F800GS: Fork Air Bleeder Valves

[Bartron]

I've seen and used these guys on some friends' KTM's and would like to install on my GS. Over the run of a day, especially if it is warm outside, the front suspension does become noticeably less supple.

So the theory is that as the air inside your 'air gap' warms up from repeated compression and external warming, it tries to expand but it has nowhere to go so it increases in pressure. Now your 'air gap' is pressurized decreases the damping that a non-pressurized 'air gap' affords - thus the stiff suspenders.

The fork caps are easy enough to take off with a 13mm cone wrench but they do have a plastic bit between the alloy of the fork cap and the spring. Presumably this piece of plastic acts as a bushing between the two surfaces.

So, in order to do the install, one needs:

1. The right fork bleeder valves
2. A hole tapped in the fork cap in the right spot

The bleeder valve is easy, with KTM making a nice valve as pictured below.

The question I have is how to negotiate the fork cap drilling with that darned plastic spacer for optimal results. It looks simple enough, but most things do when you're simple.



Anyone done this? Anyone interested?

Guys with Husky TE's and BMW X-Challenge's have been using these valves but I haven't found their secret recipe write-ups.

To the Bart-Lab!

[Ducksbane]

Strangely enough I have just done this a few weeks ago using Slaven Speed bleeders ... http://slavensracing.com/products/kt...-bleed-buttons



I have to confess I didn't put them in , but I do know you have to remove the fork internal to get the caps off (including loosening the forks in their clamps). There is apparently a definite spot to drill. You need a 4mm tap. Don't forget to re tighten the fork clamps to correct torque in sequence.

I am very pleased with the results. I have hyperpro progressive springs front and rear and felt that the front wasn't quite "plush" enough. You can use the bleeders as a sort of spring rate adjustment by varying the weight on the bike when you bleed the forks. I usually have it off the center stand with no more weight on it when I push them. You can also do it on the center stand for more pressure. Slavens also suggest that you can bleed the forks while you are sitting on the bike for a softer ride. I've only tried this once and it was very plush but felt a bit weird with the bike seeming to ride lower in the stroke. Might try it again sometime.

Every time I use the bleeders after riding I get enough air out to hear it easily. I think there is a real improvement, and in fact I am pretty happy with the suspension now. The biggest difference I noticed was on the road. With both front and rear hyperpros it wasn't quite right on rough bitumen, but with the forks bled, its pretty good. On gravel and off road I am surprised how good the set up is given what they give you standard.

And this doesn't cost a fortune, even with the Hyperpro's and an IndyUnlimited top shock bolt brace. Result, as they say!

I will take a pic in the next few days to show you what the finished product looks like.

[DockingPilot]

I gottem in mine. Done by Traxxion Dynamics, that and a whole lot more.

[Bartron]

Originally Posted by DockingPilot

I gottem in mine. Done by Traxxion Dynamics, that and a whole lot more.

Frank, do you happen to have a pic you can put up showing the placement on the cap? Stock caps? My concern is how to navigate the plastic between the cap and the fork spring. Need enough room for a socket to fit over the cap nut and don't want to place it too close to the edge for fear of being right over the spring. If in-between, then it should extend through the fork cap and through the plastic for unimpeded air flow.

Any ideas? Do your fork caps still have the plastic spacers in them?

[DockingPilot]

Well, Im not home right now, wont be until next week. Im cant remember what it looked like under the caps, but they di a super job installing them and they work well. Yes they are the stock caps too. I can snap a pic when I get home for you.

[Ducksbane]

Here are some photos of the Slaven Speed Bleeders ...

[Ducksbane]

A last update ... apparently if you examine the plastic spacer you will find a cutout on the outer edge, like a bite. I assume this is to accomodate the bleed hole. With mine they just countersunk a 5mm hole where the gap in the spacer was then drilled and tapped at this position with the 4mm tap.

Still like the result.

[Bartron]

Very useful info. Thanks man!

[Bartron]

Guess it's time to update the thread.

After a week on some of the most gruelling terrain on the Tour of Idaho with Revelstoker, these things were AWESOME. Initially I kept forgetting to bleed. After a short while, I started to feel when the forks needed bleeding.

Big rocky section? Bleed 'em.
Gained significant elevation? Bleed 'em.
Lost significant elevation? Bleed 'em.
High speed washboard? Bleed 'em.
Bored? Bleed 'em.

There was a definite increase in 'plushness' of the forks when the air pressure inside was adjusted to atmospheric. I did the bleeding with all weight OFF the front forks by lifting up the front via leverage over the side stand.

Cheap mod, huge benefits.

In terms of fork internals, nothing fancy - just Hyperpro progressive springs and oil.

[Bartron]

First off, many thanks go out to Big Paul for helping me get this done. Without his help and expertise I would have no idea where to start. God love the machinists of this world.

What you need:

KTM (or other type) fork bleeders (~30-50 bucks)
Drill press or steady hand
Drill bit and tap

Step 1:

Remove the fork caps. Do this one at a time otherwise the entire front end will drop and you'll have oil everywhere. Remember that you need to loosen the fork cap, then unscrew the fork cap off the damping rod. For this you need a flat wrench (13mm I believe). Bicycle cone wrenches work well.

You can check out my play-by-play of fork disassembly here.

Step 2:

Drill the fork cap. It's aluminum and you want to stay away from the periphery so you don't drill into the fork cap walls/threads.



For the KTM fork bleeders, which are M4 x 0.7mm pitch, you will need to drill a 3.3mm hole. It helps when you have a friend with this kind of machinery:



Step 3:

After you drill and debur, you'll need to tap with an M4 x 0.7mm tap. This is probably the most precise part of the process.

Step 4:

Once you tap, you may also need to counterbore. Counterboring creates space for the bleeder so it sits a bit more 'in' the fork cap and allow the o-rings on the bleeder to effect a proper seal. I'm not sure what size Big Paul used. There are metric counterbore charts that describe M4 counterbores like this one.

Step 5:

Hand tighten the bleeder with a small wrench. These things are SUPER easy to overtighten and snap off in the fork cap. Also, don't worry about drilling the white plastic in the fork cap. You will be able to bleed air without drilling the white plastic or even lining up any notches. I was concerned about this earlier in this thread and now realize it's a moot point.



Step 6:

Enjoy, and let the 'psssssssttttt' bring a smile to your face on terrain like this...



...or hundreds of miles of this...



...or this...



Thanks again to Big Paul for taking apart his Husaberg bleeders to check the sizes and all his help.

[EnderTheX]

Nice mill.... oh how I would love to have that in my garage

[KLRscoob]

Just installed bleeders in my F8GS. Wow what a difference. I ways thought they could use such a thing as a moto bike has. These things are the best, cheap mod you can do.