The ZA50 is the automatic, two speed engine found on some Puch mopeds. It can be distinguished from the one speed Puch engine by the more rectangular shape of the right side engine/transmission cover. See picture here.


Crank Bearings

  • L17
  • B20


  • 17x35x(7 or 8mm)
  • 20x35x(7 or 8mm)

Repair/Disassembly Videos

Check out these videos by Chris Paz if you're ever faced with a ZA50 rebuild or if you just wanna see what all is going on in between those engine cases.

Here are some disassembly/reassembly videos from Bruce Cross (brownb0x) from the Halfwits Blog:

Weak Points

There are a lot of weak points to the ZA50 motors, if they are build correctly they can live long and fulfilling lives. Here is a list of the week points of the motors and how to fix them (if possible).


The shock of the motor shifting between first and second is not enough to sheer the teeth of the gears unless the shift dampeners are cranked or no longer exist inside the 2nd gear drive shaft. The stock pucks have been inside the motor for over 20 years; if the bike sat for any amount of time without being run or without trans fluid, at least one if not all the pucks dried out. When they are used again they are quickly shredded. Even perfect pucks can be destroyed in minuets with an 80 Metra installed on a ZA50. When the pucks go there is nothing to absorb the impact of the shift between 1st and 2nd gear what takes the brunt of this is the hardened teeth of the 2nd gear main shaft, the starter plate teeth or the gear that is meshed to the 2nd gear main shaft. Since they are hardened, the teeth are quite brittle and once one or two teeth go, slop is created and more teeth quickly follow.

  • Fix- There are multiple people selling replacement pucks these days, I make my own and have not seen a broken tooth on any motor I have rebuilt with them.


Just like running a one speed stock crank on a kitted bike. They fail… The only two failures I have seen on a motor I build were my Metra that has a small end bushing failure and my friend J’s bike that had a big end bearing failure.

  • Fix – Easy, get a roller con-rod and have it pressed into the stock crank. The cost of the rod + the labor gets you in around $100.


Lots of places to mess stuff up. No easy way to measure the proper end float. If you pull the motor apart to replace the crank bearings you are going to need to re-spec the crank shims. This is a pain in the ass either without the factory tool or with the factory puller. It’s a lot of trial an error with trying to get the clearance tight enough so there is minimal crank slop, but not to tight to the point where the crank binds when you tighten the case bolts down. Unless you have spare shims (they range from .001” – .012”) this can be even harder to get right. Then there are the trans cover shims that are super easy to set if you have the tool but a pain if you don’t. Too tight and you could spin a bearing in the case of blow a hole the size of the bearing in your trans cover.

  • Fix – Get the tools, hire someone that dose, spend your time and figure another way to measure the correct spec.


These are not so much an issue with mild or even higher powered motors, after 500+ miles my Metra clutches looked new. But the Parma set-up is quite hard on clutches so I figured I would touch on the subject. My Parma has shredded 1 1st speed clutch and is probably most of the way through its replacement. The linings have a tendency not to wear evenly and tend to chip and erode at the leading edge. I think this has a lot to do with the old glue slowly letting go. I have a few clutches that linings came off as one complete piece. The other issue is the pads use links of chain to pivot. These pieces of chain bend and flex over time and it causes the clutches to kind of bowl inward. This causes there to be less surface area of the clutch to engage the bell so the area that is engaging wears that much faster.

Fix – Since this is not such a big issue with most motors I have not really experimented with fixes yet. I have been talking to a few epoxy distributors and a few companies that make flexible kevlar break/clutch lining material as a replacement to the stock friction material.

Performance Modifications

There are not many things you can do inside an ZA50 to improve performance. The one big thing you have to work with is the clutches.

2nd speed clutch flip

Changes how the clutch arms rotate in relation to the outward force pulling them toward the clutch bell. They resist the pull until a higher rpm. This can delay the shift point to second 5-10mph.

Change oil weight

Using fluid other than the recommended Type-F (most run 10w30 gear oil) will change when both 1st & 2nd gears engage. I'm assuming that this has to do with the thicker oil causing more RPMs (force) to pull the clutch arms into contact with the clutch bell. In addition the higher viscosity oil coats the internal parts better making sure the bearings stay lubricated. Please also overfill your transmission by 50% (stock calls for 9oz I run around 12-15oz). The bearing in the transmission cover are splash lubed meaning the oil level in the motor dose not reach them but the splashing from all the gear teeth keep them running smooth. DO NOT FILL the trans with too much fluid, it will cause too much crankcase pressure and could cause your seals to leak.

Remove Weight from clutches

Just like on a one speed the two speed clutches are centrifugal. Lighter weight clutch arms will require a higher rpm to be pulled out. You can go too far with this, If you remove too much weight from 1st gear it could never grab, If you remove too much from the 2nd clutch it might never shift into 2nd gear. Small amounts or weight removal & trial and error are key. To safely remove material with out damaging the springs you should disassemble them.

Cutting the clutch spring

Making the clutch spring shorter will increase the tension on the clutch arms preventing them from moving out until a higher RPM is reached.

Puch Engine Variations

Puch KoradoE50 (kickstart)Puch Magnum XAuto-engaging E50
Puch engine differences (photos)