Is the 66cc supposed to shake this badly?

[moronic_kaos]

Finally got my 66cc back from the welders the other day (stripped rear mounting stud hole) & I've been using a friend's spare 48cc for the past month or so. Geez, is this thing rattly or what!

The vibrations are so bad its to the point that every time I ride it, something breaks. Today it actually shook the gas tank's studs off. I was putting around for a mile or so & looked down to see my gas tank hanging at a 90 degree angle with gas coming out all over me.

I've tried like 4 different front mount ideas, and the rear one seems fine.

First was an actual large tube adaptor that came with some other kit. Tightened it up alright but during the ride the thing suddenly started to vibrate (even more than usual) and back at the house I discovered one side of the u-bolt's threads stripped out and the nut was just hanging there

Second was a larger u-Bolt, but that didn't solve much anything

3rd was the clam shell adapters from "ThatsDax". But, the bolt heads that go into the engine would hit the frame before the adapter sat on it. I think its meant for the mountain bikes at walmart that have the oval-shaped tubes.

Now I've got the U-Bolt adapter plate mounted on the motor, with the clamping part of a chain tensioner to hold it on the other side, secured by two 1/4" bolts (the bolt holes magically decided they lined up perfectly). Just looking at it it should have 10x more holding power than a u-bolt since there's like a 3 or 4 square inch area covering the outer side of the tube, and I've pounded on the motor with a 2LB rubber mallet and it wont move. Yet it still vibrates to the point where everything on the bike wants to fall apart. While riding, the palms of your hands feels like their getting electrocuted at mid to high RPMS.

What's my next step here? Should I just chuck the thing and get a 48cc? Should I just weld the freakin' mounts onto the frame? Totally lost (and now without a fuel tank for a few days).

 

[GearNut]

I am passing on read-say. Take it for what it is worth.
From what I have learned on these forums, all of the crank assemblies are actually 48cc units. A 66cc/ 80cc engine just has a larger piston and cylinder bore.
The flywheels in the crank assembly are not balanced for the slightly larger, heavier piston.
The only true way to correct the problem is to re-balance the crank/ flywheels.
http://motorbicycling.com/showthread.php?t=4498

 

[BarelyAWake]

It's possible - but I've found that the vast majority of the vibration doesn't actually come directly from the engine unless it's 4-stroking unduly (too rich or not broken in yet) & properly mounted - you may have just gotten a lemon, but on bikes without a "rag joint" sprocket adapter or tensioner (like a shift kit) the 66cc's hellish vibration problems seem to disappear almost entirely...

I'd double check fuel/air mix & chain/wheel/sprocket/tensioner alignments and make sure you've no binding links - pick up a sprocket adaptor if ya can before writing off that motor *shrug*

 

[moronic_kaos]

I've actually got the HD axle, and I've tried starting the thing and removing the chain all together because originally I thought the vibrations were coming from the chain possibly hitting the stay.

No dice.

Guess i could try mixture again, but the throttle response seems awesome. No bogging spots.

Think it would be worth trying to replace the crank all together? The price seems decent:
Motorized Bicycles Gas Bike Engines Gas Powered Bikes Motorized Bicycle Parts

Or would I have just the same amount of chance that one's off as well.

 

[BarelyAWake]

If it shakes that bad even w/o a drive chain attached then yea... ya mighta gotten a bummer motor... after messin' with fuel/air and checkin the mix w/the plug & it comes up perfect - I'd consider getting just another engine to get yer ride on the road, then messing w/the old one... I'd prolly just keep it for spare parts. If it's an internal flaw - it may not be just the crank *shrug*

While I love to tinker, that's offset by my love to ride & the very inexpensiveness of these engines makes me wonder if it isn't a bit of "false economy" to do a full rebuild for any other reason than boredom & curiosity - which is great IF you can still ride

 

[Bikeguy Joe]

Your crank may well be pressed together backwards. I have read some things regarding this from (I think) Manic Mechanic. Maybe PM him and ask about it. If you are taking the crank out to replace it, maybe you'll only need to fix the crank you have.

 

[BarelyAWake]

Backwards crank?

While I've not heard that before... somehow I'm so not surprised

 

[Bikeguy Joe]

I read that something is pressed together 180 degrees off.

Maybe I am just having another Flowers for Algernon moment.

 

[Bikeguy Joe]

I dunno- maybe this will help.
motorbicycling.com/showthread.php?t=18988

 

[retromike3]

The thing I did was to weld two mounts on the bike frame. First I took the half round steel clamp and brass brazed it to the seat tube.( I assembled the kit first marking the clamp were it hit the seat tube then took the paint off and brazed it in place.) With a set of steel spacers and another half round clamp I bolted the motor to the welded strap. I made the spacers just the right size so that the chain length for the motor would work without a idler pulley. I then found the spot were the bell housing was close on the clutch plate to the seat tube and made a steel strip that, with the use of a longer 6mm bolt added another contact point to the engine. Its only been on the bike for a couple of miles but it seems to have held up so far without having the engine slip like it has on other occasions.

The reason for all the extra work is because my seat tube is extra wide and so when I modified the aluminum block for the seat tube(filed it wider) it broke and then the mounting bolts sheered off at the motor. So I drilled two new 6mm holes and tapped them and replaced the cheep steel threaded rod with case hardened allen bolts.

We will see how long this set up holds. (fingers crossed)

Mike

 

[moronic_kaos]

From what I have learned on these forums, all of the crank assemblies are actually 48cc units. A 66cc/ 80cc engine just has a larger piston and cylinder bore.

Alright totally missed that point. I've got a junker 48cc motor laying around, maybe I'll just pull the crank out of that and see if it's any better.

Thanks guys, now I've got something to do today.

 

[Creative Engineering]

"While riding, the palms of your hands feels like their getting electrocuted at mid to high RPMS."

Yes...and don't forget that, involuntary bowel movement, feeling that completes the whole experience.

Close Joe! It's actually those bolt-on weights.

I've had 3 engines over the past year that vibrated really bad...so bad that the bike was not rideable.

I tore those engines down, and every one had at least one of the weights clocked wrong.

The Chinese did remove some of the material from the inside of the weights. The weights can be bolted to the crank in 3 different clock positions.

I'll get some pics at the shop and post them later for clarity.

Jim

 

[foureasy]

sounds like you should buy a crank from me

here you go jim

 

[moronic_kaos]

Yes...and don't forget that, involuntary bowel movement, feeling that completes the whole experience.

At least someone knows what I'm going though. Unfortunately I wouldn't have a clue as to how press/depress the rotors.

What is the "clock position" that the weights are supposed to be at? And how would you check for good crank balance (didn't really understand the thread about home crank balancing)? I just want to be able to compare the two cranks I've got to see which is better until I've got enough money to get a crank from 4easy, which may not be for a month or so.

Kinda need the bike to get back & forth to work in the meantime. My license history is... well let's just say the minimum insurance quote I got called for almost $1500 every 6 months. The motorbike is my loophole.

 

[Creative Engineering]

Thanks foureasy!

moronic_kaos,

In the photo above you will notice 2 cresent shaped pockets that have been milled into the weights.

These pockets must be centered over the pin that attaches the connecting rod to the crankshaft.

Notice the 3 holes...there are 6 machine screws that hold the weights on. The screws are those combo #3 phillips/slotted type. The screws have been bedded with something similar to locktite. I usually drill the heads off of the screws and then use vise grips to remove the rest after the weight comes off.

If you're careful you can get the screws out with a little heat from a propane torch. Be sure to use the right screwdriver or you will strip the heads.

I've had a bunch of these apart, and I am certain that one of the weights has been attached, "clocked", so that the cresent shaped pocket is not centered over the big end of the connecting rod...this will make the engine vibrate horribly.

If you bought this engine from a reputable dealer...I would simply ask for an exchange.

Jim

 

[Bikeguy Joe]

Thanks foureasy!

moronic_kaos,

In the photo above you will notice 2 cresent shaped pockets that have been milled into the weights.


Jim

There was no photo Jim.

 

[Creative Engineering]

There was no photo Jim.

Joe,

The photo is a couple of posts up, #13 by foureasy. You may have to wait a sec for it to load if you're on dial-up service.

Jim

 

[Bikeguy Joe]

Thank you!
. . . .

 

[moronic_kaos]

Thanks foureasy!

moronic_kaos,

In the photo above you will notice 2 cresent shaped pockets that have been milled into the weights.

These pockets must be centered over the pin that attaches the connecting rod to the crankshaft.

Notice the 3 holes...there are 6 machine screws that hold the weights on. The screws are those combo #3 phillips/slotted type. The screws have been bedded with something similar to locktite. I usually drill the heads off of the screws and then use vise grips to remove the rest after the weight comes off.

If you're careful you can get the screws out with a little heat from a propane torch. Be sure to use the right screwdriver or you will strip the heads.

I've had a bunch of these apart, and I am certain that one of the weights has been attached, "clocked", so that the cresent shaped pocket is not centered over the big end of the connecting rod...this will make the engine vibrate horribly.

If you bought this engine from a reputable dealer...I would simply ask for an exchange.

Jim

Okay, no time to work on this today after all but what your saying is the weight of the thing should be lightest at the top, where the shaft is, and heaviest at the bottom, where there is no milling done.

You're also saying that someone was dumb enough to put the milled part on opposite the shaft? Wow. Not that I didn't learn that 3 minutes ago but if that's your job, it seems pretty hard to screw up.

The only question remains that if the crank should ideally be balanced that way, what makes it perform better in a higher or lower RPM band, as 4easy claims?


EDIT: I get the string idea now from http://motorbicycling.com/showthread.php?t=4498 he wanted to make it so if he placed it on to rails, the crank arm would automatically rotate to the highest point.

 

[Creative Engineering]

"Okay, no time to work on this today after all but what your saying is the weight of the thing should be lightest at the top, where the shaft is, and heaviest at the bottom, where there is no milling done."

Yes...


"You're also saying that someone was dumb enough to put the milled part on opposite the shaft? Wow. Not that I didn't learn that 3 minutes ago but if that's your job, it seems pretty hard to screw up."

...Yes..If someone failed to show the assembler the correct clock position...well you get the picture.

"The only question remains that if the crank should ideally be balanced that way, what makes it perform better in a higher or lower RPM band, as 4easy claims?"

foureasy is right!

In simplified terms, a single cylinder engine can not be truly balanced. The best that you can achieve is a slight out-of-balance condition at an RPM that is normally not used for more than a brief moment during acceleration.

Jim