Topic: air valves in front forks, can they be added? (CB750)

[dboblet]

Years and years ago I had a friend that bought a CB750K, while I bought a KZ900.  One of the first mods he made was to add air valves to his forks and pressure them up (no idea how much).

Now, a zillion years later, I work to fix up my '78 cb750f and wonder about adding an air valve to the forks and doing the same.   Is this a common mod?  Not advised?  Has it benifits I should consider?

[bwaller]

It's a great addition for these forks. Interconnect them even better and run around six psi.

[mystic_1]

Search the site for "schrader" and you should find some good info.

http://forums.sohc4.net/index.php?action=search

mystic_1

[markjenn]

I have always heard that is it is a poor idea because it dramatically increases fork stiction, although sometimes I wonder how it can possibly be worse than it already is.

I think there is a reason that air forks, while once quite popular on factory bikes, are not not found at all.

If you need firmer springs, I'd re-spring with a higher rate spring.

- Mark

[bwaller]

Well markjenn in case you hadn't noticed there aren't a lot of options out there. 

There are 35mm emulators available, but I haven't tried these yet. Short of that about the best you can do with thirty-odd year 35mm forks is add a set of progressive springs, replace fork oil often, and add a few pounds of air. I always considered the little bit of air helps overcome stiction.

[JLeather]

I'll say one thing about it, only ever use a bicycle pump (hand pump) to fill them.  I had a set on my old YZ490 (freakin' scary fast 2-stroke).  My buddy was over riding and my air always leaked out after a couple hours.  I wasn't paying attention and he thought he could take the air-hose for the tires (120psi shop air) and if he was quick enough just tap the forks for a sec and re-fill them.  Blew out a fork seal and oil everywhere.  Just my $.02.  The 'wings back then had air-valves on the front a lot too.  I think you don't see them today because technology has changed and they aren't necessary, but I think they made atleast no negative impacts on the forks.

[eurban]

Well markjenn in case you hadn't noticed there aren't a lot of options out there. 

There are 35mm emulators available, but I haven't tried these yet. Short of that about the best you can do with thirty-odd year 35mm forks is add a set of progressive springs, replace fork oil often, and add a few pounds of air. I always considered the little bit of air helps overcome stiction.

Spend your money and efforts on installing cartridge fork emulators and forget about pressurizing the forks.  Results will be far better . . . .

[bwaller]

eurban, are you running with these emulators? I've got a set in waiting, but there are lots of miles on these old forks of mine and I recall MRieck mentioning that it's a good idea to update the hardware before installing these. I think that's good advice so I'm waiting for another winter and upgrade at the same time.

In the meantime I haven't heard too many guys singing the praises of these emulators in 35mm forks yet, so I'll keep running a little air for now!

[eurban]

I don't have them on my SOHC yet (78k with GL front end /37 mm forks) but I have helped a friend install them on his 80s GPZ with remarkable results.  Racetech's emulators are expensive and I too am waiting to find the momentum, in this case to spend the $.  For the stock 35mm forks the reasonably priced emulators available from Mikes XS site should work (is that what you have?).  There was some buzz about them a while back but never heard the results of any installs.  I would imagine that the $ spent setting up air caps and perhaps balance tubes for the stock forks would go a long way towards purchasing the XS emulators.  If they perform as well as the Racetech's on my buddys GPZ, they would be about the best thing you could do for your front forks short of replacing with modern hardware . . . .

[mystic_1]

I would imagine that the $ spent setting up air caps and perhaps balance tubes for the stock forks would go a long way towards purchasing the XS emulators.

Er,
Tire Valve Stems X 2 = $6.00
Drill Bit = $7.00
Air = Free.

Total cost, under US$20.00


mystic_1

[bwaller]

Yea I have the MikesXS version. On this 750 I'll keep the stock look and forks so will install the emulators on it. It'll be a while before I can offer feedback.......... sounds familiar huh?

[eurban]

I would imagine that the $ spent setting up air caps and perhaps balance tubes for the stock forks would go a long way towards purchasing the XS emulators.

Er,
Tire Valve Stems X 2 = $6.00
Drill Bit = $7.00
Air = Free.

Total cost, under US$20.00


mystic_1

ER, emulators from mike's XS: $49+shipping.   How about the porta pump and guage that you will need to fill up the forks before, during and after rides?  How about balancing the tubes since there not going to loose pressure at the same rate?  Do you need a tap to install those stems??

[mystic_1]

Well, if you want to go down that path....

Pump, $4.99 from Wal-mart.  Balance tube, not necessary.  Nice to have, but not required.  No tap necessary.

Now, how much to replace all the fork's interal parts in order to make installing the emulators worthwhile?    How much for the allen keys, bench vice, snap ring pliers, and so on that are needed to completely disassemble the forks?

Why are there so many people posting here about how they're waiting to install emulators because of cost?

Not saying that pressurized forks are equal to cartridge emulators, but to suggest that the emulators can be done for the same cost as the schrader valve mod is ridiculous.

mystic_1

[dboblet]

Of course, I'd have to drill and tap my caps... but that's easy, and I already have the schrader valves sitting in a box collecting dust.  Then... I don't actually HAVE to use them once installed, do I?

[eurban]

Well, if you want to go down that path....

Pump, $4.99 from Wal-mart.  Balance tube, not necessary.  Nice to have, but not required.  No tap necessary.

Now, how much to replace all the fork's interal parts in order to make installing the emulators worthwhile?    How much for the allen keys, bench vice, snap ring pliers, and so on that are needed to completely disassemble the forks?

Why are there so many people posting here about how they're waiting to install emulators because of cost?

Not saying that pressurized forks are equal to cartridge emulators, but to suggest that the emulators can be done for the same cost as the schrader valve mod is ridiculous.

mystic_1

My experience with air forks (CB650 custom, GL1000, CB900 some stock air setups, some aftermarket) is that the pressure doesn't stay around very long, nor is it lost consistently from fork to fork.  Worn fork parts will loose pressure even quicker (and exhibit even more increased stiction with air pressure applied) so what is true for emulators is pretty much true for air caps.  Every factory thought out /engineered stock air setup that I have been on came with balance tubes and I would imagine unequal pressure is a poor recipe for a supposed handling improvement.   Adjusting pressure before every ride was the only way I found to get decent results. This is a bit of a PITA to put it mildly. . . Some have suggested that the mikes XS emulators designed for the 35mm forks would work well enough on the larger 37mm GL ones but based on the measurements I have seen I don't think that they are a good fit.  This leaves me with Racetech and about $150 required vs the $50 to a typical SOHCer.  This is why I haven't made the plunge yet. Sometime soon though . . . I certainly would be interested in hearing from some SOHCer's who actually installed the xs ones. . . .
Oh and here's what I said earlier BTW
"I would imagine that the $ spent setting up air caps and perhaps balance tubes for the stock forks would go a long way towards purchasing the XS emulators."
It ain't so ridiculous in my opinion . . . 

[dboblet]

Seems like adding a T with shrader to one cap, elbow to the other with tube between would be super easy.  I have access to a drill press so I may try it.  Then I might get some use out of that old bicycle pump besides keeping my tires topped up. (huff-puff)

[bwaller]

I'm not looking to create a big dust-up over this, honest, but I have two sohc4's with stock 35mm forks that I run air, and only 6 psi. Neither leak any air.

IMHO starting with good seals, clean oil, progressive springs and a little air makes these forks as good as they can be, short of installing emulators of course. Other options like eurban & others have done is to install a more modern front end.

dboblet, pm your way.

[dboblet]

OK, can someone explain EXACTLY what is 'striction' and what effect it has on bike handleing?
Thanks.

[WFO]

I'll say one thing about it, only ever use a bicycle pump (hand pump) to fill them.  I had a set on my old YZ490 (freakin' scary fast 2-stroke).  My buddy was over riding and my air always leaked out after a couple hours.  I wasn't paying attention and he thought he could take the air-hose for the tires (120psi shop air) and if he was quick enough just tap the forks for a sec and re-fill them.  Blew out a fork seal and oil everywhere.  Just my $.02.  The 'wings back then had air-valves on the front a lot too.  I think you don't see them today because technology has changed and they aren't necessary, but I think they made atleast no negative impacts on the forks.

Yep a very smart move  i have been experimenting with my 82 nighthawk (they come stock) with that year forks, it does have a good effect in handling i started with 2lbs and worked my way up by the pound and paided close attention too handling also when using a bike pump add a pound extra then bleed it off with the air gauge untill you reach your desired poundage.

[mystic_1]

OK, can someone explain EXACTLY what is 'striction' and what effect it has on bike handleing?
Thanks.

Here's the wikipedia article on stiction:

http://en.wikipedia.org/wiki/Stiction

In this case we're talking about the sliding resistance between the upper and lower fork legs.  Higher stiction means they don't slide against each other as well, resulting in poor handling.

mystic_1

[markjenn]

I'm royally confused by this thread - not too hard to do, BTW.

My understanding has always been that air forks were designed to provide a way to vary spring rate so one could tune the front suspension spring rate for different loads or riding styles.  Conversely, cartidge emulators were designed to improve the damping response of old-tech damper rod suspension to have it better match the newer cartridge forks.  So I'm not groking why adding air would do anything to improve the damping of the fork (in fact, as I said earlier, most references I've read say that adding air pressure to a fork increases stiction), nor why emulators would provide a way to vary spring rate.  These seem like independent technologies to me, not substitutes for each other.

- Mark

[markjenn]

In this case we're talking about the sliding resistance between the upper and lower fork legs.  Higher stiction means they don't slide against each other as well, resulting in poor handling.

To amplify a bit, stiction in motorcycle forks is where the forks have high initial resistance to movement until they reach a threshold load.  Then they "stop sticking" and move suddenly.  Ideally, you want the suspension to have no internal friction at all so that it can react to any bump no matter how small. All forks have some stiction, but 70's-era Japanese bikes were pretty bad compared to modern forks.  On my CB750K1, it seems like there is almost no suspension at all over minor pavement irregularities.  Obviously this hurts handling as the suspension can't follow the road like it should - worst case, the wheel will actually be hopping over small bumps.

- Mark

[mystic_1]

In this case we're talking about the sliding resistance between the upper and lower fork legs.  Higher stiction means they don't slide against each other as well, resulting in poor handling.

To amplify a bit, stiction in motorcycle forks is where the forks have high initial resistance to movement until they reach a threshold load.  Then they "stop sticking" and move suddenly.  Ideally, you want the suspension to have no internal friction at all so that it can react to any bump no matter how small. All forks have some stiction, but 70's-era Japanese bikes were pretty bad compared to modern forks.  On my CB750K1, it seems like there is almost no suspension at all over minor pavement irregularities.  Obviously this hurts handling as the suspension can't follow the road like it should - worst case, the wheel will actually be hopping over small bumps.

- Mark

+1 a far better explanation than mine.  I also agree that emulators and schraders are not equivalent mods, either in purpose, effort, or cost.

mystic_1

[bryanj]

What most people forget is that the original manufacturer air forks need a low volume air gauge to check them as the total volume aint big, first bike with air that worked was the wing and that had a balance tube with one fill "valve" (same on rear)