Hello, 

I bought a 1978 DT 400, that is in pretty good shape. After tearing down the Engine, the cylinder & Piston have some slight scoring. It looks like the IT/YZ's of the time had a supstatial power increase over the DT's. (Im only 30 so these bikes are way before my time)

With that said it seems like you can use the Piston, Connecting Rod, cylinder & head from an IT and it will bolt right up to A DT Case/Crank. 

Am I missing anything, and can someone confirm the part numbers I need to Make this happen? Also any reputable engine guys in case I have to bore the cylinder, seems like most are not in great shape that are for sale. 

Thanks!

Welcome from NZ. Man you've got some big plans for the upgrade.
What i usualy do to see if ideas like yours are in with a chance is compare base gaskets on Partzilla or similar.
I had no luck looking above year 1976 under YZ's as list is incomplete & showed no gasket, but i've not looked at IT's.
Base gaskets are the same number for a "76 YZ400C compared to you DT400 so that's a start.
Here's two links but on the YZ parts list the numbers are hard to pin down but gasket is listed on the first part of the list with no number down the side, just 0 but says 1M2-11351-01-00 same as DT400.
www.partzilla.com/catalog/yamaha/motorcy...-cylinder-yz400c-d-e
www.partzilla.com/catalog/yamaha/motorcy...linder-cylinder-head
I'm no help really but there's a hell of a lot more to consider before ya go swapping bits.
Then also there's the exhaust to get the advantage from it.
Best of luck with what you decide but let's see what others say before ya jump in.
Now that reminds me of a lifetime ago--well more than your lifetime for sure--[im nearer 80 than 70 haha] & i had a DT250 about "77-"78 monoshock model that i put an IT400 complete motor in it i bought from the wreckers.
It was a weapon & had a good exhaust off a YZ i 'made fit', but motor had been overly ported & so i had to tame it down to spread the power lower down so was good overall & not a mad light switch power hit.
Never got any pics of that as was before digital easy camera use.

This has been done before. You might be able to find threads on here with the parts needed. If I remember correctly, you need the earlier model parts?

I found a thread on here that sounds like it discussing what parts are needed using google, but i think that it is too old because it throws an error when I try to open it. 

Yes, site is going through some growing pains. I think it was the 75 MX400 and 76 YZ/IT400 parts that were the closest "bolt on" Here are a couple threads I found before the search broke on me.

yamaha-enduros.com/index.php/forums/74-7...chamber-volume#95938

yamaha-enduros.com/index.php/forums/74-7...lock-question#146223

WRT a good source to get cylinder boring and similar work done, I think a lot of members here use Bill Bune in Anoka MN.

billbune.com
 

I second the Bill Bune doing your machine work. They did the cylinder work on my IT400 and did an excellent job. Getting ready to send a crank to them to rebuild.

I had a similar idea, but I was going to start with just replacing the head for a higher compression ratio. I can tell you from personal experience that the IT head will not simply bolt in to the DT--the fins get in the way of the expansion chamber.

I still have plans to do something along these lines, but my DT400 project is probably still a couple of years out.

.....I was going to start with just replacing the head for a higher compression ratio.....

You might have dodged a bullet...  higher compression head is not needed without higher IT/YZ exhaust port that reduces effective compression stroke.

The stock DT400 compression ratio is well over 10:1 already...  when you measure like the rest of the world did (from BDC) and not from "port closing" like the Japanese inexplicably decided to do on their two strokes. 

Back in the day the European two stroke race machines like Husqvarna, CZ, and Bultaco had advertised compression ratios in the 12:1 or higher range...  Japanese two stroke race bikes were generally advertised at less than 9:1.  The difference was in the measurement method, some of the Japanese bikes actually had higher compression ratios than the European models! 

     You know, I've wondered about that very thing over the years--as I recall my DT250A was advertised as having a CR under 7:1, and other old Yamahas I've owned have had similarly low advertised CR's, though similar vintage Euro 2 strokes were always advertised with much high CR's.
 
       At first it made sense to me why the Japanese might measure CR from the top of the exhaust port, but when I thought about it a bit more, I realised that would really be like measuring a 4 stroke compression ratio only from the point in the stroke where the valves were completely closed, which would be ridiculous.

       I'd still like to switch to an early IT400 cylinder on one of my DT's one day.  Can you confirm whether or not there is a difference between IT and YZ 400 port timing in say, 1976 model year?  I had a '76 YZ400C that I really liked, though I'm not sure I would like it as much on the road.  If the IT is a little milder, (as I would expect from a woods bike) then that might be a better choice.

        Apologies to the OP for sort of hijacking this thread, hopefully answers to my questions will help you as well?