Air assist fork caps!

[TownsendsFJR1300]

I modified a set of stock forks caps awhile ago with standard schrader valves.

Chucking in the lathe, drilling the appropriate sized hole. Then epoxy a schrader valve in each cap, lock nut on each end. (The valve stems were left over from old MC tubes.)

I looked at installing aftermarket pre-load adjusters and wasn't thrilled at what was out there..

More thought on the spring pre-load adjusters, your adding more pressure to the springs (more sag as they wear/age). Using air, infinitly adjustable, NO added pressure / weight on the springs and actually helping the springs work less(air is helping hold the bike up)

Some preliminary #'s;

Static sag bike only, 32 mm before-after with 17 PSI = 15mm's
sag with 200 lb rider-after with 17 PSI, 27mm's

Some notes;

Many on/off road bikes (IE, KLR's) use added air for off road use for decades.

Definitly picked the front up some.. Its not too harsh and still soaks up the bumps well. Definitly less nose dive with hard front braking.
It is a very small area in the fork your adding air to, thus adding air is done VERY QUICKLY if using an air compressor. (A quick shot can easily put 40 PSI in the forks.)

I made on the lathe and tried to install 18 mm thick aluminum spacers over the weekend to raise static sag. Spacers came out great but too much pre-load to install them. .

I've done research (and used air ONLY forks years ago on my YZ's) and found where once the fork seal RETAINER is removed, a very high amount of air pressure (100+ PSI) can pop the seals out without disassembly.

I can increase air pressure to raise the front end more but found 17-18 PSI to work for me without adding too much stiffness.. The low PSI should not make any sealing issues. (We did run long travel MX forks with AIR ONLY ((NO springs-less un-sprung weight)) decades ago with NO issues, AMA sanctioned moto cross so they did get a work out...

Last pic is that of the digital gauge(very accurate and well made)

This mod can be done with the use of a drill press/ drill as well..

Overall, I'm very happy with the mod. I do have to check the headlight adjustment once dark but it still should be pretty close.

 

[zpdrumer]

Wow that's pretty amazing. Are those the stock forks? Am I reading your post right that you added valves alone without any other modifications? And one last comment..... Your bike is insanely clean! Everything in that pic is sparkling without dust dirt or grime

 

[FinalImpact]

Scott,
So what was the bike and rider sag # before air add on?
Bike = 32mm, Rider+Bike = ##mm?? w/200lb rider....

IIRC your bike is less than 25,000 miles so its good info you don't mind sharing.

IME, seals not designed to take pressure are going to leak, so you'll need to be pretty religious about checking the pressure. Don't be surprised if they push an oil film up the tube too. You might grab or make an equalizer that simply ties them together too. Thus checking and setting will be quick and if they leak, they both maintain the same pressure.... You'll be sporting a Pressure Gauge next to your GPS soon! :rockon::rockon:

If you have stand alone 5 to 10 gallon air tank, just set it at 18 PSI and tap each fork. The pressures will neutralize and then your set to go as long as the tanks gauge is accurate.

 

[TownsendsFJR1300]

Scott,
So what was the bike and rider sag # before air add on?
Bike = 32mm, Rider+Bike = ##mm?? w/200lb rider....

IIRC your bike is less than 25,000 miles so its good info you don't mind sharing.

IME, seals not designed to take pressure are going to leak, so you'll need to be pretty religious about checking the pressure. Don't be surprised if they push an oil film up the tube too. You might grab or make an equalizer that simply ties them together too. Thus checking and setting will be quick and if they leak, they both maintain the same pressure.... You'll be sporting a Pressure Gauge next to your GPS soon! :rockon::rockon:

If you have stand alone 5 to 10 gallon air tank, just set it at 18 PSI and tap each fork. The pressures will neutralize and then your set to go as long as the tanks gauge is accurate.

Just shy of 19,000 miles on the clock, 200lbs (maybe a tad higher weight) rider..

I didn't do a sag measurement with rider. W/O rider, as noted, was 32mm's or so, easily picked up the front end 1" with me on it... One fork has exactly 17.5, the other 17 PSI. The digital gauge goes down to half pound increments.

Good idea with the portable tank. Tks..
I do have a 2.5 gallon hot water pressure tank I welded up as a small portable air tank and would work well for this, (also a 6 gallon "Pan Cake" compressor besides my Porter Cable 150 PSI, 20 gallon-which I used this am).

As noted, air in forks aren't anything new.. We ran them W/O springs; (YZ 125's and 250's), AIR ONLY, without leakage back in the late 70's, moto cross races (with much more pounding)... KLR 650's STILL come from the factory with air caps (for off road use to stiffen up the suspension).

Even if air should leak out, worse case scenerio, the forks drop back down to stock height (1" or so). I seriously doubt they'll be any oil leakage but of course I'll keep my eye on it. Just like topping off tires once a month, checking the forks/adding air doesn't take long at all. It should help with the longevity of the stock springs and slow normal wear and "age sag" too. The bike feels much more "even keeled" if you would.

After changing the fork oil last week, the rear felt harder (softest spring setting) for some reason. This mod definitly evened out the ride, both ends feel about the same now. So far, very, very happy with how well it works..

(As a side note, for others, I have NOT been riding for 2.5 months, ((recovering from neck surgery)) so I may very well be more conscious of the "bikes suspension" short comings, etc).

Wow that's pretty amazing. Are those the stock forks? Am I reading your post right that you added valves alone without any other modifications? And one last comment..... Your bike is insanely clean! Everything in that pic is sparkling without dust dirt or grime

Thank you.
Yep, bone stock FZ6 forks.. Just changed the oil with 7wt Maxima..Stock springs, spacers, etc. Just installed the modified caps and added air..


*Just as an important side note I thought about later. I do obviously have risers / set backs. I think with STOCK BARS, NO risers, the schrader valve would still clear the handlebars, but room for an air hose, IDK. You'd have to check that before any mod's. Risers may be needed, FZ1 bars, (flatter) may be an issue as well..

A cheap, easy mod for those NOT wanting to change out forks, mod the stockers with simple, un-limited, adjustability.

I should be on 2 wheels again mid March (if not sooner) and will update with time / miles clocked.. :thumbup:

 

[FIZZER6]

Amazing to me that the O-rings in the fork caps hold that pressure. they aren't pressure rings.

 

[TownsendsFJR1300]

Your bike is insanely clean! Everything in that pic is sparkling without dust dirt or grime

A good part of the bike was replaced with new parts when I bought it(tank fairing, side pod, fairing stay, inner fairing,etc) as the PO wrecked it several times..




A picture of the header that sparked "many an owner" to sweat and go thru many a rag and polish!;




Sorry, back to topic..

 

[FIZZER6]

Man. Stop showing that header pr0n! Makes me sick! :spank:

 

[TownsendsFJR1300]

Amazing to me that the O-rings in the fork caps hold that pressure. they aren't pressure rings.

After I pressurized them, I squirted Windex (soapy) on the caps/valves checking for any air leakage. Nice and dry, NO bubbles.

The forks have approx HALF the air pressure as your tires. You likely know, even with the smallest puncture in your tire, with a soapy solution, it'll bubble big time.. :thumbup:

 

[iSteve]

Being an old guy I have had air assist forks going back to the seventies. I made them just like you did for my first bikes a Hodaka ace 100 and a Honda CR 125. Also had them come stock on several dirt and street bikes. I had a Ninja 900 that had one air cap and a tube that connecting to the other cap.

 

[TownsendsFJR1300]

Being an old guy I have had air assist forks going back to the seventies. I made them just like you did for my first bikes a Hodaka ace 100 and a Honda CR 125. Also had them come stock on several dirt and street bikes. I had a Ninja 900 that had one air cap and a tube that connecting to the other cap.

Ok, thread de-rail for a bit!

Hodaka's!! I remember them! Mostly 100 and 125's, all 2 strokes...Silver fuel tanks, greenish tank emblem..

The CR's just came out about the same time, mid 70's and the Yamaha Monoshock, (1977 vintage) pretty much snuffed the CR out (as I re-call, Honda didn't do much competing back then with the suspension). Of course the Suzuki RM's moved the rear shocks forward for extra travel as well.. Loved the 501 Maico's. 500cc two stroke, torque monsters with 4 gears... I don't think they ever used more than TWO gears, didn't need to. Leave it in 2nd gear and throw a 30' rooster tail of dirt!!

I remember vaguely the "cross over" air line as well.. It was pretty popular back then, why it went away, dunno. I know it worked pretty good back then and seals, manufacturing, etc, NOW are much better..

 

[FinalImpact]

Just so things are clear, hopefully everyone sees that its not practical for all applications. Yes, it may be a great solution for cruising and long highway rides and I can appreciate that it now rides like a Caddy. :thumbup:

I'm just sayin, choose wisely and base it upon your expectations from the bike. For those expecting "track like performance" you must control the damping and use the proper spring rates to obtain repeatability.

That said, from the moment I leave to the moment I return, I expect the bike to deliver the same performance characteristics the whole time. It must be predictable and offer a level of repeatability that doesn't get me into trouble. Thus my needs are very different and I expect more from the bike. As such, I have more time and materials invested so the bike meets my needs.

 

[TownsendsFJR1300]

Just so things are clear, hopefully everyone sees that its not practical for all applications. Yes, it may be a great solution for cruising and long highway rides and I can appreciate that it now rides like a Caddy. :thumbup:

I'm just sayin, choose wisely and base it upon your expectations from the bike. For those expecting "track like performance" you must control the damping and use the proper spring rates to obtain repeatability.

That said, from the moment I leave to the moment I return, I expect the bike to deliver the same performance characteristics the whole time. It must be predictable and offer a level of repeatability that doesn't get me into trouble. Thus my needs are very different and I expect more from the bike. As such, I have more time and materials invested so the bike meets my needs.

It doesn't ride like a caddy, please re-read the thread, the front end is easily 1" higher, much firmer than stock. Not nearly the nose dive as before..

It is what it is.. A cheap, easy mod, without major mods/ $ invested. If I wanted the handling of an R6 or R1, I'd buy one...

For my needs it works great and is NOT for everyone, BUT neither is the R6 fork swap... Just another option, proven over time.. :thumbup:

 

[Marthy]

Kind of cool idea, glad it work for you. Once you cap the fork, the air space between the cap and oil act as a air shock. As the fork colapse under braking... the spring rate increase exponentially (smaller volume of air=higher psi) So basically all you had to do is raise the oil level... would have been about the same effect without raising the front rude height.

That's what I did on my 09 to fix the dive... raise the oil level from 148 to 130mm. Perfect now.

 

[TownsendsFJR1300]

Kind of cool idea, glad it work for you. Once you cap the fork, the air space between the cap and oil act as a air shock. As the fork colapse under braking... the spring rate increase exponentially (smaller volume of air=higher psi) So basically all you had to do is raise the oil level... would have been about the same effect without raising the front rude height.

That's what I did on my 09 to fix the dive... raise the oil level from 148 to 130mm. Perfect now.

Great idea re fixing the dive. :thumbup:

I gather it (the raised fork oil) didn't (you may have pre-load adjusters already on the bike) have any affect on static height with or without a rider?

Re-installing the caps (even with extra oil) won't/shouldn't add pre-load to the forks (for static height).. Yes there is slightly less air in the tube but its still at 1 ATM pressure when installed..

I was loosing well over an inch just sitting (1/4-1/3 total travel-roughly). As noted, adding the air, picked the nose up and literally helps support the bike and help the springs (potentially more life out them over time I'm thinking) plus helping with nose dive.

Just as a side note, as mentioned by other members above, using air (and actual air compressors on board) have been used by numerous manufacturers(including the rear suspension on Goldwings and certain BMW's). So far, nice and dry, holding air but time will tell..

 

[TownsendsFJR1300]

Just an early update.

I had about 17 PSI in each fork leg and found it to just slightly too rough. Brought the pressure down to 14 PSI, perfect. Very steady and controlled action.. I do keep my tires inflated to max spec's so that likely didn't help.

Absolutly NO oil seepage, no air leakage either. I gather a tire being all rubber, there's more surface for air to seep thru. The forks, an oil seal and o-ring. No major, large rubber componants to loose air thru.

17 to 14 PSI makes a bit of a difference. So far, one of the best mods done IMO.. :thumbup:

 

[ltdillard]

Dang Scott, could you at least spring for some chrome caps

Thanks for the write-up; it's an interesting and possible mod.

 

[TownsendsFJR1300]

I love em!

Infinitly tuneable, dial in how soft or tight you want them..

Only downside is you need an air compressor, (or hand pump) and very good digital air gauge. It does take a couple of trys to get them within a half pound of each other...

With that said, I'm getting NO leakage of air so I'll probably check them every 3rd or 4th time I check tire pressures...

I initially liked the 17psi, but found it slightly too hard and dropped it down a little. Much smother W/O being stock mushy...I can apply the front brakes hard, the nose drop 2/3's to 3/4's approx...Before, it was about bottumed out.

As noted earlier, if you don't have risers, there may NOT be enough room to fit an air chuck in there.. So check that before any modding.

 

[RoadGator]

I love em!

Infinitly tuneable, dial in how soft or tight you want them..

Only downside is you need an air compressor, (or hand pump) and very good digital air gauge. It does take a couple of trys to get them within a half pound of each other...

With that said, I'm getting NO leakage of air so I'll probably check them every 3rd or 4th time I check tire pressures...

I initially liked the 17psi, but found it slightly too hard and dropped it down a little. Much smother W/O being stock mushy...I can apply the front brakes hard, the nose drop 2/3's to 3/4's approx...Before, it was about bottumed out.

As noted earlier, if you don't have risers, there may NOT be enough room to fit an air chuck in there.. So check that before any modding.

Is this still going strong? I am thinking about doing the same thing now.

 

[TownsendsFJR1300]

Is this still going strong? I am thinking about doing the same thing now.

Yep, haven't touched them in 6 months..

No where near mushy as stock, adjust them as taught as you like.

I used a metal lathe to drill dead center but a drill press would work fine.

Also, I have risers and set backs, so I have plenty of room to get an air hose in there. If you have low bars, you may not be able to get air in there.

The schrader valves were from left over MX tubes (full threads). Just use a good epoxy, snug up and let dry overnight.



If you think about it, you top off your tires once every month or two. I suspect because there's so much rubber surface area.

In the top of the forks, there's oil below the air and you have one o-ring on your cap. So there's really nothing porous for the air to leak thru..

 

[FinalImpact]

RoadGator,
If your needs are that of corner entry/exit, it may be worthwhile to simply raise the oil level so the bike has proper turn in as you let off the gas and the nose doesn't shoot up when on the gas after apex.
JM2C... but I am not clear of your expectations....