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Makotosun

1974 Yamaha DT 125 oil seal replacement

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1974 Yamaha DT 125 oil seal replacement was created by DT Special

Hello,New to this amazing site and this is my first post. I spent some time searching this site and reviewing the 1974 Yamaha DT 125 service manual that I downloaded. If my question is covered in an existing post please direct me to the location and excuse my lack of experience navigating the site. As the subject states I have a new to me 1974 Yamaha DT 125 that has the "autolube chain feature" as others have put it in different discussions. I have already put a lot of time in fixing various issues to get it back up and running as it was pretty rough to begin with. My questions are, do I have to remove the starter/generator assembly to get to the second case to find the leak? I have read that it could be coming from the primary sproket seal or the clutch shat seal but it does not appear to be coming from the shifter seal. Also, what are the recommended sources for the seals once I determine which seal is leaking? Any replies appreciate and thanks for the great resource. I am attempting to post a pic of it, and hope it will attach correctly. 

 
17 Mar 2023 17:40 #1

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Replied by MarkT on topic 1974 Yamaha DT 125 oil seal replacement

Welcome!

Buy your seals from Yamaha.
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
17 Mar 2023 17:45 #2

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Replied by DT Special on topic 1974 Yamaha DT 125 oil seal replacement

Thanks for the reply as I really appreciate the advice! I have found many parts online for this on but have not been able to locate any of the seals that might be leaking as a OEM Yamaha part. Could you please recommend a source to look for these seals?
17 Mar 2023 18:02 #3

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Replied by MarkT on topic 1974 Yamaha DT 125 oil seal replacement

Your local Yamaha dealer or an online Yamaha dealer such as RMATV-MC (my favorite) or Partzilla.

www.rockymountainatvmc.com/oem-parts/Yamaha
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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17 Mar 2023 20:46 #4

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Replied by Ht1kid on topic 1974 Yamaha DT 125 oil seal replacement

Greetings from Tennessee 

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   Good looking bike
17 Mar 2023 21:24 #5

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Replied by AirborneSilva on topic 1974 Yamaha DT 125 oil seal replacement

I've never worked on a DT125 so can't give you an definitive answer but a sure way to find out is to remove the first cover then you "should" be able to see if the generator has to be removed. Sorry I can't give you a better answer but I'm sure someone will come along that has actually worked on the DT125.
2023 Tenere T7
1976 DT400C
1975 DT400
1981 DT175H
1972 DT2 250
1980 GT80
1972 JT2
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18 Mar 2023 01:35 #6

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Replied by MarkT on topic 1974 Yamaha DT 125 oil seal replacement

Generator only needs to be removed to change crank seal... not very likely crank seal is "oiling the chain".

If the oil is coming from the engine and not from say, the autolube tank/hose leaking, most likely the sprocket seal, clutch pushrod seal, or shift drum cover leaking/broken.
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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18 Mar 2023 15:08 #7

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Replied by DT Special on topic 1974 Yamaha DT 125 oil seal replacement

Thanks to everyone that replied to my post and I appreciate the insights that you have shared. It is nice to know that the starter generator assembly does not need to be removed as that looks like it might be beyond my capabilities to do correctly. I replaced the auto lube hose already and the tank did not appear to be leaking. After closer inspection I am assuming that it is the primary sprocket seal as it is running down the chain a few links before it drips to the floor. I will take pictures of the process and post them to the site once I get time to get to the project. Thanks again for such a great site. 
19 Mar 2023 11:33 #8

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Replied by AirborneSilva on topic 1974 Yamaha DT 125 oil seal replacement

The seal behind the sprocket is an easy R&R, the hardest part is having to loosen the rear wheel so you can get the chain off the sprocket, then have to adjust the chain again, which isn't hard just a pain. Other than that you'll surprise yourself and feel good about having changed it yourself.
2023 Tenere T7
1976 DT400C
1975 DT400
1981 DT175H
1972 DT2 250
1980 GT80
1972 JT2
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Last edit: 19 Mar 2023 11:45 by AirborneSilva.
19 Mar 2023 11:44 #9

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Replied by DT Special on topic 1974 Yamaha DT 125 oil seal replacement

Thanks for the advice. I have replaced primary sprocket seals on other bikes but not like this DT. I couldn't even verify if the starter generator assembly had to be removed prior to removing the case that covers the front sprocket. Most bikes that I have worked on did not require removing a cover to get to the primary sprocket. Hope to get at this soon and provide an update.  
19 Mar 2023 12:15 #10

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