Wild vibration

midnight_rider

midnight_rider

New Member
Hey everyone,... I have a VVM North Ridge with the 80cc motor kit, the bike is very well maintained and was hardly ridden but now I'm running the Maxxis Hookworms right off of it and it's awesome,... while riding yesterday hitting around 45 km. an hour or so , I start getting this really wild vibration... kinda freaked me out so I pull over, check to make sure all the nuts ect are tight, now.. the day before that I noticed the chain was a little loose and I raised up the back of the motor anout a 1/4 inch... do any of you think it just might be the chain buzzing like crazy ??.shft.
 
It depends on how much vibration we're talking about here. Any single cylinder 2 stroke engine is going to generate vibration. New builders will often think something is wrong especially if they have motorcycle experience and expect a smooth ride whith their motorized bicycle. Vibrations are something you learn to live with on these things unless it is so sever that things begin to fall off or break. In that case look for loose engine mounts, (eliminate any rubber you might have used to mount it) chain/sprocket/tensioner alignment. Knobby (off road, mountain bike) tires will also give you a rougher ride than smooth street/cruiser tires.
Tom
 
Everything is all tight , I have Maxxis Hookworm tires , I've had the motor on the bike for 2 months and never felt it so severe as yesterday and today...I checked it all over and it seems to be fine , but like I say... maybe it's the chain buzzing ???
 
Make sure the chain isnt hitting the gear cover case in any way. I noticed my bike doin the same thing and it was grinding against it,had to dremel out enough room for the chain to clear. goodluck
 
I found out what it is,... my rear motor mount bolts are brike off inside the casing, I drilled them out , now just have to tap new threads,... I'll lock tite the studs in this time
 
had the same problem, but when I replaced the motor mounts with grade 8 bolts the engine shattered. Broke the engine block right at the new holes I drilled and tapped. also my clutch cable mount sheared off when it all let go. The next thing I am planning is making a "cradle" for my last two stroke. Maybe I will weld a plate in the area where the motor sits and a cage around the engine so it can't slip.

I think I made the bolts two long and that gave them to much mechanical advantage.(I lengthened the spacing between the engine and the mounts to get the chain length right.) So when the mounts broke all **** was let loose.

I got this last one( a slant head 66 ) last year on a Christmas sale for a hundred bucks so after this one I think I will go with a four stroke.

mike
:-||
 
I tapped and used threaded rod and used J.B weld on the threads instead of lock tite lol, them suckers will never viberate loose , I hope they dont break or the worse is what happened to you while I'm 30 miles from home,... i'm going for a good cruise today , taking the camera to take some pics and video of it and will post them up when I get back
 
Midnight,
Use caution when installing new studs, my suggestion is NOT to loctight the studs into the motor, use grade 8.8 6mmX100 stud, if you loc-tight the studs in the motor you will play heck if they break again, trying to get them out. I have used the JB weld/stud repair my self, I applied some oil to the stud then screwed it in and packed the JB around it, all hardened up and I am still able to change the stud. Just a thought.
Mac
 
Just got my motors last friday, tore one down right away.. LOL, they use a HOLLOW crank pin, LOL! And massive full circle flyweights on the crank.. Might as well start at the root of the problems.. MAJOR alteration reequired, LOL! Best of luck with your machine!
 
talltommy46 said:
Just got my motors last friday, tore one down right away.. LOL, they use a HOLLOW crank pin, LOL! And massive full circle flyweights on the crank.. Might as well start at the root of the problems.. MAJOR alteration reequired, LOL! Best of luck with your machine!
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Thanks tommy, she's running like a champ !!!
 
Hollow crank pin is actually stronger than a solid one and helps balance out the reciprocating mass of the piston and connecting rod. Full circle flyweights are common with 2-strokes. Promotes better air flow for the intake charge and less windage loss in the crankcase. To improve it, fill in all holes with epoxy and make the overall surfaces of them as smooth as possible.
 
GearNut said:
Hollow crank pin is actually stronger than a solid one and helps balance out the reciprocating mass of the piston and connecting rod. Full circle flyweights are common with 2-strokes. Promotes better air flow for the intake charge and less windage loss in the crankcase. To improve it, fill in all holes with epoxy and make the overall surfaces of them as smooth as possible.
Click to expand...


Checked the crank on a truing stand too, woah.. Twisted right out of the box, good enough to run, but damn! Already have the crank apart, found a solid pin, gonna shave some of the massive weights, looking for primo 10K bearings, (odds are good that I'll find some) reassemble, TRUE the crank, weld it up, and rebalance. Just for starters! This is gonna be fun!
 
G'day Have you checked your chain for stretch, make sure it touches all round the rear cog [with the left hand start from the bottom of the large cog with one finger holding the chain and with your right hand follow the chain around seating it into the cog it should be a snug fit any gaps or loose parts you may need a new chain] also If you have vibration problems try lead flushing sheets [the stuff you put around skylights on the roof] for shims or spacers around the frame and or SELLEYS knead it steel polymer repair system is excellent for uneven gaps or wedged gaps on the front support but remember to put tape around frame before applying then remove after it dries
 
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