Loose Primary Chain

[nopdog]

Just need some clarification on this please.
The 3/8 inch movement is each way?
3/8in up and 3/8in down. With light finger movement only. Mine has about half that 5mm with light finger movement. This via the inspection hole only.
Also I recently changed all the oils (about 300 miles ago) and as per the manual put engine oil in the primary I can now hear a slight, low pitched wirring sound under load it’s not loud but I can hear it.
I’m about to change the primary over to ATF. Swill I need to clean the clutch plates of the old oil. The clutch is working fine.
Thanks

 

[L.A.B.]

The 3/8 inch movement is each way?
3/8in up and 3/8in down.

http://www.classicbike.biz/Norton/Repair/70up_Commando/70upCommando.pdf

Section C, Primary Chain adjustment, C41, 6 & 7:
"...total up and down movement of 3/8 in."

 

[gortnipper]

An easy way to measure with the primary cover on is to:
Take off middle inspection hole cover
Use a 10mm open end wrench, braced on the side of the inspection hole
Line up the lower jaw with the chain pressed down firmly, but not too hard
Move the chain up with the same pressure holding the wrench steady and it should align with the top jaw to the same spot on the chain.

This will give 0.5 mm extra slack. Too loose is better than too tight.