weird KX 100 issues

[Dirt Hokie]

Just bought my son a 2013 KX100.  It was well used but ran good, PO said it had a recent top end rebuild, cylinder looked newer.   Son rode it a few different times in the open fields behind our house with no issue, except a fouled plug ( he was still getting used to the 2 stroke) We replaced the plug.  He put about 1 hr on it over a few days.   We then get the time to go ride some trails, mostly slow single track stuff, after about 30 min the bike started cutting out at high RPM when in the power band.  I thought it was either overheating or fouled plug again.   It never boiled over.  We let the bike cool down some, and pulled the plug.  Plug was dry.   Tried to start it and realized the bike was seized....Could hardly get the kickstarter to move.  Loaded up and headed home, once the bike the completely cooled down, it was froze solid.   We pull the head and find this... After investigating some more i discover one of the circle clips is missing that holds the wrist pin, I think it must have come out and is the primary suspect,  cylinder does not look to bad, piston sides are gouged real bad.  I thought we may have got lucky, but the crank also has some issues, it does not spin freely and binds on about 1/2 its rotation... I figured some some metal must have got in the main bearings. The con rod bearings seem fine.  Looks like I will get to do my first complete rebuild on a modern bike.   Now for the other mysteries ( I am not a mechanic, and only have ever rebuilt one bottom end, that was on a 1978 yz 80 ) 

1.  despite no evidence of leaks, there was no coolant in the rad or top end, it was full the day before, and no puddles or leaks were ever noticed.

2. the water pump was full of oil.....but no obvious coolant in the transmission or crank case when we drained everything.

Could overheating from a coolant leak cause a circle clip to fail, or was that a coincidence?

Could overheating cause a seal to fail in the water pump.

Would a seal failure explain the oil in the water pump?

With no obvious damage to cylinder, do i need a quality micrometer to check if its still fine.  Maybe just have it honed?....Or should I go ahead and get it bored.

Can get more pics tonight.    

Thanks for any insight.  

 

 

[Dirt Hokie]

another question, does anyone make a complete engine rebuild kit, cant see to find one for this year.  Is the bottom end the same as a KX 85?

thanks

[FPMXer]

If you lost a circlip I'm betting the piston pin worked its way into the cylinder wall and left a nice divot. If not you got real lucky. The head is trash. You can find an entire rotating assembly online for that bike. ebay, rockymountianatv, there are a few others. Google it. You will need to tear the motor all the way down and replace the crank seals, bearings, crankshaft itself with all new seals for the motor and gaskets. Inspect the transmission, trans bearings, clutch, water pump and anything else I'm forgetting. Take a real good look at the cylinder wall as well. Buy either a brand new head or good used one off ebay. The bikes smaller than the 125's like a fresh clean oiled air filter every ride. All my kids 60's, 65's, 80's and 85 didn't run right unless it had a fresh air filter. Those little motors are zingin when kids are ringing the snot out of them. The dry plug could also been a lean condition on the jetting and helped burn the motor down. What premix ratio did you put in the tank before the carnage?

[mlatour]

If the cylinder wall has any damage you can hook a finger nail on or,

areas where the cross hatch isn't visible anymore, it will require replating.

[Dirt Hokie]

there is one scuff on the cylinder wall, can barely feel it on a fingernail.   Will probably send it out to get bored and matching piston.

Researching complete rebuild kits now.   I pulled the water pump apart, the back of the impeller looked like it was rubbing against the housing.

I was running 32:1.

I think the who ever rebuilt or worked on the engine last just did a crappy job and this thing was a time bomb, hopefully the trans is good. 

[sirthumpalot]

Agreed the person who "rebuilt" it didn't know what they were doing.  If it uses the "C" style circlips then my guess is they installed the circlip incorrectly. The gap MUST be directly up or down.  If it's to the side then the forces at higher RPM will cause the circlip to compress and come out.  If the water pump was full of oil then the coolant most likely went into the transmission, or out the weep hole.  Time for new pump seals.  That head can likely be saved by a good machine shop that specializes in head repair, maybe compare that price against the price of a new one.  I believe that cylinder is plated, don't try to hone it.  

[Team Buggerall]

Hokie smokes! You should sell that whole bike as a basket case and go buy a good one. 

[rholbrook]

Since you have it apart do it right.  If the cylinder isnt that bad maybe they can hone it and redo the nikasil and then you can get a plus sized piston in it.  I would suggest Andrew Cooksey to put you a balanced crank together.  You can find him online if you look up Cooksey Cranks or search his name.  Put all new bearings, gaskets and seals in it, put it together knowing that your son can enjoy a great dependable bike that you know will run great for you.  A circlip coming out can cause all kinds of problems.  I have seen bikes get so hot that it has destroyed seals but you may need to verify that your head and cylinder doesn't have any cracks in it. 

Don't blame your son for this mishap, use it as an educational opportunity for you and your son to rebuild HIS dirtbike.  Perfect time to teach him about working and maintaining a bike.

Edited January 29, 2019 by rholbrook

[FPMXer]

https://www.rockymountainatvmc.com/parts/dirt-bike-engine?v=2013-kawasaki-kx100

[Chris Russell]

2 hours ago, sirthumpalot said:

Agreed the person who "rebuilt" it didn't know what they were doing.  If it uses the "C" style circlips then my guess is they installed the circlip incorrectly. The gap MUST be directly up or down.  If it's to the side then the forces at higher RPM will cause the circlip to compress and come out. 

That head can likely be saved by a good machine shop that specializes in head repair...

I believe that cylinder is plated, don't try to hone it.  

and if they have a tang throw them away and replace with proper internal circlips...

i would fix it. thread a bit of bar in the lathe for the plug, its all easy from there. done it before will do it again! bitching when its not central though.

sometimes the best option is to sleeve them out in CI, specially when theres plenty of similar sized engines to get suitable parts from. not so easy when its an oddball size and your basically stuck with no parts... ie, you can always check out data like deck and dome height, wrist pin diameter, and find 10 or more suitable pistons for 100cc... but not a 150.

new nikasil can be expensive... so can a new cylinder! the new nikasil at least will be a lot better than the factory job. now is the time to port, to get the nikasil blending into the ports nicely!

cast iron is nearly indestructible but has different expansion ratios, more clearance when cold, has to warm up, rattles... can require some work to "wet sleeve" or it overheats when replacing a nikasil bore. always easy to replace, hone, or port.

one machine shop will do it for beer, another will tell you youre insane then quote you 6000.. .

 

as for the water, i have a different theory.

that there looks like some serious foreign body damage.

theres only a few bolts holding the head down.

bang bang bang, enough to lift the head and bypass the gasket. seen it before. mystery vanishing water. your exhaust will be damp inside. possibly green. (or whatever colour you prefer your coolant)

how are the crank bearings? with that sort of damage i would be checking a few parts... like the conrod. maybe an idea to replace the pin and bearing along with it.

[shrubitup]

Seen whole running motors on eBay for 500-600$ in 85 or 100 configurations. Both fit but electrics and jetting different. 

[GasMixer44]

Bummer thats the first experience your kid had with a green machine. I agree with everyone else that said to rebuild it, you will get that piece of mind knowing it has a fresh top and bottom end. it will be worth it to buy whatever tools you will need, they will pay for themselves quickly, if not the first use. Keep us posted

[Dirt Hokie]

Its getting rebuilt,  hope to have it all torn down this weekend, and order parts next week.  We have a race we want to do March 17th, so that's the goal.  I have done top ends before, and did a complete assembly/ rebuild on a 1978 yz80 basket case,  so I "know" what I am getting into, just don't have that much experience.   Now to find a clutch basket tool........ 

[COMotoRider802]

On 1/28/2019 at 1:58 PM, Dirt Hokie said:

another question, does anyone make a complete engine rebuild kit, cant see to find one for this year.  Is the bottom end the same as a KX 85?

thanks

You can get a full rebuild kit from Wiseco.  This comes with everything to build top and bottom end.  They show out of stock, but if you call them they are good about getting you a date when they will arrive or may work with you to put one together.

http://www.wiseco.com/ProductDetail.aspx?ItemID=PWR164-100&ModelID=229&ModelYear=2013&AppID=70754

Edited January 30, 2019 by CO MotoRider

[Dirt Hokie]

the trans looks and feels good, the main crank bearings look they got hot, but are intact.   There is mystery metalic/ cooper like greesy goo in the bottom of the crank case, the big end bearing does not feel right, but there is not enough metal missing anywhere to  explain the amount of metal I am seeing.  Its almost like it inhaled cooper dust.   The reeds are carbon and intact, the head gasket was intact and the base gasket is not metallic.

I did find out is has a Wiesco clutch basket.

I am going to check the vin number to confirm the year, then ordering parts.   Going to do the full deal, all new bearings, seals, crank, gaskets, fresh top end, and new water pump parts....  I have a shop manual that goes to 2012,  I think i have a 13, but they may be the same.  

[yz250f 78]

This was definitely a neglected bike!  But it can be fixed!  

[FaceDeAce]

Likely the remnants of a disintegrating con rod big end roller bearing cage

[Dirt Hokie]

just ordered a Wiesco bottom end rebuild kit, and all the bearings and seals for the trans that did not come with the kit.

Now just have to get the cylinder checked out.  

Everything came apart pretty easy, except i have to figure out how to remove the bearings that are installed in a blind hole,  water pump bearings and one or two in the trans.  Luckily they all feel fine, but I ordered new ones, so I want to replace them.  Then I know every bearing and seal in the engine will be new.   

[sirthumpalot]

There are a handful of creative ways to remove bearings in blind holes, but a puller is probably the easiest if you have the option.  This guy covers it nicely: 

 

[Chris Russell]

i usually have good luck with blind bearings by shoving them in the freezer overnight, turning them upside down, heat the casting til spit sizzles, then if it hasnt already fallen straight out a few gentle taps on the case should persuade it to do so.