How many of you have seen one of these before?

[mx250]

That's a Monty with a crank mounted clutch.

I'll give you a look at the insides as soon as I find my impact driver  .

Why did they do that? I understand that it was the intention to use it on the VB series of Monties and VB initially came out with the crank mounted clutch (but these are VA cases). Very quickly they reverted and retrospectively offered under warranty the parts to convert back to the more conventional primary drive clutch. Apparently the c/m clutch worked well as a clutch but for some reason it was reputed to make gear changes at high revs difficult.

So why did they do it in the first place? The only advantage I can think of is that the faster spinning weight of the additional clutch on the crank, compared to the primary driven reduction geared conventional clutch (spinning about a quarter slower), gave more crank shaft inertia smoothing out power delivery (aka flywheel weights) or maybe reduced vibes. Of course the same effect can be achieved with, heavier crank, flywheel weights and heavier mags (effectively the samething) but this approach would add overall weight.

So what does the 'Brains Trust'  think.

By the way, my intention at this stage is to use the c/m clutch and only to change if it is a real prob. I'm been told all the primary clutch parts bolt straight up with only the c/c cover needing changing (and I have a cover).

If you look closely at this early release publicity shot of the VB you'll notice that it has the c/m clutch. My VB should end up looking something like this.

[mx250]

By the way, my intention at this stage is to use the c/m clutch and only to change if it is a real prob. I'm been told all the primary clutch parts bolt straight up with only the c/c cover needing changing (and I have a cover).

I should add, if I have a gear change prob I think I'll keep the c/m clutch and add the lightweight PVL ign on the other end of the crank. The Monty already has a incrediablly heavy mag which would explain their reputation for being tractable (aka torquey) and suited to tight, rutted and technical tracks. Maybe the heavy mag and additional inertia of the c/m clutch was overkill and made gear changes difficult. If I went back to the same crank inertia with the fast spinning clutch and lightweight ign would have the same effect and take a kilo + out of the overall weight (and get a better ign).

[eno]

A crank mounted clutch does not slip, no primary reduction gearing means less torque applied to clutch. Others to share "fast" clutches, Twin Pipe CZ's and the humble posties CT110.

[Lozza]

Not to mention Hodaka's
I doubt it would be anything to do with crank inertia per se, it would be either be mechanical issue(ie spin to fast and break) or the more likely reason that the added inertia of the diameter of the clutch basket did something weird to the handling.Maybe made it plough on into corners, where as with the basket spinning backwards(rpm is irrelevant) that cancels some of the inertia/gyro effect of the wheels.
There is a complete science in itself with inertia and gyroscopic effects in a motorcycle this has to work with what most people's idea of 'handling' is.The 500cc GP days saw all sorts of experiments with crank rotation and inertia's(high inertia cranks are all the rage today,but not clutches ) with the Robert's KR 500 triple tested identical engines back to back and arrived at the conclusion that forward spinning cranks were faster around the track, as the rearward spinning crank lifted the front wheel on exit, but entered the corner much better and was more 'flickable'.The forward was not as good into but far superior out of the corner.

[mx250]

Others to share "fast" clutches, Twin Pipe CZ's and the humble posties CT110.

..and Yamaha yds3's, renowned for sudden 'take up'.

Thanks Eno, I'll have to think that through. Yeah reduced torque but spinning four times as fast. The spinning four times as fast would have an effect on the resistence to slip but if the two cancelled each other out is a concept I will have to think through.

The inertia effect would be there but how it all fits together, acts together and effects the clutch action, gear change and the tractablility of the engine is something I'll have to think through.

Not that its important, just like to think these things through to make sense - its my Alzhelmers Defense  

[mx250]

Thanks Lozza, the Roberts experience is interesting. I haven't thought too much of spinning inertia effecting handling (I don't often 'tip in' at 200kph+  ) but I have for a long time appreciated the effect of inertia on tractability and feel of the motor.

[mx250]

Found the impact driver  .

Interesting isn't it? Thats a much smaller clutch than I would expect as a driven clutch on a powerhouse 360 to smoke.

[Lozza]

Impact driver.....what are they.....?? Why no bigger hammer

Is that a Tarabussi piston?Have they go a 20mm or 18mm pin.Any chance of the compression height(from top of pin to timing edge of piston).

[mx250]

Impact driver.....what are they.....?? Why no bigger hammer

The greatest invention known to man if you have phillips head or straight cut screws made of cheese like material (e.g. early Yamaha).

Since the invention of hex sockets and allen keys I haven't used the impact driver in years - hence the search. Worked a treat  .

Is that a Tarabussi piston?

Mahle. Has a port cut into back just below (10mm) crown.

Have they go a 20mm or 18mm pin.Any chance of the compression height(from top of pin to timing edge of piston).

18mm pin, 22mm (approx) compression height.

[mx250]

Jared of South West Montesa emailed me the  following. I found it interesting and with his permission I post it here for your interest, education and edification  .

"Graeme,

I can give you a little more insight on the clutch mounted 360 motor, as we received three of them in 1976 and I actually raced one for a few months until the retrofit became available. 

First thing, the clutch mounted on the crank gave fantastic off idle response and torque!  There was talk at Montesa that they had planned to use a three speed transmission in the 360, but decided not to as they thought the public would reject a three speed transmission.  In Europe, they actually
ran a couple of the three speed trans clutch/crank units in some National events. 

To this day I am not convinced that the clutch/crank units were the cause of the problems that caused a recall from Montesa, as I didn't have any problem with shifting but all three of the bikes at our dealership would encounter shifter lockup about 1/2 way thru the moto's and the shifter would free up after cooling down, which would lead me to believe that there was an endplay clearance problem with the
gear shafts, (not sure which of the three)  At the time, everyone blamed it on the clutch mounting. (some Yamaha's and Hodaka's have crank mounted clutches)

So after about 6 months after the  release of the VA360,  Montesa started sending out the kit to convert back to a primary drive mounted clutch.  Without looking into the problem too deeply, we changed over the initial three bikes and there after, all the VA360's came thru with the new setup. 

Oddly enough, I have a couple of customers that have early 360's and they ride them all the time with no problem!  Go figure! 

While my  360VA was down, and Montesa was very slow in admiting there was a problem, I bought a 250 motor from Montesa (in the crate for $500) and raced it for a few months  while waiting for the fix.
 
                                                                                                                    Cheers, Jared"

[Lozza]

Thanks for that,I think the response maybe a product of that port . That engine could be a real flyer.

PS I know what an impact driver is I was just being a shit

[mx250]

Thanks for that,I think the response maybe a product of that port . .

You're referring to Jared comments about the bottom end response???

That engine could be a real flyer.

I've been lead to believe the the monty 360 is a flyer even without any trick porting. But then I have been talking mainly to Monty fans  .

[mx250]

Just removed the clutch; gee what a pleasure to work on. So easy. No fights, no rattle guns; just hand tools, a rag stuffed in the primary gears and gentle pressure, no sweat.

Eno's comments about the advantage of c/m clutches being lack of torque is reflected in the undoing of retaining nuts etc and in the size of the clutch components (e.g. clutch springs). They are tiny for a 360.

[eno]

MX250, the blog is an interesting thing, I'm impressed by the stark simplicity of what I can see of the motor, that shifter quadrant thing looks intriguing. My brother Spok had one of these bikes, Lazarus keeps giving me deja-vu as I recall him pulling it to bits. I can't remember ever riding it & I may have been hobbling around on crutches at the time when he was messin' with the Monty. Being a wounded duck at the time most probably helped give me the impression that it was indeed a scary beast, one look at the kick starter & footpegs had me running for the hills.
In true Spanish fashion it is a mans bike & not designed for whimps. Keep us posted on progress - Cheers

[mx250]

Eno, this is the first time I've laid my hands on anything Spanish, to ride or work on, and I'm finding it interesting as you. Simplicity is a word that often spings to mind when I'm working on the beast. But I am impressed.

One thing you have to keep in mind when assessing the engineering is to realise the biggest limtation to Spanish engineering was the lack of capital and the lack of choice when they choose engineering solutions; all thanks to the Franco dictatorship of the time. I think you have a passion for all thing CZ if I'm not mistaken. You can probably see the same type of engineering choices been made by the CZ engineers.

Ah, what if....