Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board BSA A65 Primary Cover

Notice how the middle screw hole is stepped back a bit from the gasket surface.
What is the reason for this or is it unique to my cover?

its an oil drain Channel for when the cover screw is removed ... but can leak even when the screw is in place .

look at
The screw mount boss to the left , it has a smaller hole at 90° ... this is a "fill-to" level hole
... when this cover is on ... and this screw is pulled out .

When the cover is on ... these two screws holes work as the drain- hole
and the fill-to-level hole .

A very clever design ... that is prone to leaking if you don't know what BSA was up to .
these 2 primary cover screws are sealed ... just under their heads
And not through the primary cover gasket .
( i believe the two original cover screws were painted )

you can modify the cover holes to defeat BSAs intended purpose with goopy sealer
... or carefully fit to the screw-shank and cover-hole
soft aluminum or copper... or hard rubber washers .

Ah, yes clever. I guess.

So how are those 2 screws sealed? Washers? I don't see any in the parts books but I may be looking at the wrong year.

I've got a leak there.

Page B24 WSM, 1970
Plate 9 PB, part no 40- 740 2 off.1968
Page 31 , haynes manual.

Those two screw heads were originally painted red from the factory, and were supposed to have an aluminum washer that sealed the hole from the outside of the case, rather than the cover gasket that seals all the others. The system works if you understand what was intended and are careful in assembling it as such. Looking at the screws from the outside of the bike, these two screws are at the bottom of the primary case, immediately fore and aft of the brake pedal. The screw forward of the brake pedal is the level check. Remove both screws and allow all the oil/fluid to drain. Replace the drain screw, which is the one just behind the brake pedal. Make sure the sealing aluminum washer is present, and it fits well into the screwhead well of the cover. Then fill the primary via the inspection plug until fluid begins to escape from the level screw hole. Make sure you have the sealing aluminum washer on this screw as well and install. If you have a good primary gasket, and you have taken care in installing these two aluminum washers, and the primary chain adjuster hole bolts are also installed correctly, the primary shouldn't leak. I know its a lot of holes to attend to, but is was a clever attempt to make the primary lubrication level easily maintained.
Fullminator.

Thank you. Naturally the washers are missing. I could try to make one out of aluminum but it would have to be quite small, the diameter the same as the bolt head, to fit in the recess. Is there an explanation why this would seal when the bolt alone won't?

You can use the late triumph 1/4 t100 copper rocker cover washers, they are a small o/d.

I don't think they're clever at all. What a terrible design..
The later years had casting and screws separate from the mounting screws which was definitely better. Why they didn't do that sooner I don't know...
I've had "stock" aluminum washers, copper washers and any other crush/seal washer I could think of and they all leaked 9 out of 10 times. Especially if you run atf in the primary side instead of standard oil. I tried running a silicone primary gasket and if you tighten it down enough to get the seal/crush you ruin the silicone gasket. With standard gasket majority of the time you have to use something like RTV goop with the washer just to ensure it seals. Then you get to deal with the goop stuck to the case next time you have to fiddle with it. The engineer that came up with this design was an idiot.. or the guy that signed off on the idea, one or the other or both should have been dick punched in my opinion...

We have one like that on the race bike and it's fine, just use it with a decent gasket.
Plug the level hole with a 3mm screw and drill/tap another in the cover if you wish.
The drain is more awkward but using a copper washer works if the face is dressed.
Problem is most are chewed up and need a mill cutter to dress them.
I agree the design is not terrific but people didn't worry about oil leaks back then,
everything leaked oil. (until it was empty anyway!)

The problem is aggravated by the allen-head replacement screws that so many of us use, since the heads are not as big in diameter as the original "cheese head" screws. And of course damage to the cover from over-tightening.

I never had a problem with the "level" screw leaking (probably because I always measure what I put in), but to get the drain hole to stop leaking, I had to fashion an aluminum washer. I made the o.d. large enough that the washer would jam in place on first tightening, and conform to any unevenness in the seat. Now when I remove the screw, the washer stays in place. And it doesn't leak. (BTW, neither of my A65s had washers there until I added them, and I don't see washers in the factory Spares manual.)

The original screws were Posi-driv, not "cheese head" or Philips. That was part of the problem. Americans would use Philips screw drivers on them which would cam out of the slot so they pushed harder and torqued them more. Especially if they leaked, the solution was more torque. That crushed and deformed the hole.
A hex socket screw head measures 0.372", a Posi-driv 0.395". Not a big difference but you can apply more torque with a hex wrench than a screw driver, and people did.
Once the screw seat is damaged it has to be spot faced to make it flat again. No amount of torquing is going to move the metal back into place and make a flat surface for the head to seal against.
Places such as McMaster have metal washers with neoprene seal but the 1/4" are too large to fit in the screw pocket which is about 0.420". You can drill a #12 washer (0.375" O.D.) to 1/4" (0.257" clearance) or mount washers on a mandral and turn the O.D.

Washers , part number 40- 470, quantity 2 off, plate 9 in the parts book, item 8 in the illustration.

"

The screw seat can be dressed flat with an old screw cut short and a dab of grinding paste. A fibre washer can be used , if al or cu isnt handy, fit a stack of washers to a 1/4 bolt, sandwich with a nut, chuck the bolt in a power drill, file them down to suit, poor boy lathe. most folk have a power drill and a file.

Model airplane glo plug washers work very well.

What is this flat for?

A bit uncalled for.

Modern manufacturers of cars and bikes still have issues which get resurected a few years later or factory recalled. My last Honda got an passenger air bag recall 12 years after the car rolled off the production line, I doubt anyone at BSA would ever have though anyone would still be riding their bikes 10 years later, never mind 50+. They were also a "Cheap" bike, for the ride it to work classes, if you wanted something more refined you'd pay more and buy a Norton or better still a brough superior... And like Dave Maddigan stated, they would have been fine from new, just some people think over tightening the case screws solves the problems, infact it just buggers them up. So if your going to "dick punch" anyone, it should be the DPO who buggered it in the first place.

Agree with Dmadigan's and Allans comments above about over tightening the cover screws, this is made worse when socket caps are used and more torque can be applied.

Although I do use socket caps on all my bike covers I only lightly tighten them about 1/4 turn to avoid stripping the thread or distorting the seat. Its also worth while manually running a drill down the screw hole to remove any old gasket material/gunge, its amazing how much stuff comes out. Equally its important to use the right length screw to avoid bottoming or stripping the thread.

I use fibre washers under the screw heads where there is a drain hole, the size I find works is 1/4 id, 3/8 od and 1/16 thick. These are easily available on eBay etc. See Example.

Lots of great ideas. Leaks are soooo annoying.
I was making my own washers the "poor man" way similar to what Gavin described but
McMaster has several types of sealing washers but most won't fit.
They do have copper and aluminum metric sizes (id- 6.2mm, od-9.9mm) in packs of 25 or 50, Might be a handy thing to have for a Brit bike owner.
(May still need to be drilled out for 1/4")

Get your self a set of reamers. Parallel or adjustable, they come handy quite a lot, especially for resizing holes in copper gaskets etc.

Allen, you are correct sir. My apologies. Out of all the issues that are a pain in th backside with these old bikes this is the one that gets me the most spicy. Thank you for calling me out. Cheers.

I know they were posi-drive, but the heads look like rounds of cheese, so I thought they were also called "cheese heads".

My hand-made aluminum washer fix does exactly what's prescribed; when tightened down, it conforms to the unevenness of the seat and provides a flat surface for the head of the screw to sit against. The i.d. of the washer must fit the screw closely, and the o.d. must jam against the recess in the cover so that the washer does not turn with the screw. It must be a fairly thick piece of aluminum, like 1/16". It's essentially repairing the seat.


I'll take another look Gavin; it's been a while...

ps. I had no success with fiber washers in this case; not sure why.

all ive ever done to stop the minimal oil leak at those screws is wrap quite a bit of Teflon plumbers tape around them right under the head .......works well

Ask for "posidrive" screwdrivers at most hardware stores in the USA and all you get are stupid looks from the clerks.

I dunno, my Craftsman #3 Phillips always fit them quite well. But I still like the socket-head replacement screws better. For one thing, with those, I can use a socket-drive Allen key and my crank-shaped socket driver to spin them on and off in a jiffy. I just have to remember, when tightening, only use the amount of torque that I can apply with a screwdriver.

Happy endings. Fixed my primary leak by using the (larger head) original type Posidrive screws for those two trouble spots. I think I'll paint them red
which should impress - nobody.

Also used fiber washers sized to just a hair wider than the screw head.

I left the hex head screws in the other spots.

One thing the parts manual is not too helpful with is showing which screw goes in which spot. Four different lengths for this cover.