One Weird Trick To Fix All Your Tomos Leaking Problems

If you have ever owned a Tomos moped at some point you’ve probably wondered why the wheel and chain seems like the dirtiest thing on any bike you’ve ever seen. And you would be right in your concern because the answer is simply that it’s all oil. Oil leaking from your transmission and onto your chain. You would also be right to question if there is something wrong with your bike. It turns out that it was designed that way, for whatever reason. Luckily, the good people at Treatland sells a sprocket nut that fixes the oil leaking problem so let’s go through how to fix that oil leak once and for all. This will work for all versions of the Tomos engine, A3, A35, and A55, kickstart ad pedal.

Step 1: Purchase this sprocket nut from and some oil sealant cream. Hondabond 4, Yamabond 4, Threebond 1194, Permatex Motoseal Ultimate 1 Grey (those are identical chemicals from what I can tell), are all very good sealants and readily available. The Permatex should be available at your local auto parts store as well.

The new sealed nut compared to the original factory nut.
The new sealed nut compared to the original factory nut.

Step 2: Remove either the pedal or the kick start unit on the left side of the bike. Then remove the left side stator cover. If you have the oil injection still installed you do not have to remove that from the stator cover. Using a small chisel or a flat head screwdriver bend down the locking tab that holds the sprocket nut. If you do not have an impact driver or a way to hold the sprocket still while loosening the sprocket nut another option is to use the rear brake and the chain to keep the sprocket from moving. Remove the chain, sprocket nut, the sprocket and the sealing spacer ring behind the sprocket.

Step 3: Once you’ve removed everything clean everything pretty thoroughly. The transmission has a couple of way to leak here and we will attempt to seal all of them best we can. The spacer ring seals to the back of the sprocket and around the outside by an actual seal. On some of the spacers there is one side that is tapered and one side that is squared off. If you have two different sides install the tapered side toward the engine. The sprocket will most likely have a ring groove on one side where it was sealed against the spacer ring so apply a small film of sealant cream around this ring before installing the sprocket. This keeps oil from leaking from around the end of the spacer and the face of the sprocket. Apply a small film of sealant on the back side of the the locking tab. This helps oil from leaking from behind the splines of the sprocket. Apply a small dab of grease the inner part of the seal on the new nut. Then simply install the new nut being careful not the damage the seal as you slide it past the notch on the shaft for the pedal/kickstarter assembly. TIghten the sprocket nut to 35ft/lbs (or as much as you can) and then bend the locking tab back up.

Step 4: Reinstall the chain, cover, pedal or kickstarter, and ride on.