Modern Buddy

So I totally burnt out my 4t with the Polini 165 kit coming back from Richmond. It was running too lean and overheating. This is the second time I would have to have it rebuilt this year.
Should I bother? I also know someone who has a couple of 150 low mileage engines. New engine or just part it out and get me a Zuma?

Modding always comes with risks. Too lean is probably the biggest problem with seizing. I've blown up more than one motor.

Personally, with a Stella 4T I would either put it back to stock and sell or part it out and sell. Not too many people looking for 4T parts so that path may take awhile.

If you want "classic" go for a Vespa P200 or PX 150. Pretty much as reliable as you can get in stock set up (ditch the OEM PX exhaust), with a 4 speed trans

I would skip the Zuma and go for a buddy. find a used Buddy 125 or 150, ride it and if you want a little more kit it to 161. Zumas are OK scooters...Byddys are pretty bullet proof.

Definitely no Buddy.
I do have an avenue for a stock engine with about 600 miles on it.
Wouldn't mind a PX200, but not too easy to find anymore.
Going modern there are lots of choices.

BuddyRaton wrote:If you want "classic" go for a Vespa P200 or PX 150.

Good advice! And if you don't want to go "classic", the usual suspects - Yamaha, Genuine, Piaggio, Honda, etc.

BuddyRaton wrote:Modding always comes with risks. Too lean is probably the biggest problem with seizing. I've blown up more than one motor.

How does running lean risk seizing an engine?
(I'm not questioning that it can.
I am wondering about how running lean can lead to this. i.e. mechanism)
Thx!

Don't you have a CHT hooked up to your engine? That has saved my neck many times when I see the temperature going up, I back off.

I do not.
It's totally my fault though, I should have been monitoring the plug.
I'm really leaning towards going for a new bike. Maybe a Kymco Like or Spade.
Todd, you had a Zuma, I saw a 125 with 4000 miles selling for 2 grand. What do you think?

I know the feeling of wanting to go modern, away from the headache of always tinkering with a Stella.

I have a 50cc roughhouse. Not Zuma.

IMO if I was to go get a modern scooter, I'd look at the SYM Fiddle III or the Lance Cabo - $2,899 new for a 179 cc EFI and manufactured by a reputable company in Taiwan. The 125cc is even cheaper.

Christophers wrote:
How does running lean risk seizing an engine?
(I'm not questioning that it can.
I am wondering about how running lean can lead to this. i.e. mechanism)
Thx!

To quote a responder to the same question out there in Internetland:

"Running an engine lean means changing the air / fuel ratio to have more air than is ideal (14.7:1 air to fuel).

... the fuel is an atomized liquid which has a cooling effect on the combustion chamber. So less fuel, less cooling effect.

...flames burn faster and hotter in the presence of more oxygen. More air relative to fuel than usual, means more oxygen than usual. So the flame burns hotter and faster than it should. Both are going to raise the temperature of the combustion chamber."

And excessive heat cooks engine components - piston heads, cylinders walls, etc., can melt and fuse. Ask me how I know!

Good description above. It's basically that fuel burns hotter the closer it gets to the stoichiometrric point where all the fuel is burned. Running richer doesn't really cool it....but it does...science can be tricky!

The important thing is that it burns hotter. The more heat the more metal expands. With enough heat the piston will expand to the point that it makes contact with the cylinder wall and comes to a sudden stop as it locks up. That's the usual way.

That's why some above suggested a cylinder head temperature gauge.

If you know the problem, why not just fix the problem? Jetting is easy.

BigDaddy SnakeOiler wrote:I do not.
It's totally my fault though, I should have been monitoring the plug.
I'm really leaning towards going for a new bike. Maybe a Kymco Like or Spade.
Todd, you had a Zuma, I saw a 125 with 4000 miles selling for 2 grand. What do you think?

If I may, BigDaddy: the Z125 is a terrific bike, operated within design limits, and solid for many years and thousands of miles.

I grew a tad impatient with the 55-ish top end, so I kitted mine to 164, with a custom pipe, forged con rod, etc. Glorious for 600 miles, when a slight lean condition (based, ex post facto, on the autopsy) caused the top end to melt down - literally.

Had retained the OEM 125 components, so we put those back - sold it for a speedier bike, and the buyer is using it to this day, six years on.

Out of curiosity, why not a buddy? If you can find a 150 blackjack, you'd outrun the stella 4t all day in stock format. Or are you fond, as I am, of shifting gears?

Buddies are too small. I don't like the tiny floorboard and the dinky seat. I've been known to do some serious road trips, I need a substantial bike.

As far as I can tell, the Like 150i beats them all in horsepower. I like the Fiddle, but the Like has it beat in price and hp.

I'm going to hang on to the Stella for a while to see if I can eventually put a new engine in it.

I am very fond of shifting gears. That may be the deciding factor on going with the Spade.

BigDaddy SnakeOiler wrote:I am very fond of shifting gears. That may be the deciding factor on going with the Spade.

My buddy John rode my Spade around Lake Erie on the 9th. About 650 miles in a little over a day and all I did was change the oil afterwards. I ran my K-Pipe again and it failed to explode for a second time.

Props for the Spade, though. Big hooligan fun in a cartoon bike. I need to put my MNNTHBX goodies on it.

BuddyRaton wrote:Good description above.

No no. I disagree. That was not a good answer. LOL
It didn't answer the question I was asking, but instead discussed why running lean runs hotter. Maybe it's a good answer to a different question but not to the question that I was asking.

BuddyRaton wrote: With enough heat the piston will expand to the point that it makes contact with the cylinder wall and comes to a sudden stop as it locks up. That's the usual way.

Ah! This is an answer to the question that I was asking. Thank you!
So is this really what often and usually seems to happen?
redhandmoto refers to piston heads, cylinder walls and melting fuses.

OK. So I will ask you "how you know", redhandmoto.
How do you know?

BuddyRaton's answer about the piston expanding makes sense why running lean could cause an engine to seize - so does an effect of expanding the cylinder walls, as you mentioned (although the piston see much more of the heat of expansion than the cylinder walls) - I could see both things contributing to seizing. I'm less clear on the heads contributing to a seized engine.

So for those that have seized an engine, what seemed to be the mechanical cause of the seizure, post-tear down? [What causes were observed in specific events?]

(BTW - Thank you both, redhandmoto and BuddyRaton, for taking a shot at a reply and sharing your experience. I already understand better what is going on when this happens.)

As a follow-up: Are some materials better at resisting thermal seizing due to running lean? Ceramic coated cylinders? Aluminum vs steel?

For the record, it didn't seize, I merely lost compression.

[quote="Christophers"]
OK. So I will ask you "how you know", redhandmoto.
How do you know?
?]

Sure - simply put, excessive heat causes engine metals to deform.

In the early days of Zuma-amping, a big bore kit (an aftermarket larger piston and cylinder, a stronger connecting rod, and an oil cooler) were installed. The original fuel injection nozzle size was believed to be able to handle delivery of sufficient atomized fuel to the enlarged combustion chamber, but it wasn't quite enough. I shoulda known.

So, while the increased power was great. a bigger combustion space with an unbalanced mix (too much air) equaled too much heat. I got away with it for a while, but under extended load, the heat was so great that the cylinder wall warped at the top, the piston struck the deformation and bent the connecting rod. The engine locked up.

Oddly, the crankshaft, bearings, and other engine structures were not harmed. The original piston, cylinder and connecting rod were re-installed. Lesson (expensive lesson) learned.

In other words, a totally bonehead error: I screwed up, creating a gross overheating condition by increasing the engine size with an insufficient increase in cooling fuel. Ouch.

You like to tour, right? The Spade is a decent little adventure bike. Dodge Rider on Youtube did 1000mi in 24hrs on his. The Like 150i would be good too if you wanted to stick with a scooter. The Like now comes standard with ABS which is a plus.

I am more familiar with 2T seizes and holed pistons. Yes the cylinder will expand...except at the points where the four cylinder studs are located. The rest will expand and you can get a classic four point heat seize.

Yeah...rejetting is easy...pull out a jet screw another in ...no big deal.

Correctly jetting a kitted and modified motor so you get optimum performance within acceptable limits...not so much. I mean...why bother kitting if you're not going to dial it in?

Of course I have already decided which carb I am going to use (ok,,,sometimes start with). I break top ends in very rich for the first 500 (iron) to 1,000 (aluminum nicasil lined) miles. Then it's time for some real jetting work.

Dell'Orto PHBH/L..what needle, what slide cut, what main, which clip position, air/ fuel mix.

Dell'Orto SI..What size? 20/20, 24/24, 26/26/ BGM26/26, 28/28?, what pilot jet, what size main jet, what size mixer, slide, air/mix.

On a 2T it will be running the best it ever has...right before it locks up at 65 mph.

And yeah...over heating can do much other damage, there's a lot more going on in a 4T than 2T. There is no way to definitively know without taking the motor apart...well unless the rod is sticking out the side of the case or something!

redhandmoto wrote:

Christophers wrote: OK. So I will ask you "how you know", redhandmoto.
How do you know?
?

Sure - [...] the cylinder wall warped at the top, the piston struck the deformation and bent the connecting rod. The engine locked up.

Oddly, the crankshaft, bearings, and other engine structures were not harmed. The original piston, cylinder and connecting rod were re-installed. Lesson (expensive lesson) learned.

In other words, a totally bonehead error: I screwed up, creating a gross overheating condition by increasing the engine size with an insufficient increase in cooling fuel. Ouch.

Great answer! Thanks.
This is exactly the type of information I was interested in learning!

It's also interesting that the expanded cylinder wall returned to normal after it cooled and was reusable.

dasscooter wrote: The Like 150i would be good too if you wanted to stick with a scooter. The Like now comes standard with ABS which is a plus.

Took a test ride tonight, not a bad little machine. Quick as hell.

The basic problem is I'm not mindful enough to ride a highly modified machine.

BuddyRaton wrote:I am more familiar with 2T seizes and holed pistons. Yes the cylinder will expand...except at the points where the four cylinder studs are located. The rest will expand and you can get a classic four point heat seize.

Also very good information!

"Holed pistons?" where the crank punches through a seized piston?

Christophers wrote:
It's also interesting that the expanded cylinder wall returned to normal after it cooled and was reusable.

Ah, you may be thinking of those instances where a two-stroke engine will "soft-seize", those parts temporarily expanding under heat, but returning to their correct dimensions when cooled.

Not the case here - this was a catastrophic failure of a four-stroke engine: the cylinder, piston, and connecting rod that were destroyed were the major components of the Big Bore "kit" - I had replaced the original 125cc factory parts with those to increase the CCs, to develop more power.

The cylinder didn't just expand under heat - the top edge of it deformed, melted, slagged down the side. The piston was still moving and struck the now-canted cylinder head, and the connecting rod it drove was bent. Lucky that the connecting rod did not break free and burst through the side - the famous "thrown rod."

On detailed examination, it looked like the very top of the cylinder wall may have burned through first.

Somehow, the engine block and the cam shaft and its bearings survived without damage. The ruined parts were removed, and the original factory 125cc cylinder, piston and the factory con rod were re-installed. The engine then lived again in its original 125cc state. That's a testament to Yamaha.

redhandmoto wrote:
Ah, you may be thinking of those instances where a two-stroke engine will "soft-seize", those parts temporarily expanding under heat, but returning to their correct dimensions when cooled.

Not the case here - this was a catastrophic failure of a four-stroke engine: the cylinder, piston, and connecting rod that were destroyed were the major components of the Big Bore "kit" - I had replaced the original 125cc factory parts with those to increase the CCs, to develop more power.

The cylinder didn't just expand under heat - the top edge of it deformed, melted, slagged down the side. The piston was still moving and struck the now-canted cylinder head, and the connecting rod it drove was bent. Lucky that the connecting rod did not break free and burst through the side - the famous "thrown rod."

On detailed examination, it looked like the very top of the cylinder wall may have burned through first.

Somehow, the engine block and the cam shaft and its bearings survived without damage. The ruined parts were removed, and the original factory 125cc cylinder, piston and the factory con rod were re-installed. The engine then lived again in its original 125cc state. That's a testament to Yamaha.

I mis-read your earlier post. Now I get it.
When you said "original" you were referring to the OEM cylinder, piston and connecting rod - not the big bore aftermarket parts that experienced the engine seize, as I had understood.

In was worth it to have mis-read your post for the detailed clarification that came as a follow-up!! Very very interesting!

Given the catastrophic failure it is surprising that the crank shaft and barring and other structures were not damaged.

My big bore engine Buddy 125 is in the shop now - I think with an impending barring failure. Full teardown tomorrow.

FWIW - I do have a cylinder head temperature gauge on my bike and never observed an overheating problem, despite running the bike HARD.
(I also have pressure-side aftermarket (NCY) oil coiler on the bike.)

I also run a Buddy I kitted to 161. I also opened the airbox, fitted a bigger carb instead of rejetting the OEM and put on a pipe. No problems there.

Christophers wrote:

BuddyRaton wrote:I am more familiar with 2T seizes and holed pistons. Yes the cylinder will expand...except at the points where the four cylinder studs are located. The rest will expand and you can get a classic four point heat seize.

Also very good information!

"Holed pistons?" where the crank punches through a seized piston?

Most of the time the crank will survive as it doesn't punch a hole. A holed piston generally happens from incorrect timing. The localized high heat will actually melt a hole through the top of the piston. I have one around somewhere (I didn't do that one!) I'll see if I can find it and take a photo. One of the reasons I run high octane in modified motors with higher compression.

BigDaddy SnakeOiler wrote:I am very fond of shifting gears. That may be the deciding factor on going with the Spade.

And then there is the new Honda Monkey. Don't know how tall you are but the Monkey seat is a couple inches higher than the Spade and may make you feel a little less like riding a clown bike. And what is more reliable than a Honda?

https://powersports.honda.com/2019/monkey.aspx

I thought the Monkey bike was a tiny thing, like my first Honda 50 when I was 10.

And if I wanted a Honda, I'd get a new Super Cub.

BigDaddy SnakeOiler wrote:I thought the Monkey bike was a tiny thing, like my first Honda 50 when I was 10.

Nope, the new one is quite a bit larger. In this photo you can see the one from 30 years ago to the right.

BigDaddy SnakeOiler wrote:And if I wanted a Honda, I'd get a new Super Cub.

I am tempted by that one as well, but it is not really a shifty - it has a left side foot shift and an auto centrifugal clutch.

Dooglas wrote:I am tempted by that one as well, but it is not really a shifty - it has a left side foot shift and an auto centrifugal clutch.

How does that work exactly?
(How does that work in practice?)
Does one have real gears but no clutch lever?
Normal up/down toe shifting, like on a motorcycle, but without the need (or ability) to actuate the clutch?

I guess I found the answer I was looking for by taking a peek at the Honda webpage:

The Super Cub features a four-speed semi-automatic transmission that you shift with your left foot, like a traditional motorcycle. But here’s the unique feature: there’s no clutch to worry about—you just toe and go.

Read more at https://powersports.honda.com/2019/supe ... MmWFTvK.99

I'm test riding an SMAX on Saturday. I don't really like the style, but it's got mas horses and a flat floor.

Dooglas wrote:

BigDaddy SnakeOiler wrote:And if I wanted a Honda, I'd get a new Super Cub.

I am tempted by that one as well, but it is not really a shifty - it has a left side foot shift and an auto centrifugal clutch.

Yeah...but they are so much fun!

Time for a Bajaj Cheetak. Do it!

Stanza wrote:Time for a Bajaj Cheetak. Do it!

Hah - a Stella 4T with even less parts availability! Can't go wrong there

Stanza wrote:Time for a Bajaj Cheetak. Do it!

I thought about it, there's one for sale right up the street at Philly Scooters.

Scomadi has a prototype 250cc 4T six speed twist shift. Ride report in the latest Classic Scooterist.

That would be a tempting scooter if it ever makes it into production and to the US!

I know. It's sad that my options are so limited compared to the rest of the world. I would love a Scomodi, or even a Royal Alloy.

Christophers wrote: How does that work exactly?
(How does that work in practice?)
Does one have real gears but no clutch lever?
Normal up/down toe shifting, like on a motorcycle, but without the need (or ability) to actuate the clutch?

I've seen two solutions for the semi-auto in that engine configuration.

The old Cub used a wet clutch with a set of roller weights to engage it. You could shift to 1st from idle because the clutch was disengaged. When you revved the motor, the rollers slung outward, compressed the clutch and moved crank power to the gearbox. When under way, pushing on the shift pedal did two things: 1) It moved the shift selector arm to upshift/downshift to the desired gear, and 2), it moved an arm that twisted a wobble plate that sat between the crankcase cover and the clutch. This plate mad a matching plate resting against the clutch, and three large ball bearings separating them. When the plate twisted, it pressed on the ball bearings, which in turn pressed down on the clutch, causing it to release. The clutch stayed released as long as you kept pressing the pedal. The screw and nut often seen on the outside of the crankcase on semi-auto bikes is there to set the preload on the wobble plate and bearing assembly.

The other solution came on my K-Pipe. The clutch plate assembly is paired with a three-shoe wet centrifugal clutch, which looks a lot like the driven clutch in a scooter CVT, It's declutched at idle, so you can shift to first without using the clutch lever. Once the engine spins up, the centrifugal clutch expands and locks up with the clutch bell. Shifts between higher gears should be done with the clutch lever. You can theoretically shift without the pulling the clutch lever, but it doesn't shift very softly and it will be hard on the Chinesium parts of your drivetrain. If you insist on shifting clutchless, make sure the engine is running at low RPMs to minimize shock loads on the cush drive and gearbox.

Dooglas wrote: And then there is the new Honda Monkey. Don't know how tall you are but the Monkey seat is a couple inches higher than the Spade and may make you feel a little less like riding a clown bike. And what is more reliable than a Honda?

https://powersports.honda.com/2019/monkey.aspx

Three observations:

1) Kymco built bikes for Honda from 1963 through 1989. It seems like they learned a bit from Big Red during that period.

2) I put my 6'4" co-worker on my Spade and had him take it for a ride. He normally rides a KLR650 since everything else is too small. He had a blast riding it, though he did look a little like a circus bear on a tricycle.

3) I let my buddy John, who is 6'2" and not a small dude, ride my Spade in the Lake Erie Loop earlier this month when his "red" bike got funky at the last moment. It ran like a watch at near-WOT for 650 miles and gave him no comfort issues or mechanical problems.

I know Kymco =/= Honda, but please don't knock 'em until you try 'em. At least sample the "Made in Taiwan" ones...the PRC ones aren't *quite* as bulletproof.

az_slynch wrote:

Christophers wrote: How does that work exactly?
(How does that work in practice?)
Does one have real gears but no clutch lever?
Normal up/down toe shifting, like on a motorcycle, but without the need (or ability) to actuate the clutch?

I've seen two solutions for the semi-auto in that engine configuration.

The old Cub used a wet clutch with a set of roller weights to engage it. You could shift to 1st from idle because the clutch was disengaged. When you revved the motor, the rollers slung outward, compressed the clutch and moved crank power to the gearbox. When under way, pushing on the shift pedal did two things: 1) It moved the shift selector arm to upshift/downshift to the desired gear, and 2), it moved an arm that twisted a wobble plate that sat between the crankcase cover and the clutch. This plate mad a matching plate resting against the clutch, and three large ball bearings separating them. When the plate twisted, it pressed on the ball bearings, which in turn pressed down on the clutch, causing it to release. The clutch stayed released as long as you kept pressing the pedal. The screw and nut often seen on the outside of the crankcase on semi-auto bikes is there to set the preload on the wobble plate and bearing assembly.

The other solution came on my K-Pipe. The clutch plate assembly is paired with a three-shoe wet centrifugal clutch, which looks a lot like the driven clutch in a scooter CVT, It's declutched at idle, so you can shift to first without using the clutch lever. Once the engine spins up, the centrifugal clutch expands and locks up with the clutch bell. Shifts between higher gears should be done with the clutch lever. You can theoretically shift without the pulling the clutch lever, but it doesn't shift very softly and it will be hard on the Chinesium parts of your drivetrain. If you insist on shifting clutchless, make sure the engine is running at low RPMs to minimize shock loads on the cush drive and gearbox.

My K-Pipe came in last week and I'm really digging it so far. I've had both semi-auto and manual horizontal Honda engines and it's almost the best of both worlds. My brain still won't let me come to a stop without pulling the clutch lever, though. The auto clutch comes in handy when sitting at a light.

@bigdaddysnakeoiler - I haven't been on here in a while. What kind of bike/scooter did you end up getting? Sorry to hear your Stella finally gave up the ghost, but I appreciated your advice about avoiding mods if you want longevity. I was just about to start derestricting when I read that, so I think I'll hold off...

Also, anyone have thoughts on the new Genuine G400C?

NCJ8 wrote:Also, anyone have thoughts on the new Genuine G400C?

Sure, looks like a great bike if it EVER gets here (see the long running thread under "General Discussion"). But, I don't understand weighing the pros and cons of a Stella 4T versus a Genuine G400C. Two different universes.

I know I'm late to the party but after roughly 17k miles on a stock 4T (the speedo cable bit the dust at 12k and I never fixed it) that I bought new, I sold it figuring that it didn't have much life left and replaced it with a well-kept 2005 PX 150 with 7500 miles on it last year.

What a difference!

I immediately replaced the stock exhaust with a SIP Road and carb rejet. Not only does it absolutely slaughter my 4T performance-wise, especially climbing San Francisco hills and/or with a passenger, but I can't believe how much more reliable it has been than the Stella. I constantly had problems with the 4T big and small, and the PX has been dead reliable for almost 2000 miles now. Basically this feels like what I wanted with the Stella- all the great things about a classic scoot (shifty, metal body), but with modern reliability. Oh, and the P-Series two-stroke is the VW Beetle of the scootering world. Parts are everywhere.

Just saying, if you still want a classic-style scoot, there are plenty of good P Series Vespas around that will serve you very well.

Just wait till you get bit by the P200 bug!
Power, top end, reliability, classic style and sound.
Mine is stock with a 226 pipe, rejet and it shits and gets.
Good luck

A 200cc motor seems like an option for a blown 4t motor. Ordering from a SIP dealer like Scooter Mercato would save in shipping.

https://www.sip-scootershop.com/en/prod ... +_21000010