Maxton Cartridge damper upgrade

Wheels, shocks, forks, frame
DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Maxton Cartridge damper upgrade

Post by DougB » Sun Jun 02, 2019 11:19 am

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.

fred
Oil Injector
Posts: 917
Joined: Sat Mar 22, 2008 5:42 pm
Location: retford n,nott`s working in cotswolds
Contact:

Re: Maxton Cartridge damper upgrade

Post by fred » Wed Jun 05, 2019 8:56 pm

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 .

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:11 pm

See if this makes any sense then Fred!

This was the setup up with the NSR fork uppers in, with just preload and rebound adjusters at the top.

Image
Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:16 pm

20 minutes later and it looked like this! I love how easy these bikes are to work on. Second picture is the NSR cartridge damper unit.

Image
Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:24 pm

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.
Image

Dremel with a coarse rotary drum grinds the edge off pretty well.
Image

About 1mm has to come off until the line between the inner unit and outer leg can be seen.
Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:27 pm

Once the tube is ground off the valve unit can be drifted out of the fork tube, I used a long steel rod down from the fork cap end and a few taps with a hammer out if came leaving the end of the tube looking like this:

Image
Image

The dremel came in handy again just to deburr the sharp edges.

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:29 pm

This is the Maxton damping unit. They come supplied in bits so the right hand is the unit fully assembled to show what is actually put into the forks, the left is the component parts.

Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:33 pm

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.

Image
Image
Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:40 pm

So first a spacer ring (supplied by Maxton) drops into the fork lower to keep the fork travel to standard, this drops right down to the bottom of the tube.
Image

Then the upper leg goes in
Image

Bearing
Image

Spacer ring
Image

and new seal
Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:45 pm

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.
Image
Image

So this is the full fork leg, ready for the damper.
Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:52 pm

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.
Image
Image
Image

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 3:59 pm

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.
Image

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.
Image
Last edited by DougB on Thu Jun 06, 2019 4:10 pm, edited 1 time in total.

DougB
Oil Injector
Posts: 573
Joined: Thu Dec 12, 2013 9:58 pm
Location: York

Re: Maxton Cartridge damper upgrade

Post by DougB » Thu Jun 06, 2019 4:05 pm

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.

Image

User avatar
500bernie
Avgas Sniffer
Posts: 3268
Joined: Mon Aug 02, 2010 10:22 am
Location: Teesside

Re: Maxton Cartridge damper upgrade

Post by 500bernie » Thu Jun 06, 2019 10:00 pm

Very nice Doug. 8)
Firecracker Red and Grey C3 300
Image

geezagillard
Smoker
Posts: 67
Joined: Wed Jul 18, 2007 10:31 am

Re: Maxton Cartridge damper upgrade

Post by geezagillard » Fri Jun 07, 2019 11:39 am

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?

Post Reply