engine sound

mxc235

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Joined
Jul 18, 2018
Messages
71
4 stroke engine works with too much noise and vibration. how to make it queter? when adjusting valve clearances, should i err toward big or small and how would that affect sound and vibration in each case?
 


The_Aleman

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Joined
May 2, 2007
Messages
664
Which 4-stroke engine do you have? As a general ballpark figure, if you set valves to .005" intake and .007" exhaust cold, you should be okay. You can always run a bit tighter or loose if you live in hot climes, but I've found those to work well. My HS49's intake valve was 0.022 the first time I checked it!

All single-cylinder engines have some NVH, that is just because they are inherently imbalanced. For example there is a roughly 800RPM (4200-5000) range in my 4G+SBP setup where there is a harmonic imbalance and it causes a lot of vibration which goes away if I pedal, easy because that's 60-72 pedal RPM for me.

If your setup is always shaking, there may be a problem somewhere that needs addressing.
Can you take pictures of your setup? It would help a lot for all experienced eyes to spot potential issues.
 

darwin

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May 26, 2008
Messages
2,745
Never heard anyone complain of a stock HS 142f of being too noisy or too much vibration before, unusual. What motor OP?
 

The_Aleman

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Joined
May 2, 2007
Messages
664
Never heard anyone complain of a stock HS 142f of being too noisy or too much vibration before, unusual. What motor OP?
Honestly, an HS49 with ~30" of 3/4" ID flexpipe, no muffler, is quite loud IMO.
Mine is much, much louder than all 6 of the chinagirls even with modded non-cat kit pipes I've had.

The "5-7HP" Briggs cigar muffler keeps the same snarly and popping tone, but greatly reduces the amount of sound that bounces off of buildings. These little engines can be crazy loud! I have my straightpipe pointed towards traffic LOL
 

Will'smotobikes19

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Apr 9, 2018
Messages
1,356
I think he took his apart or was going to. Remember asking about how to take the flywheel nut off. Might be why. Vibration can be a lot of things but if it’s still going normal speed I wouldn’t worry about it. If it sounds like it’s running weird maybe. They shouldn’t vibrate nearly as much as the crappy girls though. Maybe you need to tighten the mounting bolts. My 79cc vibrated because I used rubber and the whole thing would shake.
 

dparenti13

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Joined
Sep 24, 2016
Messages
82
If your valve clearance is set too low you could start burning valves, other than that I have no idea what would cause noise like that on a 4t.
 

The_Aleman

Active Member
Joined
May 2, 2007
Messages
664
Yeah, I see some places still trying to sell rubber mounts, and often they just make things worse.

The best mount is a solid mount. If you want to dampen vibrations, stuff your frame with cork, but seal the ends well.
 
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