Modern Vespa

I'm sure some of you remember "Dexter"; my experimental Viet-bodge bike.
He's got a factory LML Stella 150 motor with the following mods:
-Factory Ducati 12v ignition
-Port matching
-7 spring clutch
-Polini 177 Jug
-24/24 Si carb
-SIP Road 2 exhaust
-68/23 gears
-ScooterWorks steel rims (balanced) with Continental pneumatic whitewalls

I just passed 10,000 km and was cruising at about 68Mph true (109 kph) and the motor locked up on me. I was able to hold it upright until about 35 mph (65kph) when I lost control and low sided it. The speedo was buried at 120kph+ when it happened.
No serious injuries and minor cosmetic damage to the bike which is easily fixed. Hooray for gear!

My question is what caused it to seize? I'm certain that the timing was set dead nuts on and the mixture wasn't too lean. I'll report the exact jetting tomorrow. I checked the ring gap when I installed the jug, right down the middle. I'm also certain I didn't forget the 2 stroke oil.

Is that road speed too high for that gearing with those tires? Where is ring float with a Polini 177?

I need help identifying and correcting the cause of the accident so I'll be sure it won't happen again. That s*%t sucks!!

Thanks,
-Slashy

CLUTCH, CLUTCH, CLUTCH!

You have read in the past about having a finger hovering over he clutch at all times (specially when caning it), that's purely so when this happens you simply pull the clutch in, coast along # (ie head towards the side of the road, or head somewhere safe)... when you ar nice an slow, SLOWLY let the clutch out... then the motor SHOULD start turning & likely start... re-apply the clutch, keep the revs up, with lots of on/off the throttle to "cool" the motor (ie lots o fuel), coast to a stop... keep the revs up... wait for 5min of on/off... then slowly let revs drop ... HOPEFULLY motor will keep running... cruise nice an gently to wherever is better than where you are... stop motor & fit a BIGGER JET... Then hoping it starts again tootle (happily) to your destination.
# coasting along & getting motor running again is a shitload easier than push-starting it with a seized or hard to start motor.

That's a damn good speed... had you been at it for a while?
By any chance had you just buttoned off (even a little bit) when it happened ?

Sounds like a "soft seize" to me.

My guess: jet is slightly too small, causing leaning when you button off after running at high speed.

SEB,
I'll get back to you tomorrow on the exact jetting. It didn't behave lean all, but I might be wrong.
I wasn't that far into the trip when it locked up. Maybe a mile, mile and a half (2 or 3 km). Dexter is pretty stout and accelerates briskly. Also, I wasn't driving like a lunatic when it hit. The speed limit on that section of road is 65, and I was just going fast enough to not conflict with traffic.
And yeah, I knew I was *supposed* to pull the clutch... but somehow I froze and wasn't able to do it before I lost control. I had 2 fingers over the clutch at the moment, but for whatever reason my brain never processed that command in the midst of trying to keep it upright. I failed.

*Edit* No, I hadn't throttled back before it happened. I was entering a gentle uphill at about 7/8 throttle when it siezed.

Thanks,
-Slashy

Piston pics will tell all

Twas it sieze oclock?.....ie betwen 2pm and 4pm when it occured???

..and also what SEB said...was it just after you came over a hill/rise.?

Reducing throttle after a long thrash.(esp hills)momentarily decrease petrol washing/cooling the piston.....the heat from the thrashing stage has not dissapated yet..and so the piston expands...

or the scoot rattled itself to death via an airleak from loose component...head..pipe..seal.

Piston pics will tell all

Glad you're still in one piece. I've learned that the ground is much harder than it used to be.

I'll be interested to learn what caused it too seize too.

Bluecati,
Indeed, it was. Right about 3:45. I was at the bottom of a gentle dip, just holding speed. I had cleared a hill maybe a 1/2 mile back.
I'll post some piston pics tomorrow.

Best,
-Slashy

Killo,
I'm amazed by how little damage I and the bike took. Nothing broken or sprained, only a 3 or 4 square inch patch of scuffed paint on the bike. My elbows and forearms took the brunt of it.
Helmet doesn't have a scratch. Mechanix gloves took all the punishment and I didn't get a single cut or bruise anywhere on my hands. The main damage was elbows/ right forearm. Next riding jacket will be leather with reinforcements. A winter coat is insufficient protection.
Legs took *very* minor scrapes with regular denim jeans. Jeans trashed with some embarrassment, but not even enough to warrant a band- aid.
Best,
-Slashy

What was the timing set at? I have had a CDI go bad and cause seizes due to varying timing.

What did your CHT get to? If you say 'I don't have one' then I'll say 'This is the exact situation where you need one'. When you're flat out you need one eye on the road and the other on the CHT.

Ginch,
I set the stator at 18° BTDC. This is the part where you say "this is the exact situation where I need one", 'cuz I don't have a CHT gauge. But I wasn't flat-out. I still had throttle I wasn't using at the time. In fact, I hadn't rolled the throttle 100% open at any point during the trip. So... Invest in a CHT gauge?

Best,
-Slashy

You were so lucky, could have been a lot worse for sure.

Whats your jetting? It seems like its going to be where the problem is.

Probably doesn't help any, but this video was shot 3 days before the accident. I was pacing my GF on her Rebel. I ran at 105 km/hr indicated with no problem before slowing it down to 90 kph to keep her close. Fast forward to 1:44.
I've put a lot of miles on this bike at 60- 65 MPH with no problems. It was only when I pushed 70 when I had this problem.

Best,
-Slashy

Yes. Invest in a gauge.

A thousand times this. In retrospect, I can't believe I ever used to do highway riding without a CHT. Of course, I used to have a lot more seizes than I do today, which isa combination of knowing what the heck I'm doing, but also the gauge so I can see when something is out of normal range before I get the message in the form of a seize.

It's also worth noting that air leaks can develop over time as seals wear and vibration takes its toll. If you haven't already opened it up, you should pressure test the motor before you start tearing it apart. You might be surprised how leaky the motor now is.

Glad you're ok. Seizing at that speed could've been really ugly.

Pics will tell the story, but to answer your question, that road speed shouldn't be too high for that kit with that gearing. I've done very long stretches WOT close to those speeds on a Polini 177 with much shorter gearing (67/22 primary and 8" wheels) with no problems.

You aren't running a long stroke, are you?

SoCalGuy,
Thanks, I guess I was lucky, 'cuz that definitely wasn't skill

I'm not running a long stroke, just the stock LML bottom end.

I was overly ambitious last night when the stiffness and soreness hadn't yet set in. The pics will have to wait for a while until I'm capable of wrenching.

Best,
-Slashy

I betcha that is where you will find your problem - in the bottom end. Glad you are ok.

I remember my first sieze, [cue dreamy music and soft focus] I was doing about 85 km/h two up and I remember thinking "What's that noise"? before realising it was the rear wheel locked up... finally grabbed the clutch after I'd ruined a nearly new tyre.
Having done a few hundred km that weekend with no changes between, I put it down to the fuel I just bought 4 or 5 km earlier. That was on a Pinasco 177, the CHT - which I didn't read at the time - later told me it got to 455f.

The company that sold you the bodge prob got the batch of LML bad cranks or the motors with the bad cranks from back in day real cheap.

Glad you're up and about after this incident.

Seize story time!
I had a seize going 45 mph, what still rattles me is moments before I had just waved at a kid in car next to me.
Can't imagine what would have happened with a hand off the grip.

Crank bearing seize. It was original-ish 1961 technology.
Happened so fast (as you know) that I steered with my ass to stay upright, wore through the tire/tube. Then freaked I was going to be rear ended.
When I contacted my local vintage master, he said
"Why didn't you pull the clutch?" Oh yeah, I'm a cool fighter pilot type of guy.

Glad you're around and fit to post your bit of bad luck, get it fixed and back on the road!

rowdyc,
My motor is a factory LML crate motor. I dissected the motor that came in the bodge to document all that was wrong with it, then disposed of it. That had nothing to do with the accident, as none of those parts were in the bike. Every single part of the drivetrain is either factory new or aftermarket performance.

Best,
-Slashy

"finally grabbed the clutch after I'd ruined a nearly new tyre."

"Why didn't you pull the clutch?"

All this matches my experience and my friend's experience when he seized his motor. We all know we're *supposed to* pull the clutch, but in the moment of everything going sideways we all freeze.

I think we need to acknowledge the possibility that, when push comes to shove, we will simply freeze and attempt to ride it out instead of pulling the clutch because this isn't a situation we can practice for and make second nature. We will either go down or save it, depending on speed, reflexes and pure blind luck.

We cannot rely on our ability to pull the clutch no matter how "ready" we are to do it or how much we "know" we're supposed to. Thus... proper gear, meticulous maintenance, and a CHT gauge would seem to count for more than pulling the clutch at the moment of truth.

Just a thought,
-Slashy

Unfortunately, you do become used to hovering your left hand over the clutch, and it does become indtinctive after a while.

What he said... I have two fingers on the clutch lever at all times. It becomes habit after you seized a few times,,, ...

I've now got a Zip twistie... & I STILL find myself hovering over the non-existent clutch!

Doing some online shopping, and I'm having a hard time finding a good CHT gauge. Any recommendations and sources?

Thanks,
-Slashy

Trail Tech TTO is inexpensive, easy to fit and works pretty well.

https://www.trailtech.net/tto-1

Do they make an exhaust gas temp probe? I would've thought they'd be quicker to respond than one that fits under a head nut? And possibly more accurate too.?

Or.. do the bi-metallic washer type ones work just fine?

I ordered the TrailTech with 14mm spark plug sensor.
Thanks, SoCal!
-Slashy

You can also order the 10mm version and put it under a head nut. That way it doesn't create leaks at the spark plug. It will read a bit lower, but you can dial your expectations in accordingly.

sdjohn,
Thanks, I would've had I known it was an option, but I've already placed the order. I'll look at the 10mm sensor when it comes time to order a replacement.

*EDIT* Also... I've regained full range of motion of my arms and most of the rash has stopped leaking. I think I'll be okay to start wrenching tomorrow and post some pics.


Best,
-Slashy

I've tried both and actually prefer the plug sensor. It not only gives a more accurate reading but I think it reacts faster. It's a bit of a hassle to change plugs, but it shouldn't leak if you put it on right. Use it in place of the crush washer.

Hi Slashy,
I've really enjoyed your posts, sorry to here about your mishap.
I can't remember where the spare tyre is installed on your bike but here is how I've installed my CHT gauge.
The only hole that needs to be drilled is under the foot mat to feed the wire to the spark plug.
There is an in-line connector behind the wheel so that the tyre can be changed.
The small meter bracket comes off easily if you don't want the gauge in the future.

As an ex-Kart racer not only are you looking for head temp. but also plug temp.



Ex. gas temp. is also good to know. But that is a bit more work.

Sadly I'm old enough that my unit looked like this

Glad your OK
If you don't think Dexter will care https://cedarrapids.craigslist.org/mcy/d/for-sale-1979-vespa-px-125/6550192080.html

Fatboy04,
Thanks for the kind offer, but I've already got more bikes than I can use. It'll be easy to set Dexter straight again. Parts are already on the way.

Best,
-Slashy

Did I miss the post(s) where you told us what the damage was and what caused it?

Waspmike,
No, I just haven't posted it yet.

Aside from the damage to myself and my clothing...

Trashed jug kit, presumably from overheating.
Maybe 3 square inch patch on the right cowl
lightly flat-spotted tire
Front brake lever
Chewed throttle grip
damaged right mirror mount.
damaged right crash bars (don't care about those)

Replacements for all the damaged components (except the crash bars) are either ordered or on the way... Except for the skin, which gets delivered at its own pace.
Once I ditch the last bandage, I'll be ready to start wrenching and posting pics.

Best,
-Slashy

Forget all the cosmetics

Just the facts ma'am. Just the facts.

Ok so the next thing is mixture and stuff? Which I am no use at.

waspmike,
Next step will be to take it apart and try to document what was going on when it failed. I'll use the CHT to monitor it and give me cues so I can fix it for good.

Best,
-Slashy

Have you added a little aluminum baffle to the cowl to stop the cooling air short circuiting?
There is a picture on here somewhere.