The BSA A7-A10 Forum

Technical => Frame => Topic started by: RoyC on 03.08. 2019 15:11

Title: Fork oil
Post by: RoyC on 03.08. 2019 15:11
My forks are a little soft / bouncy.
What is the thickest oil that I can put in them ?
Title: Re: Fork oil
Post by: coater87 on 03.08. 2019 15:31
 Roy,

 I want to say i have seen 30 weight fork oil at the Harley shops, not certain though.

 I had the exact same thing, was running 20W and the forks were like mush. I also have progressive springs.

 I made a set of dampers exactly as John drew them,  then filled the forks with 300ml of 10w. They are now almost too stiff. Maybe I used too much oil? *conf2*

 But really the handling of the bike is 5x better, and i dont want to lose all of that so i may leave well enough alone.

 Lee
Title: Re: Fork oil
Post by: RoyC on 03.08. 2019 15:59
Roy,

 I want to say i have seen 30 weight fork oil at the Harley shops, not certain though.

 I had the exact same thing, was running 20W and the forks were like mush. I also have progressive springs.

 I made a set of dampers exactly as John drew them,  then filled the forks with 300ml of 10w. They are now almost too stiff. Maybe I used too much oil? *conf2*

 But really the handling of the bike is 5x better, and i dont want to lose all of that so i may leave well enough alone.

 Lee
Thanks Lee.

So more oil rather than thicker oil may be the answer.  *smile*
Title: Re: Fork oil
Post by: muskrat on 03.08. 2019 21:59
G'day Roy.
"So more oil rather than thicker oil may be the answer."
No, more oil will restrict the amount of travel.
Try 30wt, I've used 50wt in the racer. The double dampers are the way to go. The oil should just cover the valve head when fully extended.
Cheers
Title: Re: Fork oil
Post by: beezermacc on 03.08. 2019 23:35
There are some small holes at the bottom of the fork stanchions which the oil has to pass through as the forks go up and down. The rate at which the forks travel (i.e the damping effect) is controlled by the size of the holes and the thickness of the oil passing through them. Thin oil will pass through the holes easier and quicker than thick oil. So, to control the speed of fork travel you need to alter the thickness of the oil. Increasing the quantity of oil reduces the air capacity of the forks - If you fill the forks completely they would be solid! The quantities quoted by manufacturers take into account the air capacity of the forks, the spring weight and the travel. Unfortunately pattern parts are likely to vary in specification from original so setting up forks will, to an extent, be trial and error. The bushes need to be in good condition and the quantity used should be very close to manufacturer's spec.
Title: Re: Fork oil
Post by: duTch on 04.08. 2019 00:17

 I know they're a different construction, but I initially tried 10w & maybe 15w fork oil in my Conical forks until I realized BSA specify ATF....... not a lot of noticeable difference, but maybe a bit less squishy.  Modern ATF is probably diffo to what was available in the 70's though too, but maybe worth a try and if it doesn't work out you can always use it in the primary
Title: Re: Fork oil
Post by: Black Sheep on 04.08. 2019 07:29
Did BSA really specify ATF? My Haycraft book specifies such oils as Mobiloil Arctic, Castrolite, Esso 20W/50 and BP Energol SAE 20.
I use 15W/30 and get a good ride (oo err ) *smile*
Title: Re: Fork oil
Post by: BSA_54A10 on 04.08. 2019 08:43
Dextron is specified for OIF front forks and that is around 10 to 15.
Title: Re: Fork oil
Post by: duTch on 04.08. 2019 09:14

 
Quote
Did BSA really specify ATF? ............

 Yep; OIF (Oil In Frame)/ Conical forks, what Trev says;

 
Quote
Dextron is specified for OIF front forks and that is around 10 to 15.
Title: Re: Fork oil
Post by: Black Sheep on 04.08. 2019 10:17
Must be these new-fangled unit construction thingies that have ATF. They'll never catch on. 10W-30 tractor oil does all my pre-unit forks.
Title: Re: Fork oil
Post by: duTch on 04.08. 2019 16:47

 
Quote
Must be these new-fangled unit construction thingies that have ATF. They'll never catch on. .......

 Dunno- I went to a jack place for oil to use in a small trolley-jack I rebuilt, and the guy said they just use ATF, that was about  four or five years ago  *dunno*