Planet Minis

argon

I've been working on an '80 z50r I picked up in rough/incomplete condition. The engine VIN is correct for an '80, but it came with an older z50a-style flat-topped Hitachi flywheel. The flywheel sits on the crankshaft taper fine but the cam doesn't contact the full length of the follower on the points (I should have paid more attention to the weird uneven wear when I changed the original points)! Strangely, an early 80's z50r flywheel I tried won't fit at all - it bottoms out on the stator plate before it seats on the crank taper.

I had a careful look at the Honda parts fiche last night, and here's what I think is going on:

1. There was a big change in z50/z50r crank/rotor/stator part numbers midway through the '79 model year, shortly after the first z50r's came out.

2. Earlier (mostly z50a) motors had flat-topped flywheels and cranks with short tapered ends (?).

3. Later (late '79-'85 z50r) motors had higher "domed" flywheels and cranks with longer tapered ends (?).

4. If so, I'm guessing that my motor has the original stator but an earlier "short" crank and matching flywheel. Flywheel and crank mate up but the stator positions the points incorrectly.

Any experts on early 6V motors out there? Am I on the right track, or is this more complicated than it already seems? Would a mid-70's vintage z50a stator plate solve my problems?

CrawlerD

I have a 79 and an 78 and an 80 I will pull the covers and take a look and let you know what I see. -D

dax

I'm not an expert, but I do know that the 6v cranks and flywheels are different depending if the bike is a three speed autoclutch or four speed man clutch.

arlindsay1992

All Z50A's had the "flat top" flywheel. 1979 Z50R is the last year of the "Flat tops." 1980 -1987 have the "domed" flywheel. 1988 to current has CDI and a totally different crank and flywheel. IDK anything about the crank taper change from 1979-1980.

argon

Ok, I did some additional measuring of my crank, stator plate, and both z50a and z50r flywheels last night, and here are a few predictions I'm hoping someone can test for me:

-- My crank (which I'm assuming is actually an early z50a crank) extends about 1.25" past the edge of the left motor case. If I'm correct, in a completely stock '80-'87 z50r motor the crank should extend nearly 1.5" past the case edge.

-- The points in my motor (which I'm assuming has the original '80 stator plate) are centered about 1/4" outboard of the motor case edge. In order to position the points correctly on the earlier flywheel, a pre-'79 (z50a) stator plate would have to locate them about 1/2" out from the motor case edge.

If these measurements hold up, I think a z50a stator plate will solve my problem.

dirtbkr188

Left side crank shafts are indeed two different lengths...


The longer crank is a mid 80's Z50R crank, the shorter one is a mid '70's Z50A.

argon

Great, thanks for confirming the first guess!

Anyone have a loose z50a (pre-'79) stator plate they'd be willing to measure up? All I really need to know is the distance between the base (interior side) of the plate and the mounting surface for the points on the opposite side, measured parallel with the crankshaft. Or, if you have a plate that's mounted, the distance between the point mounting surface and either the end of the crank or the edge of the motor case (again measured parallel with the crankshaft) would work, too.

dax

Monkey Garage Duisburg

Go to page 27 on that document, there are some dimensions And pics. In german language.