Thinking that the front forks could also do with a full service I booked onto two of Reactive Suspension's Suspension School Courses covering shock and fork servicing.
http://www.reactivesuspension.com/suspensionschool.php
In a nutshell it was a great two days spent learning the theory and practice of how these items work (or don't in some cases) and then getting fully hands on servicing either your own items or items supplied by the school. I can highly recommend it. Classes are small - usually 4-6 students and Gareth is a great teacher. Questions are welcome and I asked several SP related questions which I'll go into later. Gareth also worked with Shane Byrne when he was riding the Honda SP-1 in British Superbikes.
Let's jump straight into removal of the shock onwards and note this isn't a 100% step by step guide, more a general review of the shock service I undertook.
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Here we have the shock off the bike, spring and lower collar removed. First useful part of the course is that if you decide you don't want to do lots of suspension servicing you can use the schools specialist tools. The first you'll need is a spring compressor to get the spring off the shock. Next we release the pressure from the reservoir body via the Schrader valve. To access this you'll need to remove, with a fine point drift or sharp instrument, the reservoir cover. Once done you expose the valve but the process destroys the cover which has no way of re-attaching later on. The SP manual pretty much describes the shock unit as unserviceable and should be replaced if you have problems (not so) and this is just one of several 'features' to stop you servicing it.
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Here we can see the notch in the Seal Head Cap that needs to come off to access the internals. The seal head is removed by using a drift placed in the notch and carefully prising the seal head up. Once the cap is off we can push the seal head down thereby exposing the retaining ring that needs to come off using another fine pointed instrument but with the ends smoothed off so we don't score the internal shock body.
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With the ring removed we carefully remove the Shock Shaft. Careful extraction prevents the inevitable bath of oil one gets if you rush this stage!
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Here's the shaft completely removed with the rubber bump stop, pistons and shim stacks revealed. Note the removed Schrader valve at top left when we released the pressure from the reservoir.
We then need to get at those pistons and shim stacks to 'blueprint' them over and above OEM to try and improve the standard shock. This together with refilling with really high quality oil are the only sensible things we can do to improve the stock shock. To remove the nut securing these assemblies together is another 'do not tamper' style affair. The nut is held in place by peening the edges of the threads at the top of the shaft so the nut can't be removed. Normally not a big problem as we can carefully remove the peening with a grinder or file but in this case the Showa unit incorporates a small disc that works as part of the damping system inside the shaft threads. Remove too much material and the disc can fall out so shock is useless. I bailed and gave it to Gareth to remove with his years of experience and skill. Removing the nut allows the stripping of the shims and piston assembly. On the course this is done the lengthy but correct way; noting each and every shim size with a micrometer and writing down their exact order so there's no chance of reassembling the unit incorrectly. You'll see from the number of shims that this isn't a two minute job.
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The parts are all throughly cleaned with brake cleaner and the piston itself is blueprinted for the best possible mating surface by rubbing down on an engineering plate and then cleaning again.
I noted that the rebound adjuster (at the bottom of the shock) turned ineffectively on my SP-1 and Gareth explained why. The adjuster has a very finely turned step in the middle so the rebound adjustment basically moves a needle along an angled surface to increase or decrease the flow of oil through the damping. The problem is that this makes the lowest setting of the adjuster very thin indeed with the inevitable result the adjuster can break off at that point. It might be worth checking your adjuster to see if it has some resistance, or if it just turns uselessly round and around like mine did
. After reassembly and stripping the compression adjuster in the same fashion, we refill the shock with oil and then can either bleed it manually or use a special vacuum refilling system that really does bled all the unwanted air out of the system. I opted for the latter, once again leaving Gareth to refill with top spec Silkolene shock oil (normally 2.5 to 5w).
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That's a really quick review of a whole day of shock servicing and pages of theory learnt and hopefully will give an insight as to what goes on inside a Showa SP-2 shock. The bearings and linkages holding the suspension together also got a full overhaul, so when my new brake lines arrive and I bleed the brakes I'll be able to give an on-road report of what the riding results are. I might even do the fork service write up
I can see now there is very little likelihood of any problem whatsoever without the reservoir cover. 
