Ok so i just built this bike with a two stroke China motor. From the first time i started it it has a scraping noise that is so loud at times it is louder then the exhaust. The noise is almost constant, idol excel decel clutch pulled in or let out hot or cold it makes no difference. I am a mechanic and know engines but can't figure this out without pulling the whole thing apart. I assume its not the clutch or any parts there because the noise is constant and clutch action doesn't affect it at all. I have removed all side covers and looked for marks and found nothing. its a metal rotational noise sounds like i lasts for 3/4 rotation of the crank.
scraping noise all the time.
- Thread starter beserkr
- Start date
Some of them do that more than others. Over time it diminishes somewhat, or your ears just lose that frequency of hearing 
Basically you'd need to tear it apart and find/grind what's causing it. But you can also just keep running it while wearing earplugs!
My last 2-stroke, a GT5, was a real loud one for the first couple hundred miles. Eventually it settled in and ran great til I sold it later.
Basically you'd need to tear it apart and find/grind what's causing it. But you can also just keep running it while wearing earplugs!
My last 2-stroke, a GT5, was a real loud one for the first couple hundred miles. Eventually it settled in and ran great til I sold it later.
Well.....they don't all do it.
I have never had one make a scraping noise. Use the old screwdriver as a stethoscope and listen to various parts of the engine to determine where it's coming from before it becomes catastrophic.
Pay particular attention around the clutch area.
I have never had one make a scraping noise. Use the old screwdriver as a stethoscope and listen to various parts of the engine to determine where it's coming from before it becomes catastrophic.
Pay particular attention around the clutch area.
I tried to use my mechanics stethiscope but the engine is so small i hear it everywhere. I am a master mechanic, u would think with twenty years under my belt this little engine would be a piece of cake.lol. So i drove it another fifty miles and it seems to either be getting quieter or i am just getting used to the sound. In either case i am just going to drive it till it brakes and then get a new motor and use this one as a parts motor.
Did you put some grease on the ball bearing behind the rod that pushes the clutch in?
http://motorbicycling.com/showthread.php?t=8939
http://motorbicycling.com/showthread.php?t=8939
try the clutch cable-end stand-off that screws down onto the top of the primary drive shaft housing area... pack some bearing grease in there and see if that improves the noise.
If you fab a Large Hawaiian clutch cable mod, or buy one from Alf, you can put a 10mm grease zerk in that threaded hole and easily lube it.
The clutch cable mod is among the best... I would advise it.
Best
rc
If you fab a Large Hawaiian clutch cable mod, or buy one from Alf, you can put a 10mm grease zerk in that threaded hole and easily lube it.
The clutch cable mod is among the best... I would advise it.
Best
rc
My last china girl motor did that. At first it was only bad at higher speeds, starting at about 25 mph, but after 550 miles got a lot worse and did it all the time.
What I found when I took it apart was that the flywheel was scrapping the crankcase. The reason it could do that was because the crankshaft was so out of true.
I might have been able to save it if I would have taken it apart the first time I heard the noise. By waiting till it got worse, the motor was pretty much ruined by the time I took it apart.
The crank was so out of true that it caused the main bearings to wobble back and forth in the block, and ended up wallowing out the holes where the bearings fit. When the holes got loose enough, the crank started grinding on the cases all the time, and making a terrible racket. Now the cases are worn out.
What I found when I took it apart was that the flywheel was scrapping the crankcase. The reason it could do that was because the crankshaft was so out of true.
I might have been able to save it if I would have taken it apart the first time I heard the noise. By waiting till it got worse, the motor was pretty much ruined by the time I took it apart.
The crank was so out of true that it caused the main bearings to wobble back and forth in the block, and ended up wallowing out the holes where the bearings fit. When the holes got loose enough, the crank started grinding on the cases all the time, and making a terrible racket. Now the cases are worn out.
Not that this is the case here (usually tell by rubbing marks on cover), at times the clutch isn't seated all the way onto the shaft. If you suspect this, remove the flower nut, gear nut and take a large socket (one that just goes over the 3 pins) and drive it on.
Your crank was that bad biknut ! What did they use to grind the thing...a bench grinder LOL. Gotta love them Chinese machinist .
It had more than 0.003" runout. I checked 4 more brand new ones before I found one the only had 0.001" runout.
Im thinking its the crank rubbing on the case halves. When i mounted the motor it want large enough to go over the front down tube of the frame so i used the flat plate and u bolt. Im thinking i may have over tightened the front and back mounts and pulled the engine case halves out of alignment enough for the crank to rub? Just guessing here as there are no rub marks in the clutch cover or behind the flywheel. I have ruled out all other problems and this is what i am left with. Anyone know if the crank weights sit close to the case anywhere? Im thinking of unbolting the engine from the frame loosening the head and case half bolts and rotating the halves to see if it gets worse or better or nothing?
Yeah, the crankcases are a very tight fit around the flywheels. Another problem is the bolt on fly weights are very imprecise from one to another, and vary quite a bit in diameter.
Enough that if you had a combination of a big flyweight, and a crankshaft with a lot of runout like I had, that's all it would need to touch.
Enough that if you had a combination of a big flyweight, and a crankshaft with a lot of runout like I had, that's all it would need to touch.
Yes, the flyweights bolt on to the crankshaft. Here's a look at how crappy they are made. This one is an example of the worst one I've seen.
Biknut...
They really are comical, aren't they?
Amazing we get the service out of them that we do!
Tnx for posting the pics
rc
They really are comical, aren't they?
Amazing we get the service out of them that we do!
Tnx for posting the pics
rc
Yes. But if we go to the trouble to get a good crank, and install good bearings, a china girl motor can be a pretty good one.
I like the design very much. The clutch, overall weight, power, simplisity, ease of installation, and looks are the best. No other bicycle motor has it all.
It's just to bad the build quality is so low, but at least with a little skill that can be corrected, and for not much money.
Yes, I do agree...
'I like the design very much. The clutch, overall weight, power, simplisity, ease of installation, and looks are the best. No other bicycle motor has it all.'
The ht chinagirl is truly a wonderful universal design.
I'd like to see someplace that has the real history of it, all in one place...
I think the Cucciolo might be my favorite, but it's much more complicated, so it's not in the same class.
Huge bonus for absolute simplicity when there is a need to get from A to B with minimal funds.
Best
rc
'I like the design very much. The clutch, overall weight, power, simplisity, ease of installation, and looks are the best. No other bicycle motor has it all.'
The ht chinagirl is truly a wonderful universal design.
I'd like to see someplace that has the real history of it, all in one place...
I think the Cucciolo might be my favorite, but it's much more complicated, so it's not in the same class.
Huge bonus for absolute simplicity when there is a need to get from A to B with minimal funds.
Best
rc
