KX Riders
Maintenance & Technical => KX250 / KX125 => Topic started by: TaKeN on March 17, 2007, 05:52:39 AM
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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 :D
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 :D
BTW when my friend was putting it back together a circlip fell into the crackcase :-o
But fortunately he was able to get it out :lol:
I look forward to reading you replies and advice :)
Thanks
John
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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
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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... :(
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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
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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 ?
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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
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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 :cry:
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.
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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
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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 :-)
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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. :-)
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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 :-o
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 )
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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.
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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.
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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!
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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.
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I will get a compression tester :)
Its a 1992 btw..
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I would look at jetting, I'm sure you didn't hurt it. The warmer the temp the richer the bike runs.
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Whilst we are on the subject :)
When i checked the bore ( Cylinder )
On the bike, there were markings on the inside of the cylinder about 1/2 an inch wide going down the bore
There were probably about 8 or 6 of these marks all around the 360 degrees of the cylinder where the piston or rings have started to grow ( I assume ) Is this normal ?
The markings are spaced equally all around the inside of the bore. They weren't deep gouges.. just a different colour to the rest of the bore.
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is the bike running hott ? can you touch the cylinder and rad cap when the power failure occurs . but you definatley need to check the compression .
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Just did a compression test with the throttle wide open,
and i got 105 PSI, this is with the engine stone cold,
Is this good or bad ??
Blackkx - Well, the cylinder and rad are quite warm, not scolding hot but hot enough to make you remove your hand after a few seconds :)
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My book says 109-171 so it is outside the service limits! :-o :-o
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Just did a compression test with the throttle wide open,
and i got 105 PSI, this is with the engine stone cold,
Is this good or bad ??
Blackkx - Well, the cylinder and rad are quite warm, not scolding hot but hot enough to make you remove your hand after a few seconds :)
Retest with warm engine. Start engine up and get it up to operation temp and retest. Then compare the two readings.
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Whilst we are on the subject :)
When i checked the bore ( Cylinder )
On the bike, there were markings on the inside of the cylinder about 1/2 an inch wide going down the bore
There were probably about 8 or 6 of these marks all around the 360 degrees of the cylinder where the piston or rings have started to grow ( I assume ) Is this normal ?
The markings are spaced equally all around the inside of the bore. They weren't deep gouges.. just a different colour to the rest of the bore.
Cold seizure? This was after your rebuild right? Can you post some photo's of the piston and cylinder??
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Will retest with a warm engine tommorow.
As for a seizure, i don't think it has seized because the engine never locked up on me or stopped at all.
The marks look like wear marks to me, i will get some pictures up tommorow :)
Yes, this is after a fresh rebuild
Had the cylinder fixed, machined, welded, nicasil plated.
Then i put a new piston and small end bearing in , oh and new base and cylinder head gasket.
The " Marks " as i call them are not realy marks, they are just areas of the cylinder that look a little bit shinier than the other bits :(
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Update !
Engine was in pieces after i compression tested it , so i stuck the head back on and stuck some oil down the barrel to seal the ring against the bore a bit better ;)
I got 115 psi this time, ive not tested it warm yet.
Right, so, i remove the head, the exhaust and then the power valve cover. " OH **** " the arm with moves the power valve control shaft out has somehow jumped off :| , so the power valve hasn't been opening.
Is this why i was getting missfires ?
" Oh well, i might aswell remove the jug now whilst i'm here "
Here are the pictures that i would LOVE for you guys to have a look at and comment on, its currently 10 minutes past 3pm here and its realy sunny :)
http://images.filecloud.com/404622/New%20Nicasil%20Plate%20--%20Possible%20Damage%20001.jpg
http://images.filecloud.com/404623/New%20Nicasil%20Plate%20--%20Possible%20Damage%20002.jpg
http://images.filecloud.com/404624/New%20Nicasil%20Plate%20--%20Possible%20Damage%20003.jpg
http://images.filecloud.com/404625/New%20Nicasil%20Plate%20--%20Possible%20Damage%20005.jpg
http://images.filecloud.com/404626/New%20Nicasil%20Plate%20--%20Possible%20Damage%20007.jpg
http://images.filecloud.com/404629/New%20Nicasil%20Plate%20--%20Possible%20Damage%20008.jpg
http://images.filecloud.com/404630/New%20Nicasil%20Plate%20--%20Possible%20Damage%20009.jpg
http://images.filecloud.com/404631/New%20Nicasil%20Plate%20--%20Possible%20Damage%20012.jpg
These are big pictures, so they might take a while to load ;)
Please be honest with me and tell me whether it needs replating again or not, the piston appears to be ok :)
If you need any more pics please ask, but i would like to put the bike back together tommorow so i can have a good ride :)
Thanks again for all your help so far gents, i realy appreciate it.
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Well, I am not a motor head by any means so this is mostly my opinion and to stir the thoughts of the pony builders here. This is a 250?
Your power valve not working will make no top end (WOT) if it is closed. Not good for breaking a motor in. You basically are cutting the flow in half... 250 a 125 at top end.
Your compression reading will be, of course, at TDC of the stroke. It looks like your ring is not seated correctly at the top of the cylinder. The marks of the piston/rings on the cylinder wall need to be the full length. It looks like yours are mostly on the top of the cylinder and quite uneven for the work you had done.
This brings a couple thoughts.
First: Improper bore size. Kinda looks to be a bit too big. The picture of your piston shows that the piston above the ring is sliding against the cylinder wall. If it is too big of a bore you can't get the piston/ring to expand enough to seat the ring properly.
Second: Is this a cast aluminum piston (like stock) or a forged aluminum piston? If this is a cast aluminum piston in a bore set for a forged aluminum piston it won't work. The cast piston does not expand under heat to the diameter a forged piston would, so it would stay sloppy and not give good compression with the resulting slop through all temperature ranges. Forged pistons are quality parts but need more warm up time before heavy operation. This gets the piston to full expansion and compression.
A solution? Well, did you get the cylinder repaired, bored, sealed, and the piston/ring from the same place? Did the machinist have the piston and ring on hand to do the bore?
Might want to get another ring, hone the cylinder, and redo the break in. Don't play around with an "easy" ring setting. Set it like you mean it.
Warm up to op temp (about 2-4 mins) at idle (not riding it) with little blips to keep it from dying. Let cool down completely (30 mins or more), and repeat once. Then take it to a riding place where you can really work it. If your skills are not up to the task, let an experienced rider set it for you. Anyway, start the bike and let it warm up a bit (2 mins). Get out to an area after it is warmed up and that you can put it under a load and get though all the gears. Now your motor will have about 10 mins of run time that will clean up the edges on the ports and get the ring settled in. GET ON IT!!! Ride it like you stole it!!! Run it up some hills to get a gravity load on it will help it alot more than just flat straight runs across a field. I break my bikes in at the dunes and that is a load, sets the ring like a champ.
Anyway, I am not a motor builder or an expert so this is my opinion on the break in and your motor. Come on you piston guys, what does this cylinder look like to you?
Sly
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Thankyou Sly, I am very grateful for your reply :)
Its a Pro-x piston, in a 125cc Cylinder thats just been remachined, welded and nicasiled.
The bike is a 1992 model - Engine Number KX125JE098791 ( I don't actually know if it is a 1992 )
All the bits came from the same place, Stan Stephens 2 Stroke Specialists.
** BUMP ** Please reply guys, i want to put the bike back together A.S.A.P !!