She's Alive !

[TaKeN]

The KX125 is alive once again,


Full repaired Cylinder
Pro-X Piston Kit

More compression than before from the feel of it, and its not even broken in yet


Any tips on Breaking the engine in ?


Warm up for ten mins ?

Ride slowly and change gears frequently to avoid labouring the engine ?

Then stop and cool bike down for ten mins and repeat ?

Fuel to oil mixture is @ 33.1 for maximum lubrication


BTW when my friend was putting it back together a circlip fell into the crackcase 


But fortunately he was able to get it out 


I look forward to reading you replies and advice

Thanks

John

[MadKaw]

glad you got her up and rollin man, according to the owners manual for initial break in, you got it right, but you're supposed to pull the top end and check your piston for uneven wear, and check the cylinder walls for any excesive wear or scoring....good luck

[TaKeN]

Hmm, thanks for the reply buddy


Surely taking the head off the bike and pushing the piston to the bottom will reveal and uneven wear on the cylinder etc ?


Because completely stripping down the top end will mean new gaskets...

[MadKaw]

yeah, that'll let you check out the cyl. but not the piston skirts and rings. gaskets aren't that high. or hellwithit and just run what ya brung. but top ends are higher that gaskets...he he he

[TaKeN]

What is the piston skirt ?

Ive never actually understood what it is


and my Bikes pistons only have one piston ring, yet some two strokes have two.


Any reason for this ?

[MadKaw]

the skirt is the part below the rings that hangs down about an inch or 2 on each side of the piston. the part thats not SUPPOSED to be in contact with the cylinder. and the pistons with only one ring I believe are a race type piston. OEM has 2

[TaKeN]

Well, its a Pro-x piston in the bike now,


same as last time, although ive just read the guide on rebuilding a KX 500 engine, and i didn't file down the edges of the skirt on my piston 


The last pro-x piston in the bike cracked at the front of the piston, middle way up the skirt.


I didn't ask for a PRO-X piston

Mitaka would have been my choice, cheap and good from what ive read about them.

[KDXGarage]

Crank and let idle until war, then shut down and let COMPLETELY cool down

repeat and putt around for 10 minutes, NEVER HARD ACCELERATION

same for 20 minutes

same for 30 minutes

[TaKeN]

Thanks,

I hope i havn't already damaged the engine 


I warmed the bike for 5 mins, then lot it cool down completely.


Then warmed it up again and rode if for five mins constantly gear changing.

Then warmed it up and rode it again for ten mins constantly gear changing.

Then last night i warmed it up and took it across the field for about 15 mins accelerating not too hard,


Then about 20 mins later i took the bike onto a flat bit of field and opened it up... not revving it flat out. But pulling quite hard

Then towards the end of the field i would pull the clutch in, then throttle forwards and backwards to lube the cylinder a bit, i went up and down the field about four times.

Then i shut off the bike and let it cool for five mins before putting it into the shed...

Is this likely to have damaged it ?

and do  you consider it to be RAN IN now ?

Thanks in advance 

[KDXGarage]

That sounds like it wouldn't do any damage.  The gear changing wouldn't affect the cylinder, piston and rings, though.  I think the main thing is the cool down cycles.  You have little choice but to go give it hell and see how it does. 

[TaKeN]

Ok, its still not running right and i can't figure out why.


It has plenty of compression because it blows your finger off the plug hole every time you push the kickstart down.


It pulls well when its beggining to warm up, but once the engine gets quite hot the bike starts missfiring and the power isn't clean...   

I'm realy confused as to whats wrong with the bike, i stripped the top end down tonight after it got hot and the bore looked fine.

There was no unburn't oil ontop of the piston...


Ive also just gone from 33.1 to 40.1... using Castrol TTS.


Is the jetting out by miles ?

could it be the timing ?


Please help my guys, i'm getting realy annoyed with this bike and its starting to make me want to go and buy something more reliable like a Honda CR Motocross bike 

There was also alot of smoke coming out of the back of the bike at one point and it didn't smell like two stroke oil being burn't

Maybe the crankcase is sucking in tranny oil ? ( Although this isn't running low )

[BigGreenMachine]

I do my break in different and the correct way IMO.

Start the bike, make sure there are no leaks and everything is fine. Ride it around a little to warm it up. Once its warm ride it like you normally would making sure to go through all the rev ranges. Make sure to keep the clutch out after downshifting to keep load on the engine. After about a 20 minute ride it will be broken in.

After the ride let the bike cool completely then retorque all the head/cylinder nuts back to spec.

[MadKaw]

you changed your oil mix, that also changes the jetting needs. have you repacked your muffler packing recently? how did your plug look when you torr it back down? probably jetting.

and don't fool yourself, all brands have to be tuned right.

[alan]

I am not sure about some of the other problems you are having, but "It has plenty of compression because it blows your finger off the plug hole every time you push the kick start down." Is not an acceptable means of checking your compression!

[don46]

I would agree with Alan that using your finger is not a adequate means of checking compression. You just rebuilt it so I wouldn't think compression would be an issue. The procedure used to break in your bike will ultimately determine the longevity of you piston, the main thing is to make sure your bike is warm before you get on it to prevent a cold seizure and that holds true even with a well used bike. Lets face it the factory boys don't go out and breakin their bikes before a race, but they do get freshened up before every race.It sounds to me like jetting, it runs fine till it gets hot then loses it on top end. I don't remember what year it is, does it have a power jet? I recently found a problem where the powerjet failed, the bike ran fine up to about 5/8 throttle, after that it would act like it was flooded out, close the throttle and it ran fine. I wasn't using the power jet circuit on the carb so I just plugged it, you may need it on your bike, as I recall there is an RPM range it cuts in and then cuts out.