Hello everyone Thanks for Letting me join . I live in Southern Indiana and I have worked on vintage 2 strokes nearly all my life. I came across a mint 1975Dt125 however it is locked up. I removed the cylinder and it is still locked up so bottom being the problem. I was getting ready to split the case . I found a 1973 with a good bottom end but bad cylinder. My question is are they the same will my cylinder fit the 73 are the engines the same.

1975 cylinder will fit the 1973 and the mounts on the engine are the same as long as you are in the USA and both engines are the 12v electric start models we got here.  You'll probably want to swap both cylinder and head as the fin design might have changed a little.

Oh dear, i want to know what stopped it now lol. Pretty unusual to tie up a big end--or a main. Does the rod move as in swing back n forth. Something in the primary case or left side but can't think what. Worth more to sell with matching numbers if that's your longer term aim. I had one the same year a lifetime ago--another one i shoulda kept.

Thank you, I think I may go that route and get this thing going. The bike looks new except it will not turn over. My only guess is from storage or it happened and that's why it was parked.