10 replies to this topic

[Stian1979]

I tyed to get my hands on a new piston for a damaged cylinder.

It has proven to be imposible to find a overbore piston.

I'm considering options now and I start to wonder about making my own.

It's for a 50cc scooter and even new cylinderkits are cheap I find it as a vaste to trow away a old one witch easely can be bore 0.5 or 1mm.

I was thinking to make a mold using the old piston probartly in concrete and machine the surfaces later on.

I'm conserned about the strenght off it since I belive to have heard that pistons often are centrifugal cast to get the material packed together.

I had a teatcher once telling me he did it in he's youth preheating the concrete mold on he's mothers kitchen and pooring melted aluminium from old pistons into the lold, but I do not remember if he did anny heat treatment on it.

Hope to recive some answers that could help me out

[Franklin Ratliff]

Originally posted by Stian1979
I tyed to get my hands on a new piston for a damaged cylinder.

It has proven to be imposible to find a overbore piston.

I'm considering options now and I start to wonder about making my own.

It's for a 50cc scooter and even new cylinderkits are cheap I find it as a vaste to trow away a old one witch easely can be bore 0.5 or 1mm.

I was thinking to make a mold using the old piston probartly in concrete and machine the surfaces later on.

I'm conserned about the strenght off it since I belive to have heard that pistons often are centrifugal cast to get the material packed together.

I had a teatcher once telling me he did it in he's youth preheating the concrete mold on he's mothers kitchen and pooring melted aluminium from old pistons into the lold, but I do not remember if he did anny heat treatment on it.

Hope to recive some answers that could help me out

Do an internet search on "sand casting."

[Stian1979]

The casting itself don't worry me too mutch.

I worry more about alloy and heat treatment.

Could I use the remains off my old piston mixed with some sea grade aluminium?

And dos it nead some kind off heat treatment or can I just machine it into a finished pice and instal it?

Would the strenght be ok or should it be casted in a centrifuge?

[hydra]

Before you worry about alloy and heat-treatment have you thought of how you're going to recreate the barrel taper on the piston skirts and the ovalled piston bore (thrust axis being slightly smaller)? Sounds like a huge waste of effort to me. What I would do is a) just buy a new replacement kit, or if waste bothers you all that much b) use Sultzer-Metco's plasma-spray process to build up the cylinder bore back to spec and re-use the old pistons. Seriously though, why bother ??

[J. Edlund]

Liners are centrifugal cast. Pistons are die cast or perhaps pressure cast.

Machining will require an expensive CNC lathe in order to create the shape of the skirt.

Have you tried to find some forged aftermarket piston? If there is some company that has such a small forging, they can make the piston the size that you want.
Another option is to fit the cylinder with a thin dry liner.

[desmo]

Is piston knurling still done?

[cosworth bdg]

Originally posted by desmo
Is piston knurling still done?

Yes..............................but not reccomended.........!!!!!!!!

[Stian1979]

I work in a shipyard where we build high speed patrol boats for the Navy so we have moust things here.

We buy MTU engines and MTU's workshop is located 100m down the road. One off the guys there is german.

We white boys tend too make contact when we are alone in a asian country.

I did not consider the oval shape of the piston since this is smal and this is only a rebuild.

I have considered puting in a new liner, but it's a two stroke.

I have ben thinking about croming it.

Dos annyone know how they do that on cylinder liners??

I had some hard crome high performance cylinders on my old honda.

A onlin piston guide would be the best.

I bet there is a motorbike off some year/make that has a replacement piston that is availabal in that bore and has the corect distance from the bolt to the top.

[m9a3r5i7o2n]

Please infrom us of the name of the engine, size of the bore. Good grief surely someone makes a piston!!! There are dozens of piston makers on the Internet. Yesterday in my search for a 1/2"-NPT sparkplug I found pistons and stuff for old hit and miss gasoline engines. If they have spark plugs such as that then I'll bet someone makes pistons for the engine you have.
Yours, M. L. Anderson

[Stian1979]

Sang Yang Motors 50cc 45,5mm or 46mm.

I can get 44 and 45mm but no biger seams so out there.

To bad since it's several mm left to bore on.

[m9a3r5i7o2n]

I just got thru going to the Internet and there are hundreds of places to get parts for scooters! Why knock yourself out trying to do it yourself? Remember they are only too happy to ship parts to you anyplace, anytime and at what seems to me very reasonable prices!!!

M.L. Anderson