Modern Vespa

4th gear @ about 5000 rpms and this piece, together with the flywheel, comes loose (or breaks off) with a big bang. The flywheel cover seemed to keep the flywheel from smashing up the cowl:



This is where it should be:


This is what the rest looks like:


If you look closely, you can see the crank web has rubbed off a little metal from the conrod as well. Except for that it seems like my crank case and rotary pad might have survived this. I haven't removed the rest of the crank and inspected it yet, though.

Right before this happened, I noticed the engine started making a subtle ticking sound at idle. Then a few kilometers later it went boom!

So now I'm wondering what could have caused this? It's a Mazzuchelli 60mm crank from 2005 or 2006. It's the so called "fine heaved" one - I dunno what SIP meant by that, but it was more expensive than the non-"fine heaved".
I've probably used it for around 30-40000 km and it's been in and out the motor maybe 2 or 3 times.

The flywheel is a regular px flywheel without the starter ring and I'm using a DRT clutch.

I had exactly the same experience with a Mazz Crank about 2 years ago. I was running a 60mm mazzy crank and stock flywheel.

I quickly found out a couple of things;

A) Mazzy Cranks are made from inferior metal
B) When running a Long stroke crank and a good pipe it's a good idea to use a lightened flywheel

I shipped my Crank to AL at Hot Rod scooter and he rebuilt it and also send me a lightened flywheel - (he machines flywheels down). But since time was ticking on a race that I needed to prep for I also bought a MerCur/SIP/Worb5 60mm crank along with a Pinasco lightened flywheel.

I have had no issues with the MerCur crank, and I am in the process of putting the rebuilt Mazzy crank into another motor but I will run it with the pinasco flywheel since it's as light as you can get.

This is not true.. not all of them.. the full circle cranks are made from different metal than the non full circle, and they make the best basis for cut or bell cranks.. the non full circle have a history of failing, but not the full circles.. the metal and processing of the two are not the same!

And I bet they were hard, fast and fun kms. in which case I reckon 30-40000 kms out of a kitted motor crank is bloody good going.

Just done its time that's all.

I stay away from Mazzy cranks; period. when mine broke, it costed me a new topend and a set of cases. here is mine:



now go out and get yourself a Tamini crank.

I tend to agree about the full circle cranks. Seen several do cannonball quite nicely in both small frame and large frame.

The thing that I really find odd is how many miles they have when they go. Based on design for infinite life with repeated loading they should reduce to about 10% of design strength after 1,000,000 cycles. Even at a low 5000rpm this only gives you 3hr. From then on if it has not broken then it will not.

Only thing I can see is that there is some infrequent events that add up down the road.

fine heaved = finely balanced.

Now, why would they do that? I can't imagine there's that much to save. To me it looks like the flywheel taper bit of the crank has been machined seperatly and just stuck onto the crank web. It doesn't look like the thing is made from the same piece of metal.

I know mazzuchelli cranks had some qc issues, but I always thought that the problem was with the bearings. I don't like lightened flywheels.. besides, the crank taper and right crank web should be the same as on any other regular crank, shouldn't it? While waiting for the taxi to come pick me up, I ordered one of those new pinasco long stroke cranks. It looks good and has slightly less aggressive timing, so hopefully it should last another few years.

How did that ruin your top end? Looking at my cylinder it looks fine. I haven't had a chance to inspect the rotary pad yet, but from what I can tell it's a pretty clean cut with a minimal amount of debris. I guess it is. The crank has certainly done its job.. But this happened in the middle of nowhere. Luckily I met a farmer after a while who could store it for me and helped me call a taxi. It cost me a $100 taxi ride and an even more expensive train ticket to go get the car and a trailer and come back and pick it up. And of course I had to give that farmer a bottle of champagne as well..

I just wish there was some way of knowing before hand to avoid this happening again.

the metal is different. it's not near has hard as say Tamini. that knowledge comes from modifying the crank webs.

rebuilding mazzy's are a bit rough. lot of slop i the pin. Tamini's are a very rebuildable crank. way more precision there.

i can't remember all the details, but when that crank failed, all hell broke loose.

You know that this failure was over time. You heard the tick tick tick shortly before as the crank began to run just out of true at the end. Looking at this piece I'd say the crack started at about 10 or 11 o'clock and progressed over time across the diameter. Might have gone the other direction, starting at 4 o'clock. Gick's looks similar.

So how did it start? A tiny flaw, even a surface scratch can become a 'stress riser' when coupled with impact, repetition and fatigue and will propagate through the crystalline metal structure, like ice cracking.

Do you see Piaggio cranks go like this sometimes too? If the Mazzy cranks were of a lesser or contaminated alloy, with lower physical properties, they would be more susceptible to this problem. The heavier the flywheel(especially unbalanced), the greater the potential problem as well. You have oscillating rotational loading(speeding & slowing that flywheel) and metal fatigue is cumulative.

I like that you fixed up the friendly farmer. Skål !

Yeah, I think that's the right way to do it. He let me ride in his tractor and gave me coffee and some cakes while he also fixed me up with a taxi and took care of my scooter for a few days..

You might want to see that Motorsport is aware of this issue - they have a positive outlook on Mazzy's as far as I know

Is this the same for front axles? I have a spare front axle that has a peen mark in it from a hammer. It looks like it was made to get the bearing to seat more snugly. Should I get rid of it?

Run a better quality crank, it is as simple as that.

I'm not sure if I know that shop. Should I?


The new pinasco crank I ordered arrived this afternoon. I put in the order yesterday morning. Less than 48 hours from Bavaria to Oslo must be a new land speed record for a box of SIP parts:




Anyway, I removed the rest of the old crank and as you can see there's a little debris at the bottom of the crank case. I can't really see where it's coming from but I suspect the left side of the crank has shaved off a little of my rotary pad:


Close up of the debris:


Close up of the rotary pad:


It's completely smooth, though. I wonder if it might have "heightened" the pad so to speak.

I'm going to do a leak down test with the new crank in place anyway. What should I expect from a rotary pad in good shape? 10 seconds, 30 seconds? I've done it before, but I've forgot how long time is long enough..

If you forget where it is, I put ALL my useful charts up on Pg 3 of Random tricks, share your best little tips & shortcuts thread.

Att'n:
Please add more useful charts & diagrams there if you have a good one that's not posted yet.
Thanks

Good eye on the contact patch.. I too am about to put my motor back together after my crank broke and after I installed the crank and bolted the case halves together I could see daylight between the rotary pad and crank. When looking into the intake port toward the cylinder (the cylinder is not installed yet).

I suppose I should do a leak down test. I have never done one before, what type of oil should I use? And how long should it hold the oil in there?

I know it's gonna leak.. I just need to know how bad of a leak i can withstand..

I have spare cases laying around.. so if I fail the leak down miserably I'll port another set and build them up... and then send this set out to HRS Al to have him remachine the contact patch.

OH.. the guy above answered my question as I typed this.. so I suppose I'll test it out.

Use regular 2t. I use Motul 710. Don't use Amsoil Saber because it is a too thick viscosity.

Anything less than 3 minutes is a leak. Now, I have had zero problems with engines where the leak-down was less than 3 minutes, but ideally it should be more.

Those Pinasco cranks are awesome. They are my second favorite after the BGM.

Polini just released some new crankshafts alongside of their 60mm P210 kits.

Thanks guys. This thread had some worthy bits of knowledge... Most entertaining/informative as I waited for my dinner.

Let me know how you like the crank Magg.. I'm going to order one for a rotary build I'm doing.. I have it on good authority that those are the Best longstroke rotary cranks available at this time... It certainly looks sexy!

I just think it's feedback they might want to get - they care about these things.

The directions clearly say to run a lightened flywheel or this will happen

A larger radius between the shaft and the web would probably solve this. Given the space between the race and the web you could easily have a 1mm radius.

Yes it is. And yes, polishing & blending the flaw out will usually help. This & to relieve surface stresses is why they shot peen some racing stuff. For a front axle though, do you want to chance it?

Oh, and good catch on the lightened flywheel recommendation! Sometimes you DO need to read the instructions.

Thanks for the response. I'm going to not chance it for future use.

i ran a lightened flywheel.

I'm curious, what makes them so good? I mainly bought it because it was a pinasco and it looked good.

Now I might actually have to start looking at one better suited for a reed valve if it turns out my rotary pad is gone. Not that I've measured the height yet, but I can just about get my fingernail to catch on that rear ridge on the rotary pad. It's less than 0.5 mm high, but certainly more than 0.1mm.

The less aggressive timing on the pinasco 60mm crank vs the mazzuchelli 60mm crank - what would that do to the performance of the engine? Less spit back I suppose, but will I loose top end performance as well?

If I end up having to install a reed valve would that mean opening, welding and widening the intake by the carb or can I just swap out that tube between the carb and the case? I'm not after more performance, noise or higher rpms than I already have. I just want that nice and torquey motor (which on a good day and with a little too much air in the rear wheel would make 18 hp on a dyno).

Here's a close up of the rotary pad:


Is that ridge there supposed to be there, or could it have been the result of the crank web shaving off a little of the pad?

Thanks again for your help, guys!

I'd run rotary with that pad.

I like the Pinasco because of their high build quality. I trust their products to last. Pinasco does short production runs and with that comes a higher level of QC compared to Mazzucchelli.

I don't know the differences in their inlet timings off the top of my head, so I wouldn't be able to comment about it. Nothing Pinasco does screams high performance though.

I'm leaning towards running rotary. I've done a sort of unoffical leak down test with the new crank in place, but without the other case half bolted on. The oil stayed in there at least 2 minutes without leaking down at all while holding the flywheel side of the crank with my hand. Once I let go it drained out within a minute.

I need to fit a new flywheel bearing race on the crank before I can do a proper leak down test and I'm missing that wedge thingie you put between the crank webs to fit the race.

Sip says this about the timing: valve timing: 123°
/6° post TDC

Anyway, that old crankshaft I took out seemed to close off earlier. I guess I need to go take another picure and show you..

Right then - the proper test is done:

With oil up to about 2mm below the gasket face on the intake, it took the oil almost 10 minutes to drain out completely. I moved the crank a little in the end and that seemed to speed up the process.



5 minutes later:


10 minutes later:




So, not perfect, but ok I guess..

Thats pretty good by my standards.

Well today I finally got to try out that new crank. The inlet timing is different - I don't know how different, because I haven't measured the old crank, but the scooter feels a little different.

I pulls strong at the lower rpms. I don't know how to describe it other than that the front wheel comes off the ground when I'm not really expecting it to. At the same time it seems a little flat (or perhaps a little lean) at higher revs.

For now I've left the timing (approx 21-22 degrees btdc) and jetting the way the way I had it earlier, but I guess I need to adjust that.

Oh, and I've got less vibrations as well..

Awesome! I've got some good suggested timing for that crank that might help! I'll go through email and send it to you!
Thanks for the update Magg!