Maxton Cartridge damper upgrade
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Maxton Cartridge damper upgrade
For the last 4 years I've been running with NSR250SP fork uppers (Showa cartridge damping units) fitted into the standard KR1S lower legs to improve the front suspension. Standard the KR uses the damping rod system and I found them way too hard and harsh for road and they gave very little feel on track.
After a discussion with Maxton while buying cartridge units for my race TZR, I decided to upgrade and fit the same Maxton SD20 units to the KR1S as well. The main advantage is that they have rebound and compression adjustments (with the NSR dampers I just have rebound adjustment). I've just finished fitting Maxton cartridges into the original KR forks, not the most straightforward of tasks but still possible as a DIY job with some certain tools so I thought I'd post up the process on here.
After a discussion with Maxton while buying cartridge units for my race TZR, I decided to upgrade and fit the same Maxton SD20 units to the KR1S as well. The main advantage is that they have rebound and compression adjustments (with the NSR dampers I just have rebound adjustment). I've just finished fitting Maxton cartridges into the original KR forks, not the most straightforward of tasks but still possible as a DIY job with some certain tools so I thought I'd post up the process on here.
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Re: Maxton Cartridge damper upgrade
i `m always interested in upgrades Doug ,hope it`s going well, ive just fitted a Paoli rear shock off a laverda formula 750 to my kr1s .
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Re: Maxton Cartridge damper upgrade
One major alteration to fit the Maxton dampers, the valve unit in the bottom of the standard KR fork tube needs to be removed. I'd kept the KR fork legs in case I ever wanted to put the forks back to standard but after this change the legs would be never be useable in the standard setup again but here goes:
The bottom of the leg showing the valve unit, the tube is rolled over by the factory to hold it in place, this needs to be ground off.
Dremel with a coarse rotary drum grinds the edge off pretty well.
About 1mm has to come off until the line between the inner unit and outer leg can be seen.
The bottom of the leg showing the valve unit, the tube is rolled over by the factory to hold it in place, this needs to be ground off.
Dremel with a coarse rotary drum grinds the edge off pretty well.
About 1mm has to come off until the line between the inner unit and outer leg can be seen.
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- Oil Injector
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- Oil Injector
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Re: Maxton Cartridge damper upgrade
So on to building the new forks up. First is clean everything completely, the new dampers have shim stacks internally and it's vital the forks are totally clean inside. The top tube will have fillings in it from grinding out the valve unit so initially to clean them I use an old broom with a sock on it and push the tube down over it, then rinse it in the parts washer then repeat until I'm happy they're completely clean.
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Re: Maxton Cartridge damper upgrade
I don't have a bearing drift to fit these bits but I have an old 41mm bottom yolk, so I clamp it to the tube then use it to knock the bearing and seal into place like a slide hammer. To get the seal in I use an old seal with a cut in it, once the new seal seats down it's easy to pick the old seal out from inside the housing and then fit the seal retaining and upper dust seal.
So this is the full fork leg, ready for the damper.
So this is the full fork leg, ready for the damper.
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Re: Maxton Cartridge damper upgrade
Next the damping units. These are handed as the left leg damper does compression and the right leg damper does rebound (important to make sure the correct top cap is on the correct damping unit). So fully assembled they drop into the leg then bolt in with the standard KR bottom bolt and new copper washers supplied in the kit.
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Re: Maxton Cartridge damper upgrade
Next is simply to put the correct amount of fork oil in (Putoline 5W is recommended). The fork oil level needs to be checked by taking the fork cap and spring off the damper unit, compressing the fork tube down and then measuring the level (the process is described in the instructions that Maxton send). Once done and put back together the cap is screwed into the fork leg and the legs can be set back into the yolks, set to the standard position.
BE VERY CAREFUL TIGHTENING THE TOP YOLK CLAMP!!! They are 20Nm in the manual but hardly a couple of turns and this happened to mine, nowhere near torque. They are 30 years old and are a real weak point. Luckily Bernie helped me out with a spare and I've sent this one broken one off now to get it drawn up into a CNC billet yolk which I'll fit in future.
BE VERY CAREFUL TIGHTENING THE TOP YOLK CLAMP!!! They are 20Nm in the manual but hardly a couple of turns and this happened to mine, nowhere near torque. They are 30 years old and are a real weak point. Luckily Bernie helped me out with a spare and I've sent this one broken one off now to get it drawn up into a CNC billet yolk which I'll fit in future.
Last edited by DougB on Thu Jun 06, 2019 4:10 pm, edited 1 time in total.
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Re: Maxton Cartridge damper upgrade
So all in all. It's a great upgrade (but not cheap). These units are Maxton SD20 dampers with their F3 fork tops to give preload/rebound/compression damping. The drawback is the tops only come in anodised colours, so I chose black, but I'd rather they were alloy like the originals. The ride with these fitted though is a world better than the standard forks, and are a step better again than the NSR setup I was using. I'll be playing with the oil level and damping settings as soon as I get it to the track but on the road they were pretty much spot on straight away.
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Re: Maxton Cartridge damper upgrade
Lovely job and had exactly the same thing in mind for mine once I can see the spare cash. Keep the ride reports coming and what setup are you running at the rear?