Seized KTM 380exc: How to fix?

[2STROKEREVOLUTION]

So, here is the story.
I had a 380SX and love the bike. I saw a good deal on a 380exc and decided to jump on it. The guy forgot to mix one ride and it seized. I picked it up for $500.
I asked a couple people what to do and they all said just get it replated(it is all aluminum). Not only was it seized, there was a small crack in a port. Munn racing said no problem about the crack they just weld it up. So I got it fixed, put back together, and took it out riding. I was riding easy, just to break it in. After a few hours it was still working perfect. It was running cool, getting plenty of oil, and then it seized. After taking it apart it looked like it did when I bought it. Completely scraped cylinder and there was a crack in another port.

I don't trust this jug anymore. I think the best thing to do is get a new cylinder or get a steel sleeve.

What are the suggestions? Any places that have good prices?

[EJ]

At first, i would ask at KTM for the price of a new 380 cylinder..

[bearorso]

If you opt for a steel sleeve - contact these blokes - I think they can provide a few different sizes to bring it up to as much as 434cc. The engine featured in there is based on a 250SX, but the barrel / piston  (and crank) are 380 based. The head spigot, exhaust manifold and exhaust boost chamber are modified because the engines going in a late model SX chassis, so not needed with a std 380 chassis.

          http://rpmmfg.com

[Coop]

Have you checked the jetting? What does the plug look like? You describe a symptom very much like a lean seize, that usually does damage like you identified. I know you say it was running cool, but I would seriously look towards the jetting and the cooling system before you trash yet another cylinder.

[2STROKEREVOLUTION]

Have you checked the jetting? What does the plug look like? You describe a symptom very much like a lean seize, that usually does damage like you identified. I know you say it was running cool, but I would seriously look towards the jetting and the cooling system before you trash yet another cylinder.

It is not jetting. If anything it is running rich. My other 380 has a leaner needle and is still a tad rich in the mid range and I have had no problems with it.
If it isn't running hot I don't see how it could be cooling.
And I was running extra oil for the break in period.

[2STROKEREVOLUTION]

If you opt for a steel sleeve - contact these blokes - I think they can provide a few different sizes to bring it up to as much as 434cc. The engine featured in there is based on a 250SX, but the barrel / piston  (and crank) are 380 based. The head spigot, exhaust manifold and exhaust boost chamber are modified because the engines going in a late model SX chassis, so not needed with a std 380 chassis.

          http://rpmmfg.com

I will definitely check them out, thanks. Any word on what reliability and powerband is for the bigger displacement?

[SachsGS]

Check your waterpump impellor.I've seen the steel shaft spin in the plastic impellor and it will still circulate some coolant - you'll pop the rad cap and everything looks o.k. but it's not.Only heat will crack that cylinder.

[riffraff]

Running extra oil? how much extra, extra oil could affect your jetting from what I've heard

[TotalNZ]

True, more oil= leaner air fuel mix. i'd be checking for air leaks too

[2T Institute]

I'll buy it off you or get the cylinder replated for you.Sleeves are bad news.

[MyckMcClung]

check that waterpump, the radiators, everything cooling system related, then check the crank, might be a bent rod..

[Coop]

Yeah all I was saying was, bikes just don't seize for no reason. Something caused that bike to seize twice.

[eprovenzano]

I had a friend go through the same thing on his 06 KTM 250SX, siezed it twice...  turned out to be a bent rod.  He replaced the crank, and now all its been two seasons, its been running great.

[Charles Owens]

If the top end locked up.. twice, more than likely it hurt the bottom as well.
The same oil that wasn't doing its job on the top, I'm sure wasn't doing it on the bottom.

[2STROKEREVOLUTION]

check that waterpump, the radiators, everything cooling system related, then check the crank, might be a bent rod..

Still don't see how it can be cooling issues when it was not running hot. It was perfect.

I will check the rod.