The Black Vault

...Got an old Honda 90 engine with a clutch which slips.

I'm used to adjusting it (undo 14mm nut one turn then use a flat-bladed screwdriver to turn the centre screw one turn clockwise - then anti-clockwise until it meets resistance and then clockwise an eighth to a quarter of a turn. Then tighten 14 mm locknut - being careful to keep screw in the same position).

- But this one doesn't seem to come completely right. It can be improved, but it will slip when the engine puts out max power along the road.

* Thing is I noticed the oil is pretty messy and I wanted to ask those more experienced with small engines than I to advise whether dirty oil is the main problem and if there's a good chance the clutch won't slip after an oil change.

I'm going to change the oil anyway, but not for a few days.

The alternative is to replace the clutch unit with one which I know works. I have a few old Cub engines knocking about the place, so I can get the part. Figuring out how to replace it might take a few cups of tea, but I'll get there.

Anyway ... Will a semi-automatic m/cycle clutch likely come right after an oil change? (Buggered if I want to replace the clutch if I don't have to).

mael wrote:Anyway ... Will a semi-automatic m/cycle clutch likely come right after an oil change? (Buggered if I want to replace the clutch if I don't have to).

I don’t work on engines, of any kind, but my father did when he was a lad. He worked on car engines rather than Bike so I don’t know if it will help.

I phoned him up (I’ve lost him I have no idea where he is today ) and he wants to know if you have you cleaned the crap that can get onto the clutch disks? Or the pressure plate springs may have weakened. He's not sure if changing oil will do anything.

He worked on old British Leyland cars for a while, for fun not for a job, I don’t know if the same principals apply.

Think about it.........
Read about it.........

Zen and the Art of Motorcycle Maintenance

Helmet?/Boner?

Hey Mael,

How ya doin'?

What's probably happened is that you're running an oil with Moly in it ... Moly and wet clutches don't get along too well causing the clutch to slip.

When you change your oil make sure that you don't get a brand with the "Energy Conserving" logo/label on it because it means it has Moly in it.

If that doesn't help, then chances are you need new clutch plates. If that's the case let me know and I'll point you in the right direction to get a good deal on them and tell you how to properly prepare them before you install them.

Does the oil smell like burned clutch material? If its real burned smelling, which you won't be able to miss, could be it needs new friction plates. Changing oil couldn;t hurt to try first.

If it really got hot slipping, could have warped things inside. Most clutches are several flat steel plates between flat friction plates, with a spring loaded pressure plate. Some cyntrifical clutches have spring loaded fiber plates that fling outward to contact a drum, similar to brake drums. I'm not sure what type yours is. Sounds like you adjusted it right, as long as you are sure when you locked down the nut, the stud wasn;t contacting and beginning to disengage the clutch. I don't recall exactly how they worked but, those models didn't have clutch levers or clutch cables, so is there some mechanism in the shift lever/shift shaft assembly that disengages the clutch, that is a separate adjustment? It may all work by engine RPM, or it could have a mechanical system built into the shifting mechanism.

When it comes to this kind of stuff, we can get along.

Ninor wrote:Hey Mael,

How ya doin'?

What's probably happened is that you're running an oil with Moly in it ... Moly and wet clutches don't get along too well causing the clutch to slip.

* Maybe. I changed the oil tonight and before I put the new oil in I flushed the engine out with kerosene. I don't know what oil was in it but it was black as paint.

When you change your oil make sure that you don't get a brand with the "Energy Conserving" logo/label on it because it means it has Moly in it.

* Nice tip. Thank you.

If that doesn't help, then chances are you need new clutch plates. If that's the case let me know and I'll point you in the right direction to get a good deal on them and tell you how to properly prepare them before you install them.

* This is what I need by the looks of things. the oil change didn't make any difference and also adjusted the clutch again - as well as it can be adjusted. - Springs or more likely plates are worn. Maybe I can roughen them up or find something?

* Replacing a m/cycle semi-automatic clutch is something I've never tried, but I couldn't fix my manual transmission 750 a few years back. - I had to buy new plates. - and pay for them to be put in. But that was when I had two pennies to rub together and this time I'm going to have to do it myself.

* But I won't be buying anything. I'll find something here in Japan. And most likely I'll swich some bits from a similar engine with a clutch that's good. I'm going to have to figure out how to get the clutch apart. I hope I don't need any special tools.

greeney2 wrote:Does the oil smell like burned clutch material? If its real burned smelling, which you won't be able to miss, could be it needs new friction plates. Changing oil couldn;t hurt to try first.

* No smell. It's a wet-clutch. Oil change was necessary but it did nothing for the clutch.

If it really got hot slipping, could have warped things inside.

* Not in this case I surmise. At least certainly not while I've used it, and I've been running it for over a year - but coming to think of it I was never completely happy with the clutch.

Most clutches are several flat steel plates between flat friction plates, with a spring loaded pressure plate.

* Yes. I can visualize this from memory. But I don't think I ever got the clutch assembly back in working order when I had a look at one many many years ago.

Some cyntrifical clutches have spring loaded fiber plates that fling outward to contact a drum, similar to brake drums.

* Yes. Like chainsaws and the final belt-drive of scooters. I don't think this is like that. (But I'm not absolutely sure).

I'm not sure what type yours is. Sounds like you adjusted it right, as long as you are sure when you locked down the nut, the stud wasn;t contacting and beginning to disengage the clutch. I don't recall exactly how they worked but, those models didn't have clutch levers or clutch cables, so is there some mechanism in the shift lever/shift shaft assembly that disengages the clutch, that is a separate adjustment?

* The Honda 50/70/90 is so simple. strong and reliable that I would imagine it is pretty straight-forward to service - But as I said, I haven't tried to fix it yet - beyond changing the oil.

It may all work by engine RPM, or it could have a mechanical system built into the shifting mechanism.

* I dunno. I usually ride these machines in top gear most of the time so it's a smooth shiftless ride to cruising speed. I appreciate the gearbox isn't just there for decoration, but those bikes have so much torque you don't really need to shift when on the level and can run all the time in top. (Says he with a slipping clutch).

When it comes to this kind of stuff, we can get along.

* Hmmmm.

If you're going to go with a set of used clutch plates make sure you find a set with as much pad on them as you can (bring your old set with you for comparison). Before installing them rough them up with a medium grit sandpaper followed by a finer grit (make sure not to take off too much material though, you just want to take the glaze off. What I usually do with a new set of clutch plates is soak them overnight in ATF to condition/saturate them ... since you're going with used pads you may not need to do this, but it definitely won't hurt them if you do.

It's also a good idea (a "must" actually) to get new clutch springs. If you install used ones you have no idea how much torsion they still have left in them, but with new ones you know they're up to spec. I've heard of people reusing clutch springs only to end up ruining their new clutch plates within a few hours of use ... then you're back at square one again.

What year is the bike Mael? If you tell me I'll see if I can find you a schematic of the clutch assembly and/or a shop manual.

Right ... well first off I'm going to attack an old Cub engine cluttering up my bench to see how these clutches work.

Then I'm going to ask someone who knows if the 90 CC engine's clutch doohickies are the same as for the 50. - And at the same time I'll get the price of new bits.

Then I'll decide what I'm going to do.

*

* And on a completely different note but somewhat related:- Someone has given me a Katana. Suzuki, 400 CC. I just got it today actually and rode it back to my den in the rain.

* I wanted some advice on the best way to ride it. Y'see I'm used to straight bars - I don't like 'easy-riders,' and I don't like racing style- low bars. Well the Katana has very low bars and it looks like I'm going to need a bit more meat on my arms if I'm going to be able to encourage it around corners confidently.

* I found the tyre was very low on air in the front and I haven't ridden it since I put some more in, so maybe it is easier now? I'll head out and try it again once the rain lets up a bit - We've got a large (very strong) typhoon meandering its way directly towards us at the moment so the weather's erratic.

* Do you ride these things with your knees? Someone give me some riding tips for low-sports-bikes, please.

... Just the soft tyre on the front which made it heavy. The bars are still too low for my tastes but now I don't feel it wants to continue straight when I want it to go around a corner.