Terrible vibration

bryanferro

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May 4, 2021
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Happy Valley's point is a good one.

Personally, I don't recommend anything over about 20 mph. I do think I'm in a minority on that one, though.

But I'd be scared to death to take a cheap bike up to 40 and I wouldn't feel very good about it on a top-of-the-line bike.

Though I have wondered about a very good bike with suspension and "weighted" wheels.
Getting the balance right would be the hard part. But with the mass of the wheels increased by some significant amount, things might become safer.
Watch the video of the foo' doing 75 mph. It's insane
 


bryanferro

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May 4, 2021
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I have a BGF 66cc motor on a Kulana moon dog, and like your build, once I get to about 28 MPH it starts to really vibrate bad. I normally just stay below that speed, since the motor seems to hit a "sweet spot" around 24-25 MPH. Also, running a bicycle with no suspension at 30 MPH on west Tulsa streets is a sure fire way to get thrown into the pavement.

Like you, I spent a bit of time on my first build. Took me a good week, working on it every day after work, but once I had it going it was great! The first machine didn't have the greatest brakes or tires, so I ended up putting that motor on my moon dog which was practically screaming "motorize me". I managed to do that install in about 3 hours, and that was without full use of my right hand. It gets easier after the first time... and MB's are kinda like potato chips - can't just build one!

-Mark
They don't get easier, you just learn to deal with problems faster. Some vibration is to be expected, but when you have everything, motor, bearings, crank shaft, casing, carburetor, chain alignment, bike condition and more, in balance and alignment, they run incredibly smooth. All things considered.🙂
 

bryanferro

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By all means, I don't think he meant that two 15 minute rides was a proper break-in, I think that was just to "stretch things out" a little, and ensure proper running during the break-in period. I would think two heat/cool cycles would show up any loose bolts or gaskets. BTW, the instruction sheet recommends checking head bolt torque during EVERY PRE-RIDE CHECK! I think that's a little excessive, and is just asking to have a head bolt broken off! I think 500 miles is much more realistic, although a single-gear setup is bound to rotate more times in a shorter period of time.

Also- I understand about the Harley being for high-speed runs, and you're right, it's probably not safe to ride a bicycle designed for 10 to 15 miles an hour at 40 miles an hour without some SERIOUS modifications! Probably need high-speed bearings in the wheel hubs, which would lead to extra reinforced hubs, larger spokes, tire balancing, and some frame bracing (especially at MY weight!). I just thought it would be cool to blow the doors off the neighborhood golf carts with my bicycle!!! :D

I'll keep it turned down... don't worry! Thanks for everyone's ideas/tips/concern! -Web
Go ahead, wait 500 miles. you won't see 100 before the bike is obviously not running optimal. Those head bolts are tricky little f'ers. Need to get stainless. W2TW.
 

bryanferro

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May 4, 2021
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probably not the problem -- but that break in ???



probably not the problem -- but that break in period don't sound proper
two miles isn't anything
if I was using straight miliage and no other known break in factors
((at least)) 50 miles -- closer to 100 would maybe even be better

when we used to buy small Hondas and Yamahas -- different beast
they called for 500 miles

ride that thing
I think even 10 miles and bolts need to be checked. Every heat up/ cool down cycle. You can do it carefully before the motor cools but you have to be very careful because although the metal has expanded, its also softer. So if you don't tighten them too tight so they snap as they cool because of contraction, should be golden. Anyone, does that make sense?
 

bryanferro

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Watch the video of the foo' doing 75 mph. It's insane. I think it makes sense to cover all speed ranges in break the break in period, just not to go balls out. If you don't vary the speed range you will have a " notch" in the motor, that includes a ridge in the cylinder wall that will waste the oil rings I. No time. I have a tendency to go balls out and one thing is out of alignment/balance, soon its game over. Great mounts are imperative.
 

Wrench

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I think even 10 miles and bolts need to be checked. Every heat up/ cool down cycle. You can do it carefully before the motor cools but you have to be very careful because although the metal has expanded, its also softer. So if you don't tighten them too tight so they snap as they cool because of contraction, should be golden. Anyone, does that make sense?
Never tighten the bolts when the engine is warm or hot You'll pull the threads
Always wait until the motor has cooled off before ya tighten the head bolts

Put a fan in front of the hot engine and it will cool off in under 10 mins
 

Chainlube

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Never use stainless fasteners on an engine, repeated heat cycles will make the brittle.
 
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Sidewinder Jerry

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I just finished my first motored bike build- a "Black Stallion" 66/80cc from Kings Motor Bikes. It fired right up (thanks to all here for your excellent tips in many different posts!) and ran well. For my first ride, I kept it on the down-low to help break in the motor. I probably did not exceed 15MPH, and rode around our block a couple of times (about two miles total). One poster recommended two slow and easy 15 minute rides, followed by complete cooling off before riding again. Nothing has blown up, so I guess he was on the money.

One thing I have to say, if you guys are putting these things together in 3 to 6 hours, you must really have it down to an art! It took me one 4-hour evening session and an 8 hour day session to finish this one off! But then, I'm a perfectionist, didn't have all my tools at-hand, and had continuing interruptions with phone calls, TV show breaks, meals, etc. I still need to install the chain guard, but that'll have to wait until cooler weather. And I didn't coat the inside of the gas tank. It's downright U-G-L-Y, and I plan to replace it with something nicer looking.

I could not restrain myself at the end of yesterdays ride (the second of the 15 minute rides) and cranked it wide open to see what it could do. As it built RPMs, it passed a certain range and the entire bike began vibrating like the engine was totally mis-balanced! The gas tank loosened and shifted, and I had trouble keeping my hands on the handlebars! I dropped RPMs, and the vibration went completely away. I tried doing this several times, and each time I crossed that certain RPM barrier, the bike would go into wild vibration!

I'm thinking this is -NOT- normal. I'm also wondering if it could possibly be one of the internal needle bearings being either out of tolerance or worse? Or is this normal for these engines to do this? If not, is there a fix? I guess I can restrain myself from cranking down on the throttle- it certainly moves fast enough before it hits this rough throttle range. But the vibration is so bad, it does concern me. It concerns me a LOT!

My build consists of the Black Stallion and a Wal-Mart "Cranbrook" $84.00 bicycle. Real el-cheapo transportation for around the neighborhood! It fits in my shed next to my Harley Ultra quite well! (And to think I wanted a golf cart!)

-Web
These are the guys who put them together in 6 hours lol
db805836ee76f70c21dd0d94ebff95b6.jpg
 
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