Modern Vespa

2009 Stella 2T 150, stock except for Polini racing box exhaust and larger main jet. Engine seized while coasting at low throttle / idle to a red light, happened just a few seconds after a long full throttle climb up a bridge. I split the cases (my first time to do that) and found the bottom end of the connecting rod was completely siezed within the crank (the connecting rod does not rotate freely on the crank). It looks tight and rusty, although the rust could have happened in the 2 months time between me removing the engine and draining oil and then later splitting the cases.

I will order a new crank and connecting rod (and piston/rings too as piston has pitting on top), but what else should I replace while I am in here, and what caused this crank / connecting rod seizure? Don't want it to happen again. Do I need a special tool to install the new crank, or can I make it go in with careful taps from a mallet?

Plan to replace:
- Crank
- Connecting rod
- Piston and rings (cylinder looks smooth)
- Oil seals
- All gaskets

Anything else I should do for preventive maintenance while I am in here with cases split?

Any recommendations for best replacement crank to order for Stella 2T 150?

Serendipity strikes. To prevent yawning too much when riding, these events can be an ideal tuning opportunity

Make sure to also replace the cruciform! Also the kickstart rubbers. You also might want to rebuild the cush gear with new springs, just as a precaution. It also might be time to replace the clutch plates as well...and possibly even the clutch basket. At that point it would probably be best to buy a new fancy billet clutch.

As for crankshafts, i'm not really a fan of the Mazzy, i think the BGM are rubbish, and for heaven's sake don't even think about buying a LML. Perhaps there's a SIP Uncle Tom crank that would work for your application?

Since you need a new piston and i assume your cylinder rebored, i would tend to look at some sort of mild cylinder kit (and NOT a DR177) instead.

Replace the crank and hub bearings. FAG, SKF, etc.
You WILL need a crank puller. You can also use the tool to pull the driveshaft into the bearing.

Get this, and a propane torch if you don't already have one.
https://www.scootermercato.com/Scooter-Parts/Factory-Tools/P-LOANER-TOOLKIT-2

Warning:
There are a lot of go-faster maniacs here. If you were happy with it don't listen to them

If your getting a crankshaft, might as well get a 60mm stroke version. Not really anymore work, gives you a bit more power and flexibility with squish and cylinder timing.

If you are happy with the stock piston and cylinder, I would keep it. A 60mm crank will increase the displacement a bit, but mostly it will give you wiggle room to set timings and squish without turning it in to a tuning project.

Early crank failure and lower quality bearings are the calling cards of an otherwise well designed engine. Replacing the crank, bearings and seals will let it live up to its real potential.

How many miles are on the engine? How much do you want to spend? Do you just want to rebuild to stock, mild or wild tune?

Don't listen to him. There's no such thing as too much go-fast.

Two years and 30+ pages from now MAYBE he'll say that too

Thanks all for the replies. Yeah, there is for sure part of me that wants to creep up the performance. I can't believe how much I loved doing the exhaust upgrade from stock (I found myself trying to shift into "5th" gear, whereas before, I had to be on a flat or slight downhill to even think about using 4th gear).

But, I don't know very much about what I am doing and so if I change anything (now after doing the exhaust upgrade to the polini racing box), I would like to do maybe only 1 simple thing or nothing. I will be actually just damn happy if I can get it all back together and it runs. I am 40 years old and this is the first time I have "tuned" anything or taken apart an engine, but yeah it is super fun.

I will try to check off all of the items you guys chimed in with for routine maintenance and parts that should be replaced due to wear. Thank you.

Also, for the record, stupid or not, I just used a mallet to tap out the old crank, and it popped out without too much force. Just a couple of good whacks.

Oh yeah, and does anyone know what causes or could cause the crank-to-connecting-rod seizure? Was that my fault with jetting or mixtures? Or does that only affect seizure of the piston itself?

I don't check the gear oil regularly, but I do change it once per year. So I would be suprised if it had leaked out. Anyway, don't know what I'm talking about or even if gear oil gets into that part of the engine.

Maybe look for a local who would be willing to spend your money and has a few specialty tools already.

Dont beat yourself up over it. Its a very common issue with Stellas. Stella cranks and bearings are made in India where quality control isnt exactly the best. The two stroke oil being mixed in lubes the bearings/ crank big end bearing. Unless you forgot to add oil, i'd say its a build quality issue.

While youre in there, plan on replacing every bearing. Even the ones in the gearbox which are lubricated by the gear oil.

Bike has 7000 miles on it. I assume nothing - no maintenance probably - has ever been done on it except annual gear oil changes.

That's about normal mileage where a factory crank gives out that we have seen here when people have issues. One of mine froze spun in the case and ruined a case half.

Thanks again. No, at least I know I didn't forget to add 2 stroke oil. I do check that every time I start the bike.

I will change all of the bearing I can find, thanks.

Have a great day.

It's not the bearings per se. It's that when the lads at LML pressed the cranks together they did not leave enough clearance between the cheeks and the bearings for adequate lubrication of the bearings. You were lucky to get 7,000 miles. Mine only went around 4,500.

So is it reasonable to choose OEM parts for everything (all bearings and seals etc) here except the crank itself?

Does anyone recommend a specific brand/model of a crank that is more reliable than stock and fits the same for Stella 2T 150 (no other mods needed to install it)?

I assume due to the visible pitting on top of piston I will get a new piston too, is OEM okay for the piston?

Cylinder looks smooth to my untrained eye. No big scratches. I wasn't planning to do anything with the cylinder.

Yeah, about 5,000 miles on my Stella crank. One of the big end con rod bearings went to bits.

The local Vespa mechanic up here in PDX was replacing those cranks right and left in the mid to late 2000's. He told me that he noticed that the cranks lasted about 2500 miles on average. I've owned two different Stellas...one crank lasted 2300 miles, the other lasted 2700 miles.

Depends start pricing out what you need for a cylinder overhaul honing or boring to next oversize etc. Get a total with labor etc if you have to go oversized. What some run into is it's not much more money to go with a 177 kit, VMC seems to be making the current go to cylinder for a few people here.

I can recommend the vmc super g, inexpensive ( you may find its similar in cost to a rebore and new piston etc.) Easy to fit, only 'mod' I had to do was a little dremel to clear the starter ring gear, Other than that I just bolted it on and jetted it and it has got tons of torque, its pulling a side car in my case.

Ok, thanks for all of the feedback, so just checking my logic here before I place an order.... if I did go for the longer crank (Long-stroke Polini 60 mm), and I did the 177 VMC Super G cylinder kit, both of which are supposedly compatible with the Stella on the SIP website, all of that sounds like fun, and I see the appeal of ordering a piston and cylinder kit rather than trying to find someone to re-bore etc. I will also re-jet as best I can guess from reading around this forum. I am using the stock carb. And based on the comments I suppose I will need to learn what it means to set the timing.

What else will I find I must do?

For example, does that mean with this extra power I will need new gearing? Or the same gearing will work and I'll just be ripping higher RPMs? New clutch? Right now I have stock gearing and clutch.

Maybe someone can recommend a book on the theory of tuning a 2 stroke? How do people learn this? And how in the world did anyone learn this before the internet?

I will do as recommended new bearings and seals and some of the other random replacements with stock parts for those that tend to wear out.

But if I put in the long crank and the 177 cylinder kit and new jets, assuming I changed nothing else, is the thing going to run well?

I recently installed the Super G kit and I really like it so far. I am running a 22t clutch cog which works well with the kit and a 60mm crank. The longer crank makes it easier to set up the timings which you will have to do anyway. I replaced whatever bearings and seals LML uses with better ones.

This is the most important step with a Stella.

Thanks everyone. This should be a fun project. I'll try the VMC Super G 177 kit, the Polini long 60-mm crank, and maybe the 22 clutch plates (My clutch plates were snatchy already anyway, so new plates probably feels nice). I already have installed the polini box exhaust, which gave me a little boost already.

Otherwise, I am still running the stock carb with stock filter (though I took out the tank pre-filter) and the stock gearing, but of course will change the jets.

Seals, bearings, and gaskets will also get new, along with anything else that looks worn.

just to be clear, the 22 tooth refers to the inside geared portion of the clutch, and it's part of the primary gearset. the plates are a separate deal. you can replace the gear without the plates if you wish.

Ok. Does the 22 tooth gear on the clutch effectively "gear the bike up"... which would make sense to me with the extra power, so it can cruise a little faster in each gear, thanks again

Yes, it's an upgear. There is also a 23t clutch cog, though I'm not sure how well the vmc would pull it.

Orwell, may I ask what jets you are using, that could be a starting point for me?

Hey...Nashville! Where in town are you? I'm in East.

Jetting is still in progress, but here is a link to where I am at the moment:

That escalated quickly-Running in & jetting VMC kit (Page 40)

Also linking this thread for ongoing jetting of a VMC Super G kit.

DR177 to VMC Super G jetting advices needed.

Last edited by orwell84 on Thu, 22 Jun 2023 16:40:29 +0000; edited 1 time

Thanks all! (I'm in East Nashville too.)

Sweet. It's gone from "I'm the lone vintage scooterist" to at least one or two other bikes in the past few weeks, a China Blue P and a black Lambretta.

If you want any help or need any tools, let me know. I have All The Tools.

And we should definitely meet up in any case.

Not to mention the need for a second scooter to ride while sorting this one out. Or to stop it getting lonely.

Or the old, my wife didnt know i bought this one so ive been hiding it, it really needs to go.

"One to wrench, one to ride" is always a safe plan. More, of course, being better. Of course.

the unspoken but useful addendum being one of the herd should be a modern or at least completely stock so it is highly likely to start and run after you blow up your tuned bike jetting it

Still trying to get to that one to ride, so I can finish the 200. Maybe the stock 200 is a better candidate. Lots of trial and error trying to make a tuned bike reliable.

Give us the details on that Polini 60mm crank. There may be options better suited to the Stella's reed valve induction.

I don't think that Polini makes a flowed crank, so that'll be the Wrong Crankshaft for a Stella.

This flowed crank is the one you're going to want for a basic long stroke.

If you want to get fancy, you can run a P200 (110mm rod) bell crank with a conversion little end bearing and a spacer. This is my personal favorite LML case build and various iterations have treated me well over the years with it.

It's not included in the Fisher-Price "My First Tuned Engine" playset, however, so probably not your best choice for now.