mxing my 125-175

Are you using a barrel from an IT 175 engine? I converted a 1979 YZ125 engine to 175 cc by using an IT barrel. I used a piston from a 1976 YZ175 as it is a single ring piston. The engine went very well but vibrated quite badly.

I found that the IT175 barrel did not match up with the YZ125 engine cases so we had to make up a 5mm thick spacer plate and use a 5mm longer con rod, which may have been part of the reason for the higher vibration. I suggest you measure up both barrels and see if the dimensions are the same at the bottom. I am sure you will find they are different.

I am pretty sure that the later engines (1980 onwards) are a lot easier to interchange.

Here is a pic of my old 125 and the 175 engine is on the ground in front of the bike. Unfortunately I do not have any pics of the engine showing the spacer plate.

It is a 1979 yz125. I am pretty sure the DT barrel is basically the same as the IT barrel, but I might be wrong.

When I tried putting the barrel on the YZ cases I found they did not match. The barrel was wider than the cases. We made a 5mm thick spacer plate so that the gap was closed, but this meant using a 5mm longer Conrod as well. I suggest you look at the two barrels and measure them up. I would be surprised if they are the same. If the DT barrel does fit then it must be different to the IT barrel. I would be interested to know.