Motobene
Well-known member
I got recently tapped for consultancy to check out a used 200 GasGas for a local fellow that desired after years to rejoin the trials fold. The bike was in unusually great shape for 17 years old and bought for a mere $2k. My summary: "This is a great bike. Anything wrong will just be chicken shit details. You should buy it."
On the drive back, I got excited over NOT having to deal with A POS squid beater! I determined to donate a full shop day and parts to leverage a good rescue find into a gem. As usual, the project has grown in scope... but been fun!
Also a reminder of the general brilliance of the GasGas Pro design. There was nothing lighter! A few things were not so smart, but on the whole those were great bikes. My 2009 280 remains a favorite.
A cracked center muffler to TIG weld (typical of the era) and a shock rebuild of the - surprise! - Ohlins instead of Sachs shock, and the need for new fork seals were the day's more major takeaways.
Had to wait a bit for me to travel to my machine shop and yesterday to dive into the Ohlins shock.
What had actually gone wrong? Silly, really, and related to Ohlins fitting rubber upper eyes then instead of the tougher steel Heim eyes. The linkage ratio of the older, eliptical-tube-frame GasGas Pros imparts a short travel feel with a spanking foot arches on drop-offs. Hard on rubber upper eyes and this shock failed mildly and slowly. The clevis at frame shock mount was hammering the tiny bleeder screw head on drop-offs, eventually loosening it enough to slowly lose the 200+ psi nitrogen, and that is why the seal had let out some of the oil. Shock seals require internal pressure to clamp the shaft and seal.
What looked like a first cause seal failure wasn't. On disassembly, I found the gas separating piston hard up against the top hat (no more gas chamber). Like the rest of the shock, the seal head was actually in great shape.
While into the shock I did the 'long travel mod' typical of Randy Lewis of R R Racing... and me. We increase shock rod travel and fit a softer spring. The result is amazing for plushness, terrain following, and for feeling 'bottomless.' I'm thinking the mod will contradict the short-harsh feel of the older GasGas linkage (boy it sure did!).
The mod is simply leaving some spacers out. But oh what a difference! I also did a touch of revalving by moving the 'rocker shims' closer to the piston to quicken terrain response and loading/unloading (body input) response. We shall see.
I'm doing one other thing: converting the shock to 'non DeCarbon' by leaving out the gas separating piston, making it a so called 'gas emulsion' shock. Every KLR 250 and 650 KYB shock was gas emulsion, for example. The Works Performance shocks I used to fit to monoshock trials bikes like my famoso green Works 305, were gas emulsion.
Why? To increase the oil volume, and to make the shock ridiculously easy to get into for further tweaks (if so needed).
Gas emulsion style shocks work the same as piston-separated nitrogen with one caveat: the shock orientation must be rod end down, which was the case with most trials bikes of the mid 2000s except the 4RTs. Turning a gas emulsion shock rod end up leads to top-out as the nitrogen bubble and the piston with shim stacks are in the same space.
My 2009 GasGas 280 had an Ohlins shock set up that way and it worked great. Too bad that was before I or anyone had figured out the long travel mod :-0
What's inside an Ohlins shock like this GG 6521? Pretty typical over a lot of years.
Just right of the P for 'piston', in the R for Rebound stack, I missed two more of the 0.3mm X 32mm diameter shims as they were stuck together:
For the long-travel mod, I left out two of the three red plastic top-out spacers. I also left out the black plastic bump cushion spacer (later left out by Ohlins with a taller bump cushion), all for more rod travel.
The addition of travel is in the negative direction, so it's critical with this mod to run little or no spring preload, or unless you weigh 250+. It's critical to fit a softer spring on some later models, but fortunately this GG had a fairly soft spring. The long travel Ohlins I have on my last competition bike has a 55 N/mm spring. Stock on the Ohlins Shercos is a 64-70 N/mm progressive spring. The stiffer spring severely degrades performance and makes the rear end ride high with stinkbug posture, especially with the usual more preload. The softer spring is a wonder, and bottomless feeling. That's contra intuitive, but true for complex reasons related to bike pitch (front versus rear ride height), steering reaction torques, and squat and terrain following.
The spring number in the old black spring was half rubbed off, and the linkage ratio is a first for me using this mod, but the 'butt dyno' showed this older stock spring with almost no preload is right for most riders.
Shop time was a lot longer to work this shock than usual. Chalk that up to a few 'senior moments', and the need to fit a Schrader valve for nitrogen fill. I also diverted myself into making a tool I've always needed/wanted: a shock tube clamp adapter to hold the tube to unscrew the 'top hat' off the shock tube. Attaining a precise bore for the tube in the block required a lot of Criterion boring bar iterations referencing the tube itself..., with the knee of the mill cranked way down then back up like 15 times..., something machinists on manual mills can appreciate.
Other work: a Schrader valves for gas fill. I found a nifty M8X1.0 with o-ring Schrader and got sucked into using it. There's VERY little room for a threaded Schrader in the top hat! Even the small M8. The last time I put one in, I machined one from a 1/8" NPT stubby Schrader, press fit. The specialized Schrader required a countersink, counterbore, and threads with barely enough room for the three.
When there's a next time I'll go back to simple press fit.
The end result from the shaft assembly perspective (left out were all above the shaft assembly):
Less can be more and that was certainly true with this bike
On the drive back, I got excited over NOT having to deal with A POS squid beater! I determined to donate a full shop day and parts to leverage a good rescue find into a gem. As usual, the project has grown in scope... but been fun!
Also a reminder of the general brilliance of the GasGas Pro design. There was nothing lighter! A few things were not so smart, but on the whole those were great bikes. My 2009 280 remains a favorite.
A cracked center muffler to TIG weld (typical of the era) and a shock rebuild of the - surprise! - Ohlins instead of Sachs shock, and the need for new fork seals were the day's more major takeaways.
Had to wait a bit for me to travel to my machine shop and yesterday to dive into the Ohlins shock.
What had actually gone wrong? Silly, really, and related to Ohlins fitting rubber upper eyes then instead of the tougher steel Heim eyes. The linkage ratio of the older, eliptical-tube-frame GasGas Pros imparts a short travel feel with a spanking foot arches on drop-offs. Hard on rubber upper eyes and this shock failed mildly and slowly. The clevis at frame shock mount was hammering the tiny bleeder screw head on drop-offs, eventually loosening it enough to slowly lose the 200+ psi nitrogen, and that is why the seal had let out some of the oil. Shock seals require internal pressure to clamp the shaft and seal.
What looked like a first cause seal failure wasn't. On disassembly, I found the gas separating piston hard up against the top hat (no more gas chamber). Like the rest of the shock, the seal head was actually in great shape.
While into the shock I did the 'long travel mod' typical of Randy Lewis of R R Racing... and me. We increase shock rod travel and fit a softer spring. The result is amazing for plushness, terrain following, and for feeling 'bottomless.' I'm thinking the mod will contradict the short-harsh feel of the older GasGas linkage (boy it sure did!).
The mod is simply leaving some spacers out. But oh what a difference! I also did a touch of revalving by moving the 'rocker shims' closer to the piston to quicken terrain response and loading/unloading (body input) response. We shall see.
I'm doing one other thing: converting the shock to 'non DeCarbon' by leaving out the gas separating piston, making it a so called 'gas emulsion' shock. Every KLR 250 and 650 KYB shock was gas emulsion, for example. The Works Performance shocks I used to fit to monoshock trials bikes like my famoso green Works 305, were gas emulsion.
Why? To increase the oil volume, and to make the shock ridiculously easy to get into for further tweaks (if so needed).
Gas emulsion style shocks work the same as piston-separated nitrogen with one caveat: the shock orientation must be rod end down, which was the case with most trials bikes of the mid 2000s except the 4RTs. Turning a gas emulsion shock rod end up leads to top-out as the nitrogen bubble and the piston with shim stacks are in the same space.
My 2009 GasGas 280 had an Ohlins shock set up that way and it worked great. Too bad that was before I or anyone had figured out the long travel mod :-0
What's inside an Ohlins shock like this GG 6521? Pretty typical over a lot of years.
Just right of the P for 'piston', in the R for Rebound stack, I missed two more of the 0.3mm X 32mm diameter shims as they were stuck together:
For the long-travel mod, I left out two of the three red plastic top-out spacers. I also left out the black plastic bump cushion spacer (later left out by Ohlins with a taller bump cushion), all for more rod travel.
The addition of travel is in the negative direction, so it's critical with this mod to run little or no spring preload, or unless you weigh 250+. It's critical to fit a softer spring on some later models, but fortunately this GG had a fairly soft spring. The long travel Ohlins I have on my last competition bike has a 55 N/mm spring. Stock on the Ohlins Shercos is a 64-70 N/mm progressive spring. The stiffer spring severely degrades performance and makes the rear end ride high with stinkbug posture, especially with the usual more preload. The softer spring is a wonder, and bottomless feeling. That's contra intuitive, but true for complex reasons related to bike pitch (front versus rear ride height), steering reaction torques, and squat and terrain following.
The spring number in the old black spring was half rubbed off, and the linkage ratio is a first for me using this mod, but the 'butt dyno' showed this older stock spring with almost no preload is right for most riders.
Shop time was a lot longer to work this shock than usual. Chalk that up to a few 'senior moments', and the need to fit a Schrader valve for nitrogen fill. I also diverted myself into making a tool I've always needed/wanted: a shock tube clamp adapter to hold the tube to unscrew the 'top hat' off the shock tube. Attaining a precise bore for the tube in the block required a lot of Criterion boring bar iterations referencing the tube itself..., with the knee of the mill cranked way down then back up like 15 times..., something machinists on manual mills can appreciate.
Other work: a Schrader valves for gas fill. I found a nifty M8X1.0 with o-ring Schrader and got sucked into using it. There's VERY little room for a threaded Schrader in the top hat! Even the small M8. The last time I put one in, I machined one from a 1/8" NPT stubby Schrader, press fit. The specialized Schrader required a countersink, counterbore, and threads with barely enough room for the three.
When there's a next time I'll go back to simple press fit.
The end result from the shaft assembly perspective (left out were all above the shaft assembly):
Less can be more and that was certainly true with this bike
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