This could have been really bad!!

[alxhtx]

So I was out riding the other day and I was coming out of a berm and my bike bogged down and died. I take a look at the motor and there was oil spewing out of the oil breather hose all over my swingarm. Also, a couple drops of oil had leaked out of the valve cover gasket. So I tore it down to find out my piston was done:bonk: . After further inspection is seems like all the other engine components are good and I just need a piston kit.

Anyway, im getting ready to do the piston kit rebuild and had a few questions...

1) Can someone fill me in on how to "deglaze" or "hone" the cylinder with a scotch pad and wd-40? (The steps)

2) Is this even necessary to do? and can the average dealer do this?

3) Those 4 copper washers that go on those 4 long bolts that bolt down the cylinder head and cylinder, do those always have to be replaced when you tear down the motor?

4) When reassemblying the motor do I need to put oil on the rings, cylinder, and piston? (I know there is a big controversy on dry vs wet install)

5) Where can I buy molybdenum disulfide oil(if its really necessary)?

Here is a few pictures of my piston ? ...

[bchristy613]

you and i just have the best luck .. lol

had the same thing happen to me last year though

[D-K]

1) Can someone fill me in on how to "deglaze" or "hone" the piston with a scotch pad and wd-40? (The steps)

2) Is this even necessary to do? and can the average dealer do this?

3) Those 4 copper washers that go on those 4 long bolts that bolt down the cylinder head and cylinder, do those always have to be replaced when you tear down the motor?

4) When reassemblying the motor do I need to put oil on the rings, cylinder, and piston? (I know there is a big controversy on dry vs wet install)

5) Where can I buy molybdenum disulfide oil(if its really necessary)?

I can answer a few of them:

1) Honing is done to the cylinder bore, not the piston. Only necessary if cylinder has many many hours on it and become "shiny" or "glazed" in some areas.

2) See 1

3) They do not have to be replaced, but they must have engine oil on both sides during install.

4) Yes, just a thin coat of engine oil on everything and some on the rings is needed.

5) It is overkill. Especially for just a new piston. Some engine oil is plenty.

I guess I answered all of them, haha:thumbsup:

[SSPI]

is that a stock piston {man are you lucky}

[spin05]

How many hours did you have on that piston ,may i ask????

[DMauro]

I heard about people cracking pistons in 07 but never seen one. man are you lucky!! this is what I did when putting in a new piston and had no problems. did not deglaze,oiled the rings and reused the copper washers . I'm not saying it is the right thing but had no problems.

[D-K]

I heard about people cracking pistons in 07 but never seen one. man are you lucky!! this is what I did when putting in a new piston and had no problems. did not deglaze,oiled the rings and reused the copper washers . I'm not saying it is the right thing but had no problems.

I can say it for you, you did the right thing:thumbsup:

[alxhtx]

I can answer a few of them:

1) Honing is done to the cylinder bore, not the piston. Only necessary if cylinder has many many hours on it and become "shiny" or "glazed" in some areas.

QUOTE]

? Sorry for the typo, I meant cylinder.

I hear you just take a scotch pad and spray wd-40 and scrub it a little bit? I guess in spiral motions? It might not be necessary but I guess I mitus well do it since I have the thing tore apart.

It is the stock piston with probably like 60-70 hours on it.

[spin05]

huh yea i just pulled mine at 60hrs.Looks good though.....

[525tom]

Fpr my 07: I reused the copper washers, did not hone, made sure that everything had a light coat of oil on it before I put it back together. You are very lucky that it doesn't have more damage. Imagine if that piston would have broke into pieces...... serious $$$$. Check your timing chain too, make sure that it doesn't need replaced. Good luck with your install.

[phatcat]

Wow my buddys 07 did that twice and he caught it both times my 07 exploded and came out the front of the cases. very lucky person you are!!

[mikekx102]

hey the exact same thing happened to my 2007 KX250F about 4 months ago.

The dealer said that i needed to do a bottom end rebuild as well because something like if you just do a top end rebuild and the power is increased you run the risk of putting the conrod through the front of the case or something like that.?

I don't know wether it was nessesary, but yeah we did a rebuild on the top and bottom, checked the gearbox and clutch (all good, not much wear) and got a mechanic to do the job.

The bike runs like a charm ???

my piston looked EXACTLY the same as the one in your pics... hmm..

anyway- good luck with the bike and hey a cracked piston's better than a grenaded one! ?

I replaced all the parts that needed replacing with genuine ones because of what I've heard about Wiseco pistons being dud's and all that. Anyway... like i said - good luck?

[alxhtx]

Did you by any chance happen to change to a new oil right when it happened?

There is no reason to do a bottom end in my opinion.

[MCL]

The pistons are designed to crack at half instead of shattering to pieces and cause expensive damage.The sound,loss of power and oil spewing out of the breather should warn even the worst noob to shut it off,running the engine just a tad longer will shatter the piston completely.Its pretty much the same thing as when the oil light comes on on a car,you need to shut it off immediately.

The oem kawi 250/450 piston is not that good,I would consider a aftermarket piston as a upgrade over the oem.

Also a lean condition causes excessive piston heat and therefore piston cracking.The hotter the piston runs the more it will cool down when fresh air is sucked into the combustion chamber,also the vaporizing fuel will cool the air even further.Temperature changes and differences cause tension which can cause bending and cracking.4-strokes are not that picky about jetting and will still run fine.A aftermarket exhaust will usually lean out the condition worsening the situation

I would also like to note that the hot start leans out the mixture to ease starting when the engine is hot.Running a engine with the hot start stuck open will crack the piston with a 100% guarantee.

[KawiRider78]

that piston should go in ur hall of fame u r 1 lucky guy haha

[Tom Southcott]

These cracks are identical to the cracks in my piston and I had the same oil leaks from the breather tube and the valve cover gasket.

Chock one up for Kawasaki consistancy.

Thanks for you r reply

[motorheaderr]

hey guys i have an 07 kx 250f and my bike just dies out on me and oil came out of the breather.... after reading this i think my piston might just be cracked like your pics!!! i dont have much compression but i still have a little is that what you guys had when your pistons cracked in half?

[kawasakimx8]

id check ur piston, better to be safe than sorry. while ur in there, rebuild it and replace anything that is worn. pending on how many hours, do they valves. and id get a new piston anyways.

[toomanytoys2]

Is this an 07 issue, or is it all years as well? What is considered the best quality piston? Thanks

[rcr_kx250f]

Never use anything but a diamond hone on your cylinder. A scottbrite pad it's strong enough to do much. Any decent shop should be able to do, takes about a minute. As for oil on the rings, just wd-40, gives it just enough lube to start up then burns off so the rings can seat.