that's what is says on the rear Sachs damper of a Monster 696. I'm definitely going to ignore that! That Sachs isn't a bad damper you know. A bit of a budget bargain bucket item and I would like to have some compression adjustment to go with the rebound adjustment that comes as standard. As ever, I want a solution that costs as little as possible. First step is to purchase a standard Sachs damper. Ebay provided one one for £31. Tatty but straight, undamaged and with a shaft that's free from corrosion. It definitely had gas in it as it returns nicely when compressed all the way. Nowhere to release the gas though. There is only one Thing for it; drill a hole! At this stage I have no idea if this thing has a separate gas chamber with a piston or if it is oil/gas emulsion. Could be either but if it is oil/gas I'm most likely going to get covered in oil when I drill the body. Fingers crossed For once I'm lucky and it has a separate gas compartment. Just a bit of wind and there's no more pressure in the damper. That allows me to strip it down completely. That done, how can I make this : 1. a working damper again 2. Double adjustable I'm going to make it into a Öhl-Sachs or perhaps a Sachsohlins. I like the second one better.
The next job is to strip the zinc plating off the damper body. 24 hours in white vinegar takes care of that and any corrosion too. A friend of mine kindly donated a Öhlins gas cannister which has a compression adjuster. It's massive as I came from a long damper with lots of stroke. Whilst too big doesn't really matter for function, I do have a packaging problem on the bike so I have to get it smaller. With the Sachs damper only having 65mm stroke and this cannister being quite a large diameter I can shorten it quite a bit. The gas piston only needs to be able to move 6.5mm to allow the oil displacement needed for the shaft at full compression. 5 times that figure gives a good gas volume so it's time to cut that cannister down and turn in the detail for the endcap again. It actually ended up shorter than in the picture. This is now small enough to be placed on the swing arm. I need to make some sort of bracket but the space is there. Back to the Sachs body. Turned up a boss with a 10x1 thread and welded it onto the body utilising the hole I drilled earlier. 15 minutes in the zinc plating tank and a dip in yellow passivate keeps the corrosion at bay. Now it's time to assemble this damper dry and then see if it'll clear everything on the bike. Time ran out today but it's looking good so far.
I had a bit of time today so I made some progress. I had a look at the Sachs sealhead . As you can see it's not pretty. What's more, they hold the main U-seal in place by pushing in a bung and swaging/squeezing the seal head. That bung also has a wiper seal fitted. That gives me 2 problems. One is the size of the U-seal. It's 14-24 which is an odd size. 14-22 is much more widely available and I have some. The other issue is installing the U-seal. Mine are very stiff and don't like to be squeezed into a lozenge and shoved down into that groove. It's time to make a new sealhead. I decided to stick with the basic design but use my 14-22 U-seal, a new DU bush and a new wiper seal. Instead of swaging the wiper seal bush I threaded both parts so I can easily install and change the U-seal in the future. There is also a kind of rubber doughnut that acts as a droop stop. I re-use that as it's in good shape . First I press the wiper seal into its housing and the U-seal into the main sealhead. Then screw the 2 together, install the doughnut and a new O-ring for good measure. That's the last of the parts I had to make so the next step is to put the damper back together.
Here is the finished article. Next step is to put it on a Dyno and compare it to the original. Rebound should be the same and I'm hoping for compression damping to be adjustable so that I can have a bit more or less than standard. Just feeling it by hand I think I can definitely have less but perhaps not more. We shall see tomorrow.
Dyno day! Went to my mate Ian's who kindly lets me use his Dyno. First we strapped on the standard OEM Sachs as it came off my bike to see what I had. I ran this with a linear spring instead of the progressive that comes as standard and I had the adjuster, which is just rebound, set at 8 clicks. They way I (actually everybody should) count clicks is this. Maximum hard is 0, then count the clicks you have from there. In this case it's 16. The reason for this is that fully closed is always a very defined position. Depending on the type of adjuster it means Spring fully compressed or needle fully seated, that sort of thing. The fully soft side on most dampers isn't so well defined and can vary a lot. It did so in this case too. Of the 16 clicks available only the first 8 have any effect on the rebound forces. Clicks 8 to 16 have zero effect. After the first run we did a second one with the adjuster at 0, so full stiff and then a third at 16, full soft. That's when we discovered that 8 to 16 don't make any difference. Did another run with the adjuster at 4 and that was pretty much in the middle between 0 and 8 on the graph so adjustment is very linear. Then it was time for the ÖhliSachs. Rebound on that tuned the same as the OEM which is what you'd expect but it's nice to confirm that 2 dampers from the same bike actually are the same. So again, only the first 8 clicks have any effect. The Öhlins canister I crafted on has 26 clicks and at 0, again full stiff, I have double the compression forces when compared to OEM. Which the same shim stack you can't really have less than the original forces and at 13 clicks I'm back to OEM forces in compression. Also on the Öhlins the clicks 13 to 26 don't have any effect. Here's a short video of 2 Dyno runs. Disregards what's being said as it's just me and Ian chatting away. I always find it bizarre when I hear stories of people going to their suspension "guru" and they apparently have magic powers to set up a bikes suspension just by a client telling them what kind of riding and ability they think they have and them making some adjustments to said bike and it's like night and day. I also know that some well known suspension shops who re-valve your damper or your forks don't have a Dyno. That's perhaps a whole other thread. Next job is to put the new damper on the bike and give it a try.
