Not sure if my 2 stroke cylinder needs bored/replated etc

[Jack wagon]

HI, I just bought a 2001 Kawasaki kx 125 and I'm pretty sure it cold seized while I was pinning it in fifth gear. This is my first dirt bike so I'm kind of just learning as I go along. I think the main cause was not letting it warm up long enough. So I tore it down and I don't really know what to look for, the piston doesn't look good, it has a lot of deep vertical scratches so I'll probably order a wisco. The cylinder looks pretty good in my opinion there is some vertical wear that I can barely feel with my finger nail, so I'm hoping I don't need to get cylinder work done because I won't be able to afford it for awhile. I'll attatch some pictures, any advise is greatly appreciated.

[450josh]

Piston looks pretty mangled, cylinder is perfectly fine. Did you run it out of oil or something? Forget to used mixed gas?

Piston looks pretty mangled, cylinder is perfectly fine. Did you run it out of oil or something? Forget to used mixed gas?

Ps, not a mechanic, but I'd say your cylinder is perfectly good

[Jack wagon]

I only burned like 5 gallons of gas since I got the bike the only thing I can think of is I used the crapy yard eqipmemt primix that I got from Walmart this is my first dirt bike so I didn't relly think about it to much I just wanted to go make some ruts in my yard lol.

[450josh]

I only burned like 5 gallons of gas since I got the bike the only thing I can think of is I used the crapy yard eqipmemt primix that I got from Walmart this is my first dirt bike so I didn't relly think about it to much I just wanted to go make some ruts in my yard lol.

Well, that could be it. The two strokes I've ridden have always been premium fuel self mixed with the specific oil. They dont take just any premix, it'll be certain specs it has to be.

[Jack wagon]

Well, that could be it. The two strokes I've ridden have always been premium fuel self mixed with the specific oil. They dont take just any premix, it'll be certain specs it has to be.

I used regular gas to, should I be using ethonal free premium?

[mlatour]

Use Premium 91 as a minimum.

 

I would'nt run that cylinder in that condition.

 

You see threads here all the time about people slapping a new piston in a worn out cylinder

and asking why their 'rebuilt' engine didn't last more than 15-20 hours before seizing again.

 

If the rest of the bike is in good condition and you intend to keep it for a while / fix it up properly

do it right and have the cylinder re-plated (about 200$).

 

Keeping in mind that's a 16 year old MX race engine with very likely an unknown maintenance history,

doing a crankcase pressure test will confirm there are no air leaks to soon ruin your newly rebuilt engine.

 

Sustained "pinning it" in top gear will also increase the chances of seizing an engine,

a MX race bike is meant to accelerate hard from corner to corner on the relatively short straightaways of an MX course,

not meant for sustained top speed wide open throttle runs down long stretches of road / fields.

Edited January 3, 2017 by mlatour

[Jack wagon]

Use Premium 91 as a minimum.

I would'nt run that cylinder in that condition.

You see threads here all the time about people slapping a new piston in a worn out cylinder

and asking why their 'rebuilt' engine didn't last more than 15-20 hours before seizing again.

If the rest of the bike is in good condition and you intend to keep it for a while / fix it up properly

do it right and have the cylinder re-plated (about 200$).

Keeping in mind that's a 16 year old MX race engine with very likely an unknown maintenance history,

doing a crankcase pressure test will confirm there are no air leaks to soon ruin your newly rebuilt engine.

Sustained "pinning it in 5th/6th gear" will also increase the chances of seizing an engine,

a MX race bike is meant to accelerate hard from corner to corner on the relatively short straightaways of an MX course,

not meant for sustained top speed wide open throttle runs down long stretches of road / fields.

so what are the Main causes of the problem I have? Edited January 3, 2017 by Jack wagon

[mlatour]

At first glance it looks to have run too lean,

 

Being your 1st dirtbike / not familiar with 2-strokes....

I'd guess the jetting was too lean for the cooler ambiant temps (winter now in Idaho)

say riding it wide open throttle in near or below freezing weather with the stock carburetor settings meant for 68°F weather.

 

but as mentioned, on an older engine you can't rule out air leaks causing a lean condition.

 

A 'cold seize' is often referred to as a '4 corner seize',

leaving distinctive marks on the piston as it's expands too fast into the bore.

 

Damage shows it may have cold seized at bit but there is no doubt it also ran too lean

both of which are two very different problems.

 

Post some pics of the top and other side of the piston.

Edited January 3, 2017 by mlatour

[kxfreak]

HI, I just bought a 2001 Kawasaki kx 125 and I'm pretty sure it cold seized while I was pinning it in fifth gear. This is my first dirt bike so I'm kind of just learning as I go along. I think the main cause was not letting it warm up long enough. So I tore it down and I don't really know what to look for, the piston doesn't look good, it has a lot of deep vertical scratches so I'll probably order a wisco. The cylinder looks pretty good in my opinion there is some vertical wear that I can barely feel with my finger nail, so I'm hoping I don't need to get cylinder work done because I won't be able to afford it for awhile. I'll attatch some pictures, any advise is greatly appreciated.

yea, I wouldn't recommend re-using that cylinder either. If you look on ebay I'm sure you could find one in much better condition for pretty cheap. Or look for aftermarket cylinders for less than OEM but that cylinder is pretty scored and swapping a fresh piston and rings in is looking for trouble.

[Jack wagon]

yea, I wouldn't recommend re-using that cylinder either. If you look on ebay I'm sure you could find one in much better condition for pretty cheap. Or look for aftermarket cylinders for less than OEM but that cylinder is pretty scored and swapping a fresh piston and rings in is looking for trouble.

you think I should buy a totally new cylinder! Why would I do that if I can just replate it for a couple Hundred.

[kxfreak]

you think I should buy a totally new cylinder! Why would I do that if I can just replate it for a couple Hundred.

It's really depends on the bike. Im not sure the cost of parts for yours, but my newer yz450f I bought a new "cylinder works" cylinder for less than I could get my old damaged one replated for. sometimes replating isn't the cheapest route. A cylinder works cylinder for my bike is $211 and many places are $250 plus shipping to replate.

[mlatour]

4 stroke cylinders are cheaper than 2-stroke ones.

[91kdx25088]

send it out with a new piston to get replated.

[kxfreak]

It's really depends on the bike. Im not sure the cost of parts for yours, but my newer yz450f I bought a new "cylinder works" cylinder for less than I could get my old damaged one replated for. sometimes replating isn't the cheapest route. A cylinder works cylinder for my bike is $211 and many places are $250 plus shipping to replate.

EDIT: I just looked real quick and couldn't find much for your bike, I guess because of its age there's not really as much aftermarket support for it now a days. so yea your best bet would probly be to get it replated. Millennium technologies is suppose to do a really good job.

I was unaware 2 stroke cylinders cost more than 4 stroke cylinders, but yea after seeing the cost of a new cylinder replating would be your best bet

Edited January 3, 2017 by kxfreak

[Jack wagon]

send it out with a new piston to get replated.

Do you mean put a brand new piston in the same package as my cylinder. Is that just to get the specs right?

[91kdx25088]

Do you mean put a brand new piston in the same package as my cylinder. Is that just to get the specs right?

correct. when you send them a new piston they match the cylinder to the piston so your guaranteed to get a proper fit.

[ossagp]

Most companies who plate can supply a piston too.  Some have exchange cylinder type services.  If you are not familiar with reinstalling power valves you should ask them about doing that for you or get some reliable help.   Sometimes getting an ovesize 134-144 cylinder built will actually work out pricewise since the ones I have bought included cutting the valves and reinstalling them.   

[turbo dan]

The plating is questionable.  From the pics I can't say for sure its toast but I would recommend a replate to ensure you don't have any issues going forward.

 

There is absolutely no reason not to reuse that cylinder as a core for replating.  They can fix them with chunks missing, they just weld them up and replate as normal.  That one looks like it would just be a simple strip, replate and hone job.  Very ordinary.

[Jack wagon]

At first glance it looks to have run too lean,

 

Being your 1st dirtbike / not familiar with 2-strokes....

I'd guess the jetting was too lean for the cooler ambiant temps (winter now in Idaho)

say riding it wide open throttle in near or below freezing weather with the stock carburetor settings meant for 68°F weather.

 

but as mentioned, on an older engine you can't rule out air leaks causing a lean condition.

 

A 'cold seize' is often referred to as a '4 corner seize',

leaving distinctive marks on the piston as it's expands too fast into the bore.

 

Damage shows it may have cold seized at bit but there is no doubt it also ran too lean

both of which are two very different problems.

 

Post some pics of the top and other side of the piston.

Here are some pics of the other side top and inside of the piston the top looks like it has quite a bit of material gone.

[ossagp]

HI, I just bought a 2001 Kawasaki kx 125 and I'm pretty sure it cold seized while I was pinning it in fifth gear. This is my first dirt bike so I'm kind of just learning as I go along. I think the main cause was not letting it warm up long enough. So I tore it down and I don't really know what to look for, the piston doesn't look good, it has a lot of deep vertical scratches so I'll probably order a wisco. The cylinder looks pretty good in my opinion there is some vertical wear that I can barely feel with my finger nail, so I'm hoping I don't need to get cylinder work done because I won't be able to afford it for awhile. I'll attatch some pictures, any advise is greatly appreciated.

A new cylinder or replating is always a nice idea. If that one was mine, I would probably reuse it though. I see nothing that tells me the plating is beyond being fixed, but it can be risky to the next piston if you don't know how to prep one. First off I have honed lots of cylinders and had EXCELLENT results. But yours can't be cleaned up by a hone, without first removing the aluminum deposits and a hone is lousy for that and will actually in most cases not even remove the aluminum left. That is something that you use an acid for (muriatic acid, which is actually sulfuric acid, for the most part) to remove the acid, the cylinder will look way different with that being done. Then I would decide whether it needed honing, scotchbrite, or plating. The piston is toast and tells me you should start by inventorying your jets and use a good oil that is primarily for motorcycles, and a 125 that is ridden in open spaces should never be mixed with a lower oil to fuel ration than 32-1 (mine are run at 20-1 for such useage).

Your KX is likely going to be jetted a bit under factory if not ALOT under factory.

In rereading that: Muriatic acid is hydrochloric acid.

Edited January 3, 2017 by ossagp