Hi Stace and Norm,
It depends what 125 cc motor it is ,the early 125 cc the seal hits in from the outside but later 125 cc motors the seal hits in from the inside of the crank case so motor must be dismantled.
If the early 125 cc motor is not apart when installing the seal you would need a length of water pipe the right size to fit the seal and fit over the crankshaft, then hit the water pipe with a hammer to install the seal.
I use a socket from a socket set that is slightly smaller than the seal and hold the socket on the seal then hit the socket with a hammer to hit the seal in evenly when the motor is apart.
I wouldn't think a mower shop would charge much to fit a seal unless they need to dismantle the engine if it's the later 125.if you don't have the right tools.
Cheers
Max.
