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White Smoke out of Exhaust KTM EXC 450

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I just got done replacing the head gasket and rings on my 2008 ktm exc and when I started it up for the first time it was blowing a lot of white smoke out the exhaust and even continued for a minute after shutting the bike off. I know thats typically a sign of a bad gasket but I just replaced it. I torqued all the bolts down corrrectly and I saw no problem with the head. Could it be something with the water pump? Or maybe i still screwed something up when putting it back together. 

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Probably a minute, at the most. I was afraid of it doing damage. Should I have let it heat up for a bit?

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Just because you replaced the head gasket, doesn't mean the gasket has sealed properly.  Water vapour in the exhaust is likely a bad seal on the head gasket.  Pull it apart and do it again.  Use some motoseal or the like to ensure the thing seals up properly.

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8 minutes ago, noacluck said:

So I dont have to get a new gasket if I take it back apart?

Anytime you remove teh head on a 4S, you must replace the gasket. But I doubt it is the gasket failing,. more likely a unflat surface, bad oring, head bolts giving a false torque reading or a bad torque wrench.

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If you just bolted the thing together you can reuse that gasket.

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Start with everything you took apart (assuming it was running right before). 

Then look where you've got intake/combustion volume next to cooling system volume.  Head (head gasket) probably most likely.  Base gasket (had problems with that on my sled a few years back).  Water pump. 

 

Review the service manual, see if there's a step you missed along the way...

 

...and good luck.  I hate coolant. 🤣

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I did a top end on my 09 450 I used OEM parts . First fire up it smoked like my snowmobile. Pulled it back apart and found a flaw in the dimple seal on the head gasket . When they shipped me the gasket I was surprised it did not come in ktm packaging. Went to the dealer bought a gasket put it back together and no issues.

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Make sure the head is still flat.  If you used a rotating tool (dremmel and brush, etc..) to remove the old gasket then that might have made the head non-flat, requiring a shave to make it flat again.  Make sure both surfaces are sterile clean before you re-assemble it.  By the book you are not supposed to re-use a head gasket, but in reality there are good odds that you can re-use it just fine if it was only installed for a short time.  

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STOP-STOP-STOP!  WHATEVER YOU ARE DOING, JUST STOP!  You are not getting sound advice on this chat board.  White "smoke" is oil burning.  Steam may at first look like white smoke; but it will dissipate into the air almost immediately.  "Smoke" will linger.  What you are describing does not sound like "steam" from a leaking head gasket.  Furthermore; if you actually do have a head gasket that is leaking coolant into the cylinder, it takes more than a minute for the cooling system to build enough heat to develop enough pressure to push the coolant past the gasket and into the cylinder.  Then the back third of the exhaust system, particularly the muffler, has to be hot enough to allow the steam not to revert back to liquid form and exit the exhaust system while still in "steam" form.  That takes more than a minute.  

Then; after you shut off the engine, unless there is enough liquid collected in the exhaust system lower than the exhaust valve(s) and there is enough heat in the exhaust system to continue heating the liquid coolant beyond its boiling point, vaporizing that coolant and further creating steam that continues to escape the exhaust system, you aren't going to be seeing any further steam.   

However, "oil" in the cylinder will burn and create "white smoke" immediately upon starting the engine and continue to smoke if even if just a little bit has collected in the hot exhaust.  You also need to consider whether or not there was any residual oil already in the exhaust system, or if you just got oil on the exhaust while handling it during the repair; and that is just old oil smoking.  Engine oil has a low "smoking" point and will do exactly what you describe.   You just need to determine the source of that oil getting into places that it should not.

There are only two places that engine oil may enter the cylinder and the engine will still run.  Those two places are the piston rings and valve guides.  In order to determine which may be the source you need to perform a leak down test.  This is a test that should be performed by a competent, experienced mechanic.  And a good leak down tester will cost you more than paying somebody to do it.  Plus they will know what to look for.  Just know that if you pay a professional to do this diagnostic test, it is also expected that you are going to employ their professional services for the repair.  So chose your shop wisely.  There are several great engine building shops across the country and one of the top shelf builders right in your neighborhood; Tom Miller Motorsports.

You are going to get into some medium size dollar amounts for either repair.  But buying the incorrect parts that do not fix your problem, then the right parts that may not be installed correctly and lead to further damage to a very expensive engine, then doing it again, but likely incorrectly again, is not the key to success or saving money. 

You have some of the best engine builders in the country in your area.  Tom Miller Motorsports is a top shelf shop that can turn out a complete top end rebuild in about a week.  For likely less than what it will cost you to buy the right tools and parts to determine and resolve the problem, a hardcore pro can deliver an engine to you that will give you years of "better than new" service; and likely some kind of warranty too.  

KTM is a top-shelf bike and it's worth reaching for the top-shelf when repairing one.  Get some overtime hours at work doing what you know how to do and do well; and use that money to pay an expert to do what they know how to do, and do well.  You'll be much happier in both the short and long run.     

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STOP-STOP-STOP!  WHATEVER YOU ARE DOING, JUST STOP!  You are not getting sound advice on this chat board.  White "smoke" is oil burning.  Steam may at first look like white smoke; but it will dissipate into the air almost immediately.  "Smoke" will linger.  What you are describing does not sound like "steam" from a leaking head gasket.  Furthermore; if you actually do have a head gasket that is leaking coolant into the cylinder, it takes more than a minute for the cooling system to build enough heat to develop enough pressure to push the coolant past the gasket and into the cylinder.  Then the back third of the exhaust system, particularly the muffler, has to be hot enough to allow the steam not to revert back to liquid form and exit the exhaust system while still in "steam" form.  That takes more than a minute.  
Then; after you shut off the engine, unless there is enough liquid collected in the exhaust system lower than the exhaust valve(s) and there is enough heat in the exhaust system to continue heating the liquid coolant beyond its boiling point, vaporizing that coolant and further creating steam that continues to escape the exhaust system, you aren't going to be seeing any further steam.   
However, "oil" in the cylinder will burn and create "white smoke" immediately upon starting the engine and continue to smoke if even if just a little bit has collected in the hot exhaust.  You also need to consider whether or not there was any residual oil already in the exhaust system, or if you just got oil on the exhaust while handling it during the repair; and that is just old oil smoking.  Engine oil has a low "smoking" point and will do exactly what you describe.   You just need to determine the source of that oil getting into places that it should not.
There are only two places that engine oil may enter the cylinder and the engine will still run.  Those two places are the piston rings and valve guides.  In order to determine which may be the source you need to perform a leak down test.  This is a test that should be performed by a competent, experienced mechanic.  And a good leak down tester will cost you more than paying somebody to do it.  Plus they will know what to look for.  Just know that if you pay a professional to do this diagnostic test, it is also expected that you are going to employ their professional services for the repair.  So chose your shop wisely.  There are several great engine building shops across the country and one of the top shelf builders right in your neighborhood; Tom Miller Motorsports.
You are going to get into some medium size dollar amounts for either repair.  But buying the incorrect parts that do not fix your problem, then the right parts that may not be installed correctly and lead to further damage to a very expensive engine, then doing it again, but likely incorrectly again, is not the key to success or saving money. 
You have some of the best engine builders in the country in your area.  Tom Miller Motorsports is a top shelf shop that can turn out a complete top end rebuild in about a week.  For likely less than what it will cost you to buy the right tools and parts to determine and resolve the problem, a hardcore pro can deliver an engine to you that will give you years of "better than new" service; and likely some kind of warranty too.  
KTM is a top-shelf bike and it's worth reaching for the top-shelf when repairing one.  Get some overtime hours at work doing what you know how to do and do well; and use that money to pay an expert to do what they know how to do, and do well.  You'll be much happier in both the short and long run.     

White smoke is never oil. Bluish smoke is oil. I've never seen an oil burner put out white smoke. So, you STOP STOP STOP

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I just got done replacing the head gasket and rings on my 2008 ktm exc and when I started it up for the first time it was blowing a lot of white smoke out the exhaust and even continued for a minute after shutting the bike off. I know thats typically a sign of a bad gasket but I just replaced it. I torqued all the bolts down corrrectly and I saw no problem with the head. Could it be something with the water pump? Or maybe i still screwed something up when putting it back together. 

It's leaking coolant. Could be head gasket, but if it didn't pop and rev high, it could be coolant in the bottom end that leaked in when you took it apart. I once had coolant stuck in the jackets and when I pulled the cylinder off it dropped into the bottom end. When I started it, it blew white smoke, then stopped after a minute and that bike is still running today after I put 50 hours on it and the next guy has lord knows how many on top of it. The rings aren't going to seal instantaneously and it could have pressurized up to the top. Look at your oil, if it's milky, refill and start again, if it does it again the head gasket has a flaw, wasn't installed right (hard to do on a thumper) or there is a torque issue. I would check oil and retorque head before I tore it apart....or just replace the gasket, it only takes an hour.

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I would say something if it is not late: same happened  to my '04 525 after replacement piston rings and head gasket. To make the long story short: my mechanic reversed piston rings (after only two beers). We opened the thing again, put everything right and smoke disappeared. Now we all know that KTM can work with both rings turned upside down:( 

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