I don't know of any aftermarket pipes specifically for the 77-78 DT400 but there is DG that makes pipes for the YZ and IT400s.

I would try to find one for a 1977 or 1978 YZ or IT400. the 1979 models of those had a smaller bore and a longer stroke if memory serves us correct. it should not take much to fit it to a 77-78 DT400 as the layout is a lot like a YZ/IT400.

for top ends,head over to the Yamaha Motor site and find out what the base gasket part number is on a 77-78 DT400 then compare it to a IT or YZ400 base gasket part number. if the part number is the same,chances are great that you can use that year model YZ or IT400 top end on it. you can also get the existing cylinder you have ported if you like.

Jemco can make a pipe for your bike if you live near them in Texas and you can drop off your bike there and they will make a pipe for it.

Cool. Been porting mine right now. I have to build the courage to do the other side of the transfers, because they need to match the front and rears on the opposite side in angle. You know one slip...

tried removing the broken stator bolt today,it did not go so well and I ended up drilling it out.
I drove a small torx 1/4" drive socket on it.

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and the result.......... sorry about the poor picture,the camera I used does not do well with close up shots well at all. I miss my Kodak which was far better in close up shots.

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here is my attempt to drill it out,at least I got a lot further.

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this easy out kit has some very useful drill guides and there was enough of the old screw left to use the drill guide.

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once the pilot hole was drilled,I incrementally increased the drill size to it was a little over 5mm.

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then I was able to run a 6 mm tap through.

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I got the Alumiweld today and attempted to fix the case breakage,this did not work out as well as I hoped either.

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I tried to use it,apparently I can't get the metal on the cases clean enough for it to stick.looks like I will go with my buddy,JB Weld which worked far better for me.

it melts at 730 degrees and you can use a Propane torch with it. I will try working with it and hopefully figure out how to use it properly. If I get brave enough,I might try it with a broken Magnesium cover I have. and of course have a fire extinguisher handy.

I got this stuff from Eastwood. it is a metal prep cleaner to clean the metal enough to paint it. I have a lot of trouble with engine paint sometimes,I really need to refine this skill a good bit.

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I went ahead and painted the lower half of the cases,it turned out so so.

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I still have to wait until that clutch actuator seal shows up. I went ahead and reassembled the engine to a point.

when reinstalling the kick start lever,it helps to remove the idler gear that goes here. I wound the spring 1 turn and pushed it home.it is not documented but I also reinstalled the decompression cable.

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I cleaned up the steel clutch disks before putting together,this is how they looked before. going by how nasty the steels are,this engine had not been running in years,years before I got it in 2011. I measured the friction disks and they came in at 2.8-2.9 mm. they can be used for now.

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I loosely assembled the clutch so that when the seal arrives,I can install the bell crank with no trouble.

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I went ahead and painted the upper part of the engine,the cylinder and the head.

I assembled the new piston with the new wrist pin,bearing and wrist pin clips. I lubed the bearing and wrist pin before assembly. I got too giddy to take too many pictures.

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here I am assembling the top end.
this is my piston ring compression tool of choice,this is great to assemble the big bore engines with and the 250s as well.

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the DT400 head gasket goes right on.

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I need to get the engine into a bike before I do the final torquing of the bolts.


these are the gaskets I used.I have used this company's gaskets before when I built the engine in the 1979 CR250.

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I went ahead and stuck the head on. it is not far away from being fired up for the first time in several years.

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I have to wait until the Boyesen reeds and that seal for the clutch actuator to show up. might put it in the extra DT400 frame I have to light it off and hear it run. and oh yes,there will be a video of the first start up when it happens.

Nice work, I'm loving the pictures of this rebuild. Did you end up re-using the clutch steels?

Clay