Fork pump help

[captaincaveman]

Anyone know where I can get a pump to pump up the forks? I believe I need 13psi, I can't use my compressor on my starter charger as gauge gone and told many pumps will risk blowing fork seals

Been told a push bike pump can be used? Anyone know if this is ok? And if 13psi is a correct standard setting for a b1?

[steve.w]

use a foot pump mate

[Pigford]

No - use a bicycle suspension pump - about £20

[Al]

I use a car foot pump and try not to drop it on the tank. For pressure check i use one of those low range gauges they have for trials tyres.

Actual pressure depends on some of the following; weight of oil used, volume of oil used, weight of rider and riding style, type and pressure of front tyre, ambient temperature, reading taken loaded or un-loaded, etc etc.
This is, i guess, why they give a wide range in the spec. but half the fun is finding youre own preference.
Most important is to get matching values left and right. Not perhaps as easy as it sounds at very low pressures since the process of checking bleeds away a large percentage of what is a very small increase internally.

When you pump it up it lifts the bike too. Co-respondingly, checking lowers it also so it fluctuates left to right.

For reference on the J1;
Front tyre pressure. 32 psi
Oil weight. 15W
Volume of oil. standard by linear measurement method
Ambient temperature. 20 deg. C
Fork air pressure. 7 to 10 PSI with bike on side stand
Standard fork springs
Rider. 12 stone
Mood. enthusiastic more than talented
Brakes. non-existent


Yes over-pumping even a little may blow the seals.


AL

[captaincaveman]

cheers guys, i'll have a look for a bike suspension one, be nice to find one with a half decent guage on it though

cheers for all that info Al, i'll probably try 8psi and see how that feels

I had a similar set up in my gs1000 but i never touched that and it felt good at whatever it was, these ones are empty when the fork seals were done

[needaz1100r]

From what I remember a pump fitting that screws on (bicycle) is more dificult to use than a push on one (foot pump) because it takes longer to remove and so more of the air you just put in comes out.

Remember, when first built there is air in the forks above the oil at around 15PSI.

When the forks compress and the air gap reduces the pressure rises, the pressure pushes on the oil, which pushes on the fork leg and adds to the sopring pressure if the air gap is halved the pressure doubles, so the forks get stiffer, as the air gap halves again, now for less travel, the pressure doubles again.

Therefore all forks are air forks, except some Italian ones that had bleed holes in the cap. What we think of as air forks are ones you can increase the initial pressure on.

You can tune the rising rate by putting more or less oil in. If there's a 100mm air gap, the forks need to compress 50mm to double the pressure, with a 90mm air gap the travel only needs be 45mm to double the pressure, but with a 120mm gap travel would need to be 60mm. So long as the oil covers the damping mechanism and does not lock up the forks it's OK.

Sorry, got carried away there!!

[big green bus]

You should use a quick release pump (like Stevew says) make sure there is no weight on the forks. pump them up to around 20 psi than use a pencil tyre pressure garage check the pressure.
then check it again to see how much is lost when to take the guage off. There is so little pressure in that small area that you can lose 5 psi every time you check the pressure so if you check it and it reads 15 when you take the gauge off you only have ten left. You may need to do this a few times to get the pressure the same in each leg. You are better off with low than high or you may just pop the seals when you brake hard

[captaincaveman]

You should use a quick release pump (like Stevew says) make sure there is no weight on the forks. pump them up to around 20 psi than use a pencil tyre pressure garage check the pressure.
then check it again to see how much is lost when to take the guage off. There is so little pressure in that small area that you can lose 5 psi every time you check the pressure so if you check it and it reads 15 when you take the gauge off you only have ten left. You may need to do this a few times to get the pressure the same in each leg. You are better off with low than high or you may just pop the seals when you brake hard

cheers mate, much appreciated