The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Goldy on 16.02. 2011 15:18

Title: Oil feed to rockers
Post by: Goldy on 16.02. 2011 15:18
Whilst working on the bike I have been studying the lubrication system. The oil feed to the rockers goes through the two banjo screws which have a nice hole up the centre of the screw, but the radial hole is very small, about the size of a pin. Is this correct or have I got two duff banjo screws. I can,t work out why they are so small. Any thoughts.
Title: Re: Oil feed to rockers
Post by: bsa-bill on 16.02. 2011 17:07
Can't recall exactly the size but they are not big holes for the A7/A10s, there are pictures on here somewhere, do a search for banjo bolts
Title: Re: Oil feed to rockers
Post by: dpaddock on 16.02. 2011 22:38
As always, it's customary and helpful to state the model and year of the BSA you're inquiring about, Goldy.

Thankfully, all A7s and A10s were fitted with the same Rocker Oil Feed Pipe Banjo Screw, P/N 67-317, which has a 3/64-inch radial hole for both inlet and exhaust rockers. This hole size is quite adequate to lubricate the rockers.

If the screw has a 3/32-inch radial hole, it is intended for the exhaust rocker on Gold Star and probably other BSA singles.

David   
Title: Re: Oil feed to rockers
Post by: Brian on 16.02. 2011 23:11
The B series also use the same ones with the small hole to feed the rocker gear with exception of the exhaust rocker on the Goldies as David says. Most of the ones you come across with the bigger hole are from the B series but are the ones that go in the rocker box drain pipe. If you look at a picture of a B31/33 you will see a pipe on the rear left side of the motor that goes from the head down to the crankcase, this pipe is held on with the bolts with the bigger holes in them as it is a drain pipe.

The part number for the Goldie exhaust one is different to the drain ones for the B series so there are probably three hole sizes available.

So there's a bit more useless information for you. *doh*
Title: Re: Oil feed to rockers
Post by: Goldy on 17.02. 2011 12:27
The machine is 1956 A10 Golden Flash
Thanks for the detailed info, that is exactly  what I was looking for. The radial hole in my banjo bolt is 1/32" which as I said just looks like a pin hole I just cannot imagine how cold SAE40 oil gets through. The oil feed pipe is 1/8" bore and the rocker spindle is 5/16" bore so why did they put in such a restriction. Obviously the larger the hole the more the bolt will be weakened but mine at 1/32" needs to be opened up, even 3/64 seems small. I am going to open them up with a 1.5mm drill.

I would suggest that anyone buying reproduction banjo bolts should check this hole size.
Title: Re: Oil feed to rockers
Post by: pbaker on 17.02. 2011 13:03
careful if you bore out the hole as increased dia will reduce the outgoing pressure and the length of spray or return might be impaired
Title: Re: Oil feed to rockers
Post by: dpaddock on 17.02. 2011 16:11
It's amazing that all those thousands of A7s and A10s have survived with tiny holes in their banjo screws . . .

David
Title: Re: Oil feed to rockers
Post by: Goldy on 17.02. 2011 19:28
dpaddock   you have completely missed the point which is that the new  ones ARE INCORRECT.
Title: Re: Oil feed to rockers
Post by: chaterlea25 on 17.02. 2011 19:40
Hi Goldy,
3/64ths is = to 0.0468 in or  1.19 mm, = 1.115 mm.sq
the amount that will flow if you increase the hole to 1.5mm is considerably more = 1.769mm.sq
you may find that the engine gets smokey as oil may find its way down the valve guides???

HTH
John O R
Title: Re: Oil feed to rockers
Post by: cus on 17.02. 2011 22:19
Being a smaller hole would probably create more preasure,
I don't think the oil volume would differ too much between the two,

Cus
Title: Re: Oil feed to rockers
Post by: bsa-bill on 17.02. 2011 22:24
Careful Goldy, the difference between 1.19mm and 1.5mm may only be 0.31 mm (25% of the radius) but it is 0.31mm all the way around the circumference (outside) of the hole and that counts for much more than 25% of the area, and will increase flow perhaps too much as John suggests
Sorry I've been left school too long to remember the formula to work that out of the top of my head