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Post by ThomasTPFL on Apr 11, 2019 10:25:25 GMT -5
I think I’d try drilling holes in the flywheel. Then you`ll have unbalanced mass on the crank itself and you WILL destroy your bearings for sure. Why would removing weight from the flywheel be worse than adding weight? I don't like how our flywheels are way out on the tip of the crank anyway, so you're probably correct. I don't want to see what it looks like if the crank snout breaks off at 10k+ rpm. If everything is taken apart the crank lobes do seem the logical place to adjust weight, but adding weight will he tricky. You could cut away at the crank around the big end to return balance, Vespa guys do that all the time to adjust intake timing. What kind of resin do manufacturers use on stuffer cranks? In case you removed enough to have a noticeable effect on case volume. Are you still using a stock flywheel? I've wondered how much more important balanced internals are when using one of the HPI style mini rotor setups. And it's being said that you can't remove piston.. I've never gone farther than cleaning up port windows but other folks do. I see 2t pistons with the skirt cut down to almost nothing and with all sorts of extra windows added for flow..... I have a Zuma engine on my shelf now that was running strong when removed from the bike that was built by a chainsaw guy. I seem to remember that he cut the piston way down.
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Post by 190mech on Apr 11, 2019 17:05:57 GMT -5
Drilling holes in the flywheel would be fine,but where???If you have the proper accelerometer,phase pickup and software magic box,then it'll be easy..Thats why I suggested something to randomly move about till it smoothes out without making permanent changes to the design..
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lupo76
Scoot Enthusiast
Posts: 157
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Post by lupo76 on Apr 12, 2019 5:30:28 GMT -5
Then you`ll have unbalanced mass on the crank itself and you WILL destroy your bearings for sure. .... I don't want to see what it looks like if the crank snout breaks off at 10k+ rpm. I´ve seen it. But not flywheel side, it was variomatic side on a 1800cc 2T Gilera Runner. Wasn´t a good feeling though...
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Post by harleyracer59 on Apr 12, 2019 15:52:54 GMT -5
yes im running stock crank at the moment. I got a lead on a lead af01 racing crank. im waiting to hear back on some measurements and what bearings it uses
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Post by ThomasTPFL on Apr 12, 2019 20:30:02 GMT -5
Thinking on it I'm having trouble working out how a heavier piston could cause a misbalance..... Even if everything was perfectly balanced it's always going to have forces acting on it either counteracting or increasing the perceived mass of the piston. Compression and power stroke....
I'm thinking it's more likely a misbalance that was already there that is being amplified by the power and rpm increase.
I'm assuming you've isolated it to the engine and that it isn't something coming from the transmission side of things? Damaged starter gear or variator? Mismatched varistor weights?
Or maybe even oil pump drive? Unbalanced flywheel?
Are our flywheels balanced at 0 or do they have a counterweight calculated in?
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Post by harleyracer59 on Apr 12, 2019 21:12:10 GMT -5
im sure itsa in the engine. the engine was running fine before I tore it down for the bbk. ive replaved the variator and the weights. ive started the engine with no belt and it still vibrates. so moving not moving it vibrates. if I kill the motor and coast it rolls smooth. I wonder if I messed with the crank trueing when I swapped out the crank bearings but while tearing down I weighed the piston and the old piston and noticed the big difference. idont see any wobble on flywheel or variator when engine is running the af05 that uses the same bbk piston is a 41mm stock and that piston weighs more stoke than the ab07 40mm piston. I found a 9.7g wrist pin so there 5g and ive shaved on the piston a bit. was thinking of swiss cheesing the piston but I don't want to disrupt flow by putting holes in the wrong spot. ill post some pics tonight of the piston. I drew on the piston where im thinking of drilling/ cutting. I know that a heavier piston causes vibration. on those 49/66/80cc bike engines, theyre built and balanced for the 49cc piston and with the 47mm piston they vibrate. lightening the piston/ and wrist pin is the solution to this. ive done it on mine personally so I can say that its true in that engine.
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Post by harleyracer59 on Apr 16, 2019 11:34:31 GMT -5
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Post by jackrides on Apr 16, 2019 13:39:19 GMT -5
Some weight could be ground (then polished) from the bore of the wristpin. A 30 degree angle extending no more than half the width of each wristpin boss. There might be space for piston holes near the bottom on the exhaust side. The widest part of the piston is up a little from the bottom, stay away from that. Blacken the piston, slide it to the top of the cylinder and mark the bottom of the exhaust port on the piston. Under a good light, study it carefully over a beer. All new piston holes should be stress relieved by polishing or glass or walnut shell blasting from the inside. Obviously protect the outside and wrist pin bearing surfaces.
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Post by houseoffubar on Jul 13, 2019 15:10:30 GMT -5
There are lots of places to safely remove weight from the piston, and considering how much more you have slinging around, the bearings are going to wear much more quickly if you run it at high rpm very long.
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lupo76
Scoot Enthusiast
Posts: 157
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Post by lupo76 on Jul 15, 2019 3:56:00 GMT -5
Seems like some people here have no idea about engines and physics.
Piston weight is NOT on the crank, nor its "rotating mass.
If you want to remove weight on crank (flywheel or vario) it must happen round on a lathe. Not just drilling around.
The crank is something like an axle and it revs fast. If it´s unbalanced you will destroy bearings. But first, your vibrations will be even worse.
Also your drilled holes was a bad idea. Now, when you´re in the pase of precompression, these holes open the exhaust port. Thst means if that bitch will run, you might have something like 0,5 hp at all....
Look, that´s all 4th grade physics logic. If you cannot keep up with this topics, you should not mess with engines in general.
There are many ways to do something, but mostly just one way to do right.
Now I´m out of this thread now. Go ahead with your idea and see what will happen.
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