Kit a Tomos A3

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Kitting a Tomos A3 requires only slightly more work than kitting a Tomos A35 engine. While there are no explicitly defined "Tomos A3" kits, any tomos A35 kit or even Puch kit can be made to fit onto a Tomos A3 crankcase with a few additional steps. Primarily, this includes pressing out the old wrist pin bushing and pressing in a new one. A3, A35, and Puch mopeds use wrist pin bushings that have the same outer diameter (OD), but the inner diameter (ID) on the A3 is 10mm, and the A35 and Puch kits use one with an ID of 12mm. The new 12mm bushing will fit into the conrod the same way the old 10mm one did, but the larger ID will allow you to use the 12mm wrist pin and piston that Puch and A35 kits use.

*treatland sells a kit for the A3 that uses a 10mm wrist pin. You might still want to replace the bushing with needle bearing though.

Items needed

  • Puch small end brass connecting rod bushing (12mm id)
  • C Clamp or similar pressing device
  • needle nose pliers
  • 11mm socket with 3" extension on a ratchet
  • 8mm deep well socket 1/4" drive
  • A35 / Puch cylinder kit

Removing the stock cylinder

  1. Unbolt you carburetor, intake manifold, and exhaust pipe.
  2. Take off the spark plug wire
  3. Loosen the four head bolts holding the cylinder head and cylinder down. They should be 11mm. Loosen them evenly and remove them. The cylinder head should slide up and out, off of the studs.
  4. Next remove the cylinder itself (barrel, jug, cylinder, whatever you want to call it). It might take a little bit of persuasion to get it off but it will come out.
  5. Now you're left looking at the piston. Along the side of the pison you will see two holes for the wrist pin. There are tiny round wire clips holding the wrist pin in place. Remove those with needle nose pliers.
  6. Now you wil want to use the C clamp in order to get the old wristpin out. Very carefully press the wrist pin out with a C clamp and 8mm deep well socket. Once it's pressed out, the piston will come out.
  7. now you will be staring at just the connecting rod. The next thing you're going to do is take the 11mm socket, and do the same thing via pressing, to press the wristpin bushing inside the top end of the connecting rod out. You're going to replace it with the Puch small end brass connecting rod bushing that you picked up.
  8. With the old A3 connecting rod bushing pressed out, you'll press in the puch bushing into the a3 conrod. Be careful and take your time. Make sure you use two stroke oil when installing it, and make sure that the oiling holes are lined up as well.
  9. With the Puch bushing on, you can now install the piston and A35 kit exactly as you would normally.

See Install a kit for additional cylinder removal and kit installation help.


Please watch the following video to see how to put a kit on a moped with a Tomos A3 engine.