Alloha everybody ;)

So, after about 500km and lots of stress, I finally broke a ring on my engine... At the same time, I don't know if it's related, but I can see that my crankshaft flywheel cone doesn't spin perfectly centered.

Thus, I have to change crankshaft and piston.

As for the piston, I'll probably go for a GS one in 58mm (My Polini cylinder/piston were previously rebored to 57.8mm).

As for the crankshaft, I'm not sure what is the best solution...

Should I go for:

* A standard "racing" mazuchelli ?

* A flow favorable one (Worb5 or home-made) ?

* The thin cheeks full-circle fabrizi one ?

Engine is: Polini 133, ~185°/~130°, zirri silent, vForce3, KOSO 32,...

http://ktylife.free.fr/vespa/KTy133/CartersFrais%e9s1.jpg

...

Engine already hit 10000+rpm, so balancing is important. I'm concerned that maybe a worb5 or a home-made crankshaft will be more badly dynamicaly balanced compared to a standard mazuchelli... But I may be mistaken

Last question: I need a small cone crankshaft because I have an ET3 ignition unit (flywheel was lightened to 1.4kg with HP4 fans)... Is it much better to have a large cone crankshaft in terms of reliability or ... ?

Thanks for your advices,

KTy -

Bearbeitet 27. Juli 200520 Jr. von KTy

Go for a 24/25mm ETS crank, either stock or Mazzuchelli or a 20/20mm full circle Mazzuchelli crank. These will last. Others are more likely to be a time bomb. Modify any crank you purchase to make it work best with your inlet. If you won French Lottery you can also go for a 53,5mm stoked crank I'd suggest about 1,5 hp more over the whole rpm range with one of these.

And get yourself a HP4 flywheel, your engine will give you more pleasure with it

You can keep your ET3 ignition no matter which crank or flywheel you use, no problem.

53.5mm crank ?? What is that from ?

So according to you, a full circle mazzu crank with a little bit of work to smooth it and make it "flow favorable" could let enough room for the mixture to flow inside the case... That's a major concern... Thus interesting...

Btw, if I change for an ETS crank, what are my options for the ignition ?

There is HP4 flywheel for small cones crank compatible with an ET3 stator ?

Thanks Gerhard, you're so kind to me :love:

KTy -

Bearbeitet 29. Juli 200520 Jr. von KTy

There is HP4 flywheel for small cones crank compatible with an ET3 stator ?

Yes it is compatible !

MFG

HARDY

The difference between a 19/20mm and a 20/20mm is only the bearing size of the flywheel side ?

I can still use my ET3 ignition on a 20/20mm crank ?

:wasntme:

The difference between a 19/20mm and a 20/20mm is only the bearing size of the flywheel side ?

I can still use my ET3 ignition on a 20/20mm crank ?

:wasntme:

yep

Modify any crank you purchase to make it work best with your inlet.

That's what I am a bit affraid of... balancing... Moreover, on a full circle one that is suppose to be best dynamically balanced, I think it could be easy to do something wrong...

Right or not ? :heul: :plemplem:

Thanks again

The difference between a 19/20mm and a 20/20mm is only the bearing size of the flywheel side ?

I can still use my ET3 ignition on a 20/20mm crank ?

yep

???

The 19/20 crank has the slim cone (for example PV, ET3 and PKS), and the 20/20 crank the fat cone (Every PK after PKS). By the way, the 19 or 20 means not the bearing size but the size of the shaft seal.

You can keep your ET3 Ignition plate, but your ET3 Flywheel will NOT fit a 20/20 crank!

And in terms of balancing: The full circle Mazzuchelli is the worst possible in terms of balancing! It has absolutely no counterweight to the rod and piston, the rotating masses are even adding with the translational ones, not equalizing each other!

I also ride it, but I cutted it to a balancing ratio of 50% with the GS Piston.

With the original full circle it was hardly possible to let the scooter run on the sidestand, now it is almost vibrationless.

Greetings, jan

Bearbeitet 29. Juli 200520 Jr. von jannek

frankly, i have been cutting away parts from my crankshafts rather vigorously, and i never bothered with balancing them. obviously there is a point from where on it starts getting a bit vibey, but one gets away with a surprising amount of removed material without harming the engine, and without fingers going numb. in my opinion people mistake vibrations caused by engines running to rich for vibrations caused by unbalanced crankshafts rather often, so my prime concern would certainly be making the inlow as flow-efficient as possible.

53.5mm crank ?? What is that from ?

worb5, it's a 51mm crank with an 1,25mm excentric crank pin which makes for 53,5mm stroke, unfortunately this is a co$tly thing.

So according to you, a full circle mazzu crank with a little bit of work to smooth it and make it "flow favorable" could let enough room for the mixture to flow inside the case... That's a major concern... Thus interesting...

well, lets say it's lots of work

Btw, if I change for an ETS crank, what are my options for the ignition ?

any electric ignition for smallframe will work. On my Malossi engine i run ETS crank, Hp4 flywheel and ET3 ignition

There is HP4 flywheel for small cones crank compatible with an ET3 stator ?

I don't know if it's available already. But in any case, if I were you, I would NEVER run a 19mm slim cone crank.

The difference between a 19/20mm and a 20/20mm is only the bearing size of the flywheel side ?

I can still use my ET3 ignition on a 20/20mm crank ?

difference is only the inner diameter of the crank seal, bearing is the same. ET3 ignition works on every crank there is for smallframes.

That's what I am a bit affraid of... balancing... Moreover, on a full circle one that is suppose to be best dynamically balanced, I think it could be easy to do something wrong...

Right or not ?  :heul:  :plemplem:

Thanks again

well, you can't do anything really wrong, you can just build in lots of vibration which can be easily avoided if you take care to remove more material on the upper half (rod side) of the crank than on the lower half. And make sure you leave enough material arond the crank pin area, otherwise the crank will be more likely to twist.

On my Malossi engine i run ETS crank, Hp4 flywheel and ET3 ignition

I don't know if it's available already. But in any case, if I were you, I would NEVER run a 19mm slim cone crank.

@Gerhard: Your ETS crank is an original one ? Recut ? Picture ? No problem to put it on primavera (VMA2T) cases ?

Does anyone want to comment on Jannek's crank ? Could this be the best option for huge case induction ? Having a look at engine like NSR 125 and TZR 125, the crank is full-circle (with counterweight) not really "flow favorable", maybe the cheeks are quite thin...

So is it really worthless to do like Jannek ?

Another thought: Due to my engine induction design, I have quite a lot of "dead space/room" in my bottom-end engine, especially just after the reed valve. Besides that, the displacement is only 133cc, so I'm actually thinking that any kind of crank (maybe smoothed a little) will do the trick perfectly (that is, make it easy for the mixture to flow inside the bottom-end of the engine).

Thinking too much ? :grins: :puke:

KTy - :wasntme:

tzr and the like have a completely different valve angle, in their case the inlet port points upwads toward the cylinder, and the conrod is much longer. in your case it points towards the center of the crankcase, so flowing the crank is much more important simply because it actually is in the way of the gas.