555 autotune porting

[Charlie Pendleton]

Just finishing this up. Welding the muffler back up and putting the saw together tomorrow. Curious about the results I will see.

 

[Chris-PA]

Did you change the port timing? If so, what numbers did you use?

 

[Charlie Pendleton]

Did you change the port timing? If so, what numbers did you use?

I did not change the port timing, wasn't a hundred percent sure how to do it properly. Decking the base and Port timing might be something I look into after this cutting season while I tear it down and give her a new top end.

 

[Chris-PA]

I did not change the port timing, wasn't a hundred percent sure how to do it properly. Decking the base and Port timing might be something I look into after this cutting season while I tear it down and give her a new top end.

OK, how about port widths at the cylinder bore?

 

[Charlie Pendleton]

OK, how about port widths at the cylinder bore?

I traced the port on the piston transfered that over to the cyl wall and held back 3 mills from the flat sides of the piston. The exhaust port ended at around 1 5/16 inches. So cut around 3/8 inch wider, didn't widen the transfers but maybe an 1/8 inch, center intake ports got around 1/8 inch each.
Now I'm not a Machinist or a builder, just a hobbiest that cleaned up the porting on my dirt bikes as a kid. So far saw runs great I'm going to throw it to some big rounds after work today so I'll video it and post it up for fun.

 

[Chris-PA]

I traced the port on the piston transfered that over to the cyl wall and held back 3 mills from the flat sides of the piston. The exhaust port ended at around 1 5/16 inches. So cut around 3/8 inch wider, didn't widen the transfers but maybe an 1/8 inch, center intake ports got around 1/8 inch each.
Now I'm not a Machinist or a builder, just a hobbiest that cleaned up the porting on my dirt bikes as a kid. So far saw runs great I'm going to throw it to some big rounds after work today so I'll video it and post it up for fun.

From what I can tell you have the exhaust port at 72% of the bore, which is pretty wide. The concern is that the ring will want to expand out into the port as it goes by, and the wider it is the further it can go. Hopefully this won't cause any problems. Good luck with it!

 

[Charlie Pendleton]

From what I can tell you have the exhaust port at 72% of the bore, which is pretty wide. The concern is that the ring will want to expand out into the port as it goes by, and the wider it is the further it can go. Hopefully this won't cause any problems. Good luck with it!

Have you ported this motor? If so how wide have you gone? I ran the saw for 20 min or so to let the autotune adjust, so far ok. Im going to cut some rounds in an hour so I'll better know soon

 

[Chris-PA]

Have you ported this motor? If so how wide have you gone? I ran the saw for 20 min or so to let the autotune adjust, so far ok. Im going to cut some rounds in an hour so I'll better know soon

No I have not. The port width opening percentage is a generally applicable rule. I don't go beyond 60% of the bore diameter, but I believe others have.

 

[Charlie Pendleton]

Wood is water logged and frozen and chain could use a file but the motor sounds great.