The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: 900triple on 13.02. 2010 21:43

Title: Bearing choice for a conical tls front hub
Post by: 900triple on 13.02. 2010 21:43
The assembly of my A7 plunger continues...

I am putting together the front end with a tld conical hub from a 1971 Lightning. Can anyone advise if modern sealed bearings can be fitted (and if so by any chance which ones) or where I can get the part number of like for like replacements.

Cheers in advance

Alan
Title: Re: Bearing choice for a conical tls front hub
Post by: BSA_54A10 on 14.02. 2010 10:31
The comical hub was by far the strongest front brake ever fitted to any BSA.
Unfortuneately no one bothered to read the instructions properly and adjust them correctly. Because you had to take the wheel off and pack out under the shoe plates and it was a lot easier to maladjust them by tightening the cable.
Then there were all the "brake experts" that fitted new linings and radiused them to the wrong size thus preventing the leading edge to bite into the drum. Should be a bigger radius than the drum.
Mine would lock the front wheel at 80 mph, even when shod with the very sticky Pirelli Phantoms.

Putting longer actuating arms on them makes the brake worse as the braking effort dose not come from the amount of pressure that you excert via your hand but from the actual rotation of the drum expanding the shoe and forcing the linings hard in against the drum, and for this to happen the shoes need to be applied quickly.

They raced Rocket III's with the same drum brake that the "popular press" of the day were too engineeringly illiterate to understand so bagged endlessly.

There are only 2 real problems with them
1) the stop lamp switch
2) the outer cable being heavier and more sluggish in movement tended to stay in place after you released the brake so the rear shoe would drag, heat up the drum and cause loss of efficiency. This was made even worse by owners who did not understand how it worked anchoring the outer cable to the frame because it rubbed on the guard & frame , scratching both.
This is best fixed by fitting a small clock spring to the lower arm so that it moves back off the drum when released.

Be careful with the cable, the outer must be made from flat steel strip ( not wire ) and wound tightly so that it dose not become a great big spring when applied.

To use them properly, jab the brake then hold it on for maximum breaking. Pull slowly for gentle breaking.
Title: Re: Bearing choice for a conical tls front hub
Post by: BSA_54A10 on 14.02. 2010 12:35
Now I have got off the soap box, I reread your post and realized that I had not given you your answer.

The standard bearing was a Hoffman 120
Size ID = 20mm , OD =47mm, Thickness = 14 mm
Yes they are metric.
Ask for double rubber seals.
I think that makes them Hoffman 120 V3
The modern "standard sizing" is size 6204, then a suffex for the rubber seals ( 2RS or ZZE )
Or NACHI 6204ZZE
Or KML 6204-2RS
No fit prefix designates a standard fit  ( old C3)
Title: Re: Bearing choice for a conical tls front hub
Post by: MikeN on 14.02. 2010 12:42
Alan,
  Yes ,Deffinately fit sealed bearings to wheels.Ive been doing it for decades now.Ideally you want the 2RS type (2 rubber shields) ,But the 2ZZ type (2 metal shields ) would be the next best option. From memory I think the conical hubs take 62042RS ball bearings. this is a very common wheel bearing on BSA's and triumphs.
   Also,When building up gearboxes  on a bike ,I always try to fit a 1RS type bearing to the main bearing that supports the sprocket (4th) gear. 
If you fit it with the rubber seal outboard,then pack in some grease ,then fit the oil seal you then have a gearbox with 2 seals. Better than new.
 If your bearing stockist doesnt hold a 1RS bearing then get a 2RS and prise out the seal on one side with a small screwdriver .
 You use a single sealed bearing so that the gearbox oil can lubricate it.So make sure it is the right way round.
Mike
Title: Re: Bearing choice for a conical tls front hub
Post by: 900triple on 14.02. 2010 19:58
Thanks everyone-  briliant answers to questions I hadnt even thought off yet. Wow. Really good that people take time to provide such detailed and informative answers.

Cheers

Alan
Title: Re: Bearing choice for a conical tls front hub
Post by: BSA_54A10 on 15.02. 2010 02:45
And don't forget to refit the original seal.
It is necessary to make up the space