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78 IT400 top end on a 78DT400

04 Aug 2020 14:39 05 Aug 2020 18:10 by Blazer.
Blazer
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78 IT400 top end on a 78DT400 #1
Hello, I have a 78 DT400 and have a complete top end from a 78 IT400. I would like to swap the IT on to the DT bottom end.
I checked head and base gaskets and they are the same. The bore and stroke are the same. What I dont know is, if the IT piston will fit on to the DT rod and match up with IT ports. It would be nice to be able to do the swap and get some HP! Im going to use the IT carb and I know I am going to have to do something about the pipe since the IT pipe exits on the other side as the DT. The number on the IT jug is 1W401 and the motor prefix number is 1W6 if that helps.
Anyone have any experience with this? Any info is appreciated.....

Update: The following items are interchangeable with the DT and IT. Wrist Pin, wrist pin bearing, crank pin and bearings. So based on that the IT piston should fit on to the DT rod with no problems. Which means the whole IT top end should swap over!
The only thing I dont know and cant find, are the lengths of the DT and IT rods. IF they are the same then its a done deal!
Can anyone help me with rod lengths?

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05 Aug 2020 00:39
elliottles1
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78 IT400 top end on a 78DT400 #2
Blazer,

hi, i researched this recently (yz on dt) and found that after a certain year, the wrist pin height on the piston changed prohibiting the swap unless you use a very early barrel/piston.

google it, it comes up somewhere.

cheers
les.

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06 Aug 2020 19:09
Blazer
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78 IT400 top end on a 78DT400 #3
Well I have been researching this like crazy. Looks like the 78 DT400E and 78 IT400E have the same rod lengths. So the 78 IT400E complete top end should swap over to the 78 DT bottom with no problems!
Now I have to get my SL70 finished and off the stand!!
The following user(s) Liked this Post FrankC, LongStride

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06 Aug 2020 20:19
MarkT
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78 IT400 top end on a 78DT400 #4
A lot of these topics have been discussed on this forum at least once...

You might want to read this thread:

www.yamaha-enduros.com/index.php/forums/...-calling-all-experts


:Buds

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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06 Aug 2020 20:42
Blazer
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78 IT400 top end on a 78DT400 #5

MarkT wrote: A lot of these topics have been discussed on this forum at least once...

You might want to read this thread:

www.yamaha-enduros.com/index.php/forums/...-calling-all-experts


:Buds


Hi Mark, I have and much more here and anywhere else I can find LOL! But from what I see as long as I use the IT piston head and barrel it should work. I have been trying to find a used 78 DT barrel on fleabay so I can do some mock ups with out taking apart my running engine in my bike. Cant find one that does not cost bunches yet.

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06 Aug 2020 22:12
MarkT
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78 IT400 top end on a 78DT400 #6
The thread I linked clearly states you will need to change the rod.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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07 Aug 2020 10:12
akara1
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78 IT400 top end on a 78DT400 #7
On page 2 of the same thread it is reported that the 1w4 cylinder fits the stock late dt400 bottom end perfectly fine with the stock dt piston or an MX400b Piston. or am I missing something

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07 Aug 2020 10:49
MarkT
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78 IT400 top end on a 78DT400 #8
I'm going by what Enduronut said. The later post says to use an earlier MX400 piston or DT/MX Wiseco piston.

An earlier MX400 top end will bolt on to the DT400 without mods. My understanding is the later IT doesn't? I'm not understanding how a piston from a top end that works would somehow convert the allegedly 5mm taller IT cylinder to fit?

I haven't done it so I can't be sure... Enduronut is not wrong very often though.

Please let us know how it works out!

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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07 Aug 2020 11:03
akara1
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78 IT400 top end on a 78DT400 #9
My understanding is the deck height is the same, but the piston must match the rod!

early mx400b piston is the same as dt400 piston, but with a half moon on the intake side instead of windows.
the wiseco dt/mx replacement piston is the same design as mx400b with the half moon, but is listed as replacement for early dt400 as well.

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07 Aug 2020 13:57
MarkT
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78 IT400 top end on a 78DT400 #10
If deck height is the same it makes perfect sense.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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