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  #1  
Old 17th April 2019
Tomcatt Tomcatt is offline
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Default 2016+ "one cartridge" Forks

I''ve got a 2017 XL1200C with the "latest and greatest" cartridge on one side forks. I've already replaced the OE 11 3/4" emulsion shocks with Ohlins HD 916E shocks.

The OE rear shocks were gawd awfull. The forks not as bad after replacing the shocks.

So I got a set of Race Tech FRSP S2938090 springs. I cheaped out and got the 29mm od springs vs the newer (and $60 more) 30mm spring. .90 kg/mm, 50 lb/in, 15 1/16" long.

I replaced the right spring (damper rod side) first as I was waiting on a spring compressor for the cartridge side. OE spring is 20 1/16" long and half of that is tight wound coils, it's dual rate. It had a 3 15/16" preload spacer and right at 4" of actual preload. One of those springs you're happy you don't have to re-install. With the OE springs the forks sagged 1/2" with me (225 lbs) sitting on the bike.

So I dropped in the right spring with a 6 1/4" (PVC) preload spacer and went for a ride. Nice improvement for just dropping in one spring.

Spring compressor arrives so I lift the front end, remove both springs and bottom (fully collapse) the forks.

Per the FSM oil levels "should" be 5.59" left (cartridge side) and 4.72" right (damper rod side). They were nowhere close. ~6 3/4" on both sides. I lost some oil removing the springs but not near that much.

So, taking an educated guess I set them at: left 6", right 5 1/4". I added some left over Race Tech 15wt I had. Springs went in, with a 2 5/16" preload spacer on the left and a 6 1/4" spacer on the right. This gives me 1" fork sag with my 225 lbs sitting on the bike. Should be about right on forks with just 4" of travel.

Ride is pretty good. Much better than with the "too soft with too much preload" OE front springs.

Still needs improving. Fork oil levels are too high for these springs. It has that feel and I'm not using all the (4"!) of travel. There's also some weirdness that feels like a hydraulic lock, a damping issue. I think the spring rate (.90 kg/mm) is pretty close to right.

So next I'll remove and drain both fork legs and try Redline Medium (10 wt) fork oil with levels set an inch lower. That awaits some more free time (and ambition) and another reasonable day as my garage isn't heated.
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Last edited by Tomcatt; 29th March 2021 at 16:44.. Reason: corrected FSM specs
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Old 17th April 2019
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Default

Not reading your left and rights.
Have you under filled right and over filled left?
FSM says 4.72" for left and you put 6"?
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Old 17th April 2019
Tomcatt Tomcatt is offline
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Quote:
Originally Posted by harley506d View Post
Not reading your left and rights.
Have you under filled right and over filled left?
FSM says 4.72" for left and you put 6"?
No, what I did was get the FSM specs backwards in my post. Thanks for catching that, I corrected it.

I went with levels lower than spec. Next go round they'll be even lower. If you're too low, it's easy to add oil. To lower the levels, take oil out, ya gotta remove the springs.
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Old 17th April 2019
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"Replacement of the fork oil is specified by the MoCo in two different terms. It is specified as to quantity (ounces) but is also specified by then measuring the distance the fork oil is down from the top of the slider tube. This measurement is taken with the fork spring removed and the slider & leg compressed together." (From the SP)

In addition to the variability created by the viscosity of the oil used, the air gap at the top acts as an air spring. Varying that gap (or distance to the oil) will alter the cushion of the suspension. Just be sure on the damper side to have enough oil for the dampers to work thru their full range...

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Old 26th April 2019
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Default

Just a follow-up.

I pulled and drained the forks. The right (damper rod) side is easy. The left (cartridge) side is a PITA. Much alternating between pumping the tube in the slider and pumping the damper rod to get the old oil out. You definitely want the damper rod holder tool. I made one. 10x1.0 nut welded to a piece of thin wall 5/8" od tubing.

Redline medium (10 wt) oil went in. 7" left level, 6 1/4" right level. Yes, that's plenty to keep the damper rod and cartridge submerged. There is no damping in the right tube.The "damper rod" doesn't damp, it just has a bottoming stop. Keep in mind I have Race Tech springs with PVC preload spacers and that affects the forks' internal volumes. The forks took (total) a little less than 1 1/2 pints of fork oil.

This set-up works. The forks will bottom but they bottom more gently versus hammering you. The ride is surprisingly good considering there's only 4" of travel. I do think I could (should?) have gone with .95 kg/mm springs instead of .90's. I may change them (that's easy) after I get some more time on this set-up.

Sooo, Harleys' "one cartridge" forks actually work with an oil change and replacing the stock "too soft with too much preload" springs.

Fork mods plus Ohlins' HD916E (13.26") shocks makes for a 2017 XL1200C with surprisingly good suspension.

Last edited by Tomcatt; 13th March 2021 at 13:44.. Reason: had oil levels backwards again...
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Old 27th April 2019
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Good news! And thanks for sharing your experiences. It doesn't sound like you will need to dive into your forks again, but an easy way to remove oil that I've found in my own attempts to improve the ride is to use a large syringe. I used a horse-sized one, but simply as it was what I had on hand at the time and was long enough.
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Old 27th April 2019
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Yep, have the Race Tech fork oil level tool. Got the real deal after using a modified baster for yrs...

Last edited by Tomcatt; 5th May 2020 at 17:25..
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Old 31st May 2019
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Being eternally fussy I swapped my .90 fork springs for .95's. Race Tech FRSP S2938095. No other changes.

The .95's are better. The process continues...

Last edited by Tomcatt; 19th July 2019 at 19:22.. Reason: updated
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Tom - Thanks for posting your experience with these forks.

Would you happen to have any photos to add to the thread showing the work you did, comparing the springs, etc.?

I placed a link in the Sportsterpedia to this thread:
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Old 31st May 2019
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Summary:
My fork mods are pretty basic:
Springs
Spacers
Fork oil weight
Fork oil levels

The left (cartridge side) fork is more complicated than the usual damper rod fork. You might want the FSM and a fork spring compressor.

Remove and drain the forks and toss the OE fork springs and spacers. Pump the forks to get the oil out. On the left (cartridge side) you need to alternate pumping the fork/slider and pumping the cartridge rod. It's a PITA and takes a while to get the oil out.

After trying both 5 and 10 wt I settled on Redline 10 wt. 6 1/2'" level in the right (damper rod) side. and an 7 1/4" level in the left (cartridge) side. (See Edit) Setting the levels is IMPORTANT, make sure the forks are fully compressed and the cartridge rod is down when checking levels. 2 pints is enough for both forks.

Once your levels are set drop in the springs (Race Tech FRSP S2938095) (see Edit) then a washer (supplied with the springs) to protect the end of your PVC preload spacer.

Cut PVC pipe preload spacers. 3/4" PVC pipe, a piece comes with the Race Tech springs. A 2 3/8" spacer for the left (cartridge side) and a 6 1/2" spacer for the right (damper rod) side. On the right side put the OE washer on top of the spacer and reinstall the cap. The left (cartridge) side is a PITA with the retainer. It's PVC spacer, OE washer, retainer under the rod nut then the cap screws on the cartridge rod.

Put the forks back in the triple clamps.

Your new springs are being installed with ~ 1 5/16" preload instead of the almost 4" of preload the much softer OE springs had. Your forks will settle ~1/2" under the bikes’ weight. They settle another ~7/16" with my 200 lbs on the bike. About right for forks with only 4" of travel. Lighter riders will want lighter springs and might want to shorten the preload spacers but I'd try these specs first. It's easier to shorten spacers than lengthen them.

Enjoy. Now you won't cringe every time you approach a pavement seam...

Edit: I've since gone to slightly higher oil levels, 6" on the right, 6 3/4" on the left, and back to the lighter Race Tech FRSP S2938090 (.90 kg/mm) fork springs, same preload spacers. The ride is better with the lighter springs and the higher oil levels keep the forks off the hydraulic bottoming stops under heavy braking.

On the rear there are 13.26" Ohlins HD 916E shocks with the light duty springs. The forks are now nicely balanced to go with them.

Last edited by Tomcatt; 22nd January 2022 at 03:29.. Reason: updated
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