Britbike forum Forums Thread Like Summary - 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?

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

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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.

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.

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 .

Model airplane glo plug washers work very well.

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.

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.)

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

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.