Custom Pistons for mopeds

[Trafficjamz]

Has anyone ever tried using lighter aftermarket pistons in a spree or elite?

http://cgi.ebay.com/ebaymotors/Pro-X-Pi ... 1356wt_939

http://cgi.ebay.com/ebaymotors/Wiseco-P ... 1018wt_939

http://cgi.ebay.com/ebaymotors/WISECO-P ... 2506wt_895

http://cgi.ebay.com/Echo-3700-Chainsaw- ... _500wt_928

[Bear45-70]

Lighter pistons will require a balance job, but the thing that I would be more worried about is wrist pin or compression height. Just because a piston is the same diameter does not mean the wrist pin is the same distance from the top of the piston.

[Trafficjamz]

Lighter pistons will require a balance job, but the thing that I would be more worried about is wrist pin or compression height. Just because a piston is the same diameter does not mean the wrist pin is the same distance from the top of the piston.

Oh yeah, I know that the bore size is not the only spec to be concerned with.

What has to be balanced to go with a lighter piston?

[Bear45-70]

I would assume (I know it is a bad thing) that the purpose of the lighter piston is to rev the motor quicker and higher. To make that happen and retain some reliability you should balance the motor. With my super stock motor we were not originally allowed to grind on the rotating assembly parts. The last 2 years I race in the Super Stock class we were allowed to balance since the motors were now out of production. My motor went from a max RPM of 7400 to 7600 with only the balancing. Maybe it was my imagination but the motor felt smoother too.

[Trafficjamz]

I understand in a multi piston setup, that the pistons need to weigh the same.

But what is there to balance in a single piston setup.

[bakaracer]

you can get ahold of wiseco and give them the specs you need. they can make a piston for you if you need

[toad772]

But what is there to balance in a single piston setup.

Crankshaft.

[Trafficjamz]

But what is there to balance in a single piston setup.

Crankshaft.

Why would I need to balance the crankshaft if I change the piston? Isn't it already balanced

[bakaracer]

its really hard to balance a single piston 2 stroke crank

[Bear45-70]

its really hard to balance a single piston 2 stroke crank

And that ia exactly why it is so important.

[Trafficjamz]

I still dont understand.

What needs to be done to the crank , if a different weight piston is used?

[Bear45-70]

When you rev the engine faster and higher, any small imbalances are multiplied for every 100 RPM you add to the top end. Anyone doing it RIGHT is gonna balance the rotating assembly. It improves performance and longevity.

[nickisaninja]

The counterweight on a crank needs to offset the weight of the connecting rod and piston.
If there is an imbalance say, 1gram, that gram gets multiplied exponentially with speed.

Say the piston weighed 1gram more than the counterweight. Every time the piston would be on it's downstroke the imbalance would push the crank into the case with more and more force coinciding with engine rpms. Every compression the piston would pull on the crank because the counterweight would not be able to cancel out the piston+rod+wristpin+retainingclips weight, since the counterweight is supposed to neutralize the weight of the rod and piston acting against the crank.
That's the best I can come up with. Make sense?

[Epschoenly]

http://www.treatland.tv/vertex-47mm-tef ... piston.htm

Moped racers are using these. Food for thought.

[Trafficjamz]

The counterweight on a crank needs to offset the weight of the connecting rod and piston.
If there is an imbalance say, 1gram, that gram gets multiplied exponentially with speed.

Say the piston weighed 1gram more than the counterweight. Every time the piston would be on it's downstroke the imbalance would push the crank into the case with more and more force coinciding with engine rpms. Every compression the piston would pull on the crank because the counterweight would not be able to cancel out the piston+rod+wristpin+retainingclips weight, since the counterweight is supposed to neutralize the weight of the rod and piston acting against the crank.
That's the best I can come up with. Make sense?

That does make sense......thanks.