Z50 Rebuild Guide
Taken/translated from puchforum.com
2-speed block overhaul
The reconditioning of a 2speed is more difficult than overhauling an automatic block. The block consists of more parts and is a little more difficult to put together, mainly because of the loose needle bearings. Yet you will see that it all fits together very logically. What you can replace when reconditioning of a 2speed block:
|Crankshaft Bearing (L17)||17x40x10||2||Treatland|
|Gearbox Bearing (6202)||15x35x11||1||Treatland|
|Gearbox Needle Bearing||3.5x3.5x7.5||46||?|
|Clutch Plate (Different engines have either 2 or 3 plates)||N/A||2/3||?|
*These are mostly loose balls, but a ball bearing can work.
However, when you usually can just replace the bearings (not the needle bearings), gaskets, seals and clutch plates. Always replace gaskets after splitting the block. Replace bearings only when radial clearance on the shaft. Replace clutch plates if you find them slipping while riding. Replace seals if they are dried out. Replace gears if they're visibly very worn. All these items are available at Toys Rinky in Dorst. ALMOST all the parts themselves are easy to assemble. One problem is the crankshaft bearings. Those are called angular contact or magnetic bearings. These are bearing whose outer ring is in the crankcase, and the inner ring and balls are stuck to the crankshaft. See the picture below:
The clearance in this bearing is determined by the thickness of the so-called crank shims. These are washer-like shims between the bearing and the crankshaft cheek. If you have too thin shims, there will be side to side play at the bearing. If these shims too thick, the crankshaft will have too much friction against the bearing and your motor should not be run. It is very important that the thickness of the shims is good. The shims that are standard on the crankshaft, will have the right thickness. If the crankshaft bearings to be replaced, then you do not change the shims. You need only be a bit concerned that the shims are not damaged by the removal of the old crankshaft bearings. You do this with a special puller, this is something to outsource. To put the outer rings of the bearing into the crankcase, heat the sump and put the rings in the freezer. The rings are then pressed in the crankcase. Similarly, do this with the ball bearing in the gearbox.
If you've lost or damaged your crank shims, you will need this to be measured out. You will send your crankcases, crankshaft and bearings, and is then measured and calculated what size shims are needed. This can again be performed at Rinky Toys. You can make it all yourself. You try it with any shim without bearing packing ietswat heavy start to turn. Then a thin gasket assembly. It sticks very closely, you've got to feel for it. (Editors Note: I have no idea what he's getting at.) You have to use the aforementioned puller so that the bearings always get off without damage.
Here's how you step by step 2speed block put together.
Now just a gasket, kickstarter, ignition, cylinder and carb on it and you have a complete engine.