Wiseco BK5003 bearing set,these fit most of my bikes,the 2 Honda Elsinores,the 1974 MT250 and the 1975 CR250,the DT1s and RT1s I have and now the 1975-76 DT400 and it will also fit a YZ400 and a IT400 as well should I pick those up someday. I think they even fit the YZ465 and 490.

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after the bearing in this case half,I reinstalled the crankshaft.

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then the other half,at least the short block is complete.

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I replaced this oring before reinstalling the gear.

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I installed the new crankshaft seals.

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then this gear.

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I installed the mag side crankshaft seal too.

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I also replaced the shift shaft seal and the countershaft seal.

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for the time being,I am soaking this frozen broken screw overnight with some PB Blaster. I will attempt removal at the next go around.

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the clutch bell crank seal should be here soon and it will be installed.

Making good progress Dave.

Looking good! Nice to see all of the photos, step by step.

Clay

Nice work!

So a cylinder, head and piaton from a mx400 will bolt right up. And be making more power? Will the factory dt400 exhaust still fit with the new head and jug?

It will bolt to the cylinder just fine - however I believe there may be some clearance issues where the pipe crosses over the head. My mx motor is too buried to go check, but I think I recall the fin cutouts were different? The stock mx pipe takes a slightly different route so it could be an issue.

I am doing a similar project (mx => dt) but will likely go with a down pipe.

thanks everyone!

Trooper,the MX400 has the 510 cylinder and these were also used on the 1976 YZ400 and the 1976 IT400 so finding them should not be hard.

if you swap the 510 cylinder to a DT or MX400 lower end,you need to use the piston for a MX400B or even the DT400 piston could be used but if you do,it will cut into the power output a amount.

the IT/YZ400 piston can't be used on a stock MX or DT lower end because the IT/YZ400 engines have a longer rod.

this was done by Yamaha to reduce the piston side loading and provides a more favorable rod/stroke ratio and the 1976 YZ400 made 40 Hp instead of the MX400B's 38 HP.

using a longer rod and a higher wrist pin location is a old hot rodders trick to get a stock displacement engine to put out more power.

the Wiseco DT/MX400 piston has a skirt like the MX400B and it increases the duration the intake port is open and can also be used. I like the Wiseco pistons and I have used them for years. if you want to wake up a DT400,use a Wiseco piston and do some light porting. it will be a better runner and will rev out further than a stock DT400 yet will retain the excellent bottom end power a DT400 is known for and it will have a longer power curve with more revs should you want or need it.

this config will work great with the stock carb and pipe and will respond well to a upgrade in either or both areas.

this video inspired my build pretty much,it is a 1975 MX400B and if I could,I would love to have one myself.
the rider of this bike is a big guy and he makes it look like a Mini bike.

Bigdog great info. I was wondering if there are any mx400b up pipes being made currently in the aftermarket. I would be interested in checking one out for my 78 400. Thanks