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  #1  
Old 02-04-2014, 02:09 PM
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Default 1986 Yamaha Moto4 smokes on deceleration

     

Hi everyone, I picked up a 1986 Yamaha Moto4 225 (or YFM225) awhile ago in very rough condition. I have since replaced part of the crankcase (due to a blown bearing and broken carrier) put in a full gasket set, new top end, cross hatched the cylinder, new plug, new oil filter, and fresh oil.

When i first started it it was smoking white just a little bit, then it sat for an hour, I started it again and it was just pouring white smoke. Once it warmed up not as much but still pretty constant. I replaced the intake valve seal yesterday and now it only smokes on deceleration (due to engine breaking) or after its been idling for a couple seconds, mostly white occasionally blue. The cylinder has 160 PSI for pressure, could it be the exhaust valve seal? I have one but it's such a pain to install I haven't done it yet. Any suggestions would be great!
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Old 02-04-2014, 02:18 PM
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Could you clarify your term, "New Top End"?
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Old 02-04-2014, 02:23 PM
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you might have installed the rings upside down
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Old 02-04-2014, 06:18 PM
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Ok, I suspect bad exhaust valve guides and seals. If the guides are worn you will still have oil sucked into the combustion chamber during deceleration even if the exhaust valve seals are new.
Are you loosing any coolant?

Paw Paw
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Old 02-04-2014, 06:23 PM
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New piston and rings, and like I said all new gaskets. I don't think I installed any of the rings upside down, the oil retention ring doesn't have an upside or downside, the other two rings have a mark on them that faces up, the compression ring is silver colored and that one goes in the top groove, and the last one goes in the middle groove That's the way I did it but correct me if I'm wrong, If you need clarification just ask, Thanks for the suggestions!

---------- Post added at 05:23 PM ---------- Previous post was at 05:19 PM ----------

Thanks for the idea Paw Paw like I said I haven't put the new exhaust seal in yet, and the things so old it's free air cooled, no coolant system. I should probably put in the new exhaust seal though, huh?
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Old 02-04-2014, 07:52 PM
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Ok, it's worth a try.

Paw Paw
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Old 02-05-2014, 12:08 AM
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the vacuum is at it's highest when you coast with the rig in gear and throttle closed. that was always the test for bad rings when buying something 4 stroke that was used. maybe your rings will seat yet though. Did you oil up the cylinder before you installed the piston and rings? Old bore?
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Old 02-05-2014, 05:57 AM
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I say valve guide seals, ive also got one that smokes but its not worth the money to me to to rip it apart.
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Old 02-05-2014, 07:12 AM
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Quote:
Originally Posted by ossagp View Post
the vacuum is at it's highest when you coast with the rig in gear and throttle closed. that was always the test for bad rings when buying something 4 stroke that was used.
This should be a sticky or a banner or a t-shirt or something
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Old 02-05-2014, 10:22 AM
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Aside from the left over honing oil no I did not oil the cylinder, I figured if I oiled the cylinder the piston would just push it into the combustion chamber. It's the old bore, I took it to Reynolds and they put a fresh crosshatch in. I'll probably put in the new exhaust valve seal this afternoon since it's snowing.
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