BSA Owners' Club Workshop Discussions

The BSA Workshop => Twins => Topic started by: Willie Dee on 28 Sep, 2021, 18:02

Title: Lightning forks
Post by: Willie Dee on 28 Sep, 2021, 18:02
Did a few miles on Saturday round Perthshire, including through a bit of heavy rain, when I parked the bike up, the fork yolks were covered in oil and everything around them. My first thought was it had came up the speedo or rev counter cable and leaked out the heads. It is clear fork oil though and looks like it came from around the chrome bolts/nuts at the top of the legs,what would cause this? One was leaking and it is on the list of things to do, but not sure why they would start pumping oil out the top. Cheers.
Title: Re: Lightning forks
Post by: idie on 28 Sep, 2021, 19:33
At a quess water has got into the forks and as there is now no room for the oil it is being forced out when the forks compress.
Title: Re: Lightning forks
Post by: Willie Dee on 30 Sep, 2021, 03:56
That's a possible, it was the first time I had been caught out in a downpour. Will have a look this weekend and see what we can see. Ta.
Title: Re: Lightning forks
Post by: Martin S on 30 Sep, 2021, 10:41
This might be a dumb question, but I've not stripped my forks down. 
Given that the drain screw should be a leak tight seal, and the top nut is secured against a washer, can someone tell me how the air in the forks vents during compression/rebound?
Thanks in anticipation of a wise reply
Title: Re: Lightning forks
Post by: ChrisG on 30 Sep, 2021, 15:25
Probably a daft question but have you the correct quantity of oil in there and not too much?
Re the air left in the forks, that will compress as the forks depress and decompress as they release. Air compresses easily, oil doesn't compress at all.
Title: Re: Lightning forks
Post by: Willie Dee on 01 Oct, 2021, 04:30
Editor, if anything the oil would have low as one of the legs has a leak and is on the "to do" list and they have never been topped up. I suspect something has vibrated loose " everything else has" but we will see what we find over the weekend. Cheers