Motorcycle Repair: Replace crank timing sprocket on Honda SL125, conn rod, wheel pullers

Question
Hi. I am rebuilding my 1972 Honda SL125 engine. I want to replace the timing chain, and cam sprocket, and noticed that the crank sprocket is very worn, so it ought to be replaced also.  The service manuals recommend that a dealer do this, but i have wheel pullers and a 20 ton press. It would also be nice to be able to separate the crank and replace the conn rod, if needed (although i don't believe it does).  Are there specific instructions for the crank timing sprocket, and conn rod replacement?  Thanks Bob

Answer
Bob, You just need to index the crankshaft sprocket referenced to the keyway slot, so your cam timing will be correct when you reassemble it again. Honda doesn't offer replacement parts nor instructions for disassembly and reassembly. It is pretty much like any 2 stroke crankshaft, however, so the critical items are that the side clearance needs to be maintained for the rod, usually about .008 - .012" perhaps and the crankwheels need to be running true and straight again, once you are finished. There are no OEM replacement parts for the rod and crankpin.

The little gear comes off with a bearing removal tool I( )I type. Using a gear puller might damage things, but if you have the new sprocket, then you can't do too much damage to it, can you? :>)
POWROLL in OR still does a fair amount of work and offers performance parts for these engines, but you really have to observe the camshaft play in the head on the early 1-piece heads. Once the cam gets sloppy in the bearings, the ignition timing goes out the window as well. There are needle bearing repairs that can save the head and cam, from Powroll and others.

If you are going to go to all this work, you might want to use a 125 rod, as it has a bigger pin size that is used on a lot of big bore piston kits. 100 wrist pins are 1mm smaller than the 125s.

Bill Silver