Modern Vespa

Hi gang, If someone can shed a light? anyway too late...

You guys remember the seized 177 (150 sprint) engine from my friend a few weeks ago?
Well, cylinder was re-bored, new piston, rings, etc. he got his Vespa back this weekend, a few whatsapp messages he said he was going to drop 4% mix just to be in the safe side? I remember reading here that would make the mixture poorer, more oil = less fuel, anyway its only 2% less volume of fuel so I have doubts but I am only a curious...

Long story short, I was shocked to see his Vespa on sale a couple of ours ago ...

WTF? immediately dropped some message to know ... it seized again this weekend !?

Don't know what to think, mechanic is very skillful and experienced, has built lots of Vespa engines (including mine) and not a single problem. There must be a reason elsewhere... so one thing comes to my mind, is it remotely possible his oil is bad? a bad batch? counterfeit? Its Castrol racing 2T he is using. User error? (4% mix). I'm still to speak to him and know better but damned, this is like a curse.

Not cursed, he is foolish if he is running 4% mix.

Sounds like a bad engine build both times… maybe the mechanic is experienced with non tuned engines?

Yeah 4% isn't going to help anyone…

2.5% is enough for a basic tuned engine…

The problems will be else where…

Air leak, jetting, ignition timing…

Do you think this could be a reason, resulting in a too lean mixture?
When he told me this it was before the incident, I asked if it was a suggestion from the mechanic - he answered "- No"

What 108 said.

There are LOTS of ways to blow up a motor besides mixture. The 4% definitely leaned it out, but I have tons of questions before I'd begin to venture a guess what happened or even malign the skills of the mechanic (although he probably does play some role here).

I agree that 108 that if the mechanic doesn't know how to build tuned motors, he could easily have both done nothing "wrong," but still built a motor that was going to blow up in short order.

The carb setup is a big factor, but probably not the only factor.

How was your friend riding it? Long WOT? Stop-light racing? Start it and immediately riding it like he stole it?

Mechanical issues:

Port Timing -- Less of a factor, but I'd still like to know, if only to find out that they weren't checked.

Ignition Timing -- What's the piston crown look like? Any pitting, or just flat-out holed?

Spark Plug -- Too warm? Should be at least an 8 for a tuned motor, especially if touring.

Rework -- Did the cylinder really need boring out? You have to mess things up pretty bad on a cast iron cylinder before you can't just wash off the smeared aluminum from the piston with muriatic acid and maybe throw a quick hone on it.

Ring Gap -- was it checked and adjusted as necessary?

Air Leak -- they happen. Was the motor leak tested after assembly?

Detonation -- what Octane level was he running? What was his squish? What was his jetting?


This is just a quick list off the top of my head, but any one of these (other than maybe port timing) can cause a motor to explode under the right (wrong?) circumstances.

Sorry to hear your friend is having such a miserable experience.

At least on last 15 years he has been building and restoring engines, including tuned small frames, 177 kits. I can't believe he could have missed some of the basics that could result in this, namely piston head gap, jetting and timing? as mentioned above, maybe it was a huge mistake to mix 4% of oil, his own responsibility...

Thanks for your feedback!

My guess is he was riding "defensively" because of the previous incident. Btw as you mentioned the spark plug, he was riding a "6" (too hot) on the previous seizure, also his initiative. I'm not ruling out completely the mechanic, but bad user decisions have a cost. I don't know more details for now, namely about those build settings, but I'll report later.

He was so desolated he immediately put the Vespa to sale with original 150cc engine. We are trying to stop him, I think he will regret in a long term

Does he have a CHT?

Also, if he was too lean in the mid-range (atomizer), then riding defensively would make the problem *worse*, especially combined with the 4% mix.

He doesn't
But all this make me think if I should get one?

My doubt is, having a CHT can effectively prevent situations like this? by other words, this will always result in a abnormal temperature reading with enough time to react?

"Always" is a very strong word, but it will definitely let you know if things are getting too hot before you could diagnose it otherwise.

It will also give you insights into what your temperatures look like under "normal" circumstances, so you can recognize that something has failed before it becomes catastrophic.

I guess, sometimes a lot of time doesn't mean "good" mechanical experience…

Not that this applies with things happening your side… but there's a local guy in my area, huge respect for him, repairing large frames for +20 odd years… but hadn't put a kit on an engine till about 9-10 years ago… everything is set so it's overly rich… nothing is strobed, everything is a guess at 23deg ignition timing… still runs though.

I wouldn't get disheartened though, I'd look into the problem before selling it, I'd love to buy it from you!

Thanks again for your feedback
It makes sense

Regards

I agree with your assumptions

He is not going back, its on sale now
https://www.facebook.com/marketplace/item/554634089185771/

I have mine 177 built by the same mechanic, in my case a bigger transformation with engine ports opened, put already around 200 miles, many times WOT and no problem at all ... knock knock on wood

Doesn't seem like your friend is built for vintage vespa ownership. Not for everyone. Seems like he's more about the "show" then the "go" with the double saddle, white walls, and chrome bits on the scoot. Nice scooter though minus those pieces. But his honesty maybe in question if the ad states "Fully restored vespa in excellent condition.
Negotiable value". The value negotiation would go way down knowing the motor top end maybe shot.

The Vespa has already installed (today) the original 150cc which is in perfect condition
Yes, he's a bit picky but the Vespa was honestly well recovered, nothing hidden, engine was glass blown, everything is "too much new"

Not very funny but I was reading my own words and thinking ... "will this one blow up also?"

After two seizes truing the crank maybe a good idea to check for damages.

I can't more highly recommend the 10mm threaded CHT sensor for your BGM, especially where you ride.

Keep in mind that the numbers you will see can't be referenced to the numbers others mention as safe with a sensor at the spark plug base. Rode with both yesterday. At some points the Koso sensor read 85 degrees+

Re-bored with new piston. They didn't break it in gently and paid the price. All the technical stuff won't matter.

Let him sell it and move on.

Just reiterating that if you head down the tuning road.. you better be interested in learning how to fix things yourself cause... shit gonna break. Often.

In my short 4-5 years owning and messing with these things, I can't count how many times I nearly threw everything up on craigslist for sale out of sheer frustration. I keep them cause I like the therapy of working on them instead of sitting in front of a computer all day.

If he's not into all the effort of maintaining a tuned bike then its wasted effort trying to convince him to keep it. Sounds like his time and money is better spent enjoying other things in life.

Maybe there's some confusion here. He's talking about both his friend's (who's done) experience and how he can avoid it himself.

Sure, but he's also torn about trying to convince this friend not to sell cause he'll regret it.

Thanks Ray, Swiss, Mj…

I guess he was brain seized after the 2nd issue.

Concerning the CHT, I've added and deleted it from my wishlist a dozen times. There's one from Malossi with dual reading (temp/revs) on SC

I've promised myselft to stop this endless loop of adding gadgets to my Vespa… its like cherries, you pull one and another 6 come attached