Very odd sounding 3.5HP

T

The Muffinator

Member
#1
#1
My friends mini bike which I occasionally ride has a very sloppy sounding engine. It still has great compression and starts up first pull every time but it sounds as if the piston is flopping around inside the bore. It has been this way since we first got the bike and apparently refuses to die. The engine is definitely worn because it burns 20W50 oil but what would be causing this sound? Is there anything that can be done to fix this? I am probably going to take the head off sooner or later just to see how badly scored the bore is.

I will try to get a video of it running.

Note: Flywheel is missing a few fins so it vibrates at certain RPMs but it is bearable. Nothing too crazy.
 
Cornishrooster

Cornishrooster

New Member
#2
#2
The Muffinator said:
My friends mini bike which I occasionally ride has a very sloppy sounding engine. It still has great compression and starts up first pull every time but it sounds as if the piston is flopping around inside the bore. It has been this way since we first got the bike and apparently refuses to die. The engine is definitely worn because it burns 20W50 oil but what would be causing this sound? Is there anything that can be done to fix this? I am probably going to take the head off sooner or later just to see how badly scored the bore is.

I will try to get a video of it running.

Note: Flywheel is missing a few fins so it vibrates at certain RPMs but it is bearable. Nothing too crazy.
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I thought that sound was my B&S engine too until I bought a new clutch.
 
125ccCrazy

125ccCrazy

Well-Known Member
#3
#3
could be the rod slapping on the journal :hammer:, or the wristpin might be sloppy, valve lash too loose and the lifters are slamming the valves ..... if it's going through oil is it smoking bad? or is it blowing out the breather?
 
T

The Muffinator

Member
#4
#4
125ccCrazy said:
could be the rod slapping on the journal :hammer:, or the wristpin might be sloppy, valve lash too loose and the lifters are slamming the valves ..... if it's going through oil is it smoking bad? or is it blowing out the breather?
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Definitely not the clutch. Engine sounds this way regardless. Oil is smoking out the breather and the exhaust. It is definitely burning it.
 
125ccCrazy

125ccCrazy

Well-Known Member
#5
#5
The Muffinator said:
Definitely not the clutch. Engine sounds this way regardless. Oil is smoking out the breather and the exhaust. It is definitely burning it.
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sounds like its time to tear it down and determine if it's worth re-building...

rod, piston, rings, valves and gaskets are pretty cheap....
 
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