As I’m sticking the crankcases back together on a Bonny engine, ya’ll may be interested in a couple of things
This is a view on the inside of the crankcase (without the crankshaft in) looking towards the primary side of the engine. You’ll notice there are 3 little holes. The holes line up with the bottom of the crankshaft bearing.
Prior to 1970 the Primary chain and clutch had their own oil. Which was kept separate from the eingine oil by a large oil seal on the crankshaft.
Later engines did not have separate oils so the crank seal was removed and the 3 holes were included to keep a certain level of oil in the primary to keep the chain and clutch wet.
I use an appropriate sized weenie drill to make sure the holes are clear, although why the oil can’t just level off through the bearing escapes me. However, they are there and the Triumph boffins knew a lot more about these engines than I ever will.
Here’s the nicely rebuilt/ground/new conrods/sludge trap etc crankshaft. Note the two slots on the righthand side of the flywheel.
These aid the timing of the engine once it’s all built. One slot is at Top Dead Centre and one slot is at 38 degrees Before Top Dead Centre.
Here’s the crankshaft positioned into the primary side crankcase.
And the timing slots on the flywheel. Note how I use gearchange rubbers on the barrel bolts to protect the conrods.
The two crankcases are now together and the arrow indicates the bolt that allows access to the timing slots on the flywheel to allow static timing on the engine when built.
The slots were added to bikes after 1965 I think so the later Bonnies and Tigers have these well handy holes.
Over…
