Anyone know how to time the counterbalance on a 1973 SC500? Thanks

No marks on the gears?  Usually you just line up the marks.

The marks are quite a ways apart ... and the intermediate gears don't appear to have marks.

Hmm, are there marks on the cases around the crank and counterbalance shaft gears?  On some of the large 2-stroke diesels I work on they run a crank gear, and idler gear, then drive one camshaft gear and then the other.  Every gear has timing marks and you line them up but after making a revolution of the crankshaft they don't line up anymore.  It takes 47 revolutions of the crankshaft before all of the marks will line up again (if you need to double check your work its easier to pull all of the gears and reinstall them).  The reason for this because the idler gear is a hunting gear and its tooth count is not evenly divisible into the tooth counts for the other gears (it evens out the wear on the gears).  This could be why your marks don't line up.  One possiblity for timing could be to position the crank at TDC and then align the counterbalance gear with a mark on the case.  The timing of the intermediate idler gear may not be important.

Go to "yamahaenduro.com" and search this.They have posted the schematic! Great guys and very knowledgeable.

Thanks to all....got the info