How often do you put a new Bottom end in your 125

chadk01

Sponsoring Member
Aug 19, 2000
171
0
I'm curious to see some replies to this post. I hear everything from once a season to not until it falls out. That pretty much covers the spectrum.
 

Durt Cycler

Trial Subscriber
~SPONSOR~
Nov 13, 2001
1,173
0
Only 40hrs on a new crankshaft is crazy. Crankshafts and ebarings will last ALONG time if you keep the bike from lean jetting, use a good quality oil, and refresh the topend often.
 

MikeT

~SPONSOR~
Jan 17, 2001
4,095
11
When it blows up. Unless you're getting rod knock, any sooner is a total waste in my opinion. :silly:
 

helio

Member
Dec 19, 2001
258
0
Thanks MikeT.
Still about this can you please give me some reasons for a piston rod blow up or knock ? I am trying to understand a little more about bottom end.

Thanks alot.
 

nikki

Moto Junkie
Apr 21, 2000
5,802
1
Originally posted by MikeT
Unless you're getting rod knock

Agreed - this is one BIG sign that it's time! :) When you let off the gas coming into the corner and hear some knockin' - time to tear her down.

We check the play in the rod/bearing from side to side every time we have the cylinder off (which is usually every 10-20 hours). If you have up and down play in the rod... it's about time for a new bearing/rod. A little side to side play is okay. (had that backwards at first - easier to think with the engine in front of you :) )
 
Last edited:

Matt_H

Member
Sep 13, 2001
365
0
I thought we were talking about just the bearing opps:eek: . I've ever had to replace a rod or crank but then with good maintaince you shouldn't have to.

Matt
 

Durt Cycler

Trial Subscriber
~SPONSOR~
Nov 13, 2001
1,173
0
Originally posted by nikki
If you have play from side to side in the rod... it's about time for a new bearing/rod. A little up and down play is okay.

I think ya got it backwards there Nikki :confused:
 

nikki

Moto Junkie
Apr 21, 2000
5,802
1
Originally posted by Durt Cycler


I think ya got it backwards there Nikki :confused:

Duh - yeah... side to side is OKAY. Up and down is NOT OKAY :p

(Note to self - fully wake up before posting)
 

MikeT

~SPONSOR~
Jan 17, 2001
4,095
11
Originally posted by nikki


Duh - yeah... side to side is OKAY. Up and down is NOT OKAY :p

Ahh, that would be that knocking sound....:confused: :confused:
 

kevinkdx

Member
Mar 25, 2001
481
0
On my 1993 KDX 250 i just had the bottom end rebuilt. The only reason I had it does was becuase i had a crank seal leaking so i figured why not do the whole thing and get a new rod and bearings. I would say wiht good matinence and making sure you are never TOO LEAN it wil last for a long time.:aj:
 

ACS

Member
Apr 17, 2001
242
0
Only do them when they need it. We have a 99 YZ125 (new September 98)which is still with stock bottom end and its done 3 full MX race seasons, X-C's and trail rides and is still sound. Its won a couple of championships in that time too so it works hard. I think its good oil, good jetting and clean and good air filter maintence and checking things out when you do rings and or pistons. (I will now throw a spanner in the discussion too. Its run Amsoil 100:1 at 80:1 for its full life up until February this year, now its on the newer 50:1 stuff)
 

fmfkx125372

Member
Feb 1, 2001
226
0
Nikki has the right idea. Every top end you do, that should be one of the things you check while the cylinder is off. Grab the rod and move it side to side, you should have some 'minor' play. If it is pretty sloppy, you may want to think about replacement. If you have any up and down play at all, you should definately have it done.

When you do get the rod replaced, I would definately atleast check the crank bearings and seals while you have the cases split. Like Kevinkdx said, good maintenance is the key!

I would also suggest getting the hot rod kit instead of OEM. You will get both bearings with the hot rod kit instead of just the one bearing with the OEM. We just did this with my old '98 kx125....Hope this helps!
 

MikeT

~SPONSOR~
Jan 17, 2001
4,095
11
"If it ain't broke, don't fix it" Tin can or not, look for the up and down play, otherwise leave it till she blows up!
 

helio

Member
Dec 19, 2001
258
0
I would like to thanks all replies, but I would like to know a bit more...

- Just more this point...Under normal conditions(right jetting, fresh gas, good oil, clean filter, right plug and so on...) how many time (aprox.) a piston rod can run ?

Thanks again
 

MikeT

~SPONSOR~
Jan 17, 2001
4,095
11
Eric Gorr has stated that pistons can last much longer than most manuals say. I personally will leave mine in an estimated 25-30 hours in my 125 with a ring change thrown in. I say that probably running 1.5 - 2 hours twice a month for about 6 months. Anymore than that and I think, I'd be pushing it. That is being honest. With that schedule I haven't had any problems over the years in any of my bikes.

Now Mr. 96whyzee125 has a "special" bike with a top secret piston made of the same stuff they use on the Space Shuttle's heat shields. That's why his pistons last "1248 hours, 17 minutes, 36 1/10 seconds... " For the rest of us, I'd only go about 25 -30 hours. ;)
 
Last edited:

whyzee

Never enough time !
LIFETIME SPONSOR
Dec 24, 2001
2,282
0
Mike,
Helio was asking about the "Rod", he does not get my humor, welcome to the club, I don’t either!:scream:

Now Mr. 96whyzee125 has a "special" bike with a top secret piston made of the same stuff they use on the Space Shuttle's heat shields. That's why his pistons last "1248 hours, 17 minutes, 36 1/10 seconds... " For the rest of us, I'd only go about 25 -30 hours.

If you go telling my secrets, I'm going to have to tell everyone about the time you stole that cow, and then....
:debil:
 

MikeT

~SPONSOR~
Jan 17, 2001
4,095
11
It was a good barbeque!

Anyway, Ahh, the rod I thought we were talking about the piston, sorry. Forget about the rod. Just check it when you change the top end. I have never had to replace a rod on any bike.
 
Top Bottom