BSA Owners' Club Workshop Discussions

The BSA Workshop => Twins => Topic started by: AdrianS on 21 May, 2020, 14:35

Title: Primary drive venting
Post by: AdrianS on 21 May, 2020, 14:35
I've block off the chain oiler on my early a50.
I am a bit concerned re venting of the primary drive as I believe the oiler also acted as a vent for any pressure built up.
I've seen part 70-9800 which looks like a filler cap with a hole in it. Can anyone confirm that it is just a cap with a very fine hole drilled in it?
Also, my primary drive cover has what appears to be 2 holes adjacent to the 2 caps which are centrally placed on my chain case cover. Without removing the cover,can anyone tell me what they are for?
Cheers for any help
Adrian
Title: Re: Primary drive venting
Post by: ChrisG on 21 May, 2020, 14:47
The small hole in the caps is sufficient to relieve any pressure build up. There won't be much pressure as the oil seal keeps most of the crankcase pressure where it belongs. The two holes with caps were there for clutch adjustment. One for the centre, rod adjuster and the other so you can get at each spring adjuster in turn. They discontinued this on later models as getting the clutch to lift evenly by adjusting the springs needs to be done with the cover off so you can see the edge of the pressure plate when spinning.
I cant remember seeing any extra holes as described, can you tell us what dia. they are?
Title: Re: Primary drive venting
Post by: AdrianS on 21 May, 2020, 15:02
So is it ok just to drill a tiny hole in a cap ( I've got a couple of spare ones)?

I'll take a picture and post it showing the other 2 holes
Title: Re: Primary drive venting
Post by: AdrianS on 21 May, 2020, 15:11
Photo of chaincase
Title: Re: Primary drive venting
Post by: DAVE BRADY on 21 May, 2020, 15:45
I have found an image of another such case.  The holes correspond with two bosses on the inside of the cover such as on one I have but with no holes.  Marks on the case in the image seem to suggest that there was cover over the two caps ????

Dave.
Title: Re: Primary drive venting
Post by: DAVE BRADY on 22 May, 2020, 10:32
Hi,

Found another image with the cover this time.

Dave.
Title: Re: Primary drive venting
Post by: AdrianS on 22 May, 2020, 10:52
Thanks Dave. Clears up the mystery!