Sand in my motor!! 2012 KTM 250SX

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10/20/2018 10:59 AM

I bought this bike less than a year ago. A couple things went wrong and I decided to have the full motor rebuilt - partly because it needed it and partly because I wanted a brand new motor. This included re-plating the cylinder.

10 hours later, I pulled the filter off (as I do after every ride) and saw the sand in the pic below. The week before I had put the filter on and it had a small chunk out of it in the area that seals. But it didn't seem to be enough to undo the seal or let anything through. I don't know if that was it. I still can't tell how all that sand got through. Anyway, you can see the damage it did to the cylinder. Also, you can see the magnetic drain bolt that collected a bunch of metal shavings. It did that twice after two flushes.

So, after going into a catatonic state for two weeks and my wife telling me that she was worried about my health, I've finally started to deal with the problem. I cannot afford a new bike and I can't really afford to have a mechanic rebuild the damn thing again. I have never rebuilt a motor but have a friend that rebuilds and mods his own road race car motor who says we can do it.

My question is, what all exactly is jacked up in there? If I get it replated and buy one of those wrench rabbit rebuild kits, will I have everything I need? Or is there more to it than just rebuilding the motor? Is it possible that it destroyed the transmission also?

And after that, I still don't know exactly how all the sand got in.

Thanks for the help. I'm a weekend warrior office jockey who can do basic maintenance and some bolt on stuff.




10/20/2018 11:48 AM

Sand in the engine does not equal metal on the drain plug. With 2 strokes, the only way the two are connected is through the right side main bearing and seal. Even then, you aren't going to get metal from the cylinder in to the gearbox.

Your cylinder looks fine in the picture. Plated cylinders are unbelievably strong, I've seen them with seized pistons that had aluminum adhered to the wall get cleaned up with some muriatic acid and a scotch-brite pad. It's actually more likely the crank and/or rod bearings were affected and/or the piston itself. It's actually possible that the sand made it's way through the engine with no ill effect.

For the filter, you may just have a bad seal between the airboot and the airbox. Be prepared to pull that apart and re-seal it. I would suggest a DT-1 filter in the future as the neoprene seal is simply the best at keeping grit on the outside and things clean on the inside.

You may well need to split the cases to find the cause of the transmission shavings (clutch is the most likely) as well as replace the main bearings. It would be advisable to have the crank rebuilt while you're at it. comes highly recommended for that work.

The good news is that working on a two stroke is really simple. If you friend has rebuilt race car motors, he's going laugh at how simple your KTM is. I would suggest using a case splitter and a proper ignition rotor removal tool (RMATVMC and their Tusk tools are cheap and work great), but most everything else should use regular hand tools. Take lots of pictures, particularly of the transmission and power valve, though you can probably find videos of the assembly on them anyway.


10/20/2018 7:38 PM

Buy a manual before you start and read it thoroughly before you start and follow it like the bible when you start working on it. It's a lot of piece of mind.


The older I get, the faster I was.

10/21/2018 3:48 PM

Thanks Matt. Really appreciate the insight. I'm gonna summarize to make sure that I understand correctly -

- Motor sand issues are unlikely. However, if something is wrong, then it may be Crank, rod bearings, piston. The cylinder appears ok

- Filter sand issues - check seal between air boot & air box. Re-seal it. Possibly try a DT-1 filter for peace of mind because it gets a better seal

- Most likely unrelated to sand
- Likely to be clutch issue. Is it possible the shavings are coming off gears? or anything else in transmission?
- May also be main bearings

You also mention that I might as well rebuild the crank. Is that just because I'm in there or it may be affected by the metal shavings issue or the sand?

Tools to buy
1. Case splitter
2. Ignition tool

Thanks for the help.


10/21/2018 8:52 PM
Edited Date/Time: 10/21/2018 8:53 PM

kage173 wrote:

Thanks Matt. Really appreciate the insight. I'm gonna summarize to make sure that I understand correctly -

- Motor sand ...more

Kind of went through the same issue and haven’t attacked it yet so don’t feel bad. I completely restored a junked 1997 yz125. Had the engine professionally rebuilt bottom to top and trans gone through by a reputable business.

Well not only did I get a little sand sucked in their, but the transmission won’t go above 2nd gear anymore. Pretty sure it’s a shift fork, I’m annoyed because that should not happen after a professional rebuild.

Also, there were some metal shavings, but it was definitely from my completely junked clutch basket and hub that I was too cheap to replace which was literally the only thing that I didn’t replace lol.

Anyway, figured I’d share my story with you so you don’t feel as bad, and I will be doing my first splitting of the cares as well. Gotta order those tusk tools grin anyways good luck and I hope it all goes well for you.


10/22/2018 1:32 AM

Probably won’t get much help here at VitalMx. We specialise in sand in vaginas


10/22/2018 7:15 AM

Always double check that the air filter is properly seated in the airbox before clamping it down. I would bet a dollar that you had the filter/cage installed 90 degrees off and it didn't seat in place. Ask me how I know....blush

When I bought my 2013 , the first thing I did was order up the Twin Air aluminum cage and some filters to go with it. If you look at the shape of the filter cage, you will see the issue. It fits in one way and one way only.


10/22/2018 7:26 AM

Matt mentioned the cylinder looking in good shape. If there is no real damage to the plating, you may be able to step up to the next OEM piston. Pull the cylinder and have it checked and measured. Inspect the crank area for signs of any sand. You may have caught it before doing any damage. Pull the engine out and flush the lower end thoroughly. Dump it out over a clean white paper shop towel and inspect for what washes out.

Our 08 KTM144 stuck the ring and lost compression when it sucked sand. Cylinder and crank were fine. Chip Munn at Munn Racing will probably answer the phone when you call for parts...he is extremely knowledgeable and helpful. Just sayin'

The seal between the airbox and airboot I don't believe is an issue on a KTM. The boot fits through the airbox and seals directly to the filter, correct???


10/22/2018 7:27 AM

The airbox seal could have failed or the airfilter lip was not sealing properly. A lot of people use rim grease on the filter lip. The air filter cage could also be flexing not creating a good seal. Filter could be leaking around the center screw. Twinair aluminum cage will take care of the flex..

As for the sand. If you want piece of mind I would split the cases and just clean it all up good. Sand will eat everything inside the crank/cylinder area. Inspect everything and deglaze the cylinder with some scotch bite. Piston and rings I would replace though im sure the rings took a beating from the sand.. The service manual will give you service limits for ring gap, crank, cylinder etc.

The metal shavings are from the transmission and clutch. That seems like a lot of metal but that depends on how long your oil change intervals are. The steel plates in the clutch wear and break down which is the shavings you see on the drain plug. It is normal to some degree.

10hrs is to much for a filter and oil change..


10/22/2018 9:19 AM

kage173 wrote:

Thanks Matt. Really appreciate the insight. I'm gonna summarize to make sure that I understand correctly -

- Motor sand ...more

I wouldn't say unlikely. More like possible there isn't any damage.

The metal shavings aren't from the sand. Sand in the top end of a two stroke causing excessive metal deposits in the transmission is about as likely as you getting some chick pregnant because you jerked off in the shower, then she came in, sat down and took a bath. Possible- well, yeah. So is winning the current 1+ billion dollar lotto.

The common metal shavings in a two stroke transmission is usually from the clutch, but bearings, gears, shafts, etc can all wear and leave deposits too.

Rebuilding the crank- it's a gamble to run it or rebuild it. See below.

Splitting the cases and going through everything is the safe thing to do. The cheap and not so safe way is to pull the cylinder, dump some premix in the crank area and spin the crank over by hand, hoping to knock any bits of debris loose. Dump the premix out and cross your fingers. Cheap route for the transmission would be change the fluid with some Walmart branded ATF, and change it really frequently until it either stops shifting properly or stops having very much metal come out between changes.

capmoto's advise of a manual is a good one.


10/22/2018 11:41 AM

newmann wrote:

Always double check that the air filter is properly seated in the airbox before clamping it down. I would bet a dollar that ...more

Yup, always reach far back corner of filter/ cage to see if its seated. We pulled sand through our 2012 KTM 450 that way. Lip wasn't seated........ouch, that was expensive.


10/23/2018 8:07 AM

Until 2016 SXF models it was/is risky business not checking the air filter properly sealed with every air filter change.


10/23/2018 8:10 AM

this is exactly how my 16 250sx blew up with only 20hours on it. sucked in dirt.