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350 Top End Fried, Thoughts?

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Just looking for some thoughts to what you guys might think is going on here. So I went out for a day of riding at a local mx track, the bike was fine all day, started and rode perfect all day. A few days later when I got around to cleaning it really good, I found a bit of a coating of dust on my intake boot. Somehow dust/dirt got through my air filter. It was oiled well and seated well with grease on the rim. It was also infact very dusty that day. So after cleaning everything as usual I went to start the bike the same way as always. The bike ended up being impossible to start with kick starter or e start. I ended up trying to bump start it and that worked first try. The bike actually ran surprisingly well, no bogging, foreign sounds or anything out of the normal. Even after finally getting it going, it still wouldnt start at all, except bump starting it.

So I ended up bringing it to my shop for diagnosis, and after a leak down test it showed the bike was down 20% on compression. Also after bringing the bike to the shop, my mechanic was able to get it fired with e start and some throttle. After a little bit of running the bike, a gas started coming out of the overflow tube. More and more it started becoming blue, like it was burning oil.

So here's a list of facts to what's going on right now.

Bike is very hard to start.

Film of dust/dirt was found coating the airboot.

Down 20% on compression.

After running the bike for a little while, stuff (exhaust?) started coming out of the overflow tube, became bluish like oil after a while.

So what do you guys think?

The bike is a 2011 KTM 350 XC-F, with about 75 hours on the stock top end. (Was trying to hold off till the off season to replace.) Valves were checked and confirmed to be in spec about 10 hours prior to this. We have a piston and ring kit on the way, hopefully that is all it is. Maybe a worn out head gasket? Just a worn out top end? Any thoughts? I should hear from my shop within a couple days when he tears it down.

Edited by motonack

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your supposed to change piston at 50 hours and a crank at 100... you mine as well do it all!!

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What are the valves at now?  When they go they usually go quickly.  So, even OK 10 hrs ago does not mean good now.

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It went lean & siezed the compression ring.

Replace piston & ring. Correct all air intake issues, be sure air filter is sealed. Clean/replace fuel filters.

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It went lean & siezed the compression ring.

Replace piston & ring. Correct all air intake issues, be sure air filter is sealed. Clean/replace fuel filters.

How would it go lean?  I just recently started mixing 100 octane VP race gas with my regular 93.  Would that do anything?

 

Edit: I have been mixing the race gas in for races recently, but not for just a practice session.  If there was any race gas, it was only like 1-5% of the total gas in the tank at the time.  It is the VP VPR 100 octane stuff.  The guy said that is the stuff he would recommend.  After looking it up, it said it was preferred for 2 strokes, but all they had was that and 110 octane stuff.

Edited by motonack

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the same thing happened to my new (7 hours at the time) 12 350. super fine silty dust got through the filter in a 3 hour race. the dust was outa control had to stop twice to clean the inside of my goggles. after that the bike wouldn't start with out starting fluid and some throttle action or a bump start. checked the valves they were in spec so then we did a leak down and it showed 80% leak, pulled the oil filler cap off and you could hear the air blowing through the crank and out the filler hole. however No air was going out the exhaust or the intake or the overflow tube like yours. took it apart and everything looked perfect like a bike would at 7 hours.  put in a new top end and it was back to 12% with out starting it for a break in. bikes fine now but that stock single element twin air wasn't enough for those conditions. expensive lesson learned that day hahaha

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the same thing happened to my new (7 hours at the time) 12 350. super fine silty dust got through the filter in a 3 hour race. the dust was outa control had to stop twice to clean the inside of my goggles. after that the bike wouldn't start with out starting fluid and some throttle action or a bump start. checked the valves they were in spec so then we did a leak down and it showed 80% leak, pulled the oil filler cap off and you could hear the air blowing through the crank and out the filler hole. however No air was going out the exhaust or the intake or the overflow tube like yours. took it apart and everything looked perfect like a bike would at 7 hours.  put in a new top end and it was back to 12% with out starting it for a break in. bikes fine now but that stock single element twin air wasn't enough for those conditions. expensive lesson learned that day hahaha

Good to hear it wasn't anything catastrophic.  I'm due for a piston and rings anyways.  I'm just glad it didn't blow up.  I should hear any day now to what is actually going on.

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So I just heard back from my shop yesterday. Bike's ready for me to pick up, it ended up just needing piston/rings and fresh gaskets. Just in time for my race this weekend. Woohoo!

Edited by motonack

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So I just heard back from my shop yesterday. Bike's ready for me to pick up, it ended up just needing piston/rings and fresh gaskets. Just in time for my race this weekend. Woohoo!

 

like i said!! your over your hoursssssssss hellloooo noone listened to me!

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wel meby you get lucky ,but our crank (con.rod) did not least a 100 hours on a sxf 350 2013 . its broken within 25-30 hours and distroid the crankcase,s and cilinder/piston . so look out with 100 hours . this is one with the new plain bearing and this is perfect but the rod itself did not life so long.

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