Monday, January 17, 2011

Fork seals

While it's the middle of winter here in Canada, I figured it couldn't hurt to tear these fancy Showa dual-chamber upside-down cartridge forks apart and have a look inside -- just so I know for sure what I bought. They came off a 2007 RMZ250, and from what I know, the bike belonged to a motocross racer and had been re-sprung and/or re-valved for his weight. He was apparently ~ 175 lbs, which is 20 lbs less than me. Judging by the Race Tech stickers, I assume any upgrades were done using their parts.

Well, after taking them all apart and fitting new seals and dust covers, I am pretty sure the springs were replaced. The OEM springs are supposed to have a marking at one end, and the springs I found inside do not. I have no idea what the spring rate is, but I only assume they are probably stiffer than stock springs. As for valving work, I can't say because I can't tell what was supposed to be in there from the factory. If I had to guess, then I'd say only the springs had been swapped out.

The Suzuki service manual calls for 370 ml of 5W oil in the outer chamber, and 193 ml of 5W oil in the inner chamber. But I found something very different the old oil: in the first fork leg, the outer chamber had about 600 ml in the outer chamber, and 200 in the inner chamber. Yikes!  Then when I disassembled the other fork leg, the outer chamber had almost nothing (like, maybe 50 or 100 ml) and the inner chamber had about 200 ml.  What the hell happened there? Was the person who previously serviced/upgraded these forks drunk? Sniffing glue?

Anyway, here are a few photos:

Because I am too cheap to actually buy a seal driver, I improvised. After an unsuccessful search of the basement for a piece of ABS or PVC pipe that would fit, an idea popped into my head when I was looking at my caulking gun. So I cut a short piece of the heavy cardboard from a tube of caulking.

A set of All Balls fork seals and dust caps cost about $35 at a local dealer.
2 litres of Motul 5W Factory Line synthetic fork oil cost $30 at a local dealer.