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1991 TRX250X - smoking - lots of smoke!

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1991 TRX250X - smoking - lots of smoke!

  #1  
Old 12-25-2018, 08:24 AM
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Default 1991 TRX250X - smoking - lots of smoke!

Hey guys, so I picked up a non running 250x. Put a new timing chain and valve guides, new valve seals, new head gasket and corrected the timing

Went to fire it up, started right up and sounded good but lots of white smoke. There is an exhaust leak at the muffler connection that will be addressed but don't think thtt is why Its smoking so bad.

I notice there is some weeping around the base gasket, even before I started it. Possibly the base gasket needs to be replaced? Piston looked good but I didn't take the cylinder off to give it thorough inspection.

Any thoughts?
 
  #2  
Old 12-26-2018, 03:30 AM
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When you have the head off it is always best to remove the cylinder, doesn't cost anything, except possibly a base gasket, and you can check for scoring low on the bore and piston skirt, excessive ring gaps etc. However, white smoke could be due to stabiliser put in the fuel, give it a couple of good long runs on fresh fuel before jumping to any conclusions.
 
  #3  
Old 12-26-2018, 09:14 AM
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Needless to say, I am kicking myself for not taking the cylinder off. I did drain the gas, cleaned out the carb before starting it. The gas I put into it had Startron fuel stabilizer in it but it has never done that to any of my other 2 or 4 stroke motors. I was wondering if maybe it was from some oil I put into the cylinder to keep it lubricated, but that should have burned out pretty quickly.

I agree though, I'm going to take it for a longer ride and see what happens (of course keeping an eye onl oil level).

Thanks for the info!
 
  #4  
Old 12-28-2018, 10:56 AM
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Wanted to give an update. I took the top end apart last night, noticed all the head bolts had oil on the threads (not sure if this is normal or not) and the piston was covered with oil as well. Took it for another ride before tearing the top end down, and was shocked at how good it ran despite all the smoke, which never went away. I'm suspecting it's the rings incl. the oil control ring or the base gasket. The base gasket looked to have a couple tears in it, but could have been from me taking it apart. I'm going out to buy a bore gauge today, measure piston and order some rings. Would that be the best option, at least cost effective way? Cylinder looks great FWIW.
 
  #5  
Old 12-28-2018, 05:00 PM
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When you took the head off and did all that work was there an O ring and a guide pin? You could've not put that in and that could be where your oil is coming from. I know more about Yamaha wheelers but Honda has to have an oil passage up threw the jug to the head too.
 
  #6  
Old 12-29-2018, 03:33 AM
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You can get some idea of bore and ring wear by putting the top ring in the cylinder and measuring the end gap, above about 0.020" on an unworn part of the bore (right at the top or bottom) and you need new rings. If the gap gets a lot bigger in the worn part of the bore, you need a re-bore. if you were thinking of re-using the rings, make sure you know which is the upper side, as the markings will have worn off.
 
  #7  
Old 12-29-2018, 08:35 AM
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Originally Posted by Jered651 View Post
When you took the head off and did all that work was there an O ring and a guide pin? You could've not put that in and that could be where your oil is coming from. I know more about Yamaha wheelers but Honda has to have an oil passage up threw the jug to the head too.
There is an oil line going from the clutch cover area up to the head, to pump the oil up there.

Originally Posted by merryman View Post
You can get some idea of bore and ring wear by putting the top ring in the cylinder and measuring the end gap, above about 0.020" on an unworn part of the bore (right at the top or bottom) and you need new rings. If the gap gets a lot bigger in the worn part of the bore, you need a re-bore. if you were thinking of re-using the rings, make sure you know which is the upper side, as the markings will have worn off.
I ended up buying telescoping gauges to measure the bore, it's 74.50. I also measured the piston rings end gap and they were definitely beyond the service limit of .50. I decided to order new rings, going to hone the cylinder & hopefully that'll get me back into business!

Regarding the rings, I did notice the bottom one was bigger than the top. I'm assuming I'll be able to figure out which is the top ring and which is the bottom by looks?
 
  #8  
Old 12-30-2018, 03:23 AM
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Honda quad pistons have three rings, the bottom is usually a composite ring made of three separate parts, middle ring is sharp edged, and top ring has a curved outer surface. Middle and top rings have R written on the surface which goes to the top, on any I have come across. I would be a bit worried if the ring gap isn't well over 0.5mm as to whether you have found the fault. Double check the valve stem seals while you have the head off.
 
  #9  
Old 01-02-2019, 11:21 AM
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Thank you for the info again Merryman! I did check the ring gap and they were definitely over the .5mm. The piston seems to be in great shape, so I lightly honed the cylinder and ordered new rings. I will also check the valve seals again to make sure the new ones are seated correctly. FIngers crossed the rings solve the problem!
 
  #10  
Old 01-17-2019, 01:04 PM
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Through on new rings and good to go, thanks for the help!
 
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