Strange rear suspension units

[iansoady]

I'v just bought a bike (BSA Starfire running gear, Suzuki DRZ 400 engine) and am a bit confused by the rear suspension units. They have a label but can't see that for the springs. However, what really puzzles me is that both have a Schrader valve in the top. The previous owner said "don't touch them". However, being of a curious mind, I'd like to know what they are for. There is no preload adjustment

Here:

[ogri]

Air preload, on my old kwack gt550 used to be a couple of lb pressure, always leaked though.

[KungFooBob]

Show us the full bike, sounds interesting!

[Skub]

The forks on my old GS1000 were air assisted,the shocks are either the same,or it's a handy way to re-gas them.

Oh and yeah,get a thread and pics up in the 'owners/projects'.

[Mr. Dazzle]

Even fancy McLaren suspension uses schrader valves for this. That'd what goes in the hole in this bit.

20240327_125851.jpg (117.47 KiB) Viewed 352 times

[iansoady]

Of course.... A fair bit of fettling to do - control cables feel as if they're full of gravel, that exhaust heat shield looks awful - but it starts on the button, runs very nicely, and generally seems well conceived and executed. The bloke I bought it off (who isn't the constructor) has done 6,000 miles in the last 2 years according to MoT history so I'm feeling quite happy so far.

[Skub]

That's pretty cool Ian,it seems very well sorted and quite unusual.

[iansoady]

Yes, I'm quite impressed. Less so with the seized rusty bolts holding the seat on. How on earth could the PO get to the battery? All in all though more to like than dislike. The worst aspect (aestheticaly) is the radiators but I don't think I can do much about them. The PO (who didn't build the bike) reckons it's actually a CCM-supplied engine - maybe from the truncated product run of the SR40 which I was actually aiming for.

As for unusual I suspect it's unique. Therefore must be worth a fortune......

[Rockburner]

I bet that gives the old-belstaff brigade the shudders.


(what's happened to the bars??)

[iansoady]

The bars are weird as are the footrests which are halfway to a highway peg setup. But rotating the bars back 30 degrees or so makes them better although still higher than my preference.

I suppose some may consider I'm part of the belstaff brigade although I ditched the leaky filthy things decades ago.

[mangocrazy]

I remember that Fournales (French?) used to make air shocks many moons ago. As others have said, the problem is keeping the pressure constant. My previous VFR had air assist in the forks and in the time it took me to travel the 20 miles from the dealer to home after a service, the air pressure in the forks had gone from 6psi to zero.