Well done Robshave...?...
I was about to sit a six hour exam "Power Engineering"...?I could hear my Instructor reiterating?."be sure to READ the questions and then and only then through out the nonrelevant information!"
Glad to see you read everyone's contribution to your challenge, and systematically discovered the little beasts weak spot!
A service manual is a must!.....a parts Book is also a must!
As your engine was conceived by British parents.....you have a "Standard Engine".
Here's some info I kept from my last Timing Chain and associated parts change out:
Info I compiled when REPLACING Crank sprocket ,Cam sprocket and Timing Chain.
(1) 85 MM Bore Engine:
(2) Front Lip Oil Seal "National /Federal Mogul Lip Seal" # 472164V A SMALL amount of BLUE Silicone was placed around the inside bore of the front timing chain cover before Lip seal was installed:
(3) I installed a repair SLEEVE on the front drive Pulley, make "DURA SLEEVE" # 99175. The sealing area were the LIP SEAL makes contact was slightly grooved. Dura Sleeve specs. 1.745">1.753" Diam. # 68 Rockwell Hardness:
(4) On installation the Governor plunger shall be reseeded tight against the Flyweights and no weights shall be loose or hanging down:
(5) A small amount (only enough to make the surface shiny) of engine oil was added to the shaft of the governor PLUNGER as well as the timing chain:
(6)There are / was NO timing Marks on the NEW Sprockets. You may wish to line the timing marks up (facing each other) before you remove the sprockets:
(7)Place the old sprocket (CAM SPROCKET) on top of the new sprockets and accurately scribe the new sprockets as to the timing marks. There are FOUR holes in the hub of the CAM SPROCKET. Keep turning the old sprocket until the four holes and all teeth line up. These holes are slightly off set. I used several SHOULDERED cap screws to ensure I had the new and old sprockets properly aligned. You may have to flip the old sprocket over...see right up:
(8) It's good practice to measure the thickness of the hub of the old crankshaft sprocket and the new crankshaft sprocket as the teeth on the two sprockets should align for both proper operation and longevity.(there were shims between the old Crankshaft sprocket and the shoulder portion of the crankshaft):
Cheers
Bob..
There shall be others who shall assist you as to a parts supplier as I'm from North Western Alberta.
Diamond Farm Tractor Parts ..Ont. Canada may be able to assist you?
When ordering Parts / Components you should consider having the Make, Model, Serial # of Tractor and the Fact your Engine is "STANDARD ENGINE "made in the British Isles.
Pics. as to explain how I checked the correct placement of the Camshaft sprocket, and the Crankshaft Sprocket:
The last three sets of sprockets did NOT have any timing marks scribed on the sprockets: