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RT360 Smoking Excessively

  • Steven050497
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RT360 Smoking Excessively was created by Steven050497

Hello everyone, haven't posted in a few years but I started working on my Yamaha again. My bike is far from original so I figured the motorcycle gods would be alright with me going in a different direction with this build. Here's a before and after so far:

The problem i've got today is that the bike smokes excessively and I can't figure out how to get it to stop. Little backstory, I was riding the bike in the desert back in its dirt bike days and it randomly started smoking a lot! I brought it home, disconnected the oil pump (which was rebuilt by DEET) and ran it on premix. Smoking still remained, so I kinda just assumed that oil was getting past the rings and that I needed to do a top end rebuild. 

Fast forward a couple years and I finally decided to bore out the cylinder. I bored it out 2nd OS, got a NOS piston and rings. Bored everything to spec according to the owners manual by a professional machine shop. Got everything back together, started it up....and it's still smoking excessively. 

My oil pump had some rust pitting on the main shaft and was leaking so I decided to buy another pump and give that a try. Just cleaned up and installed the new pump, adjusted and shimmed everything to spec according to the owners manual, and guess what.... still smoking. 


As you can see in the picture, there is a lot of smoke and a lot of oil leaking out of the front of the exhaust. This is not normal, because it did not use to smoke this much. Just started out of nowhere. Has anyone seen this before or have any suggestions?

Thank you!!
23 Jun 2022 18:06 #1

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Replied by MarkT on topic RT360 Smoking Excessively

Not uncommon.  Not a four stroke so not rings. 

Best guess is bad crank seal allowing trans oil to be sucked into engine.  Is your trans oil level dropping?
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
23 Jun 2022 18:23 #2

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Replied by RT325 on topic RT360 Smoking Excessively

Yes my guess too, is right side crank seal, especialy if it was an almost instant happening. In saying that they're a pretty robust seal & are double sprung. Crank nut might have unwound but highly unlikely. Seal could be damaged by something stray that shouldn't be floating around. Maybe its just blown out but would run super bad & not just smoke. Crankcase joint--ok don't even think like that--well not yet. Problem now 'is' the pipe will be soaked from end to end so even after fixing the sealk [if seal] it'll smoke the same for 100 miles unless you give it a burn out.
23 Jun 2022 19:16 #3

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Replied by LETSJET on topic RT360 Smoking Excessively

Could be your exhaust pipe full of oil from sitting, take it off and see what drains out.
23 Jun 2022 19:22 #4

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