Loud engine

Jaycee604

Jaycee604

Member
Ive been building these bikes for a couple of years now. I realized one of my bikes is pretty loud at high speed. Sounds rough. And i can hear the reeds on the reed valve alot. I will list below what the engine has installed on it. Its a new engine i have built, so im thinking its breaking in and or it is not jetted right. There is some vibration when it gets louder too at higher speeds, but has great accereation and holds speeds good. Also really good up hills.

66cc 2 stroke
Case matched to cylinder
Not ported
G2 Reed valve with windowed piston
High performance cdi and magneto
Ngk br6hs plug
Cdh power high comp head
Mz65 clone on amazon with silencer (yes i know a real mz is better)
420h chain
Old style NT carb with after market cone air filter
New bearings
 
Did you check for proper squish? Noise at high rpm sounds like the piston is tapping the head slightly. To test add a second head gasket and see if the noise is gone.
 
Greg58 said:
Did you check for proper squish? Noise at high rpm sounds like the piston is tapping the head slightly. To test add a second head gasket and see if the noise is gone.
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thats a good guess, squish gap is crucial but i dont have a battery powered caliper or solder. Kind of pricey to but both but i may have to. I will add a thin gasket and try it out. Dont you think if the piston was hitting that i would have seen marks on the piston or head? I took it off to check, looks fine. Its more so the reeds that are loud, followed by vibration
 
Jaycee604 said:
thats a good guess, squish gap is crucial but i dont have a battery powered caliper or solder. Kind of pricey to but both but i may have to. I will add a thin gasket and try it out. Dont you think if the piston was hitting that i would have seen marks on the piston or head? I took it off to check, looks fine. Its more so the reeds that are loud, followed by vibration
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The piston won't actually be touching the head; (but it will sound like it)!
Just add a 2nd head gasket like Greg said & see if that helps.

Sometimes it's the chain whipping around at high speed that's causing the vibrations!!
Make sure your sprockets are in line with each other (so the chain runs nice & straight), & also make sure the rear sprocket spins as true as you can get it. (spin the wheel without the chain to see if the sprocket wobbles in any direction).
 
Venice Motor Bikes said:
The piston won't actually be touching the head; (but it will sound like it)!
Just add a 2nd head gasket like Greg said & see if that helps.

Sometimes it's the chain whipping around at high speed that's causing the vibrations!!
Make sure your sprockets are in line with each other (so the chain runs nice & straight), & also make sure the rear sprocket spins as true as you can get it. (spin the wheel without the chain to see if the sprocket wobbles in any direction).
Click to expand...

checked squish gap (got some solder) its 0.6mm
Maybe a hair off because i have regular calipers (non battery kind) chain isnt wacking around. Everything on the bike is solid. I tune it up all the time. I tightened down my muffler a big more and it seemed to help a little bit. My reeds or reed valve might have a problem. Just bought a new g2 reed setup again so i ll see what happens after that.also sometimes it can be the piston touching the head.Happend to my friends. Ended up cracking his head over a day or two
 
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I mentioned twice that the reeds sounded pretty loud. Other bikes i have with same setup dont have this sound or problem.
 
Normal squish gap is .8mm, I've seen videos on YouTube of the same problem you're describing, I think his was .5mm. unless you've balanced the crankshaft you will get vibration at higher rpm. These engines are balanced for 5-6k rpm, drilling the crank will move the balance higher.
 
Greg58 said:
Normal squish gap is .8mm, I've seen videos on YouTube of the same problem you're describing, I think his was .5mm. unless you've balanced the crankshaft you will get vibration at higher rpm. These engines are balanced for 5-6k rpm, drilling the crank will move the balance higher.
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lots of ppl say 0.20 to 0.30 is good. Lots of ppl say its bad. Works good for me. My crank is balanced. All of them are. Im not a rookie to these engines which is why im asking this question.
and to clear this up. I did try a bigger head gasket. It just ran with less power and died faster.
Squish gap is fine and nothing is loose on the bike
 
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