Unique Cylinder Design!!!

[shadow745]

Of course this is a chainsaw section, but you guys are very knowledgeable with small engines, so here goes.....

I'm stripping various parts off my brushcutter for maintenance. The thing has been used year after year and has needed nothing other than the usual yearly maintenance. It was put out in the early 90s by Sears and is 38cc. It's called the Bushwacker. Commercial quality construction and apparently the engine was made by Robin (from what I found in another small engine forum). Anyway, upon looking in the cylinder from the spark plug hole I noticed the cylinder doesn't have the usual smooth/flat surface. All around the cylinder (as far as I can see anyway) there are small slits in the cylinder wall. Apparently it was machined that way. They look similar to the porting you'd see on the end of a gun barrel to reduce the kickback. Ever seen this in another small engine? Thanks in advance. Later!

 

[bullseye13]

I replaced a piston on a robin engine that was on a ground compactor and it had the same slits in it, not sure what their purpose is though.

 

[shadow745]

Thanks for the reply. You ever seen any other engine like that? That brushcutter still runs great and I'm trying to keep it that way. To replace it with something modern with that power level would be $400+ from the research I've done. It must have over 1,000 hrs. on it but keeps on going. I've noticed it has a rather large piston, but a very short stroke. The recommended max RPM is 6,000 and it has a buttload of bottom end torque. Never have to run it wide open, even when cutting brush and small trees. Thanks again. Later!

 

[Javelin]

They at that time used a chrome etched cylinder! Tanaka also did this the idea was the etches would trap oil and allow less friction!