If it is in pieces the toss the big end bearing out & fit a B44 one with the 1/4" rollers.
The Australian army specified the higher rated B50 needle roller big end which is great if your engine is running at blue smoke speeds. Then they specified 3 off road gears and a standard top so you have to valve bounce in 3rd in order to change into top without the engine boging down.
Similarly when you change down you have to valve bounce the motor before you release the clutch or your filling will be catapulted out of your teeth.
labouring the engine in top gear will cause the cage of the big end bearing to scuff on the outer race, eventually breaking up.
If you are lucky it will drop into the sump so you can at least ride home.
If you are not lucky it will hammer weld onto the outer race and seize .
I had a box full, 73 in fact , con rods with cage hammer welded onto the outer races.
I got them from Gladesville Motorcycles who had a contract to maintain the few remaining servicable B40's before they were replaced with Suzuki 400's and Honda Elsinore's.
The armed services ordered 490 ( or there abouts ) B 40's in three colours, green ( army ) grey (navy ) and blue ( airforce ).
228 were disposed of when Defence Stores were taken over by clvil servants and DAS cleaned out all of the obsolete stock hiding at the back of the warehouses before they sold the land to property developers.
All of them were labeled " PROV UR " , provisional uneconomic repair or CERT UR , definate uneconomic repair.
The only reason they became UR is the big ends were stuffed.
I can account for around 60 of these bikes and each & every one eventually dropped the big end, so don't be fooled, your is stuffed, you just don't know it yet.
The external oil filter is a Britfilter and the replacement filters are available in the UK.
Don't bother trying to use any other gaskets than Steves, his are the only ones that will stand up to service.
It is a 6 Volt system, all other military specifications were 12 V.
When you get around to fitting the carburettor which is slightly down draft on the Aust bikes make sure you fit the 1" spacer between the carb & head and make sure you fit an 18" long tube to the drain outlet or you will never get it to run reliably.
Be very careful if you start it on the emergency setting because if you try & run the bike that way it will blow the battery
The cam is the ET type with a flat on the base circle so it stays open , then closes & reopens.
Because the points cam is cantilevered on the ned of the valve cam any wear in the bush can cause the cam to bounce as the valves open & close thus giving you 3 sparks.
If you are going to persist with the original ignition toss the points plate & fit the latter 6CA type as fitted to late models A 65's and mount the capacitor remote, near the coil . Also buy aftermarket A 65 points so you get a spare set which you can handily store on the points plate. Because the points are held open for 80% of the cycle, the rubbing block wears quickly so the gap will always be closing up.
You can also fit a "normal" type A65 cam but if you do you can not use the emergency start facility.
Get a copy of Rupet Ratio and do the mod to the valve lifter as there is a 99% chance that the hole will be flogged oval and they leak a lot if they are.
Pull the cylinder studs and dress the crankcase mouth, they are never flat.
When done put a small counter sink around the studs and fit the thinnest O rings you can find to stop oil running up the stud and leaking out from under the head nuts.
Similarly dress the floor of the head where the rocker cover goes on, they are generally badly damaged from over tightening by DPO's trying to stop the oil leaks which will happen if you do not use Steves gaskets.
The brake drums are significantly harder than the normal BSA nikasil drums and can only be rotary ground. DO not let any idiot try and machine them no matter how space age he tells you his gear is, rotary ground or nothing.
The exhaust is very loud, that is normal. Apparently totally inaudible at 1/2 mile in open territory, all of mine almost made that spec, but if it is too loud, weld a washer to the open end of the pipe, make no difference to the performance of the bike a but a big difference to the close proximity sound level.
I bought 2 from the first Morebank auction and ran them for around 12 years, as daily transport including two All British Rallys at Myrtleford, ridden from Sydney 2 up and 2 more solo. I geared mine up drastically and ran it as a 3 speed with top as overdrive for highway use only. Loved every minute of it.