SQ Engineering - Projects - Custom 2 stroke engine

Custom two stroke engine

This is another project that is slowly coming together and being machined up at a slow pace. The concept is to make the greater part of a two stroke engine using only the crankcase, flywheel, ignition system, crank and the clutch assembly. The donor engine is a low powered, low revving and poorly designed Chinese engine. I plan on turning this into a 6 port fire breathing monster with approximately 4 times the original power rating. Currently I am waiting on a four stroke barrel for which I can machine to have the windows for the two strokes ports. I also plan on making a two part barrel to allow me to gain full access to the ports for maximum porting. The displacement would increase from 40cc to approximately 60cc, predominantly through the increase in the bore.

Reed block and bottom barrel:

Originally the plan was to have a barrel reed induction via a V-type reed block. This would of bolted to either side of the two parts of the barrel. So starting with this concept the first part of the barrel was laid out.

This has had the first piece machined out for the reed opening. The outlines are the rough bore shape and the planned transfer ports.

Over-laid with the gasket off the donor engine, this shows how limited the port size is in the standard engine. This is the main reason why this original engine is so limited in performance upgrades.

From here I needed the bolt on reed block. The reed block was sourced from a different donor engine thats a high revving and high power unit so flow wasn't an issue. This part has already been fitted with triple stage reeds and despite the surface rust on the screw will perform well.

So to start, the basic shape was machined to suit the opening of the reed.

Then the two parts where drilled and tapped to be bolted together through two counter-bored bolts through the sides. The same was also applied for the reed block bolt down. This covered the basic function and from here..

Every last bit of material was removed, fanatical perhaps but this is a long term project.

Ironicly I may abandon both of these parts to instead go for a reed block that feeds though the crankcase. This would mean a completely different reed block shape.

More some day..