Sunday, September 5, 2010

case matching my E50 puch engine

i have finally gotten around to case matching my E50 puch engine. for those of you that don't know what case matching is... well, when i upgraded the cylinder on my moped the transfer ports (see diagram) on the new cylinder are much larger than the transfer ports on the crank case. the transfer ports are the path the fuel/air mixture takes from the crank case to the top of the cylinder where it's compressed and then ignited. because the stock ports and the new ports don't line up properly, the flow of air/fuel is restricted and the engine is not running as efficiently as it could. so, that is where "case matching" comes in. case matching is removing material from the transfer ports on the crank case side so that they match the ports on the cylinder side.

here are are transfer ports on the stock crank case:

you can see that the transfer ports are considerably larger on the new kit:

anyway, i used the gasket to mark the area on the crank case that needed to be removed. the area that's coming off is marked with sharpie:

ideally you case match when the the crank isn't in the engine, this makes it easier to keep the crank and the case clean. when case matching there are tiny pieces of aluminum flying around as you are expanding the port. obviously little flecks of metal are not good for the engine. they can easily wreck pistons, cylinders, and bearings. i did not want to take my crank case apart again, so i masked the crank and the bearing on the connecting rod with lots of tape and plastic. a much cleverer solution is to use silly putty. i would recommend that if you're not willing/able to tear the whole engine apart.

i did my milling with a dremel and a 1/4" and a 1/8" carbide burr (which are generally meant for more brittle materials, but didn't seem to get gummed up on the aluminum). while doing the case match, you don't need to cut the port straight down, and you don't need to go super deep. i angled the port in and went down about 0.75"- 1.0". here is what the port looked like after the milling:

then i just hit it with some 200 grit sand paper and cleaned it like crazy. i put the engine back together and i'm probably getting 2 extra miles per hour. now i'm just eagerly awaiting my new sprockets.

also, i found confirmation of how that voltage regulator is wired. i was right, it does act like a shunt: