A man after my own heart GT performance do some really nice shock overhauls but much like you I find it more satisfying to do stuff myself. I have rebuilt my SP, F3 and RS250 shock and really quite straight forward if you have the tools required. The only really specialised/expensive tooling is the nitrogen charging equipment, I have access to a nitrogen rig at work but most motocross dealers should be able to recharge a shock for very little cost.
What type of shock do you have? I'm presuming its an SP remote reservoir type. The next question is what are you aiming to achieve, a full restoration or just an oil change and re gas?
I should have some pictures of my rebuild, I will have a look and start posting some up. If you havent done so already have a look on you tube, lots of videos of shock rebuilds on there.
Okay, got to strip and rebuild my MC28 SP shock today and have taken some pictures. Please bare in mind I'm not a suspension technician and this is just how I have rebuilt my shock using information from various sources and a bit of common sense.
So first off remove the spring, wind the preload all the way off until the spring is slack, pop the retainers out of the bottom and slide the spring off. Before I stripped the shock I made some dot punch marks on the hose and body to ensure correct orientation of the hose on re assembly.
As mentioned these are a sealed unit not intended to be rebuilt, I released the gas pressure by drilling a hole in the end cap. Be aware that this chamber contains pressurised gas so please proceed with caution.
once you have released the gas pressure you can safely remove the banjo bolts from the hose ends. To disassemble the reservoir tap the end cap in untill you can see the retaining circlip and flick it out with a paick or small screw driver. you can then pull out the end cap. To remove the top cap of the reservoir you need to remove the compression adjuster, this just screws out using a spanner across the flats of the adjuster. Then push the cap into the reservoir and you can remove the retaining circlip.
As I had a new bladder I cut the end off the original so I could use it as a seal on the top cap.
To disassemble the main body first of all you have to remove the dust cap, I used a small pin punch in this slot to knock it out. Be aware it is very soft and easy to damage so go steady.
when you have removed this you can see the seal head, this is retained by a circlip. Just push or tap the seal head into the shock body enough to reveal the circlip and flick it out.
If you have to disassemble the shaft you need to remove the end nut, these are normally peened or dot punched to lock the nut. Usually you need to grind or file the peening off but I managed to remove the nut from this one without doing that, I did need to clean the thread with a needle file after I removed it.
Once the nut is removed you need to take great care removing the piston and shim stack. I use a screw driver pushed into the end of the rod and slide the whole assembly across and cable tie the end, obviouslly it is critical to keep all the shims in the correct order.
You can now slide the seal head off and replace the seal if required. assembly of this part is just the reverse of taking it apart. I have a set of seal bullets to save damaging the seal on the thread when removing and installing. This is the only specialist suspension tool I have. I use Loctite on the nut and dot punch the thread nut interface in a couple of places for good measure.
Reinstall the shaft by sliding into the body until the seal head is just past the circlip groove and install the circlip and tap the dust cap back into place. Push the shaft all the way into the body and I then clamp it in the vice with the hose hole at the top.
I use a small funnel and slowly start pouring shock oil in, I normally fill the funnel. You will see air bubble out of the oil and the oil level drop just keep topping the funnel up until you get no more air bubbles.
When the air bubbles stop pull the shaft out a small amount, you will see more air bubble out. Keep topping the oil and pulling the shaft out a little bit at a time until it is fully extended. Now I install the hose to the shock body and submerge the end of the hose in a pot of shock oil like this.
Then pump the shaft in and out you will see air bubble out of the submerged hose, keeping pumping until you no longer see any air bubbles and the damping feels smooth and consistent.
Next install the reservoir with top cap installed and hold the reservoir in the vice like this.
I fill the reservoir about halfway and once again pump the shock shaft in and out until you get no more air bubbles. Then fill the reservoir to the top with oil and carefully push the bladder in until it the end cap is just past the circlip groove and install the circlip.
I now use compressed air to inflate the bladder enough to seat the end cap against the circlip. I will charge it with nitrogen at a later date. I used a 86 CR250 workshop manual as a guide for this rebuild as they have a remote reservoir shock and they suggest charging to 142 psi. Most shock rebuilds I have seen usually have a charge pressure aroun 140 to 150 psi.
I didn't change the seal on this shock but I did change it on my NF5 shock and used a K Tech Showa 46/14 seal head service kit, cost about twenty quid. 46 is the OD of the seal head, 14 is the shaft size. I'm pretty sure they are the same as the SP shock but just measure up you're disassembled parts they do a lot of different kits and they come with all the seals and bushes and a self locking nut so no requirement to dot punch the shaft to lock the nut.
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GT performance do some really nice shock overhauls but much like you I find it more satisfying to do stuff myself. I have rebuilt my SP, F3 and RS250 shock and really quite straight forward if you have the tools required. The only really specialised/expensive tooling is the nitrogen charging equipment, I have access to a nitrogen rig at work but most motocross dealers should be able to recharge a shock for very little cost.
you will see air bubble out of the submerged hose, keeping pumping until you no longer see any air bubbles and the damping feels smooth and consistent.
