Subject: Re: Reworking Sachs shock ... Sat Dec 29, 2018 5:36 pm
Thinking about the valving changes and had a crazy idea ... this picture shows the rebound stack side ... during compression, oil flows thru those scoops cut out in the piston, so it is partially blocked by the rebound shims.
So I'm thinking, I should remove that largest rebound shim, the 38mm. That will make rebound lighter (faster) and it would allow more oil to flow thru the piston on compression. This would help high speed compression IF the problem is not enough oil flowing through the piston. It will not help if the issue is mostly with the compression shim stack.
The reason I say this is crazy ... rider says "Hey, I need to reduce my high speed compression damping" ... suspension guy says "Sure, let me pull that thar big ole shim off the rebound side" (In this case I am both the rider and the crazy suspension guy)
And then I'm wondering if I should double down ... remove that thar big rebound shim and also make a change on the compression shim side. Hummm ...
Adding some logic? and reason? to the crazy plan, I should just remove the largest rebound shim. Already making a number of changes: stiffer spring, different shock oil, probably higher nitrogen pressure ... not sure I want to make 2 shim changes with this round.
Gotta do some
usedtobefast GRiSO Capo
Posts : 207 Join date : 2018-08-29
Subject: Re: Reworking Sachs shock ... Mon Dec 31, 2018 11:56 am
Reservoir wrap up time ...
One option was to drill our flat reservoir cap, tap it, and screw in a schrader valve. Sounds reasonable enough and low cost.
There is an option that some KTM dirt bikes have ... they have a valve where you insert a needle. That would be the same idea, drill our flat cover, tap it, screw in that needle bolt/valve. This looks like what Traxxion Dynamics did in the early picture that was posted. I didn't really want to go that route.
The Racetech option I showed earlier is an "High Volume" cap, so it would stick out a lot more, so I skipped that one.
Found this one, called a "Elka Reservoir Cap - 46mm" [You must be registered and logged in to see this image.]
Bought it from Hygearsuspension and it fits perfectly! Seems like it is from an ATV/four wheeler shock.
For putting this all back together, I really liked this info I found from Race Tech: http://www.racetech.com/PAGE/TITLE/IP%20SK%20Rebuild%20PISTON%20RESY
In those steps we have the "Open End Reservoir" so skip the "Closed End Reservoir" parts. Also no need to read the "Seal Head" stuff, just ignore that.
So the first step is getting the piston out of the nitrogen reservoir side. Hum, it was all the way in, nothing to grab on to and pull it out. Snap ring pliers can't reach it.
What to do. Figured I needed to put some air pressure in the other side to blow (push) it out. And lucky lucky, that chamber is also ~46mm, so the Elka reservoir cap for the nitrogen side also fits over on the shock/oil side!
So I pushed the Elka cap into the shock chamber, put in the clip, got my mountain bike shock pump and slowly added air ... and that pushed the piston out of the nitrogen side. Success! Whew, got lucky that those two chambers are both 46mm.
Then, following those Race Tech steps ... you fill up the nitrogen side completely with oil, and press that piston back in place ... so did that.
I then opened up that bleed screw on the shock body ... pushed the nitrogen side piston in a bit more ... oil flowing out the bleed ... then tightened up that bleed screw.
Then push the nitrogen piston all the way in. This has pushed the oil through and into the shock chamber side. And when looking into the nitrogen chamber you see that piston all the way in (so it is an empty chamber at this point).
Install the Elka cap into the nitrogen side, push it in, need to push a bit, release some air, push some more, release some more air, continue until that cap is past the clip grove in the body. Put the clip in place.
Then put in 20-40psi of nitrogen gas. (OK, I cheated, and used my mountain bike pump again)
Backing up in time ... getting the shock valving ready.
So I decided to double down on a "fix" for the high speed comp issue.
I removed the largest rebound shim ... idea here is that will allow more oil to flow during compression (shim not in the way) ... and if that lightens up rebound, that's ok as that was a need/goal too.
On the compression side I removed the 18 x .2 shim.
Put all the washers, shims, piston, shims, washers in place. Wee bit of blue loctite and put the bolt back on.
I did all that before messing with the reservoir.
Last edited by usedtobefast on Tue Jan 01, 2019 3:40 am; edited 1 time in total
Ok, so I had the shock guts prepped ... and the reservoir side done ...
So I filled up the shock side to about 10mm from the top.
Put the piston bushing on and gently worked that into the shock. And pushed everything in, slowly pull it back out (but leave all that valving stuff in the oil), then press it back into the oil again ... do that 3-4 times to remove any air.
Then top the shock body 100% to the top with oil, and then press the last part into the body. Yes this is messy and oil overflows down the side of the shock.
As the rubber o-ring gets inside the shock body, you can't press any more ... you have a shock full of oil and 20-40 psi of air on the other side pushing that piston back.
So you press the schrader valve a wee bit ... then push the shock guts in another 2-3mm ... press the schrader a wee bit ... press another 2-3 mm, etc.
Do this until the shock guts are in beyond the clip grove. Insert the clip into the grove.
Then you are ready to put full pressure in the shock. Pump it up to 180 psi.
Then push the aluminum dust cover back in place ... tap it in with a rubber mallet, pretty soft metal and it is just a dust cover so easy taps to work it into place.
As a refresher, the shock I've been working on came from woodrow53 . This allowed me the time to investigate all this stuff and still have my GRiSO all together and available for rides. Thanks again for this!!
So shock all together I walk over to my GRiSO ... huh, how do I get the shock off.
I have read a bit about this ... pulling off the airbox and a bunch of stuff ... oh well, time to read up some more on this.
And also, my first time with this was a lot of learning and discovery ... if you handed me a stock shock now (with spring and reservoir cap), it would be very easy to pull it all apart and get it back together again.
Oh ... price breakdown so far ...
$12 - oil $25 - spring (ebay, GSXR shock) $30 - Elka reservoir cap
Subject: Re: Reworking Sachs shock ... Thu Jan 03, 2019 9:08 am
So I read about the "remove it from the bottom (RFB)" approaches, and the "remove it from the top (RFT)" ones.
I like the from the bottom better, and started out going that way, RFB. When I hit my first snag, I switch to RFT. Then hit a snag that seemed more of a pain than the RFB snag, so switched back to RFB.
Then hit a snag, repeat, repeat, repeat. Whew.
I can see that RFB with the left side plate off would be a winner ... but ... my stand lifts the bike from the side plate bottom bolt.
So finally, just like those little metal puzzles, the shock came out! I really have no idea how it finally happened, just the right twist, lean, twirl, something. RFB was the winner for me.
Putting my rebuilt shock back in place was equally puzzling ... just lots of metal puzzle play and somehow it got in there.
While I was doing this I decided to grease up all the shock linkage bearings ... wow ... glad I did. I've probably seen 37 posts from Roper saying to grease this up, and he is 100% right, there was really no grease in there.
I didn't have the mental energy to do the swingarm bearings at this time ... but I will be going back for that in the future.
usedtobefast GRiSO Capo
Posts : 207 Join date : 2018-08-29
Subject: Re: Reworking Sachs shock ... Thu Jan 03, 2019 9:18 am
Now on to preload setting ... for wording, I like "bike sag" and "rider sag" as it makes sense to me ... some call this "static sag" and "race sag", but I ain't racing.
I had read many versions of the "right" thing to do, here are 4 I found:
Source 1 - Bike sag = 11mm; Rider sag = 27-33mm Source 2 - Bike sag = 10mm; Rider sag = 30-35mm Source 3 - Bike sag = 3-5mm; Rider sag = 33-35mm Source 4 - Bike sag = 10mm; Rider sag = 30 mm
So I ended up with Bike sag = 10 mm, and Rider sag = 29mm
This is an indicator to me that the spring is a bit stiff ... if I was a bigger guy it would sag more than 29mm when I got on it ... but that is very close to these difference suggestions.
usedtobefast GRiSO Capo
Posts : 207 Join date : 2018-08-29
Subject: Re: Reworking Sachs shock ... Thu Jan 03, 2019 9:43 am
Ahhhh, test time! And off I go ...
First thing, rebound is much faster/lighter than stock. And that was a goal. And that should be the case, stiffer spring, largest rebound shim removed.
So I went to 10 clicks out on rebound (vs. before I was around 25 clicks out).
Ride was still very firm, spring felt too firm. I went to 2.5 turns out on compression.
Rode some more ... still some high speed hit happening, much much better, but still there. Small ripple bumps were very nice, kind of float-ie.
As I rode more I liked it better & better. Ride is still on the firm side, but the GRiSO is a beast-o, so I don't want it cushy cushy and then not be able to handle a faster pace.
I also realized that in "test mode" you try to run over everything and evaluate each bump So I got out of that and just rode it another 15 minutes like a normal ride, very nice.
Then I headed over to where I knew there were 2 sharp bumps in a row, 45 mph road ... headed for the sharpest/tallest part of the bumps ... and it did not magically float over them as if they weren't there, and actually I don't think a Matris/Mupo/Ohlins would float over them either ... but it really wasn't bad. The sharp jolt did not happen ... no hammering from the seat ... yes, I felt them, the bike hit some bumps, but way better than stock.
So now I have my stock shock off the bike, sitting on a work bench. Do I go for a round II? Not sure.
If I did a Round II, I think I would: 1. Leave the 38mm rebound shim in 2. On the Compression side, switch out 3-5 0.2mm shims with 0.15mm shims 3. Get a spring between the stock 8.2 and this 9.5
In the meantime, I will work on those metal puzzles to keep my shock removing skills honed.
Its length, retracted, is 34mm. Fully expanded (24 clicks) is 42,5mm. Before instaling it, I measured the distance from the top of the spring to the shock head - was 28mm (sag adjusted for solo riding). Had an other bottom spring retainer machined, 6mm shorter thatn the original.
Now, changing preload from solo to full load, needs less than a minute.
So things are certainly better than stock, glad I've done this so far, but I'm going for a Phase II on the shock.
I went too stiff on the rear spring I believe. Stock spring is 8.2 kg/mm, and I went to a 9.5 kg/mm. To me, I feel like the rear is sprung stiffer than the front (stock springs). It is kind of nice that the rear is held up higher, probably benefiting from a more gentle leverage ratio, but the bike just feels a bit off to me with the rear being stiffer.
Also, the high speed comp is still a bit abrupt, still more hit getting to me than I'd like.
So plan is: 1. Get a spring between the stock 8.2 and the 9.5 I have 2. Leave the 38mm rebound shim in place 3. Go to thinner shims on the compression side
Be careful I went down that road lookig for springs for my tuono, CBR1000xx springs should have done it but turns out the stock Honda springs were rising rate and also too long to work with the spacers I had...