ZA50 Stock Clutches 101

This post is devoted to the stock version of the PUCH ZA50 motor's clutches.  In this post, I will record all my findings, tips, tricks, mods, research, and tests from all my experiences.  I will continue to update this post as I get more information. So keep checking for updates. Also, please chime in the comments area if you know something too.  I'll incorporate it on this page.  This will be the one stop for everything ZA50 stock clutches.

ZA50 Stock Clutches 101:

The perfect set up for ZA50 clutches are optimizing their shift points (or times when the clutches engage) in the power band of the motor for both 1st and 2nd gears.  The 1st gear clutch should allow the motor to rev up the power band high enough then engage to optimize the bike's start / low end. The 2nd gear should engage further up in the power band right before or at the bike's exhaust power band for ideal mid range speeds.  The secondary effect to optimizing 2nd gear's clutch is that the bike would downshift at higher RPMs which is great for stop and go riding (i.e. city riding).

These optimization can be achieved by a number of ways. They are modifications of the springs, shoes, and/or installation configuration. Also, type of oil plays a big role on the behavior of these clutches.

Here's a picture of clutch modification at it's finest provided by the d-funked website www.project76puch.com by the legendary Puch builder Curtis of Hawaii:

11 grams per shoe drilled away, and the springs shortened 3 coils.

Here are pics provided by Curtis of various sets of stock clutches from motors from different years:

Stock clutches from Curtis

Dismantled 2nd gear and springs from various clutches

INSTALLATION CONFIGURATION

What I call installation configuration is what is know as "flipped" or "flipping 2nd gear". The theory behind "flipped" is that a clutch in the "flipped" position engages or opens up in the opposite direction of the engine's forward rotating motion. Because of this, the "flipped" clutch requires a higher RPM for it to engage, hence a longer "stall". On a stock ZA50, 1st gear is already "flipped" and 2nd gear is not. The trick is to simply "flip" the 2nd gear clutch around so that the open direction of the clutch is the same as the stock 1st gear clutch configuration (counter-clockwise). This trick should be a minimum to any ZA50 build especially if your running a stock top end setup. Moped Army's MopedWiki explains the how to here.

SPRINGS

Curtis explains some spring theory:

There is a theory that there are different springs made in different years.  The factory color marked the clutches as yellow/blue, blue/green, and green. The yellow/blue marked clutches have the tightest springs and green the weakest.  But not all clutches have these marks, so it's hard to figure out how tight the spring are.

Various springs from top to bottom: Spring of a yellow / blue clutch;  Spring of an unmarked clutch;  Spring of a green clutch which is clearly longer and thinner (that is weaker than others )

 Here is a 1st and 2nd gear spring set I removed for a yellow/blue clutch set.

Stock length and thickness. 1st gear right - 2nd gear left

For some reason, I have an excess of ZA50 clutches on hand. This is great since these wear out fast especially if you use kits with these motors. While taking them apart to do some spring mods, I came to realize that 2nd gear spring is thicker and longer than the 1st gear spring (I'm speaking for the set with the yellow/blue dots on them). I never noticed this difference before because back in the day, I barely got to see a set of stock clutches. Most of the clutches I came across were already cut, switched, or modified in some way by my predecessors. Only now I get a chance to examine stock clutch setups.

My theory behind the spring size differences might be because the 1st gear clutch doesn't require a high spring tension for it to "stall" since the stock position of 1st gear is already "flipped". The 2nd gear clutch's stock position is not "flipped" so it would require the spring tension to be greater to achieve a favorable stall. Here is a excerpt from my "Puch ZA50 Clutch Rebuild Part 2: Second Gear" page explaining the theory of "stall". It explains it via "metal mass" but the theory is the same for spring tension:

Optimal location to lighten the clutch shoes is along the outer edge as shown below because it has the most "metal mass" that can be removed. Also, you want to take out the most "metal mass" toward "that side" of the linkage hole pivot point to optimize the "lightening" effect on the clutch. The outer edge of the pivot point has the most mass that produces the centrifugal force which the clutch shoes needs to generate to overcome the centripetal force created by the clutch spring. When this happens the clutch will engage. Less mass on the shoes means you need more angular velocity to generate the centrifugal force. Hence, the clutch shoes will engage at a higher RPM giving you that longer "stall".

Spring Mod #1

Here is a modification I did on my Hawaii Five-O Puch Maxi with an 70cc Autisa top end set up. I also did this on my Old School 50cc Racer bike. I cut the 2nd gear spring (thicker one) to the same length as the 1st gear spring. Then I cut the 1st gear spring equal to the length I cut from the 2nd gear (not shown). Then installed the springs back to their original clutches.

Here is a short video on the performance of my Hawaii Five-O Maxi and here is my Old School Racer Maxi.

If don't want to cut springs but need more stall, you can simply swap the springs around.







For my Gila 75cc top end set up, I opted to replace both springs with Tomos SS springs. These springs work great with no cutting required. Check out these these how-to-pages:

• Puch ZA50 Clutch Rebuild Part 1: First Gear
• Puch ZA50 Clutch Rebuild Part 2: Second Gear
• ZA50 Clutch Update

Of course with spring mods you'll naturally need my spring installation tool to make your life easier. Invest the time in making one:

Puch ZA50 Clutch Installation Tool

SHOES

There are two modification you could do to the shoes: 1) Lighten them or 2) Modify the clutch material.

1) Lightening - As mentioned in the Springs section, an example can be found in my Puch ZA50 Clutch Rebuild Part 2: Second Gear write up. Here is the same excerpt:

Optimal location to lighten the clutch shoes is along the outer edge as shown below because it has the most "metal mass" that can be removed. Also, you want to take out the most "metal mass" toward "that side" of the linkage hole pivot point to optimize the "lightening" effect on the clutch. The outer edge of the pivot point has the most mass that produces the centrifugal force which the clutch shoes needs to generate to overcome the centripetal force created by the clutch spring. When this happens the clutch will engage. Less mass on the shoes means you need more angular velocity to generate the centrifugal force. Hence, the clutch shoes will engage at a higher RPM giving you that longer "stall".

Moped Army's MopedWiki also explains it here.

2A) Modify the clutch material. This can be achieve many ways. A lot of people on the E50 motor side change the friction material of the shoe to all kinds of stuff. There are a ton threads on Moped Army about success and failures. I never attempted a material change myself. But I will in the future. I found this thread to be the more informative ones.

WEIGHT IN: Best Tomos Clutch Pad Material Clutch Lining and Bonding

2B) Another mod we did it back then was to "burn" the clutch material against the motor's clutch bell. We would "burn" the clutch by holding the bike stopped against a wall then holding down the throttle and not let the tire spin. We would hold it down for a good 5 minutes. Then change the oil out with fresh oil. This would glaze the friction material causing them to become more slippery. A slippery clutch would stall more because it slip first before it engages. This extra slip raises the engagement RPMs. It definitely changed the performance of the clutch. This is another trick I would do as a minimum to a stock ZA50 top end set up.


OIL

There are tons of discussions on the different oils to use. I stick to ATF or Type F myself.  But the right oil will give you the right slip.  Again, tons of oil debates on Moped Army on this.  Just try a search.

Happy Tuning!!!