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Has anyone make air fork caps for their TW?
Back in the day we uses to fit a schrader valve to the fork cap of out vintage mx bikes (which were current dirt bikes at the time) to assist the too soft fork springs .
If there's room I'd like to try it on my 87. The suspension is so poor on these bikes, I'd like to get an aftermarket shock and do something with the forks
 

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My DIY Air Fork Caps ...

Has anyone make air fork caps for their TW?
Back in the day we uses to fit a schrader valve to the fork cap of out vintage mx bikes (which were current dirt bikes at the time) to assist the too soft fork springs .
If there's room I'd like to try it on my 87. The suspension is so poor on these bikes, I'd like to get an aftermarket shock and do something with the forks
Here is my solution ... Done ten years ago ...

DSC02102.JPG DSC02103.JPG
 

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But don't forget the add says: "It may need to up or back the steering wheel because there is a possibility that it will interfere depending on the body SR400/500 TW which has TYPE-I (with air valve)." :p
If Ido get that TW500 they're talking about I'll figure out some way to deal with the steering wheel.

Damn, I can't find a Japan TW500 anywhere! :(
 

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If you want to get real fancy put a cross over tube from one cap to another. That way you have just one filler valve and equal pressure in both forks.
 

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If the mythical 500TW 's steering wheel is anything like Triumph's handlewheel then those Wetbike schraders might be too tall without handlewheel risers. :p HandleWheel2-1-1.jpg
 
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This is sorta funny. On my dirt bikes I install bleeder valves so I can bleed off pumped up air as it warms and expands. Also add air tanks to increase the volume of air for each fork so they are not as sensitive to temperature changes with air pressure. As I ride, I stop occasionally and bleed off the air pressure so the forks are softer and don't get pumped up.
One time a valve busted off. When I hit the next big jump, I got a face full of oil as the forks compressed and the oil shot out the snapped off valve like a squirt gun. What a mess! Luckily I was looping back to the staging area where I took one off a spare bike I had with me. After that, I always carried a spare valve in my fanny pack.
 

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I haven't done it on a TW, but see no reason why you couldn't. I did this trick with my KLX110 pitbike to beef up the fork, intended for about a 100lb rider. 5psi gave a noticeable improvement, I found 7-8psi to be ideal. 10+ even on those spindly little forks was overly stiff and harsh.

I got a couple brass threaded schrader valves at NAPA for a couple bucks each, removed the fork caps, and just drilled/tapped them. Bit of thread tape or other sealant compound on the threads and they never leaked whatsoever. Took maybe 30 minutes and $5 in parts.

Don't use shop air to pump them up unless you have a suitable regulator that can dial down to only 10psi or so. Hitting them with 90+psi shop air even for an instant can blow the seals- they take such a small volume of air. Otherwise, use a bicycle tire pump or other low volume manual pump.

Using thicker fork oil can often help, as can running the level slightly higher than recommended. Careful with that though, going too much higher can cause the fork be extremely harsh near the end of it's travel and potentially blow the fork seals from hydro-locking. Thicker oil has the effect of turning up BOTH compression and rebound damping, not that those are adjustable on damper rod forks anyway (without changing internal parts). Most damper rod forks come with something like 10-15wt oil, although up to 30wt is available. Again, going too far on the thickness can cause the suspension to be soft (that's spring/air pressure), yet very harsh, especially in cooler weather. Too much spring/air pressure and not enough damping leads to the "pogo stick" effect.
 

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Note schrader: YZ80 AIr Caps. I did it 9 years ago with cartridges and progressive springs.

Barkbuster 2.JPG
 

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Back in my enduro bike days we usually used the air caps to bleed off pressure build-up on the trail simply using a finger nail, stick or rock. However the fork pump with check valve & pressure gauge usually also went along too for adding air if desired. Funny how times change.
 

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These air-assist forks were quite common in the 80s on street bikes and dual sports. Touring rigs like the Goldwing even had onboard compressors plumbed in, with buttons on the console to adjust in-flight. For a little while the anti-dive systems would use hydraulic brake pressure to also force a piston down in the forks, temporarily boosting fork air pressure while braking, but those all vanished pretty quickly too. The anti-dive systems were kind of complex and relied on several seals to work correctly and weren't super reliable as they aged, but a simple shraeder valve in the fork cap is about as simple as it gets. Not sure why those fell out of fashion.
 

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Back in my enduro bike days we usually used the air caps to bleed off pressure build-up on the trail simply using a finger nail, stick or rock. However the fork pump with check valve & pressure gauge usually also went along too for adding air if desired. Funny how times change.
Same deal today. When I load up for camping I add air. If not it's usually at 1lb (to keep water out in deep crossings)...
 

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At the last Wrench & Ride, Mel was kind enough to give me a trunkload of various bits and pieces that came from the estate of our late, great friend - Lizrdbrth :D. Included were these valved fork caps that fit the TW fork tubes perfectly. As Jersey Jeeper posted above, these are likely stock parts from a Yamaha YZ80, which unfortunately are no longer available :(. It's too bad, because these are nicely made and would offer a quick and easy upgrade for our TW's.

https://www.partzilla.com/product/yamaha/58T-23111-L0-00?gclid=CjwKCAiAs8XiBRAGEiwAFyQ-enGN9-djGa9Us4lJ93MhjY4TJksVmf7oUjwsZiiLdiNQkcrWC_nG_BoCw64QAvD_BwE

Valved Fork Caps.jpg
 
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