Honda 4-takt forum

Hello from France,

Please tell me if you prefer french or english text as I am sorry to be not very easy with Nederlands ?

I finished to restore a very rare Z50M French type, with a frame number under 100, so one of the very first produced in 1967.

Some pics :








The engine is running very well, it has only 4500 km and I totally dismantled it with new seals and complete metrology.

But I have a problem with the clutch and after many long thoughts I don't understand why !!!

The problem :

- when stationary, the kick engages the engine correctly, OK
- at idle, the clutch is disengaged, OK
- by accelerating the clutch engages, OK
- but when changing gear the clutch does not disengage

I verified the assembly of the clutch and selector control system, all is OK.
The clutch clearance is correctly adjusted and gear selector control works.

So it's a great mistery for me, do you have any idea ?

I can publish many pictures of the clutch if you want, I totally dismantled it but found nothing abnormal ...

Thanks in advance for the help

The pics when dismantling the clutch :

I would like to help you, but I'm new to the Honda 4-strokes and I've only worked on manual clutch gearboxes.

The experts on this forum will give you advice for sure.

Nice bike and nice pictures by the way!

Hello Patrick,

that's strange.
With the engine turned off, and you are sitting on the moped, engage first gear, press and hold the gear lever down, then the clutch should release the moped as you push the moped back and forth.
Then the clutch works well together with your other findings.

You have the right oil? At least as Honda prescribed in the 1960s. If you want to use more modern oil, then at least use JASO MA1. Of course, with the correct viscosity that Honda prescribes.

And try again to find the perfect adjustment with the adjuster on the clutch crankcase outside the right side of the engine block.


Gr. Wim.

Thanks Wim !

Very strange in fact ...

As you know the clutch on Z50M is centrifugal and also controlled by the selector when changing gear.

So when the engine is turned off the clutch is disengaged, even if I engage first gear, press and hold the gear lever down.

I use Motul 3000 20W50 Jaso MA2 as the bike is used only in summer, no problem ...

The adjuster on the clutch crankcase is perfectly adjusted, I restored many Honda with this type of centrifugal clutch and never had problems ! I really don't understand why the changing gear selector does not disengage the clutch when it is centrifugaly engaged ...

Could it be that a clutch plate is bent? I've had that before with a manual clutch that it didn't disengage

Thanks butt head,

Plates were inspected and were perfectly plane, and centrifugal clutch is fully operating.

Another information : when pushing on the outer clutch it presses in perfectly, releasing the clutch plates, which is what happens when you change gear :

What happens when you adjust the screw to press the clutch a little bit? From the top of my head I say clockwise. You feel tension building up in the screw, then lock it and then try the kickstart. Can you get it to slip? It should slip.
If it does slip, adjust the screw so that it just avoids tension and try kicking again. It shouldn't slip. Now try to shift.

Sidenote: Please replace the generic bolt of the oilpump for OEM, don't cheap out (or get lazy) on a build like this. And add the copper washer under the headbolt that has the oilguide.

Thanks gerbrandicus, I'll try to do what you say, adjust the screw (anti-clockwise) and press the clutch a little bit, and try to kick.

About your sidenote : all the bolts fixing the oilpump are original, this engine never was open before, a picture when I opened it :




Sorry but I don't understand what is the copper washer under the headbolt that has the oilguide, this one ?

Who knew!

I think he means #17

ildert schreef: ↑03 okt 2024 14:46 Who knew!

Whoops, my apologies. Never seen that.
It looks like Z50A also has the new type pump that has these bolts. There might be others. You just keep learning with these old Honda's.

Thanks gebrandicus, no problem, we learn every day about our beloved Monkeys !

And you were right about the copper washer under the headbolt, I corrected its position

So, I already have my clutch problem, do you think this clutch could be fitted on my Z50M : https://www.ebay.fr/itm/315520552551 ? I asked the seller but no answer ...

just buy the kitaco or takegawa version. They might fit, sometimes the sprocket on the primary shaft is different.
I used this clutch several times in the past on higher cc engines.

I wouldn't just swap out the entire clutch. There's a problem, you're a man, you solve problems!
In stead of going around the problem.
What happened when you adjusted the screw? And can you adjust it so that the clutch slips when you kickstart?