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Honda 300ex has smoke coming out of engine case


Jacob Blocker
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I have been trying to get my 300ex to start for sometime. a few days i got it to start over and over and then the next day it wont start. I do the value lash and keep the covers off. I was (prob exhaust) smoke coming out of the covers with for the valves. I also noticed that the crank position marker had smoke also coming out, but i just thought it was from the head and it being in the cold. The hole for the position marker also has air come out when it turns over, but it is very light of air flow.

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Dream Car Giveaway

I'm  not  sure  what  your  smoke is ..  It  could  be  from  ring  blow by  if it is   smoke  from fuel  actually igniting even though the  motor  refuses to  start or  it  could  be water  vapor  if  there  is  a lot of  humidity  and  cold  air from the  crank  case  " breathing".  There  will  be  movement  in and out  of the  crankcase  as the  piston  moves  up  and down  in the  bore.  You  normally  don't  see  that  because  the  crankcase  breather is normally  connected  to  the  air box so  it is  "breathing "  clean  air and it  is  the  only way  the  air  has access  to the crank case. The  reason this  happens  is  because as the  piston  rises  to the  top of the  bore  for intake  or  exhaust it is  in effect  making the  airspace  inside  the  motor  greater, so  air   comes in to  fill that  space. When  the  piston  moves  down  in the   intake stroke  or  power  stroke , it effectively  makes the  air  space in the  crank  case  smaller,  compressing  the  air  in there which then  vents  out through the  breather  tube to  the  air  box. There  isn't  a  great  deal  of  air  exchanged  during  each  cycle ,  but if that  breather  was plugged, any ring blow by would  build  pressure in the  crank case  and   soon  blow the  seals in the  motor.  Under perfect  conditions  of  zero  blow by, you would  never  get crank case  pressure  build  up since  the  piston  moving  in the  bore  would  only  slightly raise and  lower  crank case  pressure  as the  volume  changed  up  and  down  with the  stroke.  Long  story   to  say that  light  air  flow  you  find is  perfectly  normal  and expected.  :D

 

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7 minutes ago, davefrombc said:

I'm  not  sure  what  your  smoke is ..  It  could  be  from  ring  blow by  if it is   smoke  from fuel  actually igniting even though the  motor  refuses to  start or  it  could  be water  vapor  if  there  is  a lot of  humidity  and  cold  air from the  crank  case  " breathing".  There  will  be  movement  in and out  of the  crankcase  as the  piston  moves  up  and down  in the  bore.  You  normally  don't  see  that  because  the  crankcase  breather is normally  connected  to  the  air box so  it is  "breathing "  clean  air and it  is  the  only way  the  air  has access  to the crank case. The  reason this  happens  is  because as the  piston  rises  to the  top of the  bore  for intake  or  exhaust it is  in effect  making the  airspace  inside  the  motor  greater, so  air   comes in to  fill that  space. When  the  piston  moves  down  in the   intake stroke  or  power  stroke , it effectively  makes the  air  space in the  crank  case  smaller,  compressing  the  air  in there which then  vents  out through the  breather  tube to  the  air  box. There  isn't  a  great  deal  of  air  exchanged  during  each  cycle ,  but if that  breather  was plugged, any ring blow by would  build  pressure in the  crank case  and   soon  blow the  seals in the  motor.  Under perfect  conditions  of  zero  blow by, you would  never  get crank case  pressure  build  up since  the  piston  moving  in the  bore  would  only  slightly raise and  lower  crank case  pressure  as the  volume  changed  up  and  down  with the  stroke.  Long  story   to  say that  light  air  flow  you  find is  perfectly  normal  and expected.  :D

 

I would rather not take the engine apart to find out, bu i might have to soon. The one time i was able to get the engine to run (it was cold) it had a good bit of white smoke and when i killed it it left a kinda lingering smoke at the tip of the pipe. I also find it strange how hard it is to start it, although it could just the the carb (i have cleaned it a few times).

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