Before I get started on what is needed, I wanted to provide some background on my Yamaha DT1B, 1969. I purchased the bike back in May. It ran when purchased but needed some work. Most of what I focused on was regarding the fuel system. Rebuilt the carb, which included adjusting the float bowl level, cleaning, and replacing the gas tank seals and replacing the air filter. Now on to other items on the bike. I am looking into rebuilding the engine and have questions.

1) I am looking to replacing all bearings and seals. I understand that Yamaha does not provide replacement parts. Wanted to ask who you recommend for engine bearing and seal replacement.

2) I have the Yamaha DT1F manual and parts catalog. I also have the Clymer's (sp?) manual on the DT1 as well. I will use these to go through the engine rebuilding. Wanted to ask if there are other manuals, videos or something else you would recommend to help with rebuilding. This will be my first time rebuilding a two stroke. I do have experience working on the newer Yamaha 450YZ's and auto engines.

3) I have an oil leak and wanted to determine the potential source. Included is a picture of the left side engine with the two covers removed. The leak appears to be from the bottom opening located on the left side of the engine cover screw in the attached photo. Any ideas on what might be the cause and source of the leak?

Thanks for you help.

Steve

My 250 or one of my 360.s had an oil leak from that screw where someone has either fitted screw too long & forced into the gearbox, or tried to thread the hole deeper & forced the threading tap pointy nose through. Might've been me lol, or i bought it like that, can't remember but came up with some dodgy plan to stop the leak. By memory i sealed a long threaded stud in there to use the length of the threaded hole so i didn't have to remove it every time & just take a nut off that one & leave the stud in place.

I am also doing a full engine rebuild on a 69 DT1B.

For the service manual, look to the top of this screen and click on Tech Library. Click on Service Manuals, then click on the 69-71 DT1 maunual. I did this for my CT1 also, printing it all out and putting it in a three ring binder.

The proper OEM seals can be purchased from Enduronut on this site. I just received two crank seals from him. I recommend the OEM seals and bearings.

Keep posting pics of your project. Folks here love to help.

Thanks RT325 for sharing your own oil leak experiences. I will keep an close look out for what you had seen and experienced.

Thanks also to Midlife Motor for tips on using the service manual on this sight. Thanks for the recommendation on seals as well.

Whoever told you parts are not available from Yamaha was incorrect... many parts are.

Crank seals on that model aren't available from Yamaha... but many other seals and bearings are still available new from Yamaha. Pays to check before buying overpriced "NOS" parts from eBay you could have ordered from Yamaha for half the price.

Enduronut and DEET on here have a lot of NOS parts as well.

MarkT - Thanks for your input. Very helpful and much appreciated. In trying to get up to speed on Yamaha DT1's, and reading a whole bunch of material, I somehow became a bit confused on what is available and what is not.

I have seen posts from DEET and purchased a few items. Enduronut is someone I will reach out to as well.

Steve

STEVEBONES - good timing with this post as I'm dealing with the same issue with my 1969 DT1B. What's weird is that it only leaks from time to time. Haven't nailed down the cause yet as I'm having too much fun riding around town. Gotta take advantage of the nice weather while I can and adding a little oil here and there is easier than replacing seals at the moment... Rainy days aren't too far away.

Best of luck and please keep us in the loop with photos on replacing the seals. Dig the high fender, been on the hunt for one.