'77 Yamaha RD400 "Lost and Found"

NSNickName

Active Member
Good morning, just thought I'd throw out another RD update. Not much to mention just some pics of parts being disassembled cleaned up and revived. Along with some new plug wires\end caps.
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NSNickName

Active Member
Hey everyone, RD update coming at ya. I'm not sure if you can see in the picture above, but my rear fender was basically destroyed due to various taillight configurations being bolted to it. I wanted to use the original fender even though it had been slightly cut down. To patch the hole I pressed in the surrounding steel and welded a solid washer over the hole to patch it while maintaining two spots for mounting. I then used some short strand reinforced bondo to finish the surface, here's some pics and outcome. Please don't hate on the weld job, its a cheep welder and I can only run it at the lowest possible settings or I will blow the breaker in my 100 year old garage.

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NSNickName

Active Member
"A grinder and Paint makes a welder what he ain't" Turned out nice.
HAHA That's a funny one, I'll have to remember. When I use to do lots of it I wasn't half bad, but I've been away from it for so long now every time I turn it on it's a chore.
 

NSNickName

Active Member
RD Set GO!!! There was a particular delivery day that made me very happy. I could finally start ripping into the motor. More to follow!!!
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NSNickName

Active Member
Sorry I have to go back a step, as I wasn't sure what pistons to order for the bike. After the dreadful day on the highway I had pulled the motor to asses the damage and look at the cylinders. Needless to say there was a lot of aluminum transfer in the hole and some scoring on the cylinders. I wanted to know how much I would need to punch the holes as I obviously wanted to go as little as possible. The local machine shop told me that if I could remove the aluminum they could give me a better answer. A task I was hoping they would have done, but for some reason they didn't seem to keen on the idea. (Key research montage music) EUREKA, MURIATIC ACID!!!! MUHAHA I have discovered the magic solution, a dangerous chemical that will do all of my hard work and labour for me, of course it was so simple and right in front of me the whole time. I built an awesome fume hood with an old server rack fan, sealed it up and got to work. A few hours later I had clean cylinders that the machine shop could assess. I ended up ordering Yamaha banshee pistons at 64.25mm which is the next smallest size up.
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pidjones

Over 1,000 Posts
Last photo in post #42 - upon mounting the engine, I think the rear lower mounting bolt (with the long spacer) goes in left-to-right. I've read that the head of the bolt is slightly shorter to avoid interference with the chain. Mine was forgotten (by me) and is in the box of parts still to go on. BTW, what luck to be able to go with first over! Check on the Banshee pistons however - I've seen something about a minor mod that is needed when going in RD jugs.
 

NSNickName

Active Member
Last photo in post #42 - upon mounting the engine, I think the rear lower mounting bolt (with the long spacer) goes in left-to-right. I've read that the head of the bolt is slightly shorter to avoid interference with the chain. Mine was forgotten (by me) and is in the box of parts still to go on. BTW, what luck to be able to go with first over! Check on the Banshee pistons however - I've seen something about a minor mod that is needed when going in RD jugs.
Good eye and yes you'r right it does only go left to right. I will add the detailed piston modification later in the thread, it is very simple and only takes a few minutes.
 

NSNickName

Active Member
RDaily update!!! I spent some time going over the wiring harness and replaced what needed replacing. I next built a temporary electronics trey to hold a battery and components. It's temporary because I'm building a custom harness for the bike around a vape ignition system. More to follow on that down the road. Here are some update pictures of the trey and harness before I went over it. Also one with the tank on because I was desperate to see her look like a proper bike again hahah. The battery is out of a fire alarm emergency lighting system.

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NSNickName

Active Member
Hey, good to be back with an update. I have some pics of the motor tear down, something I was both looking forward to and dreading. Everything looked pretty good inside. I will clean all the parts, replace the seals and gaskets, the two outer crank bearings, and put it back together. This is the first time I've been this deep into a 2 stroke so I'm really taking my time and learning a lot.
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NSNickName

Active Member
Good day, I thought I would throw up a few photos and a write up on how I replaced my outer crank bearings as it was way more simple then I had anticipated. First I pulled the bearing using a gear puller, this may not go as smooth for others as it did for me. Once I put tension on mine and gave the outer ring the smallest tap it popped right off. I then measured the bearing, inner, outer, and width to find the dimensions, with my best Nova Scotian memory I believe they were 25 X 62 X 17 which equates to a C3 rated #6305, but don't go ordering bearings for your RD based on those numbers, measure for yourself. There are also grooved and pinned style bearings, you need to know what you need and how to ask for it, consider this CAUTION NUMBER 1. I made some calls and found a local millwright who could get me the bearings for $7.50 each, and it only took 24 hours to get them. I placed my cleaned crank into the freezer overnight to shrink and in the morning I baked the bearings on a cookie sheet to between 175F - 180F. I had a hammer and a deep socket nearby thinking I would need to apply some horizontal thrust, but to be truthful the bearings slid right on and stayed in place. Although I had heard of people using this method in the past, this was COMPLETELY EXPERIMENTAL for me. I DO NOT in any way suggest you do this or consider any of this a HOW TO demonstration. It's just how I did it, and it worked well for me. THAT WAS CAUTION NUMBER 2. Pics below, PS: The bearing oil seal is easily removed with a seal pick and as I wasn't sure how this process would go I did one at a time.

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pidjones

Over 1,000 Posts
Hope it works well. I had to go the spendy way and sent mine off to Lyn Garland for a full rebuild (all bearings, seals, and rods for the crank). But, I could feel roughness in the right outside and right center bearings plus the rods were right at the side-to-side limit so it had to be done. I first pulled the crank to replace the right seal as it failed pressure test. Probably a good thing because the right bearing would not have lasted. Some talk about replacing the labyrinth seal, but that should only be necessary if foreign material got loose in there as its rotor should never contact its stator in operation.
 
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NSNickName

Active Member
Hope it works well. I went the spendy way and sent mine off to Lyn Garland for a full rebuild (all bearings, seals, and rods for the crank). But, I could feel roughness in the right outside and right center bearings pkus the rods were right at the side-to-side limit so it had to be done.
Everything in mine was tight, but the bike is SUPER low mileage. I checked everything 10 times, I was driving my wife nuts with constant dwelling and considering options. Finally she said, "You know if its good or not, so fix what you need to a move on." Haha I replaced the outers because one of them looked at me funny and I could hear noise in the other with a stethoscope...was more or less just curious if I could.
 

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