I just completed an upper end renovation of an S-40 engine with some changes.
The big change was a 96mm Wiseco piston that brings out the displacement to 680cc. When I weighed the old piston and pin it was 510 grams. the new Wiseco was 477 grams. I was concerned about possible vibration from unbalance. To make them weigh the same, I machined two half slugs of aluminum to fit into the ends of the wrist pin. The outer ends are tapered to match the inside of the new pin. A hole was drilled in each and threads cut in one end. An allen screw was fitted after generously filling the threads with JB weld so that the screw will never come loose. (see the photo) this made the piston assemblies weigh the same.
Valves were hand lapped to insure a good seal.
One of Mysterious Johns' copper colored cam chains was installed, I worry a bit about this as the pin diameter of this chain is a tiny bit smaller than the stock one but at least it is new.
The apply proper tension to the chain, I installed my modified tensioning device. This will be the first on the road test of this thing.
( see the photo)
When taking the engine apart, I noticed the horizontal position of the timing marks on the starboard end of the cam. (see Photo)
At this position TDC, a center punch dot was noticed at the BOTTOM of the starboard end of the crankshaft. This can be used to set the crank at TDC during reassembly, no need to open the port side cover to see the mark indicated on the alternator as the book says.
I replaced all gaskets involved and replaced all four copper crush washers under the nuts of the head bolts.
Upon disassembly of the clutch,( I had bought a full set of friction discs), I miked each friction disc and found that only two of them were actually less than the new ones so I only replaced two discs.
NOTE one of these discs is deliberately thicker than the rest. Note the position of this disc upon reassembly.
When all this goes into the bike, it will exhale through a new fishtail muffler that should give less restriction.
I have already installed a 152 and a half main jet in a new carb to feed the beast.
I will give more results after I have put some miles on this engine and dare to open it up to compare hill climbing speeds with those I have noted in the past on some local roads.
Additional photos show milling the valve spring compressor tool,
and the piston pin removal tool I made from threaded rod and plastic pipe.