Shock gas options

[swazi_matt]

Ok i am going to give this a bash! have printed out the sachs shock manual (although will not be as thorough as i am just going for a service not a full rebuild)

2 questions

what weight oil? (and how much)
what was the trick to getting the shock out without stripping the bike down? seem to remember being able to drop it down, twisting and pulling it out sideways

ok that was 3 questions

[hamilton]

Found this on the beta site, nice detailed A&D manual.
Might be a help to you.

http://www.betausa.com/sites/default....manual-HR.pdf

[Jakobi]

Great find hamilton.

Removing the shock I've always found it easier to just remove the lower subframe bolts and swing the back end up. I tried the drop and twist but in the end it was more work for me.. more frustration anyway!

Viscosity of oil around 15cSt at 40C, with a high VI rating (wouldn't consider anything under 200). That viscosity could put you in a 2.5wt/5wt depending on brand.

[swazi_matt]

That is the document i have, but i think it is a bit overkill for a simple service and possible revalve

@jakobi where do you see the VI rating of oil? I have about 800ml of belray 2.5 that i am hoping will suffice.

[swazi_matt]

ok just done some googling and see that the bel-ray 2.5 fork oil has a vi of 60
the best i can get locally is silkolene 05 synth fork oil which is about VI220

I suspect i will be redoing this in the near future so may just use that with air until i have my valving correct and then replace with shock oil and N2 gas

[Jakobi]

http://mahonkin.com/~milktree/motorcycles/fork-oil.html

Google "Suspension Oil Viscosity" and you'll turn a few charts up.

Remember, the viscosity will also impact on your valving. A thinner/lighter oil will flow quicker (faster/softer compression, and faster rebound too).

Silkolene 05 is too thick 43@40C.. The 02 wouldn't be a bad choice if you could get your hands on it. 17.94@40C VI260. From here (http://shop.penskeshocks.com/files/d...ct%20sheet.pdf)

[swazi_matt]

Originally Posted by hamilton

Found this on the beta site, nice detailed A&D manual.
Might be a help to you.

http://www.betausa.com/sites/default....manual-HR.pdf

Has anyone tried the beta shim stack suggested at teh back of this document?

I am not sure what was OEM GG, but this is the comparison between the document and what i have with my racetech gold valve:
Beta ***** ***** Racetech
2 24 2.00 ***** 1 24 0.30
3 22 0.30 ***** 1 26 0.30
1 24 0.25 ***** 1 28 0.30
1 26 0.25 ***** 1 30 0.25
1 28 0.25 ***** 1 32 0.25
1 30 0.25 ***** 1 34 0.25
2 32 0.25 ***** 1 36 0.25
1 34 0.30 ***** 1 38 0.25
1 36 0.30 ***** 1 40 0.25
1 28 0.10 ***** 1 30 0.10
4 38 0.20 ***** 2 40 0.20
valve valve valve *****
3 44 0.20 ***** 6 44 0.20
3 44 0.15 ***** 1 32 0.15
2 40 0.15 ***** 1 44 0.25
1 28 0.15 ***** 1 42 0.25
1 44 0.15 ***** 1 40 0.25
1 42 0.15 ***** 1 38 0.25
1 40 0.15 ***** 1 36 0.25
2 38 0.15 ***** 1 34 0.25
1 36 0.20 ***** 1 32 0.25
1 34 0.20 ***** 1 30 0.25
1 32 0.20 ***** 1 28 0.25
1 30 0.25 ***** 1 26 0.25
1 28 0.25 ***** 1 24 0.25
1 26 0.25 ***** 1 22 0.25
1 24 0.30 ***** 1 20 0.25
1 23 0.30 *****
1 24 2.00 *****

[twowheels]

I wouldn't worry so much about the air and oil causing an explosion ... if you've done it right they never meet

The compressed air is on one side of the sliding piston and the oil is on the other. Nitrogen is adventageous in that it is more temperature stable, and due to larger molecule size less likely to leak past seals.

[swazi_matt]

ok i have started

took a bit longer to get the shock out than i remember, but there is a possibility that the last time i did it i was busy sorting other parts out already.

did it late last night so got as fat as loosening the spring, now - the spring is just about the same length as the free space on the shock so what are the tricks to compressing the spring so i can remove the lower collar?

PS with the shock last being serviced in about july 2012 it was nice to discover that it still has over 150 Psi in the reservoir. But i am guessing that the oil is well past its use by date

and on the tpic of oil, the suspension fluid that i was told was available was incorrect, it was actually the silkolene pro rsf5 which has a vi of 378 so score there. close match with the sachs spec.

[Jakobi]

RSF 5wt is probably a bit heavier than I'd prefer (2.5wt would be better) but it will get the job done and hold up well.

Removing the spring you'll need to rig something up to compress the spring slightly. If its just a few mms a bit of body weight applied carefully in the right places can make it happen (with someone else pulling the retainer). Otherwise you'll have to get creative. I have some little threaded rod ones that clip over a coil each side and you crank down on them. Real pain in the bum to use, and also mark up the spring if you have to get heavy on it.

Regarding disassembly, if you just want to change the oil you don't have to do much.

Turn all the clickers wide open (especially rebound, to seat the needle)
Let the N2 out of the ressie, and remove the valve stem.
Remove the cap from the bottom of the shock body to expose the seal head.
Push seal head down into the shock.
Remove the circlip (have fun!)
Pull the shaft, seal head, and piston up from the shock (watch for when it lets go).
Push the res cap into the body, remove the circlip, and pull the cap out.
Remove the separator piston.

From there drain and clean up with compressed air.
Make any adjustments to valve stacks.

Reassembly follow the manual.
Fill N2 ressie to top (with oil).
Drop separator piston in and be sure some oil overflows (no air).
Bottom it out - This forces oil past the comp adj. I actually like to insert the cap and circlip and use air pressure to hold it bottomed.
Add some more oil to the body.
Bleed the main piston up (slow strokes).
Top up and draw the rod up also (don't come high enough to let air in).
Bring the seal head down and let more oil overflow as it seats against the o-ring.
At this stage if you have put some air into the ressie, you'll need to press the valve down and let air out as you push down on the seal head. It will allow the seal head to drop in and displace the oil over to the ressie side.
Insert circlip and pulll assembly back out to bottom the seal head.
Remove valve stem and ressie cap again, double check measurement down to piston.
All good - put everything back together and gas it up to 10bar.