Guys:
Currently over on the auction site there is a Sachs cylinder with some strange modifications to the sleeve, item number 161469065907. Any idea what the purpose of these mods are? I would have copied the pics here if I could figure out how to so.
Todd Rovello
Todd they are finger ports that allow the air/gas mixture to come directly up from the bottom end. Same as the transfer ports, but more of a direct charge.
Ron Carbaugh
Thanks Ron. Would one expect to see increased throttle response, or what? Usually a modification has trade offs. Would the changes in performance in one area be offset somewhere else, say power in a different rpm range perhaps?
Todd
Todd,
The question (s) you are asking cannot be answered unless you take one carburetor and one pipe and then make the change to the cylinder. In other words you will change power curve of the engine, but it also depends on the pipe and the carburetor. We normally made this modification to help with mid to top end power for Moto X. You could really tell the difference on the track on a big fast track.
Ron Carbaugh
Good info Ron. I had heard of finger or boost ports years ago but never saw them in practice.
Todd
My 100 and 125 have porting done with finger porting, 100 has custom made pipe.125 has a circle F pipe, both have PVL's with mikuni carbs. My bikes run with any thing here in the NW. Including reed valve bikes. I have been running the 100 for 3years now with no top end problems,and 125 all last year, Both bikes are class winning AHRMA bikes. 100cc expert and 125cc classic expert
I don't know if this applies to these particular cylinders, but if I remember correctly from days gone by, when some of those finger ports were cut in it would require relocating a pin or possibly both pins in the piston that locate the end of the rings. Just don't want to see one of you get that cylinder and have a preventable issue.
Paul
Excellent point Paul. I always marked the cylinder as to the pin location before I cut the finger ports. When I did buy a cylinder that the ports were in the wrong place (they could snag a ring) I relocated the pin on the piston. Actually, I remember having cylinders given to me back in the day that had the ring problem, and only after lining up the piston pin I found that was the problem.
Ron Carbaugh