Experimenting With A 2stroke Trimmer Piston

[petcnc]

The square opening around pin bearing? You don't need mill it.

You mean not to mill it but to drill? Or not to bother at all?

 

[cascao]

Or not to bother at all. It's there due cast process in piston fabrication.

 

[cascao]

You removed material from piston diameter. Check if you need to remove material from rings groove too. (rings radial thickness need be smaller than groove depth)

 

[petcnc]

You removed material from piston diameter. Check if you need to remove material from rings groove too. (rings radial thickness need be smaller than groove depth)

Rings fit ok I think the initial depth was more than needed.
On the piston port issue I think its part of the design for the particular engine to run with these ports. as there is a provision to the cylinder for fuel mixture circulation through these ports as you can see in the next photo of the cylinder.

 

[ndnchf]

Very interesting - I'm learning a lot, thanks.

 

[cascao]

When piston goes up. there is vaccum on crankcase and fresh mixture air+combfrom carburetor goes there.
At same time other mixture from previous cycle is burned.
Than piston goes down. mixture goes by this shown ports (transfer ports) to upper part of engine at same time when burned old mixture goes out by exhaust port. Its always about transfer por angles and exaust pipe to clean cylinder from burned gases and not lose fresh mixture.
When piston goes up, it closes the transfer and exhaust ports, compress the mixture and explodes again.

Its {WATCH YOUR LANGUAGE.**G**} simple,free revving and powerful engine. Its one of these things that everyone someday would be given opportunity to race a motorcycle with

 

[petcnc]

 

[Silverbullet]

Doctor Frankenstein , if the monster lives it won't know how to run. I've done lots of rebuilds using odd parts from different manufacturers. For fifty years small engines have been my way to earn spending money. There shouldn't be any problem with your machine handling the piston your making . When you install it use plenty of two cycle oil in the rebuild on the piston and cylinder. Some pistons only mount one way ,, toward exhaust ,,. Hope your carbs adjustable . Sealed ones with your rebuild may not run right , never know till it's running. Good luck be careful pushing piston and rings in cylinder they snap easy. I know many times over.

 

[petcnc]

Doctor Frankenstein , if the monster lives it won't know how to run. I've done lots of rebuilds using odd parts from different manufacturers....

He he he I like it! I never thought myself as Dr Frankenstein.

Well I see the crankshaft of the engine on the neck! The piston must be behind the intake port (nose)

 

[crazypj]

Bit of an old thread but I didn't want to start a new one if I didn't need to.
The slots in side of piston are very unusual, normally it's to lighten piston as the transfer ports are fed from the bottom and discharge over the top. It may be to limit crankcase compression and max rpm possible? (plus much lower power output?)
For a single piston modification the faceplate method works well but if you have a set (usually 4 or more) making the piston holder with locating diameter is much faster to set up (I'm doing at least 8 and possibly 12 Honda CB750 motorcycle pistons to fit into CB550 giving a 591cc motor) There is only one critical dimension and that is the locating spigot, the rest can be roughed out.
There is a machined section inside skirt plus all are machined to a fixed inside diameter (evenwhen oversized on outside diameter)I will be doing multiple operations including cutting new valve pockets so te holder is 'double ended' the opposite end will be machined to fit piston crown. I'll post more pics or start a new thread if there is interest?
Couple of pictures