1975 DT 400 worth fixing?

[al_ngl]

Is yamahaenduro working yet? Last I checked registration was down. It never let me register.

[B.C.]

Works fine. I was on there today.

[al_ngl]

Ok I have decided to fix the DT400, but I don't know exactly what to buy for rebuilding the bottom end. I figured as long as I replaced the bearings, seals, and gaskets I should be fine. Should I also replace the connecting rod or do anything to the crank? The everything besides the connecting rod is about $150, and I also need tires, so I need to know if I need anything besides what I know I need. I don't want to spend more money than absolutely necessary. Also, I heard that I would need a machine shop to put the connecting rod bearing on the crank. Please tell me what all I need to put into consideration doing a bottom end rebuild. Thanks.

[webbcraft2150]

The bottom end is pretty simple on the DT. The crank rides on caged roller bearings. I was able to source the crank bearings at a bearing house. Try to get Timken brand bearings is you can find them. They will be a little more money, but well worth it in the long run.IIRC, the rod rides on neddle bearings. If there is no slop in the lower rod bearing, it should be good unless water got in and rusted things up. While the lower is apart, check the clutch bearing also. Course you are gonna need all new seals to put it back together. DO NOT let anyone talk you into pulling the Yamalube system unless its broke, it is bullet proof and ensures proper lubercation of the rod bearing and the cylinder. Try to allocate 'nuff bucks to do the lower end right the first time 'cause its alot of work to go back in and do it a second time. The top end is a pretty easy, straight foward fix. Make sure you stagger your ring end gaps on the piston. Check ring end gap twice. The DT400 is a low rpm motor as two strokes go so depending on how you ride, the top end should hang for a long time. Use top grade oil in the Yamalube system. I had bagged the stock air box and went with foam Uni filter. It worked well for any water crossing that wasn't over the pegs. I did end up fabricating a snorkel for the air filter but thats a whole nuther post. Once you get it up and running, there are a few, low $$$ mods that will make it a real stump puller. Just remember, the bike will go faster than the brakes can stop it, and the suspension system is lacking travel. Any airborne antics will surely set off any sesimogragh within a 'hundert miles and have you reaching for the Motrin bottle at the end of the day.

[al_ngl]

The bearing that is causing my problem is the center bearing that you have to disassemble the crank for. The bearing allows way too much travel of the connecting rod side to side. This causes the piston to be able to go sideways . I did the top end rebuild already. Someone had a theory that since I didn't do the top end and bottom end at the same time, the weak old bottom end broke because of the new top end. After I did the top end, the bike didn't even run 5 minutes before the bearing went out and the piston went sideways. Luckily the cylinder wall and the piston weren't damaged. After I do the bottom end, I'd really like to know about these mods you were talking about.

[webbcraft2150]

Git 'er up and running, then we can talk about making it go quicker/faster.


BTW, I found the guy I sold mine to in Albuquerque years ago. He cratered it. Sitting under a tarp on the side of his garage. He said to come and get it out of his way!!!!! "Someones gonna get hurt"!!!!