has anyone heard of an engine breaking from high revs

Prasinos

Prasinos

Member
my buddy goes 40+ with a 44 tooth sprocket and his bike seems fine. I know people say high revs are bad for these things but has anyone heard of a engine blowing from working too hard?
 
Have you seen him do 40 or is he telling you he is doing 40, he is probally really only doing 25-30mph. If he has a 44t on a 26" bike his top speed will be around 30-32mph unless he has a jackshaft kit on his bike.

Its possible his speedo is set wrong or he means kph.
But if he really is doing 40mph(LOL here)tell him when his motor explodes that zoombicycles has a good deal on a new motor.
 
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actually, downhill might count, in this case. if he were going full throttle downhill at 40mph with a 44 tooth sprocket, he'd be overrevving it so bad it could blow.

by my mythbusters reasoning, i'd say this one's plausible...
 
i blew a chung yang engine on a go-ped... lol i did it on purpose...........i was going max rpms for about 2 mins and it blew bits of burning steel out of my exhaust about 1:55 longer than i should have
 
2 strokes can rev very high...IF BUILT FOR IT. Balance is critical and the strength of the rod is very critical...
 
I had a 44 tooth sprocket on my 66cc with 26" wheels and my friend clocked me @ 40mph on his motorcycle. There might have been a slight down hill and his speed-o might be a little off...
 
No boys, i have a 36 tooth setup with a 16mm carb and a sbp expansion pipe and he definitely keeps up with me at 40 on the flats. I removed some of the baffles for him and matched the intake and exaust, but other than that the only upgrade is the dellorto 12mm carb.

Ive run 12 engines and never seen an 80cc that pulled that late in the rev range, still, it doesent seem to be damaging the motor...
 
bairdco said:
actually, downhill might count, in this case. if he were going full throttle downhill at 40mph with a 44 tooth sprocket, he'd be overrevving it so bad it could blow.

by my mythbusters reasoning, i'd say this one's plausible...
Click to expand...

yes! +points for mythbuster reference!
 
Just remember that rotating loads and forces increase exponentially at higher rpms. The difference of g-forces and bearing loads between 2000-4000 rpm and 4000-6000rpm are probably staggering.

To get an idea, tie a lug nut on a piece of string. Throw the lugnut. Now repeat this excercise, but swing the lugnut round and round and let go at your fastest possible speed. Goes a long way, right?
 
i run mine full throttle for hours at a time. could it blow? yes. has it? no.

from reading this forum, it sounds like some motors could blow just by sitting on a slow boat from china...
 
im not sure ive never heard of a catastrophic failure due to high revs. All of the failures Ive heard about seem to be defects...

personally ive red lined my engine for 3 seconds at a time, after doing that i really dont worry about the thing.
 
I remember reading about two cycles that have kept a low rpm for awhile. This will wear a grove in the head, then when the engine is revved up high the rings catch on the grove, causing engine death.

It might be an old wife's tail but it might have a grain of truth in it.


Mike Frye the bike guy:-||
 
retromike3 said:
I remember reading about two cycles that have kept a low rpm for awhile. This will wear a grove in the head, then when the engine is revved up high the rings catch on the grove, causing engine death.

It might be an old wife's tail but it might have a grain of truth in it.


Mike Frye the bike guy:-||
Click to expand...

it sounds plausible to me. because the con rod will stretch a very small amount at high rpms, and if it was used to being at low rpms i can see how it would wear a ring at the top of its stroke, but i think the engine would needed to have been used for something like a military generator or some application where it was run at a constant rpm for most of its life, then revved up. i had an old 4 cycle lawn mower that was about 30 years old. it was used as a lawn mower the whole time and one day i by passed the governor and revved it up, it was good for about an hour then it lost compression and died, i just chucked it, but maybe what your speaking of applys to 4 cycles as well?
 
When i first broke in my stock 66cc and i hadn't broke anything on it, and my chain was lubed and everything was perfect, birds were singing, etc. it went 39 once. Then i took it offroad and broke some stuff it would only do about 35. Since some motors are better then some, I totally believe he could do 40mph. Btw you guys that are gearing them up and expecting to go faster... my Dad had a Honda cl90 and he geared it down and let it rev more it would go 70. (moral of story, if engine won't pull gearing it won't go faster)
To some people this will seem "duh what n00b advice", but this is new info to some people lol
 
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