Hello All,
It helps if you can tell us which locomotive.
Hope this helps.
"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"
Remember this "HOseeker is my friend" Check out the Kato section on this page and see if you can find the name and part number of what you are looking for in the exploded diagrams and parts list, then contact Kato Customer Service Katsumi, Baker, Gem Models, Lindsay, Kato, and Model Engineering Works M.E.W Information - Literature Page 5 (hoseeker.net) Just guessing, it sounds like you need a worm gear. Telling us the type of loco beyond "diesel" would also be helpful. Give us the description on the box if you still have it.
Kato USA has a pretty good Parts Department online. Even if they don't have the part in stock, you may find the name of the part and it's ID number that you can use to search the web. (Or, you may need to track down the parts diagram that came with the instructions for the engine.)
https://store.katousa.com/product-category/kato-parts/ho-scale-parts/ho-diesel-locomotive-parts/
I have lost part of my kato diesel drive shaft. Not sure what to call it but it looks like a brass screw. Can anyone tell me where I can find this item and what it is called. Thanks