I got this bike in 2011 and now I am just getting started on it. the engine when I did a compression test only had 75 PSI. I got a 1975 MX400B top end to go on it and a 38mm carb from a 1976 IT400.

here is some pictures of the bike as it sat. these pictures were taken in 2011,back when the 1978 DT175 was a real steaming pile.

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this is another picture,the DT175 as it was when I got it and the DT400 in this thread is in view.

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the ignition system is also trashed. hacked up wires,broken pulsar coil and the infamous white flywheel syndrome going on.

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here is the pics of the flywheel,truly crusty!

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one of the screws for the stator is broken off.

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case is damaged in this area.

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Looks like you are in for some fun! These projects seem to be a job primarily of finding parts the previous owner dismantled or corrosion control. At least it is one of the few where the cylinder head is still on.

yeah,it has a cylinder and a head.it is not quite as bad as say the 1978 DT175 was. it has a ton of missing parts though.

however I got a 1975 MX400B top end to put on. I will take pictures of the crank and show why it needs a rod kit. this engine had water get in it at one time or another.

Edit 4-14-15: I managed to clean up the rod on the small end and remove all the rust,I used Pb Blaster and a 1500 grit wet sand paper and managed to get all the rust out,it was surface rust and it cleaned up great.
then I checked it with a new wrist pin and bearing and it is smooth in rotation and no axial nor up and down play in the rod,small or big end.

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besides the rod cleanup.I sized up the parts to be used in this restomod.
I checked to see if the existing throttle cable and throttle assembly would work. it sort of works.

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closed throttle is fine.

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wide open throttle is not quite wide open throttle,more like 3/4 throttle.

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I found oil pump block off plates on Ebay,so abandoning the oil injection and using a Gunnar Gasser throttle with a traditional cable is one option,the other one is re engineering a throttle cable to work with the stock throttle and oil injection on a 38 mm Mikuni. I really would like to use the oil injection. time will tell pretty much.

I am going to try to go for the Sleeper look,in other words a stock appearing bike with real firepower available

rotating the engine revealed it needs main bearings,sounds rough and nasty when the engine is turned over.

next step was seeing if the DT400 automatic compression release will work.
it bolts right on with no trouble.

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now for some differences,besides the 32mm carb vs a 38 mm carb,that is a huge difference alone there!

here is some pics with the obvious improvements in porting and the cylinder head.
back view of the cylinder. the stock MX400B cylinder is on the left and the DT400B is on the right.

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here is a shot of the heads.

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some cylinder and piston differences,if you are hopping up a DT400 by porting it and modding the head,either a Wiseco or a MX400B piston will fit the bill. these pistons allow a lot more intake duration than a stock DT400 replacement piston can.

first the DT400 piston skirt.

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now a MX400B 510 piston.

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I don't have a degree wheel to mock up and use the engine to find out actual port duration. all I have is these pictures.
this is the DT400 cylinder.

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the much more free breathing MX400B cylinder.

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finally I could not resist stacking parts.it all fits really nice.

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I got most of the parts and rebuilt the bottom end today,basically I split the cases and replaced the main bearings. I used a Wiseco BK5003 main bearing kit in it and it fits like a glove.

ready to go under the knife so to speak.

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after removing the side cover and the clutch,I removed the kickstart assembly.

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this allowed access to remove the decompression cable.

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then the cable pulls out of the crank case boss.

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the clutch bell crank shaft seal appeared to leak at one time,it is getting a new seal there.

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remove the nut and then the screw.

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then the bell crank assembly can be removed.

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after removing all the case screws,now we can split the cases.

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keep the cases parallel while separating them to prevent warping the cases.

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I got it apart.

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no wonder the bearings failed,it ingested a lot of dirt.

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once I pressed the crankshaft out,it was the same on the other side,both bearings are thoroughly roached.

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here I am pressing out a bearing.

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