My 66 cc Flying Horse crank balancing

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M

misel

New Member
Nov 22, 2012
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Jakarta
These are the measured weights:

Con rod small end = 26 gr
Piston + rings + needle bearing + pin + pin clips = 106 gr
Balancing weight = 57% × (26 + 106) = 75.4 gr
Ballast = 75.4 - 26 = 49.24 gr

I ended up shaving this much from flywheel = 36 gr (at crank pin side)



 
Last edited:
mew905

mew905

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Sep 24, 2012
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Moose Jaw
Im interested too, as I've lightened the piston a bit thanks to the new reeds, I'm thinking I may need to rebalance
 
M

misel

New Member
Nov 22, 2012
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Jakarta
I still got vibration, but in lower rpm.
When the engine was stock, the vibration was at 5000 rpm up, now it's a bit lesser vibration and at 3500 rpm to 4000 rpm. I am still not happy with this, the vibration can still make hands numb.
I am using modified cdi and MM hi comp head and banana pipe right after the crank balancing.
I will try to put back the standard head and see if it can give better result.
 
M

misel

New Member
Nov 22, 2012
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Jakarta
I replaced the banana exhaust pipe with stock gutted pipe. The vibration is much less now that my hands are not numb when riding.
I am still using hi comp MM head, still enjoying it.
I feel the stock gutted pipe gives better torque and a bit louder but nicer bold sound. I am not going back to banana pipe.
 
Last edited:
mew905

mew905

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Sep 24, 2012
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Moose Jaw
you didn't need to split the crank? what tools would be required to do the job? I've never taken a motor down that far before (mostly because I keep stripping the stupid gear puller and give up, or because the flathead screws under the gears [on a different, gutted motor] are so tight I strip the heads off them too
 
M

misel

New Member
Nov 22, 2012
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Jakarta
My crank shaft is one piece type.
I think impact screw driver can be very useful for some screws in there.
And while in there, I changed all 4 bearings with Japan made ones.
I splitted the crank case carefully, then I could reuse the crack case gasket with no leaking problem.

The flywheels have a metal cover each side.
I used angle grinder to shave some weight off inside both of the flywheels.
Then when I put the covers back on, the shaved cavities were all covered, thus no change in crank case pressure ratio.

I found trouble when unscrewing the wide flat head screw on the small pinion gear, even the impact driver couldn't work, it still stripped the flat head screw, so I machined a flat head screw driver out of a chisel that can take the whole width of that stubborn flat head screw. Using this, it unscrewed easily by also using other tool to help turn the chisel.
 
M

misel

New Member
Nov 22, 2012
39
0
0
Jakarta


Update about vibrations.
I added a brace to hold the exhaust pipe (as shown in the picture - pardon the dirtiness)
After a few test runs, I am sure the exhaust brace took away some more portion of the remaining vibrations.
 
B

BOYGOFAST

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Sep 28, 2013
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Citrus Springs Fl.
In regard of my last post which I'm well aware is accurate related to assembly these engines will reply to command as expected if all centers are accurate without exceptions these exception are usually found in the bearing's as these are pressed in place.Anyone building one of the to race will gain an advantage by excluding bearings a film of oil is the only bearing needed in precise assembly another advantage is platinum enhance alloy composite over the standard alloy composite as well flawless diamond mounts to decrease drag or friction on the rotating assembly Boy Go Fast.
 
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