Help forum pros please!?!?

GoldenMotor.com

J_Blitsch5150

New Member
Jun 28, 2014
3
0
0
Virginia
help me forum!! very new here and to china girl engines. ive put about 120 mi. on my 66cc 2 stroke. everything is stock except i put the NT II speed carb and a low profile air filter on it. recently i am getting a very awful almost metallic vibration coming from the top end. its terrible and what was running 25-30mph wont go over 23 now. im thinking maybe its a unbalanced crank. not sure but it vibrates all the way up to where my spark plug is a blur. mounts are tight. head bolts also. this happens right at 17 mph. engine starts and runs fine up to 15 then suddenly it becomes a rattling monster. any input will do. thankszpt
 

Theon

New Member
Jan 20, 2014
1,440
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FNQ Australia
Personally, I'd pull the motor down completely, but start with making sure the motor is mounted securely, if so, take covers of motor and inspect gears and clutch.
But if it's coming from the top end, pull the head off, if you can't see anything wrong, pull the barrel off.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
I'd be looking for a crack somewhere near a motor mount, or other mount problems - that spark plug can't shake unless the whole motor is shaking.
 

CTripps

Active Member
Aug 22, 2011
1,310
1
38
Vancouver, B.C.
The first thing I'd check, actually, is the torque on the head bolts (followed by every other fastener).. because that's somewhat like how one sounded for me recently when I got distracted and neglected to finish tightening them down. It ran, but clattered at the top end terribly.

The distance you've put on it will be enough cold-warm-cold cycles to have all the fasteners streched out, many may be slightly loose now.
 

The_Aleman

Active Member
Jul 31, 2008
2,653
4
38
el People's Republik de Kalifornistan
I don't want to sound like a pessimist, but it sounds to me like the ol' "rattle of death" caused by the upper end, the piston pin needle bearings specifically. My first 66 did that back in 2006 after running around 27-30MPH. My second did it after a couple thousand miles. With a 26" wheel and the kit 44T, 26MPH is 6K RPM, 30MPH is 7K. Some chinagirls don't like to spin over 6K, as they are anything but uniform in assembly and balance from the factory.

Hopefully for you, I am merely being alarmist!
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
I agree cometely with The Aleman here, Ive had two engine do exactly what you describe here and both times it was the upper needle bearing more commonly referred to as the wrist pin bearing.

If that is the trouble you stop running that engine immediately because if that bearing comea apart you will likely trash the piston and the jug/cylinder.

use the search feature here on the forum to search out wrist pin or upper needle bearing, off the top of my head I cant remember the dimensions right now for some reason, but I order mine from bearingdirect.com which have proven to be very good quality bearings, there are other places to get them also and remember if you replace that bearing the wrist pin itself should also be replaced because if it has any flat spots on it you will just destroy the new bearing by running it on a bad wrist pin in a very short amount of time.

map
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
22
0
memphis Tn
I hate to say it, but I agree with Aleman too.
A scary noise makes me check the small rod bearing first. Then the large.
NOTHING good will come of running a worn needle bearing to failure.
 

J_Blitsch5150

New Member
Jun 28, 2014
3
0
0
Virginia
thanks guys. i appreciate the input. i have ordered a new bottom end from gasbike. that way i will have time to actually figure this out and hopefully have the opportunity to start another build.
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
be sure you'll also order a couple good quality upper bearing from bearingdirect.com or another company that sells something other than the cheap china Mar needle bearings.

best wishes with your builds.

map
 

J_Blitsch5150

New Member
Jun 28, 2014
3
0
0
Virginia
after taking my bottom end off i have found that the crank has some left to right play. not the crank arm but the entire lower crank can move left to right inside the lower assembly approximately a QUARTER TO HALF INCH! i know that cant be right so im going to break it down. fingers crossed, this will be my first. ill keep you posted.
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
22
0
memphis Tn
Most engines lately have been tight, but I have found a LOT of the older engines have a lot of sideplay in the crank. This is fairly easy to shim but I don't mkinow who sells the shims as I use parts from busted engines when I do it....
Someone here may know a source for the shim washers...
Anyone?