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A 2 stroke engine leaking oil???

  • Billy Mild
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A 2 stroke engine leaking oil??? was created by Billy Mild

1971 AT1-c with a CT-2 topend. 

I appears my bike is leaking oil from somewhere. It doesn't look like transmission fluid and those seals don't appear to be leaking. I did have a leaking oil pump supply hose which I have cut the end off and secured via ziptie. This doesn't look like 2 stroke oil either. 

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Any ideas what this might be? 
08 Aug 2022 08:44 #1

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Replied by Tom P on topic A 2 stroke engine leaking oil???

Might be the clutch pushrod seal? Mine leaks just a little bit. I have a new seal but I haven't put it in yet.
08 Aug 2022 09:14 #2

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Replied by RT325 on topic A 2 stroke engine leaking oil???

Three options but should be traceable. Either gearchange as lowest constantly wet part & when on the side stand. Sprocket seal or nut loose. Pushrod seal. Or getting desperate the three screw plastic cover which looks like it has unusual screws in the pic. Is it an over-oiled chain. Or trans breather pipe or oil tank breather routed there somewhere. Trans way overfull will force it out the breather or any weak point.
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09 Aug 2022 05:33 #3

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Replied by Brzn on topic A 2 stroke engine leaking oil???

I'd worked on oil leaks on my '72 DT2 since picking it up last fall. The last oil leak was a tough one like yours. The oil was inside the flywheel cover and was yellow, not the bluish/green of the Yamalube S2 I'm using in the 2 stroke oil tank. The yellow oil didn't smell like 2 stroke or transmission oil. I finally decided to replace the left side crank seal. I took the cover off and it had the yellow oil all over the inside of it. When I pulled the stator plate it was covered, front and rear, in an oily film. There was slight evidence of oil on and below the seal, but not very much. Only one small drop was visible on the lowest point of the stator plate. Since I've replaced the left side crank seal (100 miles ago) there's no oil evidence anywhere inside the cover, or leaking out of the cover. I'm figuring the 2 stroke oil had turned yellow due to the heat under the piston inside the crankcase. The leak was very slight, not pulling in air, just letting a bit of oil out.
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09 Aug 2022 08:31 #4

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Replied by Sneezles61 on topic A 2 stroke engine leaking oil???

My RT2 is leaking oil.. I believe the oil pump needs attention… once I get my new clutch cable and install it… I need to ride it.. I believe the carb needs jet attention.. when I do that I’ll look to see what’s going on with the pump… I keep a pan under it..
I think it might even give an old Harley a run for its money on drips… But I wouldn’t trade mine…
Sneezles61
09 Aug 2022 13:14 #5

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Replied by Brzn on topic A 2 stroke engine leaking oil???

My RT2 is leaking oil.. I believe the oil pump needs attention… once I get my new clutch cable and install it… I need to ride it.. I believe the carb needs jet attention.. when I do that I’ll look to see what’s going on with the pump… I keep a pan under it..
I think it might even give an old Harley a run for its money on drips… But I wouldn’t trade mine…
Sneezles61


My Autolube pump gasket and seal were both leaking. I had to take the right side cover off to replace it's leaking gasket, so took care of those while the cover was off. The Autolube seal was the easiest of all the seals I've replaced to take off. I'll bet I could have pushed it out with my thumb.
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10 Aug 2022 06:00 #6

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Replied by Tom P on topic A 2 stroke engine leaking oil???

After noticing more and more transmission oil on the bottom of my left case (CT-1) I finally replaced the clutch pushrod seal. It seems like that solved the problem. Oil was not getting into the flywheel area, it was only in the area behind it and leaking down underneath the case. I still haven't replaced the counter sprocket seal or gear shift seal, but I think the push rod sort of acts like a pump. Every time it pushes in and out it pulls oil through the seal, when it gets old. 

I thought I was going to have to pull the counter shaft sprocket to get to it, because I'd put a larger 17 tooth one on, but only had to get the chain out of the way. The seal popped out easily using an angled pick, and as I read before, the ball bearing falls out immediately after the seal. I could easily see that happening and it rolling away unnoticed, but I had a metal pan below to catch it. I put the ball bearing and push rod in, then installed the seal with the push rod in place.
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Last edit: 13 Sep 2022 08:29 by Tom P.
13 Sep 2022 07:43 #7

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Replied by Tom P on topic A 2 stroke engine leaking oil???

RT325: "Or getting desperate the three screw plastic cover which looks like it has unusual screws in the pic."

What the heck is that white plastic cap with 3 screws? Is there an oil seal under it?
13 Sep 2022 18:48 #8

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Replied by MarkT on topic A 2 stroke engine leaking oil???

Covers end of shift drum shaft, retainer, and shim.  No seal except cover itself should be sealed to case.
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
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13 Sep 2022 20:16 #9

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Replied by Tom P on topic A 2 stroke engine leaking oil???

Thank you for the reply Mark. So does that mean there is a o-ring or something underneath this cover?
Last edit: 13 Sep 2022 21:05 by Tom P.
13 Sep 2022 21:05 #10

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