Ported cylinders vibrate

[INTP_ty]

Is this true? Zeda will port cylinders for a $45. Im worried it will vibrate more.

 

[FurryOnTheInside]

Porting is part of the fun. I would spend the money on a rotary tool and have that fun myself, personally.
And no it won't, I don't know what gives you that idea.. You might be thinking of raising the RPM? Higher RPM will obviously have more energy so the imbalance of the crank will vibrate more strongly and at higher frequency. Porting doesn't have to mean higher RPM. You can port for more torque and use that torque to turn a slightly smaller rear sprocket so you get the better speed and no added vibration.

 

[INTP_ty]

A rotary tool in my hand always seems to get away from me.


What can you tell me about the longetivity? Will it crumble like the sphynx?

 

[FurryOnTheInside]

A rotary tool in my hand always seems to get away from me.


What can you tell me about the longetivity? Will it crumble like the sphynx?

Concave surfaces like ports are okay, it's convex shapes, outside of square shapes, like brake adapters that are more tricky to control.

Idk about the longevity yet. I don't see how porting it makes a difference.
If you have the cylinder off you might want to try rebalancing the crank.

 

[Deleted member 12676]

Yes it will vibrate more. obviously my dear Watson.

 

[HeadSmess]

the piston is the bit that moves. the cylinder stays still. how would removing bits from the part that stays still cause extra vibration?

change the max rpm of the engine and yes, vibration will increase, but thats not due to the porting itself.

furry said it perfectly. port for lower torque, run a smaller sprocket, go faster with the same rpm. vibration will be no better nor worse than it is currently.

until you start removing weight from the piston itself.

 

[Spare_Parts]

Yes it will vibrate more. obviously my dear Watson.

Lol. Mine vibrated in the same range as it did before the port work.

 

[Deleted member 12676]

HS on most engines if you raise the exhaust port you raise the top RPM.
But there may be exceptions. What fights high RPM on these engines (after raising the exhaust) is the vibration. It can cause it to run too lean by foaming the gas in the float bowl.
With these three items you may not have to pull the crank to drill extra balance holes in it:
1) drilled out lightened wrist pin
2) lighter motorcycle piston
3) CDI that properly retards ignition at high RPM (Jaguar CDI)

 

[FurryOnTheInside]

HS on most engines if you raise the exhaust port you raise the top RPM.
But there may be exceptions. What fights high RPM on these engines (after raising the exhaust) is the vibration. It can cause it to run too lean by foaming the gas in the float bowl.
With these three items you may not have to pull the crank to drill extra balance holes in it:
1) drilled out lightened wrist pin
2) lighter motorcycle piston
3) CDI that properly retards ignition at high RPM (Jaguar CDI)

Porting doesn't have to mean raising the exhaust port, raising the top RPM.
For me, widening the top of the exhaust port and bottom of the intake port, redirecting the transfer ports and knifing the transfer walls at both ends gave enough torque to drop sprocket size to 42T on a 700c wheel (equivalent to around a 40T on a 26"), and still the top speed of the bike feels like it is limited by the engine's top RPM, by which I mean it has torque to spare and I'm going to have to try a 40T this week.

It is totally possible to drill the extra balance holes without removing the crank. The crank cheeks are not hardened steel, but the wrist pin is, which makes it impractical for most people to drill it out.
I used the radial drilling technique we discussed to make the extra balance holes, and with the drill sizes and depth you advised, plus 1.5 grams removed from inside the piston skirt and a small unknown amount shaved from the upper half of the connecting rod, plus the 1.2mm offset magnet key you suggested, the vibrations on my cheapo 66cc are nothing more than a gentle massage up to about 7000 RPM, and not at all serious above that up to my self-imposed limit of 8000 RPM.

I am assuming that I lose some bottom end power with the offset key technique, and if that is correct then I'm sure that I could have that back plus a smoother top end of I get a Jaguar CDI with a proper timing curve.

 

[Deleted member 12676]

I doubt you lost hardly any low RPM power.
What was the specs on those crank holes you drilled?
To your credit you are the only one to do that so far. I want to do that to my Suzuki with heavier over-sized piston throwing the balance off a bit.