Forks wont hold air

I have an 83 XJ750K Maxim and I just rebuilt my forks by replacing the seals and all the o-rings. I used 15w fork oil and the forks seem to bottom out. I added air to see if that would help stiffen them a bit but the air seemed to leak out because I checked the pressure a minute later and no pressure was there. What might I try to hold the air?

 

When you pressurized your forks, how much pressure did you put in? If you used the compressor down at the service station, your seals are blown now. If you are doing this with a hand pump (which you should), and are not holding pressure, you need to pull it apart to see if any of your o-rings slipped or got pinched.

 

I use a bike pump on mine but they hold so little air that I think I loose a lot just checking the pressure with a traditional pressure checker. Battery is dead in my digital.

You may want to try putting air in and then gauge the stiffness later. Mine is easy to tell the difference with and without air.

 

What does "seem to bottom out" mean?.

Forks can be harsh for three reasons

1 = they are bottoming out

2 = too much damping transmits excess force to the bike.

3 = too much fork oil hydrolocks them.

Did you check the spring length when you had them apart? Shot springs would be the most likely cause of bottoming out.

You've lowered the viscosity of the fork oil. Book is 20w and you used 15, so too much damping isn't likely to be your problem.

How much oil did you put in? There should be 257cc in each fork.

**EDIT**

If they are bent that could also make them harsh. Did you check to make sure the upper tubes are straight?

If you're really losing air (as someone already pointed out it's easy to let it all out checking them) it can be from the o-rings on the spring seats. Did you replace those? If you're leaking air at the fork seals you'll also get oil on the uppers.

The air isn't your issue though. It doesn't make a nickel's worth of difference.

 

You might need some (or all) of these items:


HCP8241 OEM inner fork tube CAP BOLT LOWER GASKET, fits either side. Used on all XJ650 Turbo and XJ750 Maxim and Midnight Maxim models. Each:
$ 6.95

HCP8241SET2 OEM inner fork tube CAP BOLT LOWER GASKETS, fits either side. Set of two:
$ 12.95



INNER FORK TUBE AIR SYSTEM PARTS:

Air Joint O-Rings:


HCP8238 OEM inner fork tube air joint O-RING, fits either left or right air joint on the following models: XJ650 Turbo and 1982 XJ750 Maxim models. Uses 2 o-rings (above and below each air joint) per tube. Each:
$ 9.00

HCP8238SET2 OEM inner fork tube air joint O-RINGS, fits either left or right air joint on the following models: XJ650 Turbo and 1982 XJ750 Maxim models. Uses 2 o-rings (above and below each air joint) per tube. Pair:
$ 17.00

HCP8238SET4 OEM inner fork tube air joint O-RINGS, fits either left or right air joint on the following models: XJ650 Turbo and 1982 XJ750 Maxim models. Uses 2 o-rings (above and below each air joint) per tube. Set of 4:
$ 32.00



Air Inflation Valves and O-Rings:

HCP8274 OEM inner fork tube air joint AIR VALVE, with cap, fits the following models: 1982-83 XJ650 Maxim (use 1 per tube), XJ650 Turbo models (use 1 per bike), 1982 XJ750 Maxim models (use 1 per bike), 1983 XJ750 Maxim and Midnight Maxim (use 1 per tube), and XJ900RK Seca models (use 1 per bike). Each:
$ 17.00



HCP2322 OEM inner fork tube air joint air valve and air hose O-RING, fits the following models: 1982-83 XJ650 Maxim (use 1 per tube), XJ650 Turbo models (use 3 per bike), XJ750 Maxim and Midnight Maxim models (use 3 per bike), and XJ900RK Seca models (use 3 per bike). Each:
$ 4.00

HCP2322SET3 OEM inner fork tube air joint air valve and air hose O-RINGS. Set of 3:
$ 10.00



HCP9108 Aftermarket air-assisted forks LOW PRESSURE GAUGE, heavy-duty 0-20 psi pencil (stick) pressure gauge marked in 1/2-psi increments, perfect for checking fork air pressures on models so equipped. Very high quality and much more accurate than standard tire pressure gauges, which is very important on the fork pressures as an imbalance between the fork pressure can lead to steering and stability issues, while too much pressure can blow out the lower tube oil seals!
$ 4.95

 

I had an issue with my Max bottoming out.
I a real heavy guy though. (280+)

So, I filled the forks with the right level of Hydraulic Jack Oil and added a Pre-load to the Springs.

I'm happy.
(I forget how much Pre-load ... and, I'm not taking them down to find out!)

 

IMO and experience the Air assist is unmistakeable.. It Does in fact work.
However it ONLY works if yer forks are either in as brand new condition ..or.. just competently/totally rebuilt.
Problems involved are that getting the pressure right is tricky (some leaks out on measuring) and in my experiences there is no advantage whatsoever in this with a digital gauge (have both) both types have the exact same air spillage problem. Also the air pressure must be checked weekly.

 

my forks tend to slowly leak down, put air in about once per week, my leak is due to a scratch under the air valve, check to make sure the seals under the valves are in good shape. this winter i plan on taking them apart again and taking the dremel to the seat area to smooth it out.

 

mine was losing air also.
I replace the air valve (schrader valve).
Bought them at the parts store about four to a package
and a couple of different sizes in the package.

 

Bottoming-out won't be corrected by adding Air to the Forks.
The AIR Pressure (7.5 psi) is low pressure. Real low.
Kids exceed 7.5 psi blowing-out the candles on their B-day Cakes.
Not enough ( 1/2 Atmosphere ) to blow-up a balloon.
"Less energy than in a room-evacuating, board-warping fart."
---- Murray Frompson / Suspension Specialist

Bottoming-out is corrected by installing stronger Fork Springs.
Having a Hydraulic Fluid of sufficient viscosity to dampen motion.
Dampers functioning properly. Metering the Fluid through Oil-locks and Valves operating correctly.
And, adding a Pre-load to the Spring to increase its compression value.