Chris-PA
Where the Wild Things Are
I have a nice running ported 42cc Poulan which was the subject of this thread: http://www.arboristsite.com/community/threads/yet-another-42cc-poulan-porting-thread.262612/ However, the squish clearance is large on these engines, and I wondered if I could reduce it. I believe it has been done before, mentioned in this thread: http://www.arboristsite.com/community/threads/wildthing-races-at-gtgs.140451/ but I did not know how. The problem is that the crankshaft must be repositioned in the cylinder:
I got to looking at this design. Unlike some other clamshells these engines are not machined other than the bore and the spark plug hole. The bearing pockets and bottom surface are as-cast (they are actually very nice castings):
Further, the bearings have a pretty thick rubber outer boot that surrounds them and forms the crank seal:
That means these engines can tolerate some slop in the location of the bearing pockets, and that with some sealant it really should not be hard to grind out those pockets - I can get that close by hand. I considered filing the cylinder lower surface with a hoof rasp (OK, a good flat file), but decided to turn it on a lathe instead.
That presented a problem, because these engines are not turned at the factory and so they do not have a boss on the top for a tail support during turning:
There's just a spark plug hole. I wonder if they have a better plug location because of that?
I got to looking at this design. Unlike some other clamshells these engines are not machined other than the bore and the spark plug hole. The bearing pockets and bottom surface are as-cast (they are actually very nice castings):
Further, the bearings have a pretty thick rubber outer boot that surrounds them and forms the crank seal:
That means these engines can tolerate some slop in the location of the bearing pockets, and that with some sealant it really should not be hard to grind out those pockets - I can get that close by hand. I considered filing the cylinder lower surface with a hoof rasp (OK, a good flat file), but decided to turn it on a lathe instead.
That presented a problem, because these engines are not turned at the factory and so they do not have a boss on the top for a tail support during turning:
There's just a spark plug hole. I wonder if they have a better plug location because of that?