Lots of smoke

5 replies to this topic
  • dcecar

Posted May 12, 2008 - 02:57 PM


I just got a '01 YZ429F. After riding about 2hr Sat, and 2.5hr Sun, engine started making lots of smoke. After looking at it I found the oil breather hose broken at the engine end and the clamps on the end of the hose were both very loose, and also found the coolant way bellow the proper level.

What's the oil breather hose for and would the bike smoke if this was broken before the ride?

How long can the engine run if the coolant wasn't circulating, and at what point does it get damaged, and what kind of damage happens?

What's the best way to find radiator leaks, and best way to fix?


  • grayracer513

Posted May 12, 2008 - 03:16 PM


The crankcase breather is there to vent off and normalize the pressures in the crankcase. Some oil can be ejected from this tube, especially if the engine is run very hard, the rings are weakening, and/or the engine has too much oil in it.

Coolant leaks can be found by means of a pressure test, although head gasket leaks may not be discoverable in this way. running the engine without coolant can lead to extremely serious damage to the cylinder and piston, among other things.

At this point, you should check the amount and condition of the oil, add coolant, and test run the engine to see how it runs when it has the right amount of fluids in it.

Where was the smoke from?

  • dcecar

Posted May 12, 2008 - 03:36 PM


I looked up the manual, I had the Oil tank breather hose broken at bottom. Is this hose == the crankcase breather you mentioned?

There was too much smoke to tell exactly where it was comming from. There was liquid all over motor, not sure if oil or coolant, plus it was mixed in with mud-water, but I was empty on coolant when I checked at the end.

When i cleaned the bike back home, started and it seemed to smoke a little from the big hose on the right side. I didnt run long enough, and it didnt seem to be the same amount and color of smoke as in the bush.

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  • grayracer513

Posted May 12, 2008 - 03:47 PM


Was this the smaller of the two hoses at the head cover? The one that runs between the oil tank (in the frame) and the head cover?

  • dcecar

Posted May 12, 2008 - 11:41 PM


yes it is

  • grayracer513

Posted May 13, 2008 - 07:34 AM


The larger of the two is the crankcase breather. Check along its length for places where it may be pinched shut. Look in particular at the two metal clips that secure it to the frame under the engine. If the breather gets pinched or blocked, the resulting build up of pressure can force out seals or blow off the small line you see loose.

That smaller line is a pressure balance vent between the tank and crankcase.

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