Topic: Air front shocks, any pit falls?

[Hush]

Am rebuilding a GSXR250 for my son and I find it has air shocks, at the top there are tire inflating valves.
As I've done many many shock seal replacements this does not worry me too much but first time I've struck this so are there any things I should look out for, like will springs under high pressure shoot across my garage and scratch the paint of my new love "Ruby"?

[brooze72]

#1 protect Ruby at all costs!
#2 stand aside when filling shocks (protect yourself!)
#3 old Honda's didn't have air shocks, so we don't know sh%^ about that. 

[grcamna2]

I've riden & rebuilt plenty of air forks before...I recommend only filling them to the pressure that the manual tells you to;if you run pressure in the higher range it can cause "stiction",which makes the forks kind of sluggish.I have always enjoyed using preload adjustment to stiffen my forks for that main reason.

[Hush]

Ha ha lol Brooze, actually my CB650C Custom had them but she was the last of the SOHC4's ever built so Honda were playing with a few things on the 82 model.
OK I'm reinforced by your confidence that nothing can go wrong (famous last words of Captain Smith of Titanic) so I shall attack these suckers with full gusto.
Once that is done I'm kinda screwed for wrenching as my new bike don't need jack, my partner's Suzuki GSX400 is running great and I can't rebuild the GSXR until the frame has been painted so guess that just leaves riding a few hundee miles....damn!

[d9canada]

The forks on the CB900C/1000C (1980 to 83) all had air fittings.  I don't know for certain but I believe some 750s of about that vintage had air over hydraulic as well.

In fact you can add air to any forks, just drill and tap the top caps, put a hose joining one to the other and a common air fitting.  Do NOT exceed about 15 psi.  I have heard of a few guys who have done this with 550s and enjoyed the results for cruising.

If you want to change the oil in air assisted forks at any time, or replace the springs, delate them first.  That's about the only real thing to watch.

[Johnie]

Be sure someone with experience fills them up and maintains them. You can not hold that air nozzle on there but for a mili-second or you will blow out the seals. Not like filling up a tire. I have seen some younger teens think this air valve is like a tire and blow the seals and fluid all over the place.

[w1sa]

Monitor the upper pressure limit closely and only top-up with a hand pump.... in small tested increments.........

[d9canada]

If you have your own compressor with reservoir, run it until the compressor shuts off.  Connect a blow gun, turn the line pressure down and hit the air and watch the line pressure gauge.  Keep adjusting and testing until you get it down to about 10 pounds line pressure, then put on your tire chuck. 

If you don't have an accurate indicating one just use quick 'blips' and test with a tire gauge.  I've done my 900Cs with only marginally larger forks and I've never had a problem.

Also you can fill the forks yourself.  Just check the factory service manual for the volume and type of oil.  Flush the forks first, I use diesel and let them drain overnight.  Put in the drain plugs, put in your springs (& spacers if used) and pour in the measured amount of oil, then install your top caps.  Hardly rocket science. 

[Goofaroo]

Are you sure that the forks are actually designed to use air pressure?  I've had lots of bikes that have an air valve simply for bleeding air out of the system. My XR350 has valves on it and after a few rides it will generate a bit of air pressure in the forks that I can quickly bleed off via the valve. On other bikes without valves, you can crack the fork cap loose past the o-ring and get the same results. If it is properly sprung you might find that adding air will make the front end unbearably harsh. If it does in fact call for air in the system, my guess would be that 2 to 3 psi would be all that is needed. You didn't specify what year this bike is but I would find the specs online for that particular bike and see what the manual says. Then of course it all comes down to your preference and the type of riding you do. I would just get the internals all cleaned up, install new fluid and seals (if needed), and then try them out once the bike is up and running. It's hard to tell what you have until the rubber hits the road.

[d9canada]

The 900C uses air over hydraulic front and back.  Earlier in this thread I mentioned that you can drill and tap the caps of pretty much any forks, put in a crossover hose and filler and use up to 15 pounds.  Several people on this site have done this with 550s. 

I've never seen bleeders used to remove air, that would be like a negative preload but I guess there's always another approach.

[grcamna2]

I have always preferred spring preload over air pressure...I would start w/ 5 lbs.

[d9canada]

This is much like guys debating about fork oil, some like Honda fork oil, some like 15 wt mixed at some proportion with ATF, others ATF straight..

The air setting according to Honda for bikes made with air over hydraulic is adjustable with a max of 15 .. so fill yer boots.

[Goofaroo]

I've only had bleed valves on dirt bikes so I'm not sure about street applications. The only air suspension I have had on street bikes has been the rear shock on my 86 VF1000R and my 04 Kawasaki Concours. Both of which worked fine for a few days until the pressure went down.

I am curious to see what his manual says about the forks on his GSXR250. If we knew what year it was we could find out.  By the way, a GSXR250 sounds like loads of fun. It's too bad the Japanese manufacturers never sent us any of their serious small bikes here in the states.   

[grcamna2]

It would be fun to have access to all the different nice 250cc class sportbikes in the World market...Vintage to present day;  +1 on what you said Goofaroo !

Does anyone have any nice pictures of some sweet little 250's ??

[Terry in Australia]

Air caps were a common aftermarket accessory "back in the day", I've got a few sets in a box that I bought on EBay, plus a nice S&W set that I bought for my Suzuki GS1000 that came from the factory with air caps, but weren't linked. The S&W kit looks cool, and comes with a pressure gauge that mounts on the handlebars.

I like them, they take any sag out of your forks, and give a nice smooth ride with a little less "dive" under braking. I've heard some negative comments about possible "oil foaming", but I'd still rather have them than not. As has been said previously, don't use a compressor to pump them up, a bicycle pump is fine, and the S&W kit actually comes with a hypodermic syringe with an internally threaded fitting. You don't need much air to fill them. Cheers, Terry.

[grcamna2]

It would be fun to have access to all the different nice 250cc class sportbikes in the World market...Vintage to present day;  +1 on what you said Goofaroo !

Does anyone have any nice pictures of some sweet little 250's ??

Anybody have any pics ??

[Goofaroo]

Here's a link to some info and pics of the GSX-R250. It's hard to imagine it uses an air assisted fork instead of a proper spring but who knows. Pretty sweet little bike. My dad never restored a bike like this for me!

http://www.suzukicycles.org/GSX-R-series/GSX-R250.shtml

[Goofaroo]

Here's the Honda offering.  Another beauty that we weren't allowed to purchase.

[grcamna2]

That is one Hot little NSR ;was it sold in Canada ? Maybe I could find one some day.

[Hush]

This year we rebuilt: Honda CBR400RR  CBR250RR two Yamaha FZR250'S and now this Suzuki GSXR250 so I'm kinda getting used to this early 80's late 90's machinery but the variations between manufacturers is phenominal!
Unfortunately I find I cannot do the seals on the Suzi myself as I require special tool #00-1234567 and only dealers have them! Shame I like doing fork seals, I have found Honda to be the easiest and Suzi/Yams the hardest, not sure why they made them so complicated?

[grcamna2]

Hush,
   Those are some sweet little sportbikes;you rebuilt them for friends? or...kept them??