Air Tanks

After reading about air tanks in this forum I decided to make some myself. I have finished making them and the last thing to do was to drill and tap the fork end cap. After doing this I noticed that it appeared with the bump stop and a white plastic seal that air cannot freely move into or out of the fork through the tapped hole. Is this correct or is something not fitted correctly but looking at the parts book it is fitted correctly.

Any help would be appreciated.


Kaj Coulter

do you have any pics? I would like to make some myself.

I dont know what you meant by the bump stop, but remember air is a gas and it will flow throught the tiniest of holes.

The drilling is generally done through what is originally the vent screw hole. The bump stop (cushion rubber in the manual) should not interfere with air getting by unless it is really beat up, or something. As 'Rider points out, it doesn't need a huge passageway to escape from. If your bumper totally covers the hole, it may be smashed, or it might be in upside down. Turn it so the chamfered ("pointey") end is up, against the cap.

There are pictures located within this thread:

After JohnB located the perts source, I have a set in the works for both my bikes, too.


drill a hole in the side of the cup yamaha calls it a spacer it will vent past the rubber stopper :cry:

Thanks for the reply's. The hole itself is not blocked by the bump stop but as you assemble the end cap assy with the bumpstop, metal spacer and a white washer you will find that it pretty much seals the area within the metal spacer. I agree that air will find its way through the smallest of holes but the idea is to have a free flow of air out of the bleed hole of the fork cap and into the air tank. I believe that I will have to drill a hole into the metal spacer as suggested by YZF450jack to allow air to flow freely. Maybe the stock setup is to allow for the bleed screw to be removed so it bleeds the air slowly and doesn't rush out mixed with oil.

I haven't completed the fitting of the tanks as yet but will post photos when completed, but I will explain how I have made them.

Firstly I went to a stainless steel dealer and purchased 500mm of 32 mm ($5)stainless tube and was given a 100mm offcut of 40mm stainless bar. I cut the tube into 150mm lengths. I machined the bar into 4 end plugs for the tube. I then drilled and tapped 2 plugs with 1/8 BSPT and drilled the other 2 plugs 7.5mm. I removed the shraider valve from 2 old tubes and silver soldered them into the 2 caps that had been drilled. I next TIG welded the end caps into the tubes. I fitted a plug into the threaded hole and pumped air into the tanks to test for leaks.

I remove the 2 front screws that hold the front mudguard on and refitted 60mm set screws. I made a bracket that would fit over these 2 screws and had 2 holes to attached the airtanks to by the shraider valves. I had 2 stainless steel braided hoses made 200mm long ($60). I purchased 2 speed control valves ($54) from SMC Pneumatics part number AS2200-01.

I have drilled out the bleed holes in the fork end caps to 1/8 BSPT and fitted a barrel union, then barrel nut and then the speed control valve. The braided hose is then fitted between the valve and tank.

That is where I am up to. Next I think I will drill a 6mm hole in the spacer under the fork cap to allow the free flow of air as mentioned before. Then it will be off to the track on the weekend to try it out.

I will post photos and what happed over the weekend next week.

If anyone whats further info PM me.

I got to try out the air tanks on the weekend for mixed results. I did 3 laps with the flow valves shut to have a starting point. I then adjusted the flow valves to about half open and did another 3 laps. There was a dramatic difference in the plushness. The front seem to almost float over braking and acceration bumps, whereas my wrists constanly pounded now I hardly felt the bumps. On the big table tops I don't quiet make the down ramp and it was bottoming. I increased the compression 2 clicks and went out again. I did another couple of laps but it was still bottoming. When I came back in I found that I had oil leaks from around the connections. I again increased the compression 2 clicks. This time the bike was very harsh over the jumps and it had lost the earlier plushness. I returned to the pits and found oil was leaking everywhere and when I pushed in the shraider valve the air tank had a lot of oil in them.

So in conclusion they worked very well initially but I thing that once I started to get oil transfer to the tanks it effected their preformance. I wonder if drilling the hole in the spacer has caused the high rate of oil transfer.

So it is back to the drawing board, I think I may try a tank running horizontally across the top of the forks like the too tech but instead of it being one tank I will weld a divider in the middle to make it 2 tanks.

Will let you know of the outcome. Will post photos when I find out how to.

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