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New Engine re-build question... New Engine re-build question...
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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
Photo by Sean Howman, The Pamir highway in an unseasonably cold late October, Tajikistan

I haven't been everywhere...
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Photo by Sean Howman,
The Pamir highway in an unseasonably
cold late October, Tajikistan



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  #1  
Old 13 Apr 2009
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New Engine re-build question...
I just finished putting everything back together on my 84 XT and fired her up on Sunday...Happy Easter! Anyway, once she started running (a bit rough at first) I noticed bluish smoke coming out of the tailpipe. I know this screams of piston rings, but I had the cylinder honed and put in new rings on during the rebuild. Any ideas what may be causing this? Inspection of valves during teardown showed no sign of leaks or cracks in the head. Piston rings were nice and tight when they went in...all seals were replaced on rebuild. I'm stumped. the only other thing missing is the silencer for the inside of the muffler. I guess the previous owner thought this would increase performance...I just think it's noisy as h*ll and my neighbors agree. Would this smoke be less noticeable if this silencer were in place?

Thanks for the help,
Andrew
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  #2  
Old 14 Apr 2009
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could be a valve stem seal not sitting correctly or torn when putting valves in.
no silencer insert won't make the smoke less noticable.
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Old 14 Apr 2009
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i would have oiled the rings etc to get it back together easily and this could poss then burn off on start up???
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  #4  
Old 14 Apr 2009
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I did use generous amounts of oil and assembly lube when re-assembling...maybe I've just not burned off all that good lube.
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Old 14 Apr 2009
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More than likely oil being burnt from the assembly process. Ride it around and get it nice and hot and it will probably go away.
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  #6  
Old 14 Apr 2009
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Also, it will burn a lot of oil until the new rings bed in nicely.
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Old 14 Apr 2009
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That's reassuring...Thanks everybody!
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Old 15 Apr 2009
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is there any crankcase ventalation?? how much was it to rebuild?
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Old 15 Apr 2009
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There is a stock crankcase ventalation tube that was not hooked up to the airbox...I'm sure that contributed to the issue. I re-built the engine myself, so only the parts that didn't pass inspection (tolerences listed by my manual) were replaced. I re-honed the cylinder and replaced the piston rings just to get a good seal for her second life. I tore down the carb's and ran into a snag...the main jet was frozen in place and I had to drill it out to get it removed. So now I'm waiting on the parts to come from Boats.net since they beat anyone's prices I've seen. So far I've got about $450 into it and that's including 2 second hand rims since both of mine were severely cracked and not road worthy.
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Old 16 Apr 2009
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Blue you say???
i did the very same job on my xt's second life.... if its pumping blue smoke only when opening the throttle the its ok, it'll go, but if its consistent then ride it for about 50 miles (i hope its not too blue) and check the temperature of the engine as best you can, more heat than normal is still ok,(the beauty of aircooled) but overtemp is bad bad bad, if in doubt relax the engine. the smoke will actually remove heat better than normal fumes, but anyway, if the blue smoke is still there after your carb rebuild, then BRIAN E is right, and thats where i'd look too. but consider if oil leaks past these seals aftershutdown... then the next day or whatever your lovely engine will pump out blue smoke again and again and it'll get worse, so oil collects behind the valves and enters the chamber when cranked.... hope you find the problem, be safe... ken
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  #11  
Old 4 May 2009
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Valve Clearance...
The blue smoke is gone! Must have been assembly lube I used for the piston.

My next question is what valve clearance should I use on this re-built motor. The manual shows the exhaust valve anywhere between .12mm - .17mm cold...currently I have them set to .14mm when cold. What's the best setting??? :confused1:

Thanks gents,
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Old 4 May 2009
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I believe i set my intake to 0.12 and exhaust to around 0.15-017 så that seems just right. Mine's an 03 tho'
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