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#498939 - 07/25/13 2:18 am a65 fork oil weight  
Joined: Sep 2004
Posts: 680
gunner Online content
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gunner  Online Content
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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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#498946 - 07/25/13 3:18 am Re: a65 fork oil weight [Re: gunner]  
Joined: Aug 2001
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Mark Z Online content
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Mark Z  Online Content
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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.
#498954 - 07/25/13 4:36 am Re: a65 fork oil weight [Re: gunner]  
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CaptainPugwash Offline
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CaptainPugwash  Offline
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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

#498977 - 07/25/13 12:40 pm Re: a65 fork oil weight [Re: gunner]  
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markoz Offline
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markoz  Offline
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Au
Last change I went back to 20/30 weight engine oil and I noticed less rebound on return, offered a good ride.

#498980 - 07/25/13 12:55 pm Re: a65 fork oil weight [Re: gunner]  
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Lannis Online content
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Lannis  Online Content

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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


OK, I admit it, I'm addicted to brake fluid.

But I can stop any time I want.
#499071 - 07/26/13 5:38 am Re: a65 fork oil weight [Re: gunner]  
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Stuart Online content
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Stuart  Online Content
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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,

#499091 - 07/26/13 10:35 am Re: a65 fork oil weight [Re: gunner]  
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Jeff B Offline
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Jeff B  Offline
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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.
__________________
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#499105 - 07/26/13 12:48 pm Re: a65 fork oil weight [Re: gunner]  
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Ola Offline
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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)
#499139 - 07/26/13 7:14 pm Re: a65 fork oil weight [Re: gunner]  
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gunner Online content
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gunner  Online Content
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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
#499153 - 07/26/13 9:21 pm Re: a65 fork oil weight [Re: gunner]  
Joined: Feb 2007
Posts: 2,200
Semper Gumby Offline
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Semper Gumby  Offline
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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
Parking lot Elf in training
#499160 - 07/26/13 9:48 pm Re: a65 fork oil weight [Re: gunner]  
Joined: Aug 2006
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Pelle Offline
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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.

#499195 - 07/27/13 4:24 am Re: a65 fork oil weight [Re: gunner]  
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CaptainPugwash Offline
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CaptainPugwash  Offline
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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

#499200 - 07/27/13 5:52 am Re: a65 fork oil weight [Re: Semper Gumby]  
Joined: Jul 2001
Posts: 12,056
Lannis Online content
Life member
Lannis  Online Content

Life member

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Posts: 12,056
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


OK, I admit it, I'm addicted to brake fluid.

But I can stop any time I want.

Moderated by  Allan Gill, Jon W. Whitley 


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