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I fail to see how tapping the screw holes to a bigger size will fix the primary from leaking oil?
Although the primary will never be completely oil tight, you can make it so it only leaks a little bit. The usual problem is the primary outer cover is warped around the screw holes. When the primary leaks oil the first thing people do is to think they should tighten the screws even more which only makes the problem worse. Put a straight edge on the sealing flange and check that it is straight and flat on both inner and outer covers. It most likely is not. Fix this first.
When putting it together, coat a new cork gasket with grease. Synthetic grease works best as it does not wash away as fast as petroleum grease. And finally the screws do not need to be tight! Just a little snug. The star washers under the screws will keep them from coming loose. If you over tighten them you will warp the cover and have to fix it again.
My M21 primary only leaks a few drops of oil after a long ride. Once parked and the motor has cooled down, the primary does not leak at all.
It wasn't me that suggested tapping the holes out bigger. Like Bruce says, I can't see the point in that. The original size was was 3/16" but all the suppliers will sell you 2BA screws or if the threads are weak or gone you can run a 5mm tap through which is slightly bigger.
I've glued my cork gasket into the outer cover with Evostick and grease the other face on assembly. The gasket has been on there for some years now and been off and on a few times and no leaks. Ron
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sorry guys, i knew what i meant as i was writing but did a poor job of explaining, most of the threads are gone in the holes and the screws wont tighten, some even have wee nuts on the backside, i have done my best to true up the cases but as i have to take it off again anyway for another issue i thought i would resolve the issue with the holes by tapping them out but couldnt remember what id read regarding this, so 5mm it is
thanks so much for the info again
Kevin, one thing you could try is a UNF 10-32 screw. The listed diameter of a 10-32 is a hair bigger in diameter compared the original 3/16" Cycle and I have had success with these without resorting to tapping the captive nuts on the inner.
If your captive nuts are really flogged out then this is probably not going to help but would be worth a look I think.
The original 3/16" Cycle are listed as having a major diameter of 0.1875" (32TPI).
2BA are a whisker thinner at 0.1850" (31.4TPI).
10-32 UNF are a whisker larger at 0.1900" (32TPI).
Of course manufacturing tolerances will mean the 2BA & 10-32 screws available now will vary slightly from supplier to supplier but I have found the 10-32 screws to be a really nice fit and they are available with fillester heads as a bonus.
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Ditto...I use those as well...Along with the fillister head they are also available in stainless (if you like that sort of thing)....Ian
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When I was building my primary case, I brazed new nuts on all round. The bottom half I then filled with extra braze around the holes and dressed back & /tapped through to increase the mating surface, no leaks so far, 300 miles into bedding her in.
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