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02 Sep 2019
Your admin has not been on the site much as of late as my main computer apparently seized up :( I have had limited access, but will be back soon. Thanks. Mako
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TOPIC: Proper way to replace left side main seal in the case?

Proper way to replace left side main seal in the case? 09 Sep 2019 10:20 #1

  • Kosmo
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Hi all...I basically finished my build last night (no project is every truly done but you know what I mean) just to find out that the left side crank seal is apparently leaking again! No other place for oil to come from on that side and the bottom-side of the cover gasket is soaked soo it must be the seal again. I replaced this recently but I was never 100% sure in my work. My biggest question is how do I know how far to push the seal in? There's three things that could have happened I suppose...seal wasn't in far enough, seal was in too far and got mulched by the bearing, seal was inserted slightly on an angle thus allowing some seepage. I don't think I went in too far as I knew that was a possibility and tried not to...but who knows.

Just looking for some guidance for when I do this repair again this week.

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Proper way to replace left side main seal in the case? 09 Sep 2019 14:40 #2

  • Blackhat250
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The left crank seal usually sucks Air,,, what type of oil you seeing ,?

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If you aint mixin gas " you aint haulin Ass

Proper way to replace left side main seal in the case? 09 Sep 2019 15:31 #3

  • Kosmo
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well, that's weird...I had oil come out of there the first time it blew, and the bottom of the stator cover gasket is soaked in oil this time as well. My buddy who has a 175 as well had oil come out of his too. What's going on!! I'm going to go take the cover off again and take some photos, determine what sort of oil I am seeing. It looked darker which made me automatically think transmission oil

The weird thing is...I was looking at exploded diagram the other day and noticed as well that seal is not in contact with oil...so now I'm just all around confused as to where that oil is coming from.

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Last Edit: by Kosmo.

Proper way to replace left side main seal in the case? 09 Sep 2019 15:33 #4

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wait....could it be from one of the case bolts that's behind the stator? I remember one of those was loose the first time I took the cover off and it seemed like oil might have come out of there, so when I did the seal I tightened it up...but maybe it came loose again.

edit: talking about either #5 or #6

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Last Edit: by Kosmo.

Proper way to replace left side main seal in the case? 10 Sep 2019 02:19 #5

  • darinm
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Over time a surprisingly significant amount of two stroke oil can build up in the crank case and if its a one way leak when the crank case is pressurized, perhaps it's pushing some two stroke oil out. Some like the Lucas are pretty darned dark and look like used transmission oil.
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1972 Yamaha CT2 175
1972 Yamaha RT2 360
1972 Suzuki TS 185 Sierra
1995 Suzuki DR 350

Proper way to replace left side main seal in the case? 10 Sep 2019 05:26 #6

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Is that...normal for these bikes haha? Should I be worried or be mitigating it somehow? Not sure if you caught that from my other thread but I HAVE been using Lucas. And I am also running premix, no reservoir/unhooked pump. It's hard to tell because my gasket is a shade of green, but the soaked part on the gasket looked like it might have been soaked in premix/2 stroke oil when I first took it off. I dismissed it because in my mind there's no way 2 stroke oil could have gotten on that part...guess I was wrong.

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Last Edit: by Kosmo.

Proper way to replace left side main seal in the case? 10 Sep 2019 09:47 #7

  • darinm
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I've seen a bit in mine, but I think it's mostly from a leaky float bowl gasket that was dripping gas when parked if I didn't shut the petcock off in the last 1000' of riding. I'm guessing this gas was making its way into the stator area when the bike was parked on it's kickstand and then evaporating, leaving a little oil in the bottom.

So just a guess on the seal letting some into yours if said crank seal is leaking. Fixing the float bowl gasket solved the issue for me. And the Lucas, saw you've been running it and I've been using it recently too. It's annoyingly similar to used oil color imo.
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1972 Yamaha CT2 175
1972 Yamaha RT2 360
1972 Suzuki TS 185 Sierra
1995 Suzuki DR 350

Proper way to replace left side main seal in the case? 10 Sep 2019 09:53 #8

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lol funny you mention that...my petcock was leaking recently and I was wondering why I was wiping premix from the bottom of my engine cases...then I noticed some forming on the bottom of the petcock. maybe that's all it was and it was just getting behind the stator cover...which is ALSO weird because you'd think the gasket would stop that. Guess I'll keep an eye on it, thanks! New seal is on the way anyway so if I do have to do it, I'll have it.

The Lucas stuff is certainly quite dark!
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Last Edit: by Kosmo.

Proper way to replace left side main seal in the case? 10 Sep 2019 11:45 #9

  • MarkT
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What year is the engine that's leaking?

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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

Proper way to replace left side main seal in the case? 10 Sep 2019 12:55 #10

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'78

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