Silencer repacking on the Gas Gas Pro

If you’re running a trials bike for longer than a year you’ll need to re-pack the silencer.  Obviously we’re talking two strokes here. You may need to do this more frequently, depends how often you ride and how hard the bike works. When I had a Beta rev3 200 I did this 3 times in the year, always with good results.

The benefits: Trials bikes are quiet, lets keep it that way. From a rider’s point of view: As the packing deteriorates the engine response gets harsh, the bike feels more pokey as the power is shifted up the rev range.  We’re trying to restore the original “as new” performance.  You remember that – a smooth soft torquey feel, not short of power, but rather more effective in the way it makes it, hopefully  giving the rider the option to back off and find grip.  If you have doubt’s – try your pal’s newer bike – see what I mean?

The problem: Most bikes have an easily repackable rear silencer (some don’t). Most bikes centre silencer needs to be cut open to re-pack. Heres the easy way to do that.

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This is the Gas Gas Pro silencer from my 2011 250. It’s been a one-piece unit for the last few years.

Using a cardboard pattern, I’ve cut two holes on the blind side on the middle silencer. The original packing is a stainless wire wool visible in the smaller hole in the pic. The white string like Silentsport type packing is left over from a earlier experment. The wire wool was wrapped tightly round the perforated inner baffle on assembly and is a messy and time consuming job to remove. You need to cut and tug this out, you can’t really get behind that baffle but just remove as much as you can. You can then pack this middle box quite firmly with fresh stainless wire wool.  Using the cardboard patterns I cut two plates from 1.5mm alloy sheet and the drilled and pop rivetted these in place, adding a bead of silicon to the edges on assembly. The 1.5mm sheet is surprisingly stiff, 1mm would probably be sufficient.

Okay, it doesn’t look pretty, but it can’t be seen on the bike. The larger panel needed a little hammer work (!) to give clearance for the shock on the 09 – the 2011 has more clearance.

The rear part of the Gas Gas silencer has a removable end cap (pop rivets again) so pull this off, remove the old packing and baffle tube. Clean up the tube, my one had some netting wrapped around the tube. This was fitted by the factory so I put that back. The rear silencer should be repacked with the loose Silentsport type packing or similar. Packing this firmly – but don’t ram it down. Make sure the  baffle tube lines up with the end cap and rivet this on.

Originally I packed the middle silencer with the string type packing, this worked well, but the stainless wool is longer lasting and gives a smoother response – very near to the new bike feel. And quiet…..

Further testing (the 09) – gone back to the string type packing! It calms the engine response a little, but needs changing more often.

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Update: same mod to my 2011 GG Raga – much neater job – a Dremel is the tool! On this I used the stainless wool in the front part of silencer. It worked well and I recently tried a new 2014 Racing 250 for comparison. Engine response was broadly similar, with slight differences in carburation that only the picky would notice. The Racing comes with a Keihin & was “crisp” even brand new, I assume it will get more so when it loosens up. My Raga has a flatslide Dellorto fitted for now. It’s that progressive smoothness of new that we’re chasing. Forgot to take pic of finished silencer – so here’s some of it fitted.

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Steel Wool Silencer Packing

Merlin Motorcycles can do this job for you or would be happy to sell you a new Gas Gas silencer which retails at £513….now cheaper!…Gas Gas rear silencer