Modern Vespa

Hi, a weekend with some emotional stuff
4 friends, 3 kitted 177cc and 1 with a standard PX200, gathered after a couple of covid years, fun and joyful, nice ride and a few beers. That was the good.

The bad, getting back home, me and one of the friends on the highway, his engine seized 12 meters in front of me, on a descent after 3 miles climbing full throttle… around 50 mph… tire smoke and a few twists, I got really scared seeing how it would evolve, avoides the rails thankfully… not a good spot to stop 1 mile aftter the same but we had one exit, engine dead no compression. It seems cylinder is broken. That was the bad

The good again nobody was injured but wtf, will try to know the cause, nod a fun moment and I don't want it to happen with me. His engine is a sprint V 2 windows late 60's, I guess cylinder is a Pinasco and he fitted recently a SI24 carb…

That would be scary, glad everyone is ok.

Was he engine braking going downhill?

Yes, we were going downhill, I can't speak for him but I was just letting go under compression, maybe 4-6% steep

Hey PSMA. Sounds like a great day, until the seize.

My understanding is the engine is lubricated by the gas/oil mixture. When going downhill if you're not giving it a little gas, or at least blipping the throttle, the engine isn't getting fuel, or lubrication, and can possibly seize from lack of lubrication.

I'm glad your friend is safe. Got any pictures of your ride?

Yeah, that makes sense. Not many pics, this one was taken on one of the stops. The Vespa that seized later is tbe grey, what a bad fortune

Beautiful!
Rough guess is your pal had a lean idle setup. The check being in the mail from the uphill ride. I gear brake with a rich idle jet quite a bit with no issues.

See if your pal would consider a CHT. Tells you a lot about your engine's health.

Happy your all ok…

Dont want to take advantage of your lucky escape but it would be interesting to get some feedback about how to prevent such a seize when coasting at idle..
Maybe some of you can give some advice to those with premix in such situations when coasting down passes at idle?
Is the only remedy to pull in the clutch and blip the throttle a few times to prevent a seize?
Would such a seize be less likely with auto-lube?

Moments ago he posted the guy that sold him the exhaust, a Polini box, said that with the 177 kit and this exhaust, if he's using the original carb mixer size 118, less lub and seized, he needed a 130… ? I don't know but I think my carb is the same dellorto SI24… knock knock on wood…

Thanks! Indeed, I also would like to learn a bit more on this. Afaik there may be many causes, knowing the most common and how to avoid them is most helpful

The CHT port on your BGM 177 affords you a close to immediate response to temperature changes, as it seats against the top of the combustion bowl.

Good to hear you are safe and sound. I will never fit another Pinasco product on a vespa. In my opinion and from experience they are crap. I am currently helping a fellow scooter owner with a Pinasco kit that runs horrible.

So one 177cc was a BGM, the other was a Pinasco and the last one?

It's a scary thing, once was enough for me and now I always cover my clutch if I'm thrashing it hard.

I saw a great tip here if you ride where you might need some compression braking and don't wanna blow up. I think it was Scooter Raton who clued me in to just wire in a convenient ignition kill switch so you can give it a bit of throttle without speeding up when you just wanna slow down.

Purely anecdotal result from an experiment last Summer (premix):

Climbed up a hill, around 1000ft, close to WOT on a hot day.
CHT 290.
Blipped the throttle a few times to cool things off.
CHT went down 5 degrees.
Gear braked all the way back down, no throttle. One eye on the Trail Tech.
CHT went down another 5 degrees

Going to do the same with the (scary-responsive) Koso sensor on a BGM 177, autolube.

Interesting…test…

Your using the Koso sensor with which temp guage? I couldnt find a Koso guage that went higher than 250 degrees celsius….

You shouldnt need to go past 150c... above 130c interesting things start to happen to engine cases...

Just asked, its also a Pinasco. The guy of the grey sprint ordered a Pinasco but it was wrong, it was a 3 window version and his sprint V is a 2 window - instead of returning he sold it to the red PX and bought a new one. I have the BGM Pro on the yellow GTR

Update: I called the mechanic, its not correct, his main jet is not the original. Mine is a 140 btw

140 Main Jet?
Seems like a big main jet ?
I thought you should be around 130?

Yes, 140. Full throttle drinks like Dionysus but I don't care, it delivers! Had to buy a 2L jerry can that fits the glove box on the GTR, by a millimeter...

Nothing like another local friend that has a modified sprint, a total beast reaches 100 mph and 14000 rpm, has a fuel pump, no gravity can feed that kart carburetor ... its a 220? kit don't know the brand. Ps: Its a PITA since even in short rides he has to be always refueling

He's crazy anyway ...

Great photo…..👍
Can you explain your set-up a little as to why you need a 140 main-jet?
Carb-Filter set up, pipe cylinder mods….

With my BGM177 I will be starting with about a 130 main for the 24 SI, but apart from a little porting and a polini box, its pretty much plug and play.

Just interested why your set-up has 10 main-jet size more?

Hi Robbie,

My knowledge on this is limited, it was the mechanic who made all the build and tuning.
I had an original 125 GTR engine and gave wings to the mechanic to do advise and do the work, I bought the parts. Engine was ported, all 3 cylinder ports and the carburetor window to crankcase, check bellow the before and after porting. These are some of the main parts I bought:

faster flow fuel tap BGM Pro
Dellorto SI24/24E
Polini racing crankshaft with extended intake
BGM Pro 177 cylinder
Polini IDM ignition, variable advance
CNC superstrong BGM Pro clutch
SIP road 3.0 exhaust

Ps: He also opened the filter air intake (holes on filter?)

Looks Really Nice….👍
Explains the needed jetting…

With ports that WIDE you are lucky that the piston rings don't fall into them when things get hot (been there, done that!)

Ouch, crossing my fingers it doesn't happen. Anyway, love these smoky, dangerous, hot, loud, dirty (did I forget something?) engines… fun factor 10!

Pretty sure Mine was from measuring distance from side to side of port, rather than around the circumference

Wow! If that engine could talk it would say FEED ME!

From what I have read here, a seize would be much less likely with auto-lube.
It is a mechanical link to the engine that runs the pump.
Therefore the amount of oil pumped is based on RPMs - not throttle position.

It's based on both, there is a cam in the pump that changes the pump action based on the throttle position, as well as the RPMs.

Here it is, RIP
Judging by the spark plug and a quick analysis of the fuel, most probably a "mix" problem, or mistake…

With all that massive porting, it could be it wants an even BIGGER main jet. I don't know , but just grasping at straws here and wondering how the plug looked. I scrolled back, scanned and saw nothing on that. Also as mentioned, maybe get a CHT so you will have some kind of normal baseline to watch for changes starting if you got potential problems heading your way. Cheap insurance, they don't cost much.

Looks like the head was leaking. Cylinder looks salvageable. Use muriatic acid to clean the melted aluminum, honing, new piston, leakdown test, proper jetting...

Hi, just to note the engine that seized was not the mine pictured above with the big ports. This is the 1st picture I post of my friends seized 177 Pinasco.

His spark plug was white and clean as a ghost, an evaporation test on recycled paper, in comparison with a normal mixed fuel, seems to have no oil at all. Everything indicates a problem with the oil itself (less likely) or with the mixture. My theory is he forgot to mix oil in his last refuel

Pinascos brags about Nicasil liner wall on the cylinder yet they fail miserably. I am currently running two Malossi iron kits and two malossi sports and not a single hiccup. I had Polini iron kit before and it was very strong. The only one that failed me was the Pinasco kit.

I'm with SaFis and V oodoo. That cylinder was killed by a too-lean atomizer combined with the head leak that you can see in the picture. He rolled off the throttle after the motor was too hot and that was all it took to kill it. I've done it more than once myself.

The good news is that the cylinder will clean right up with muriatic acid. I'd assume the piston and rings are toast, though.

Thanks guys for your feedback!

A leaking head wouldn't loose compression and power? The engine was running very well.
If it helps diagnosis I add a picture from the head (yes unfocused) ... ?

Losing compression and power was either the aluminum melting and sticking to the cylinder or freezing the rings in the piston so they couldn't flex and stay sealed.

I don't know where you're at with this, but once you get it back together, be sure to pressure test it to make sure you don't have and air leaks that will cause it to happen again.