And know where you can draw the line on calling it race ready, for you. Someone else's opinion of race ready can land you in the hospital or poor house. A 93 is neither currant or ahrma, just a play bike for you? Vintage Bob
 
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sr5bidder

Member
Oct 27, 2008
1,463
0
julien_d said:
If you just bought a used 2 stroke, it needs a new top end ;). While you're in there, you can check the powervalves and such as they might need attention as well.
Click to expand...


most of the time this advice is spot on,....couldn't have said it better myself
 
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akagalford

Member
Jul 1, 2010
18
0
sr5bidder said:
most of the time this advice is spot on,....couldn't have said it better myself
Click to expand...

I'll second that as the used one I purchased was a perfect example of this, go through the ENTIRE bike with a fine tooth comb before you consider it safe and reliable. Mine was missing the top bolt that holds the top of the rear suspension in place along with a blown piston and cylinder, list goes on and on of things wrong with it that I didn't notice at first glance. I chalk this one up to a learning experience at this point. And yes I have more $$$ into the darn thing now than its worth, I have yet to ride it too.
 
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scottiedawg66

Member
Sep 26, 2006
75
0
sounds to me like you got your power valve installed wrong some how.

that should be the last time you take your cylinder off with out at least replacing the piston ring (s?)! They are cheap and are part of regular maint. on a two stroke. I do mine every 15 hours on my 125. I recommend an hours meter, and a compression tester.
 

IndyMX

Crash Test Dummy
~SPONSOR~
Jul 18, 2006
5,548
2
Amo, IN


If he only removed the head and didn't remove the cylinder, the power valve didn't come apart.

Likely just needs a top end.
 
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rm1125er01

Member
Jun 16, 2010
14
0
Ok so I did a compression test and it was only gettin about 30 psi with a real good kick lol. Also the top of the piston looks domed not flat. I've gone over alot of things on it and found a couple loose nuts and bolts that arent the right size but mostly it's a solid bike. I'm going to replace the piston, needle bearing and gaskets. Any advise on any other things I should replace since I'm in there? Thanks for all the help so far!!
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Now is a good time to check the crank for wear. Lube the linkage and change suspension fluids. Next month do all this again?
 
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julien_d

Member
Oct 28, 2008
1,788
1
Just fyi, you don't test compression with "a real good kick". Hook up the gauge, hold the throttle open, and kick the crap out of it until the gauge stops rising. That highest measurement is your compression reading. It might take 6 - 10 kicks...

Good call on replacing whatever you can find worn now though, it will save you headaches in the weeks and months to come. :)


J.
 
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rm1125er01

Member
Jun 16, 2010
14
0
thanks j.
so bad news... took off the cylinder and there is quite a bit of play in the rod from side to side. looks like i found out the hard way what to expect from a $500 bike... thanks to all for the help. but now how deep did i just get myself??? lol
 
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dirt bike dave

Sponsoring Member
May 3, 2000
5,348
3
If the rod slides a little side to side with the jug off, that's common.

Any up and down play is bad.

Personally, I'd probably just put in the fresh top end and run it (make sure you use lots of oil in the premix). Save your crankshaft replacement money for your next bike.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
The rod will have some side to side, rock if you will, radial play? Its the NO, up and down play, and the thrust washer clearance(feeler gauge) that are crucial. And of course the needles, cage and pin are still intact, not dis-colored. A good light and magnifier help. Vintage Bob
 
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akagalford

Member
Jul 1, 2010
18
0

Same question I was asking myself this last week as I am in the same position, project bike with a blown piston/cylinder (and seller didn't disclose this info though they knew it) - I just bought all the tools to brake the lower apart to clean it out and verify no shavings are left in the bottom. Between all the tools/parts and cylinder work I'll end up having another $1000 into this project on top of the other stuff I just had to fix. In my case more than the bike is worth, but on the bright side its a good learning experience and next time I'll already have the tools. Guess I'll need to find a few more project bikes to justify the tools.

As said above a little side to side is ok. Its the up and down that is not.
 
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rm1125er01

Member
Jun 16, 2010
14
0
Thanks I was really worried for a second. Now to get the needle bearing off... I see the clips but I'm a lil unsure on how to get them off. Also any hints and tips to get the bearing out would be very helpful.. Like I said in the begining I'm a nooby and appreciate all the help you all have given me!!

Akagalford: Ya I hear ya on that one the previous owner seemed to leave out a few things that needed to be fixed but weren't visible to the naked eye. On the bright side you know what to look for and which questions to ask next time.
 

ellandoh

dismount art student
~SPONSOR~
Mi. Trail Riders
Aug 29, 2004
2,958
0
never buy a bike without riding at least a city block, shifting through all gears at least once
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
The less questions you ask, the less lies you will hear. Take it for a ride. 3 to 400 to fix the motor fresh, minus fixing the cylinder. The tranny would be a nightmare, and so is the suspension $$$$.$$ A 4 stroke, as long as no internal parts are external, add a few hundred more to the parts price. Then if the seller was truthful, you are money and parts ahead. Vintage Bob
 
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