If there's not enough backlash you'll get an awful whine from the gears. Best take the time to get it right. Use the backlash in the other timing gears as a guide.
This won't solve your oil leaking problem! though
There have been previous posts on this leaking not long ago
Hi Jim,that 035"shim sounds far too thick,it usually only takes a few thou to sort
out.It could be that the shim has lifted the mag past the designed "out of alignment limit" allowing oil to pass.A check of the breathers and pipes is a quick operation.As to the backlash,quickest way ,start with no shim and test the feel of the gears,then pack up with paper shims until you have discernable backlash.It after all is a bit trial and error,once you are happy you can order the required amount by measuring the paper ones.
hope this helps
cheers Rick
email (option): richardholt@rocketmail.com
Last year I'd done a little bit of work on her, a rebore (thanks Dave) new gaskets and oil pipes etc. When I fired her up (2nd kick, lovely old girl) I noticed that see was blowing oil out from the mag drive, ie where the mag goes into the back of the timing case) now I'd fitted a new oil seal there last year, so this shouldn't have happened. Taking the timing cover off, there was quite a bit of backlash in the gears there, probably too much. Lifting the mag out to give it a proper look over, there's rather a thick piece of "shim" underneath the mag, obviously home made, and is around 0.035" (0.70mm for the foreigners) Checking Russels part numbers, I see they sell these shims in 0.005" thick, that would need quite a pile to get 35thou and a fare bit of cash!
I believe the 35thou shim is far too thick. Is it just keep trying until there's just the right amount of backlash when it's all tightened up? or is there an easier way to get it right first time? I also don't want to bend the mag shaft if I tighten it up and it needs more shim.
The platform on the engine cases is quite good, not showing signs of wear.
As previously described, the proper mag shimming should be easy to address by stacking shims as needed to achieve the minimal pinion gear/ magneto drive gear lash.
The other issue which you mention of oil issuing from the magneto drive seal; I suggest this could be a function on "wet dumping".
In my reading, you seem to indicate that the machine had been sitting for some time prior to starting when the oil leakage was first noticed; if the oil had pooled in the engine, it is possible that crankcase pressure upon starting pushed some of that excess oil out past the magdyno seal. There are several threads on the forum on solving wet slumping, or at least on how to minimize it.
Get the gear lash sorted on the magdyno, and while you have the timing gear cover off, you can see to the potential wet sump issue.
email (option): teladelujo@ msn.com