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2018 390 Duke
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Discussion Starter · #1 ·
I couldn't find a discussion of the new model forks getting oil changes or preload spacer replacements, so here goes.

I am 200 lbs without riding gear, so the stock suspension has been pretty lackluster for me. I forgot to grab pictures, but the front sag with rider was ~45mm from static bike sag. I don't feel like Bajaj/WP designed this suspension with your average Yankee in mind.

I am going to try out a few different thickness preload spacers to see if I can improve that a bit. I am also adding some heavier weight oil to slow down the rebound and compression.

The bike is stabilized with a paddock stand in the rear, a floor Jack with a piece of plywood between it and the bike in the middle, and jack stands under the frame sliders on the engine guard. The jack stands are there for additional support, you could probably get away with just the floor jack.

It was lifted just high enough to allow for free spinning of the front wheel.

Loosen both caps on the fork body (24mm spanner) before loosening the bolts on the triple clamp.

I took the clamp off the handlebars so that I could move them out of the way and have easier access to the fork caps.

Make sure you don't let the brake caliper free hang from the brake line; I hung mine with zip ties from the lower triple clamp.

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I started with the left fork leg (brake side). The top cap is easy to unthread from the upper fork tube since you already broke it loose while still on the bike.

Once the cap is off, you can pour out the oil. I measured mine as I wanted to used that as a baseline for how much to put back in. You will need to work the stanchion up and down in the fork body to pump the oil out. I found that compressing the stanchion all the way in gave the best results. I also threaded the top cap back on and compressed the fork a few times, then opened it back up and poured out what came out of the cartridge. I repeated this process a total of four times until there was no more oil coming out.

The left fork (brake side) only had ~350 ml while the right side had ~400 ml. I'm not sure why the discrepancy.

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The cap is threaded onto the fork cartridge. Use zip ties to compress the spring and allow easier access to the nut on the top of the cartridge (22mm spanner).

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The preload spacer on both legs of my fork measured just over 10 mm.

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I found that a 3/4" schedule 40 coupler from the hardware store was similar enough in dimension to work as a custom preload spacer.

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I cut the coupler in half using two different types of pipe cutters; trial and error due to it's thickness.

I then sanded down the surfaces of the cuts and the sanded off the raised markings.

I made two spacers, both ~25.5 mm.

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Reassembly is the reverse. Retighten the top cap onto the cartridge using the 22 and 24 mm spanners.

My preload spacers, at ~25.5mm, did contact the 22 mm spanner. Once the top cap was tightened down, this made it difficult to remove the spanner. A little persistence and the spanner will come out. If you were to try using thicker spacers, you would need a better way to compress the spring so that the spacer could slide below the cartridge nut during reassembly.

I am trying out the Motul 7.5 weight fork oil. If I don't like the performance, it should be pretty easy to pour it out and try another.

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2018 390 Duke
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13 Posts
Discussion Starter · #2 ·
I used 400 ml in both fork legs.

Tip the leg slightly away from the measuring cup and pour the oil slowly. If you pour against the spring, the oil will adhere to it and you won't spill.

Old Oil, Left Fork.

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New Oil.

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After reinstalling both legs, I followed these two videos for realignment of the fork legs



It's raining here this weekend, so I won't be able to give it a full test until Monday.
 

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2018 390 Duke
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Discussion Starter · #4 ·
Hey Mad, apologies, work picked up lately and haven't had as much time to ride so hadn't been thinking about a forum update.

The sag was just about right with the new spacer. I'm not sure I like the way the fork is performing, seems just a bit bouncy over rough surfaces so I'm thinking it's under damped. I am going to drop back to the original oil weight or a 5wt when time allows
 

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The sag was just about right with the new spacer. I'm not sure I like the way the fork is performing, seems just a bit bouncy over rough surfaces so I'm thinking it's under damped. I am going to drop back to the original oil weight or a 5wt when time allows
I saw a build somewhere that they had the front forks modified to include adjustable compression and rebound I think, It was way less than replacement forks... want to say around 600,let me see if I can find that info.....
 

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Hey Mad, apologies, work picked up lately and haven't had as much time to ride so hadn't been thinking about a forum update.

The sag was just about right with the new spacer. I'm not sure I like the way the fork is performing, seems just a bit bouncy over rough surfaces so I'm thinking it's under damped. I am going to drop back to the original oil weight or a 5wt when time allows
Older thread but just what I was looking for..... I am going to have to make some spacers for mine while I have them off to change the oil.

Yours may be spongy due to not enough fork oil....... This is snipped from the 2018 service manual, should be 450ml in both legs:

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