ZA50 Overhaul: Part 01 - Performance Crank, Bearings, Seals

It's been a while since my last post. Main reason for my lack of posts

is that I've been riding my DR-kitted, Proma-piped PA50-II a bunch.

It's my first running and registered, moped here in the city. I'll post

some photos of the Honda and videos soon.

I've organized my work space a bit in preparation for finishing up

the Mini Mag.

The big "To-Do" on this build for me has been to install this ZA50

performance crank I ordered from 1977. I finally got my hands on both

the E-20 and L-17 crank bearings I needed to start this installation.

The key to doing this task properly is using a set of digital calipers to

take several measurements to make sure everything fits properly.

Any miscalculation here creates slop in the crank and could easily

destroy an engine.

My goal here was to match the width of the outside width of the stack

crank and both bearings with the new bearings and crank. I took

severalmeasurements and got an average width of 58.35mm

(see below).

Next I measured the new crank before mounting the new bearings.

My average width measurement here was 36.35mm (see below).

I next measured the width of the e-20 bearing (without the race).

My average measurement was 12mm (see below).

Same procedure goes for the L-17 bearing. Average measurement I

got here was 10mm (see below).

So, as luck would have it 36.35 + 10mm + 12mm = 58.35mm which

equals the width measurement I had for the stock crank! Any

difference below 58.35mm would have to be made up with shims.

A good resource for shims is McMaster-Carr.

Next step was to remove the old bearing races and install the new

ones. The tools which come in handy here are WD-40, some

3-in-1 motor oil, a Bernz-O-Matic torch, a hammer, and a set of

flat punches.

The stator-side race is the easiest of the 2 bearing races to remove.

I heated the inside of the stator engine half with the torch for about

30-45 seconds. I then flipped the engine over and tapped on the race

the the opening on the stator side. There is a little notch

(pictured above) where you can rest a small punch on the edge of the

race to tap it out.Throw some 3-in-1 oil in there if you have any trouble

getting it loose.

The transmission side bearing race is a bit trickier. There is no place

to seat a punch on the race to pop it out. You have to rely soley on

heat and lubrication, plus some smacking to get this guy to fall out.

Again, torch for 30-45 secs the inside of the transmission half of the

engine then lubricate with 3-in-1 oil. Repeatedly smack the engine

case, crank side down on a towel covered hard surface, such as a

concrete floor or metal table. You should start to see the race move

after a couple of hits (see photo below).

Reheat and repeat smacking until it drops out. Also, wear

heat-proof gloves or oven mitts. I should have mentioned this

earlier. Below is a photo of my old bearing races, pretty

tarnished from years of the bearings resting in there unused.

I used the same process, heat, tapping and lubrication to get the

new races in. Be extra sure that the races sit flush to the surface of

the engine case when installing. YOu should not need to strike them

very hard to seat them properly, you might damage or crack the

engine case. Your best bet is to just add more 3-in-1 oil to slide

everything into place.

Next are the oil seals. Going with the same theory as installing the

bearing races, I also used heat and lubrication here, but in the form

of dish soap and warm water from the sink. Any force via tapping was

done by gently tapping with a hammer and a wooden chopstick. You

have to be careful not to puncture, tear, or stretch the seals. Again,

make sure you seals are facing the proper direction as depicted

below as well as make sure they are seated flush.

Make sure everything is dry before bolting everything together.

In Part 2 I'll go into detail about final assembly and measuring end

float, etc.

Please leave comments regarding my process. I'm no expert for

sure and this is my first ZA50 build. My goal as always is to share

in order to create a resource for others. Above is just what worked

for me with the resources I had available at the time. I consider this

a work in progress. Thanx!