Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board BSA gearbox oil question

Hi all, I'm knew to classic British bikes. About a year ago I got a 1970 Lightning in a hard tail frame that I've finally got running and trying to get on the road. My question is about how to service the gear box oil. This is the first time I've had a bike that transmission isn't lubricated by the engine oil. I have a manual and it tells me to take the filler plug out of the engine case behind the barrels but mine does not have that plug. Mine does have a dipstick in the inner timing cover though.

Is this where the gear oil goes?

Yes
And the drain is underneath

In some year between 1967 and 1970, the gearbox filler cap was moved from the crankcase to the inner timing cover.

Up to '67 at least (I don't know if this was changed later), there's a small plug threaded into a stand-pipe, which is in turn threaded into the case. To drain the gearbox, you must remove both. When filling, you can put in just the standpipe, leaving out the small plug, and fill the gearbox until the oil reaches the top of the stand-pipe and runs out the hole vacated by the small plug.

OR, you can put in both the standpipe and the plug, and fill the gearbox to its specified capacity.

68 was the year they went to the plastic dipstick in the inner timing cover. I always thought the stand-pipe was the better setup.

Heres a tip for finding the gear box drain plug... look at the motor and think " in what worst position that would i have to grovel on the floor unable to see properly with a sore back already "

YEP well done you found it ahahha

It will be a Whitworth size hex to undo.

there will be nay-sayers but might i suggest a good gearoil of SAE 70??/90 and just fill it to the amount of CCs in book

My 70 loves the Penrite gear oil doesnt leak a drop

And the larger hex-head of the stand-pipe is rather thin, and if it's tight, you'd better have a good-fitting 6-point socket, or you will round the corners. (Tip: If you don't have the correct British socket, a 21mm socket fits very nicely.)

no standpipe on that?

Right, must be the later type. My comments about using a good fitting 6-point socket still apply, assuming they did not change the wrench size.

They changed the hexagon size, Mark.

The later drain plug has 15/16" AF at least on my 69 and 71-A65s.

Cheers!

Phil

not so sure about the 15/16 AF ...that is a seriously big nut ... approx. 23 mm af ... doesnt sound right to me ?... my 70 has some whit worth size ...but someone said a 21mm socket will do the job ( probably will) ... its enough to drive a man to drink so thank you hahhaahh

Sorry for playing the wise guy.

My 71 Firebird is on the bench currently and I had the drain plug out and measured it. The hexagon is 15/16" AF, same as for my 69 Lightning.



I have no clue whether or not the thread itself is UN-type, but I assume it is.

Cheers!

Phil

DANG ...my memory like much else is failing ... well done Phil

but at least i got 1 bit right about it being a Whitworth hex

hex size for 1/2 BSW and 9/16 BSF are 0.920" , 23.4 mm AF as shown in your picture

looks like 1/2 in your pic Phil ?

Not on '68. Went to a dipstick filler cap that year.

Hi!

I did not measure the thread, I can do on the weekend if deemed necessary or helpful. The hexagon measures 15/16".

When doing a parts-# search via Google, you'll end up soon at Baxter's. They state the thread was 13 tpi which would make it 1/2" UNC.

Anyhow...

Cheers!

Phil