Air assist delete

Hello everyone

I'm deleting the air assist front fork system on my GT550. My reasons are as follows:

1) I'm switching to an upper yoke from a different bike (LTD), in order to swap the clip-ons with a normal handlebar
2) Using the upper yoke from an LTD is only possible by creating some more space along the upper part of the fork stanchions, if I'm to keep the original headlight brackets intact
3) Removing the air assist part from the fork stanchions creates exactly enough room to fit the LTD yoke (note that the LTD yoke has the fork pinch at a lower level relative to the ground than the centre pivot hole

The forks with air assist work well. There is no problem with them at all. The forks are in good condition and well maintained. The handling is OK but not great.
The air assist system is nearly 40 years old, and it still holds air, but I don't like systems which depend on rubber seals - they're just another thing to check and renew and they're not appreciably better in performance than 70s-style basic forks.

Am I correct in thinking that I can preload the existing fork springs with a spacer, and forego plugging the air assist holes on the side of the stanchions?
If not, what can be used to plug the holes in the stanchions? Does someone make a product for this purpose? If not, would a small brass screw work?

Yes, you can put in a small spacer to make up the preload. Air creates a more progressive rate than springs alone, so if it still feels like the tire is bouncing up further than you like, you may need a stiffer spring rate. I make stiffer springs from the stock springs by simply cutting them down. This increases the rate of the overall spring. Then I make up the preload with a spacer. It has worked great on several bikes and costs basically nothing. You do have to dress the ends properly to prevent the springs from sitting uneven. Just copy how the ends looks from the factory. I use a propane torch to bend the spring into the correct shape then grind it flat. You want to reduce the diameter a bit on the last ring so it doesn't scrape on anything.

Cutting the springs will help for sure. I've done that on several bikes before. Buying stiffer springs is an even better option in my opinion though. Not sure what's available on your island there but in the states I like Sonic springs.

Thanks guys. Good to know spacers will work. I'll give that a try then. There are a couple of companies here which make progressive fork springs and sell them in the UK. I've shot a message off to one of them (Wilbers) and will see what they say when they respond. In the first instance I'll try just spacers though, and see how it works out.

How about the holes in the fork stanchions? The air assist system on these bike is located mid-stanchion, so there are 2 exposed holes in each stanchion about 12 inches above the fork seal. Would they need plugging? My understanding of how forks work is that the fork oil should mostly remain in the bottom of the fork, passing through holes in the damping rod, and shouldn't be kicked up that far to leak from these exposed holes. Fork springs normally have a coating of oil which gets kicked up though. Could I get away with leaving these holes exposed?

Those holes will breathe a lot and spit out oil. The problem is not the mess, but that there will be no air compression. And when you hit a bump, air will shoot out, but will not get sucked back in with at the same rate. A few bumps in a row could lead to the front end pumping down. I haven't tried it, so I can't say for sure this is a concern, but I don't see a scenario where the hole is beneficial. So I say plug it.

Will the hole be out in the open fully exposed all the time? There are probably a lot of way to seal it. You could wrap electrical tape around the fork there and put a hose clamp around that. You could find a ball bearing to fit in the hole like a cork and put a hose clamp around that.

Obviously you just don't want something that will fall into the fork tube.

That makes a lot of sense - thanks. I'll plug it then. The old seals from the air assist apparatus should do the trick. If not, I have plenty of inner tube. A brass wood screw would plug it, but it might also hit the coils of the spring. If the worst comes to the worst, there's Milliput.