a few problems

chaser said:

hey i have been on and off searching this fourm, this is my first post on here though. i have a few problems with my 80cc kit that i put on my mountain bike.

it vibrates ALOT, everything is tightened down well and i check everything before i ride. it usually helps to take the slack out of my chain. is alot of vibration normal? (ie. its uncomfortable to hold the handle bars at higher speeds)

one of the nuts for my exhaust came loose today so i tightened it and the bolt came out of the engine block?!!?! how do i fix this?

my chain is wearing down that little plastic wheel that keeps tension on my chain... do i need to buy a new one?

my bike feels like it is losing alot of top end power, and i think it is linked to my exhaust. (i routed my exhaust myself so it would fit my bike.) i guess my question here would be, if my bike gets up into higher rpm and then it starts vibrating wildly and not feeling like its reaching its full speed, do i have too much or too little back pressure with my exhaust?.... i guess im just not sure how to tune my exhaust so it just works haha

someone try to make sense of everything i said plz

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Make sure your chain is not too tight, about 3/4" of slack is good. Your tensioner problem can be addressed several ways, one of which is to replace it with a skateboard wheel.

The vibration problem could be anything from the "natural" vibrations these china engine put out, to you frame type.

As for the exhaust stud, you'll have to heli-coil it, or tap it out to the next larger size and use the appropriate bolt.

put rubber behind engine mounts,it helps a lot.
replace the tensioner wheel before it wears out,but they last a while.
and for the muffler bolt,did it break off inside the block or just come loose and fall out?
if it fell out use loctite,if it broke off do what bikeguy joe said to do.

Do you have room on your chain to remove a link, or remove a link then get a half-link to get ride of the tensioner. My motor vibrated alot too but after I trimmed the piston skirt (I believe the small amount of metal i took off was enough to balance the crank) their is alot less but if you do not know what you are doing do not do that mod I am a metal fabricator/ TIG welder plus I grew up repairing small engines so I have the experience to do it. Yes they are right about the stud question did the whole stud come out or did it break off? To help with the muffler stopping from rattling off you can make up a brace for it so that it does not move that much, can you post a few pictures for us so we can give you a good description on how to do things.

Howdy Chaser, I'll add to the good suggestions from the other folks.

chaser said:

it vibrates ALOT, everything is tightened down well and i check everything before i ride. it usually helps to take the slack out of my chain. is alot of vibration normal? (ie. its uncomfortable to hold the handle bars at higher speeds)

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How many miles do you have on this engine? I have found the engine will vibrate more at higher speeds when it isn't broken in. Keeping the chain tensioned properly will help significantly but it is no comparison to the "boost" you will feel right around the 60-75 mile mark. Try keeping the throttle right at the point where the motor is running smoothly and, assuming this is a new engine and you are following other recommended break-in procedures, that point will gradually increase and you'll be zipping along like nobodies business. It also could very well be the natural imperfections of the motor but give it some time and see.

If your engine is "mature" then I've had this problem too and never found a solution. One day I was zipping along at 30 mph and the next I couldn't go over 18 without the motor vibrating out of the frame. I took the engine completely apart and couldn't find one thing wrong with it. I just bought a new one and use the old one for spare parts.

chaser said:

one of the nuts for my exhaust came loose today so i tightened it and the bolt came out of the engine block?!!?! how do i fix this?

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As you are looking directly at the exhaust side of the motor, is it the stud on the left or right? If left, look behind where the stud is you should see a little clearance so you can drill straight through and tap. If not, or right, then a broken screw extractor or helicoil will be your best bet.

chaser said:

my chain is wearing down that little plastic wheel that keeps tension on my chain... do i need to buy a new one?

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If you haven't seen it already, do a search for the skateboard wheel tensioner or look into the umpteen odd million other mods people have done to the tensioner.

chaser said:

my bike feels like it is losing alot of top end power, and i think it is linked to my exhaust. (i routed my exhaust myself so it would fit my bike.) i guess my question here would be, if my bike gets up into higher rpm and then it starts vibrating wildly and not feeling like its reaching its full speed, do i have too much or too little back pressure with my exhaust?.... i guess im just not sure how to tune my exhaust so it just works haha

Click to expand...

How did you "route your exhaust"? Did you chop and weld, bend, slot, twist, etc.? Take a look around your gaskets and check for leaks. I've had that same problem and found nonexistant exhaust gaskets many a time. However, it could be any number of other things. Just an idea.

Good luck and keep us posted!

That also happened to me in several of my bikes that ive built. What seems to help for me is putting rubber between every other fin on the engine. Try to get thicker rubber mats from your local hardware store and cut it up to size. That should help.

I've had quite a few of these engines...the ones that vibrated badly had bent cranks!

You can't break-in a bent crank!

Jim

Creative Engineering said:

I've had quite a few of these engines...the ones that vibrated badly had bent cranks!

You can't break-in a bent crank!

Jim

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My engines have started out vibrating pretty hard at higher speeds only to smooth out as they break in. Just my experience...take it for what its worth.

chaser said:

thanks for all the responses. first, the motor is NOT broken in, iv had way to many problems for it to even break in yet. i have looked into a few problems and spent a few hours looking over the motor. i wont be able to add any rubber between the motor and the bike.. the frame is already way too large.. i have been considering just taking the motor off this bike and putting it on a shwinn beach cruiser i have as it would solve a few problems (the exhaust routing and the vibration problem) speaking of vibrations, i had another thought.. has anyone considered that having a mountain bike with shocks on the front forks might just amplify the vibration? i might be totally off with that but i was just wondering. also, would it be a problem if i just removed the chain tension wheel and made the chain tight to the sprockets?

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Chaser, the rubber Macaddict was talking about goes between the cooling fins on the engine head. Take a look here: Cooling Fin Dampers

Though it probably won't help with the major vibration issue it does do wonders to quiet the motor.

I would think the shock absorbers would help quell the vibrations.

Also, if you have the clearance to run the chain without the tensioner...many have done it and many have liked it. If I had the clearance, I would too.

What other problems are you running into? Post a picture and I'm sure you'll get some more ideas.

Yeah, you get to a point with these motors where once you fix one thing, two more issues pop up. I, and I'm sure everyone else here, feels your pain.

You'll have nothing but trouble trying to weld steel to aluminum. Get a broken screw extractor and redo it with grade 8 hardware. You'll get there

I have been following your post and as far as the vibrations in the engine i would say that the engine most likely was put togeather with a bent crankshaft. I would stop were your at and call the dealer that you bought the engine from and explain your problems as best as you can. You donot wand to alter the engine in any way or the dealer would most likely not replace it with a good engine. I had the same problem with a bad vibration in a new engine i bought. I called the dealer and he said to send back for a replacement engine as long as i had not opened or altered the engine. If you send back the engine take it to Post Office and put it in a flat rate box . This is the cheapest way to ship.

All that vibration prolly caused the head bolts to come loose hence your lack of power,,snug them up 10-12ft.lbs or 120"lbs,check the carb and intake also,,they always need to be snugged up after a good ride,,get the motor mounted flush and solid to the frame,,get a good eye on the chain alignment,,and if the vibration keeps up I would look into a crank balance,piston skirt job.
Does it vibrate standing still at high rpm,,or only while cruising,,this will narrow things down quite a bit

I know its an old post,,just wanted to throw my 2 pennies in...

loctite red/blue, heli-coils=magic