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a65 fork oil weight #498939
07/25/13 2:18 am
07/25/13 2:18 am
Joined: Sep 2004
Posts: 850
Farnham, Surrey, UK
gunner Online content OP
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gunner  Online Content OP
BritBike Forum member

Joined: Sep 2004
Posts: 850
Farnham, Surrey, UK
IM about to change the fork oil on my A65 and was wondering what weight others are using?

Despite having a 68 Firebird engine, the frame and forks are actually from a 63 A65 Star. The forks have the internal damper rods and the front wheel uses the single sided 8 inch sls brake.

I know at one point BSA recommended using engine oil in the forks but I dont like the idea of that. IM a road rider so IM looking for is a reasonably supple ride but dont know what grade of modern fork oil is best.

All info welcome.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
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Re: a65 fork oil weight [Re: gunner] #498946
07/25/13 3:18 am
07/25/13 3:18 am
Joined: Aug 2001
Posts: 4,550
Owego, NY, USA
Mark Z Online content
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Mark Z  Online Content
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Joined: Aug 2001
Posts: 4,550
Owego, NY, USA
You want to use a non-foaming oil like ATF or fork oil. ATF is recommended for the later ('71-'72) forks, but too light for the earlier forks. Fork oil comes in a variety of viscosities. It's somewhat a matter of preference, and you can experiment to see what you like. I've settled on 15W for my '66 and '67.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: a65 fork oil weight [Re: gunner] #498954
07/25/13 4:36 am
07/25/13 4:36 am
Joined: Nov 2008
Posts: 69
Conisbrough,Yorkshire, UK
CaptainPugwash Offline
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CaptainPugwash  Offline
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Joined: Nov 2008
Posts: 69
Conisbrough,Yorkshire, UK
I find my 70 Royal Star works well with sae20 fork oil but I am also using progressive springs.

Cheers and beers
Dave

Re: a65 fork oil weight [Re: gunner] #498977
07/25/13 12:40 pm
07/25/13 12:40 pm
Joined: Feb 2010
Posts: 451
Au
M
markoz Offline
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M

Joined: Feb 2010
Posts: 451
Au
Last change I went back to 20/30 weight engine oil and I noticed less rebound on return, offered a good ride.

Re: a65 fork oil weight [Re: gunner] #498980
07/25/13 12:55 pm
07/25/13 12:55 pm
Joined: Jul 2001
Posts: 12,962
Central Virginia
Lannis Offline

Life member
Lannis  Offline

Life member

Joined: Jul 2001
Posts: 12,962
Central Virginia
20w BelRay fork oil for me. I've tried different weights to try to control topping-out, etc, but always come back to 20W as the best overall ..

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.
Re: a65 fork oil weight [Re: gunner] #499071
07/26/13 5:38 am
07/26/13 5:38 am
Joined: Jun 2002
Posts: 10,233
Scotland
S
Stuart Offline
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Stuart  Offline
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Joined: Jun 2002
Posts: 10,233
Scotland
Hi,

Originally Posted By: gunner
IM a road rider so IM looking for is a reasonably supple ride but dont know what grade of modern fork oil is best.

Ime, one of the advantages of using, specifically, modern fork oils is that, if you want to try a viscosity that isn't available off-the-shelf, it can be created by mixing different proportions of lower and higher viscosities. E.g. having fitted twin front discs to my T160's, 20w allowed too much fork dive under braking while 30w caused the front wheel to skip across series of small road surface ripples; frown I eventually ended up with 25w bigt - a half-and-half mixture of the aforementioned two.

Hth.

Regards,

Re: a65 fork oil weight [Re: gunner] #499091
07/26/13 10:35 am
07/26/13 10:35 am
Joined: Dec 2001
Posts: 123
Germany
Jeff B Offline
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Jeff B  Offline
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Posts: 123
Germany
I always use 20W dedicated fork oil. Works fine for me. Any thinner oil is too light for these relatively crude forks.
Change it once a year as the forks let water in and the oil turns into an emulsion.


Jeff B.
__________________
67'Hornet
71'B50SS
73'Ducati 450 SCR
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Re: a65 fork oil weight [Re: gunner] #499105
07/26/13 12:48 pm
07/26/13 12:48 pm
Joined: Oct 2001
Posts: 529
Norway
Ola Offline
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Ola  Offline
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Posts: 529
Norway
Drilling a tiny hole in the oil seal holder, flush with the oil seal top, will prevent water filled forks.

Regards


There are no bosses in a technical discussion
(Doug Hele, 1919 - 2001)
Re: a65 fork oil weight [Re: gunner] #499139
07/26/13 7:14 pm
07/26/13 7:14 pm
Joined: Sep 2004
Posts: 850
Farnham, Surrey, UK
gunner Online content OP
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gunner  Online Content OP
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Posts: 850
Farnham, Surrey, UK
Thanks for all the replies, today I decided to investigate why my forks were not performing as expected. I removed the wheel and mudguard, drained the fork oil and extracted each fork leg.

I found several issues as follows:-
- although my frame is from a 62 A65 Star, the forks are from a later bike, probably a 67 A65 lightening. My forks use the damper rods and have the QD front wheel, which I believe were not used on earlier bikes.
- the fork springs measured 10.75 inches, however my understanding based on the 67 workshop manual, is that they should be 10 inches long. I expect this may have contributed to the harsh ride.
- there was approx 140cc of oil in each leg. This is less than the specified 1/3 pint (190cc) that I filled them with last year. This may have contributed to poor damping. There were no leaks from the forks, so IM wondering where all the oil went, maybe the socket cap at the fork base was leaking slightly?

I have now ordered some progressive fork springs from SRM and will be using synthetic fork oil. I will have to experiment to see which weight is best but expect it to be somewhere between 10w and 20w,

Last edited by gunner; 07/26/13 7:22 pm.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: a65 fork oil weight [Re: gunner] #499153
07/26/13 9:21 pm
07/26/13 9:21 pm
Joined: Feb 2007
Posts: 2,252
Atlanta, GA USA
S
Semper Gumby Offline
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Semper Gumby  Offline
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S

Joined: Feb 2007
Posts: 2,252
Atlanta, GA USA
20 Wt I think. Whatever your favorite brand. Or there is good ol' ATF....

(Is this an ADOT?)


Gaggle of BSAs
a Honda
an old BMW
and a Montesa
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Re: a65 fork oil weight [Re: gunner] #499160
07/26/13 9:48 pm
07/26/13 9:48 pm
Joined: Aug 2006
Posts: 193
Sverige
Pelle Offline
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Pelle  Offline
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Posts: 193
Sverige
The SRM progressive springs are 285 mm, so slightly more than 11".

I use them on my WD B40. However, the standard WD B40 fork legs (41-5116) are 21-7/8" long and will put some pre-load on these springs. I use the slightly longer A50/A65 legs (68-5144), 22-5/8" long, which put practically no pre-load on the SRM springs. To match the longer legs I've lengthened the damper rods. With SAE 15 oil the the front end is comfortably soft but not mushy.

Check the length of your fork legs. Shorter legs = more pre-load on springs and possibly a harsher ride.

Re: a65 fork oil weight [Re: gunner] #499195
07/27/13 4:24 am
07/27/13 4:24 am
Joined: Nov 2008
Posts: 69
Conisbrough,Yorkshire, UK
CaptainPugwash Offline
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CaptainPugwash  Offline
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Joined: Nov 2008
Posts: 69
Conisbrough,Yorkshire, UK
I was very surprised at the stiffness of the SRM springs compared with my old ones. But the difference in ride is so much better than before and gives me much more confidence with the bike.
Cheers and beers
Dave

Re: a65 fork oil weight [Re: Semper Gumby] #499200
07/27/13 5:52 am
07/27/13 5:52 am
Joined: Jul 2001
Posts: 12,962
Central Virginia
Lannis Offline

Life member
Lannis  Offline

Life member

Joined: Jul 2001
Posts: 12,962
Central Virginia
Originally Posted By: Semper Gumby
20 Wt I think. Whatever your favorite brand. Or there is good ol' ATF....

(Is this an ADOT?)


Sort of. It's ADFOT!

Lannis


I stopped believing for a little while this morning. Journey is really going to be upset.

Moderated by  Allan Gill, Jon W. Whitley 


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