But I have never seen any british bikes with a felt filter in the tank or feed
My 1955 plunger BSA M33 had a felt filter in the tank, on the return. So had my 1955 AJS. Velocettes and Vincent’s had one somewhere in the system too.
Good to know, I will keep an eye out on some of my BSA singles, I have a late 40s BSA B33 and some Goldies (49-57) and sooner or later I have a 32 Blue star sitting in the UK I hope to see sometime soon.
I am also assisting a younger guy with his Vincent Rapide project but I am sure he is ahead of me on this,, I dont have much Vinnie knowledge. I would not have a lot of faith on any oil system with a felt filter in place.
On a tangent,, I used to make fun of these (Frantz Oil filters) as they use a roll of toilet paper as a filter. Typical old gimmick type product seen in ads in magazines. I saw some farm vehicles growing up with these fitted but as I said,, I used to laugh at the idea. I got yelled at for doing so in aviation mechanics school by the instructor as he felt very strongly they were an excellent device. (Not suitable for acft tho..) So, he showed me some tech materials and test reports that showed very effective filtration. So, amusing as they are.. they DO actually work well, but I cannot see fitting one on a vintage bike. (Well, Maybe a Harley
)
(But I DO fit a return line filter too ALL my classic bikes)
See:
http://www.frantzfilters.com/The modern version of the company is a totally different animal from the original frantz products from the 60s-80s) and much more expensive,.. But its still a hot topic on many forums still today.