how often do you put a new topend in your bike

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spanky250

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Dec 10, 2000

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• Jan 5, 2002

• #26

Re: Couple of questions re:

Originally posted by Jeff Gilbert
2nd question may sound anal. How do you guys determine hours on your machine? A 12 minute moto could be much more stressful on a top end than 2 hours of trails.

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Your engine doesn't know whether it is being raced or not. All it knows is how hard you push it. When my buddies and me get together, we ride as hard in the woods as we would if we were racing.

 

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jboomer

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• Jan 5, 2002

• #27

Is it wise to rely on compression testing to determine when to put in a new top end or should you do it regardless, periodically?

 

Jeff Gilbert

N. Texas SP

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• Jan 5, 2002

• #28

Re: Re: Couple of questions re:

Originally posted by spanky250
Your engine doesn't know whether it is being raced or not. All it knows is how hard you push it. When my buddies and me get together, we ride as hard in the woods as we would if we were racing.

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I think the key word here spank is could . I don't get the chance to ride trails hard so in my case 2 hours of trail riding would be less stress on my motor. When I race mx I keep the thing wound out for the entire race. Gotta keep the r's up on a 125.

 

marcusgunby

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• Jan 5, 2002

• #29

Jeff it also depends on the type of piston used-typically a KTM piston will hold up alot better than a jap bike.You can get as much as 2* the use from a ktm top end than a jap bikes.If your racing for less than 1 hour you could easily go 20hours on a top end.I would have no worries about doing 12hrs on a ring and 25hrs on a top end on your bike at expert level.We tested a KTM 00 125sx to destruction(in the name of science) and with a british championship rider abord it took approx 55hours for the pisiton to break .This was using a wiseco piston kit.I wouldnt use comp readings as just before the bike went bang it had 165psi.

 

Jeff Gilbert

N. Texas SP

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• Jan 5, 2002

• #30

I agree Marcus

I only use OEM pistons in the KTM. My dealer says it's not unusual for them to go an entire season on a top end in supercross. I can tell my bike is due for a ring, it makes this sort of rattling noise when the compression gets to about 160. It still runs good but the compression test shows about 162psi and I think my gauge may be off a little. I've been racing it since October so I have about 8 to 10 races on it myself. Since I bought the bike used I don't know how many hours were on it previously. It belonged to Paul Carpenter I believe but I was told it was only raced for the LL qualifier and he didn't make the 125 main. It supposedly went into the trailer until I bought it.

My last KTM went almost 2 years on a top end. I know the guy that previously owned that one too. The piston looked almost brand new but I replaced it anyway just because I had already bought a new one.

 

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Jimmy!

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Jan 7, 2001

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• Jan 7, 2002

• #31

I'm with Spanky on this one too. I do my top-end when I lose about 10% compression. This typically nets me about 60-70 hrs of woods time.

 

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spanky250

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• Jan 7, 2002

• #32

Originally posted by Jeff Gilbert
Break in after a ring only. Is it advisable for a break in like you would do after a complete top end or just do a warm up and cool down to get the ring to seat?

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All you are trying to do for a ring-only rebuild is to get the ring to seat properly. Just take it easy for a few minutes, then you are good to go. No heat cycles are neccessary.

Originally posted by a454elk
From what I understand, when you are breaking in the new top end, it's the marriage between the ring and the cylinder. The piston will follow on it's own, I may be wrong though. It doesn't hurt to break it in the same way everytime, rings only or piston and rings.

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When breaking in a new piston, you have to put the piston through several heat-cool cycles to relieve the pent-up stresses that are trapped in the metal, left from the manufacturing. If you push a brand-new piston too hard before these stresses have had time to find an equilibrium, the piston will distort and expand unevenly, with predictable results. The rings only need to “get to know” the cylinder, so a ring-only rebuild doesn’t require any elaborate break-in.

 

a454elk

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• Jan 7, 2002

• #33

Thanks for the clarification Spankster.
Elk

 

F

Fox Racing

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• Jan 7, 2002

• #34

I1

 

Last edited: Mar 24, 2003

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spanky250

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Dec 10, 2000

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• Jan 7, 2002

• #35

Originally posted by Fox Racing
I have a 2001 CR250, I just finished doing a top end on my bike for the first time...I use Amsoil at 50:1 and there was hardley any carbon build up. I went a whole year before I tore it down!;)

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If you would change to 32:1, your bike would run better and make more power. (OK, I opened the can, now where are the fish?:p )

 

a454elk

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• Jan 8, 2002

• #36

You're a bad boy Spanky! :debil:

 

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fatty_k

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Jul 3, 2001

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• Jan 8, 2002

• #37

Just got back from taking my cylinder and piston to the local shop and they said everything is in perfect shape. The catch?
My bike is a 1998 and the top end has never been done! I bought it used last spring and after asking the guy (original owner) if he has done a top end job, he said no, so I though for sure it would need one. Maybe it does pay off to buy high quality, pre mix.

BTW, I am a newbie at wrenching on my bike and this was my first engine tear down. It was so exciting :)

 

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Scarylong

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Jun 20, 2001

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• Jan 11, 2002

• #38

I keep one on there all the time. I find it starts much easer that way.

:uh:

 

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F3504X4

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Nov 7, 2001

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• Jan 12, 2002

• #39

I do my top end every year on the 125,however i only ride on weekends.

 

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motometal

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• Jan 13, 2002

• #40

after reading this thread in its entirety, I feel much dumber.:uh:

 

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FNINJA

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Jan 12, 2002

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• Jan 17, 2002

• #41

geezzz...

I don't feel dumber...maybe better informed, a little confused and scared as hell about trying to figure out if I need to be doing a rebuild on my used 00 kx125. How much would it all cost? I have no history on the bike,Damn...If I only knew then, what I know now.....