Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board 67 68 BSA primary cover.

Sorting parts for my Bitsa I picked up my primary cover and found this:



I briefly used this cover on my 70 A65 and found it constantly leaking,
Now I know why.
One central bolt is used as an oil dumping bolt, so cover has an indentation here to let oil into the bolt opening, adjacent one has a small orifice for primary to breath outside?
Can anybody explain why and how to successfully make this cover tight?
No amount of orings or fibre gaskets under the bolts made it for me in the past.

The one hole is to drain primary and other is to set level of oil in primary. Check cover for warping, cracks or deep scratches on gasket surface. If all that is ok should seal with a gasket. I tighten bottom screws first and then tighten others. There are 2 fiber washers that go under the 2 cover screws to prevent leaking.

A '70 cover has two separate screws for drain and fill level. You have the earlier type. You likely have to spot face the outside of the cover to get a good seal. Clean the screw and hole well and put Loctite Gasket Eliminator on the fibre washer. Hylomar is another alternative. One washer per screw. Over tightening the screws will warp the cover.

Its a good plan to lightly countersink all the perimeter female threads, they get pulled up over the years, then gently run a dead flat file across the face to highlight any potential high spots ( right at the front , stones can ding the case joint), scrape down as required.
Test fit the outer with some blue to highlight areas of bad contact, , if needed , lap the outer down on a dead flat surface with a figure of eight motion.
I have a set pattern to tighten this case , start with the middle pair , ie the pair at 12 oclock and 6 o clock, then work out evenly on each side until the last outer pair at 3 and 9 oclock. this helps prevent bowing. i do this in two steps , one light nip only, 2nd time tighter.

OK thanks for all the answers, I will try all suggestions.
Will check a flatness of the case and cover having them both apart, where can I get proper fiber washers for it?
Some gasket eliminator is a good idea, however nothing worked before.
Cover gets hot and cold regularly, surfaces of a cover under bolt's heads were perhaps flat when new, but now they are not.
In contrary 70 cover worked great and never leaked.
It was probably a big nuisance for customers if BSA decided to change it.

Here is a shot of Baxter Cycle with fiber washer. Shows size so may be able to source them. Flatness of surfaces is critical for a good seal.

A THICK piece of plate glass (available at a glaziers' shop) makes an ideal surface for lapping an aluminum gasket surface.

+1 That's my go to also.

Another place that they can leak is around the drain screw, especially if you have the Allen-head replacements, as the heads are not as big as the original "cheese heads". Also, the cover where the screw head seats may be galled.

I found that a fiber washer under the screw head did not fix the problem, so I made an aluminum washer, which DID fix the problem. On installation, the alu. washer conformed to the seat as the screw was tightened - so well in fact that when I remove the screw, the washer stays in place.

I use fairly thick neoprene cork gaskets on alloy primaries.
Once sorted out as per the above suggestions just nip the screws up.
I usually put Hylomar on the cover and axel grease on the crankcase that way it will come off cleanly in future,
And the important thing is try to do all of the screws up the same amount ,
If some are looser then others then you create a weak spot where the oil can leak from.

I am positive my major oil leak was created by unadecuate seal under those 2 bolts - drain and oil level bolts, the rest of the cover was tight. Interesting info about allen head replacements and aluminum washers from Mark Z., I read somewhere about washers being aluminum originally as well, Beach picture also shows aluminum washer rather than fiber.
How did you make them Mark?
How thick are there?

Like these: ebay link

If you have the space, button head hex socket screws have a larger head than the Posi-driv screws.

I agree with all the above suggestions and what I would do to stop oil leaks is as follows:-
- get some double sided self adhesive carpet tape and glue one side to a 2x2 ft square sheet of plate glass. On top of this attach some 120 grit wet and dry paper, now you have a relatively flat surface where you can check the chain case for flatness. Gently rub the chain case over the wet & dry paper, the first few passes should show where any high spots are. Keep gently rubbing until the gasket faces are uniformly grey showing no high spots.
- next, get a bottoming tap or an old bolt with cut outs which fits the threads in the crankcase and clean out any old gasket gunge which may be lurking in the threads and preventing the screws from bottoming.
- as Gavin mentions, use a 90 degree or similar countersink to remove any pulled up metal from the screw holes in the crankcases, only a few light passes are needed.
- then get a very large flat file and run it across the crankcase/chain-case gasket area to remove any remaining high spots. On the crankcase side you may need to remove the clutch, alternator etc. to do do this fully.

Once this is all done I would use a new chain-case gasket and glue it to the crankcase side using Blue Hylomar or similar gasket cement. This will allow the gasket to be reused if subsequent disassembly is needed. Sometimes thicker cork based gaskets are useful if there is significant distortion between the crankcase and chain-case so use these if needed,

When assembling the chain-case outer cover to the crankcase, make sure you have the correct length screws. Its easy enough to assume that you do have the correct screw lengths, but if you don't, potentially all you are doing is screwing in until the thread bottoms instead of pulling the chain-case tight against the crankcase.

Regarding fibre washers I suggest you try and find some which are 1/4 in internal diameter and with an outside diameter no larger than the OD of the screw head which is about 3/8 inch.

old microwave oven glass turntable things make good flattening surface for smaller items

I'm sorry, it's been a while. I know that I made the washers, by first drilling in a piece of stock and then trimming the o.d. The hole should fit the screw snugly, and the o.d. should fill the recess in the cover. All I can say with regard to the thickness is "fairly thick". BTW, another good application for an aluminum washer is under the head of that allen bolt in the end of the fork leg that holds the damper in place. Copper would probably work as well, as long as it's soft enough to conform to the irregularities in the seat when tightened down.

My recollection of A65s when they were still original is that there were NO washers on the cover screws.

The 1970 manual says "See that the oil level and drain screws are correctly positioned with washers under the heads of the screws.", it also shows the earlier 69 style with red painted oil and level screws, the 70 definitely has washers, earlier has part number 40-740 , 2 off washer shown in the parts book just after 68 -234 oil drain screw, and 68 233 oil level screw.

yes , those 2 screw holes can leak even if the the gasket is perfectly sealed .

1. the over-fill-hole can be sealed with the threads outer-half smeared with little silicone ,
( the leak is through the threads )
2. the drain hole , if you keep the feature , can only be sealed right under the screw head .
( the drain path is milled in the primary , just under the cover )

all ive ever done is wrap plenty of that PTFE tape (like plumbers use) under the head,. works pretty well.

Yes ok, my experience was all with '67 and earlier models.

Later covers with their separate oil level and drain screws don't have a problem with screws being tighten down with relatively big torque to help keep a cover oil tight so fiber washers work, earlier covers certainly have it and fiber washers are not good enough.

The use of socket headed Allan bolts also distorts the hole so can cause it to collapse and cup in where the smaller head has compressed the alloy.
Allan headed cap screws were designed specifically to be used on steel so they have very small head with relation to the shaft size.
Thus when used on alloy they need a thick washer underneath them to spread the load.
Have a close look at your holes. good chance they will need spot facing to make the bottom flat & true to the hole again.

kevin now realizes why his B44 has piddled all its chaincase oil all over the shop floor.

on a different note,



i've often wondered why aluminum castings have this cross-hatched pattern on the inside. what's the purpose of it?

"i've often wondered why aluminum castings have this cross-hatched pattern on the inside. what's the purpose of it?"

It has obviously taken considerable effort by the casters, so would be for a reason. My guess would be to allow a slight thinning of the material, while retaining rigidity. So less alloy used = money saved.

Of course after the expenses of the lady, no money was left for casting!

this is a 67-68. why did they abandon it for later castings? here's a 70: