Date: 29-03-24  Time: 06:57 am

Author Topic: Fork overhaul procedure  (Read 2482 times)

teecee90

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Fork overhaul procedure
« on: 22 May 2020, 12:48:20 pm »
I'm about to overhaul my forks (when the Hyperpro springs arrive) and have put together this procedure from reading and consolidating various forum posts. Grateful to the original contributors (no credit is due to me for any of this) and welcome any comments and/or corrections.

TOOLS REQUIRED
1. Torque wrench
2. Fork seal driver (or home made equivalent)
3. 6mm hex/allen key (pinch bolts)
4. 24mm socket/ring spanner (fork caps)
5. 17mm socket/ring spanner (pre-load adjuster)
6. 19mm hex/allen key (front wheel axle shaft)
7. 8mm hex/allen key (damper rod bolt)
8. 12mm socket (caliper bolts)
9. 14mm spanner (damper rod nut)
10. 8mm socket (fender bolts & brake line brackets)
11. P2/JIS screwdriver (fender screws)


PARTS REQUIRED/RECOMMENDED
1. Oil seals (x2) 5VX2314500
2. Dust seals (x2) 4TX2314401
3. Snap ring (x2) 4TX2315600
4. Upper bushes (x2) 4TX23125B0
5. Lower bushes (x2) 4TX23135B0
6. Copper crush washer (x2) 90430-10171
7. Fork oil of choice (1ltr)


FORK OVERHAUL
1.     Fully back off the pre-load to reduce spring pressure on the caps for later removal and loosen upper yoke clamp pinch bolts
2.     Loosen fork caps but don’t remove the caps at this stage
3.     Jack up and remove front wheel, fender/mudguard and brake calipers
4.     Loosen lower pinch bolts and remove forks
5.     Unscrew the fork caps from upper tubes carefully (will be under some spring tension)
6.     Loosen the lock nut and remove the caps from the damper rod.
7.     Check the cap o-rings for damage and replace if necessary.
8.     Remove the thin damper adjustment rod from the centre of the damper rod.
9.  Remove the damper rod nut, spacer and washer/spring seat.
10.  Remove the spring, noting orientation (tighter section/pitch at bottom, although probably not critical provided both forks are the same orientation).
11.  Drain oil.
12.  Remove dust cover/seal.
13.  Remove oil seal spring clip
14.  Clamp lower fork leg (workmate or soft-jaw vice) and hold damper rod with special tool (e.g. a broom handle or preferably a 26mm socket taped or welded to a 18-20 inch long ½ inch diameter tube/conduit/plastic pipe with a hole drilled through the top for a screwdriver to act as a T-bar). Note - special tool might not be necessary for disassembly if using air/battery impact wrench but may still be required for assembly (stage 31).
15.  Remove damper rod hex bolt from bottom of lower fork leg.
16.  Remover damper rod/unit.
17.  Separate the upper/inner tube from lower/outer tube by pulling the inner tube forcefully but carefully (in a slide hammer type action). NOTE – avoid bottoming the inner tube during this procedure as the oil stopper will be damaged.
18.  Clean/flush the forks and components with brake cleaner. Use compressed air to blow out all oil passages and dry the components.
19.  If necessary, polish the steel tubes with fine scotchbrite pad or 1000 grit wet/dry to ensure a smooth finish for the new seals to slide on.
20.  Install the lower bushes onto the upper/inner fork tube. Use assembly grease or fork oil on the bushes and lube the outside of the tube with fork oil.
21.  Turn the upper/inner fork tube upside down.
22.  The oil flow stopper is tapered with a machined collar or lip on the other end. Place the tapered end into the end of the upside-down fork tube with the small end facing up.
23.  NOTE – the service manual indicates that there is a flat section that needs to be aligned “downwards” in line with the compression adjuster – see picture. Not sure there is in fact a flat section as shown in the picture so orientation may not be that important provided the shoulder/lip is properly located.

24.  Slide the lower/outer fork tube over the upper/inner tube trapping the tapered oil stopper in place. The stopper MUST fit flush and flat in the recess cut into the bottom of the lower tube.
25.  Holding the two sections together, turn the assembly to the upright position and clamp the lower leg/tube in a workmate or soft jaw vice.
26.  Keep the fork vertical for the rest of the assembly.
27.  Insert the damper unit ensuring it locates properly in the recess in the lower leg. Without moving the upper/inner fork tube in the lower/outer leg, install the bolt up through the bottom of the fork leg and secure the Allen bolt into the damper rod. Use a new copper crush washer and torque progressively to 35Nm.
28.  You may need to hold the damper using the special tool (step 16) to stop it turning whilst tightening the bolt, but it is most likely not needed at this stage.
29.  If the damper rod tips to the side during this process….STOP. Wiggle the damper cartridge a bit to get everything into proper alignment. If you can’t get it to stay straight as you tighten the bolt, remove the upper/inner tube from the lower/outer leg and START OVER. If you don’t…. the aluminum oil stopper will be damaged, the damper will bind and the forks will suffer extreme stiction and internal wear.
30.  Once the damper is in straight and the bolt torqued to specs, use assembly grease/fork oil on the rest of the components before installation.
31.  Install the upper fork guide/bush, with guide washer. User a fork seal driver or equivalent to set it in place in the lower/outer leg.
32.  Now fit the seal – lubricate the seal lips with LS grease. Apply fork oil to the upper/inner fork tube. Use some plastic/cling film over the top of the fork tube to get the seal started without damaging it. Use a fork seal driver or equivalent to set it in place in the lower/outer leg.
33.  Fit the snap ring and dust seal (push fit only).
34.  Add approx. 350ml of fork oil initially (final spec is 440ml). Standard grade oil is SAE 5w. Some prefer 7.5w or 10w for a firmer ride.
35.  Slowly stroke/pump the damper rod in and out at least 10 times to bleed air from the system. Do not pull the damper up to its full extent or this may re-introduce air into the system
36.  Slowly stroke/pump the inner tube up and down at least 10 times to distribute the fork oil once more. Limit upward strokes to about 150mm to avoid air entering the system.
37.  Leave to settle for at least 10 minutes and then top-up with sufficient oil to ensure there is a suitable air gap, as measured from the top of the fork with the spring out and tubes compressed. Standard spec air gap is 140mm.
38.  Install the spring (tightest section at bottom is standard) and the thin rebound adjuster rod down the centre of the damper rod.
39.  Install the spring seat/washer, spacer and nut. Wind the lock nut all the way down the thread initially.
40.  Falcon recommends before refitting the top cap to wind the rebound adjuster screw out all the way, then back in again by 42 clicks. Eight clicks equates to one full 360 degree rotation of the screw. This ensures that you retain the full range of adjustment on re-assembly.
41.  Fit the fork cap and wind it down as far as it will go on the damper rod. Then back-off the lock nut up the damper rod until it tightens/locks against the top cap.
42.  If possible, torque the top cap down now (25Nm) while you can still get a socket to it. If you do it back in the fork clamps, you will need to remove the handlebars. Might also be worth setting the preload and rebound to the required settings at this stage as well for the same reasons.
43.  Refit the forks into the yokes. Consider setting the top of the forks 5-10mm through the top yoke (a popular mod to quicken the steering / turn-in). Temporarily tighten the lower yoke pinch bolts. Tighten the fork cap 25Nm (if not already done at step 42). Tighten the upper yoke pinch bolts to 30Nm. Fully tighten the lower pinch bolts to 23Nm.
44.  Reset preload, rebound and compression settings, if not already done.
45.  Front wheel/fork alignment – install the wheel and axle. Leave the calipers off or open the pads so they are loose. Torque the axle to normal spec (72Nm). Now, the right side is fixed (from the front looking to the rear) or non-floating and the left side fork is free to float or move slightly on the axle. Push the left fork tube at the axle as far in towards the wheel rim as possible. Let it spring back on its own. Note this position in relation to the end of the axle (preferably using a Vernier caliper to measure this distance). Now pull out the same fork leg at the bottom and again, let it spring back on its own. Measure and note this location in relation to the axle. Now split the difference. Set the floating fork in the middle of those two points. Now tighten the pinch bolt for the axle on that fork (23Nm).

Useful Links

https://www.fowlersparts.co.uk/parts/4180044/fzs1000-fazer-5lvf-2003-080-b/front-fork

https://www.tapatalk.com/groups/fazerowners/fork-settings-for-gen1-t17903.html

http://www.fz1oa.com/forum/forum/fz1-fazer-owners-association/tires-brakes-suspension-steering/gen-1-tires-brakes-suspension-steering/69674-time-for-front-fork-overhaul-and-upgrade?t=67950&highlight=fork+overhaul

http://www.fz1oa.com/forum/forum/fz1-fazer-owners-association/tires-brakes-suspension-steering/gen-1-tires-brakes-suspension-steering/129177-gen-i-fork-issues-exposed?t=126071&highlight=fork+alignment&page=2

http://foc-u.co.uk/index.php?topic=20136.msg232963#msg232963

http://foc-u.co.uk/index.php/topic,15263.0.html
« Last Edit: 20 December 2021, 02:38:35 pm by teecee90 »
FZS 1000 Gen1 (2003)
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Trebus

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Re: Fork overhaul procedure
« Reply #1 on: 22 May 2020, 01:15:18 pm »
Excellent, thanks for taking the time to post. Just done mine.

PieEater

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Re: Fork overhaul procedure
« Reply #2 on: 22 May 2020, 04:14:09 pm »
Really useful thanks, I've asked the Mods if this can be pinned as a sticky thread.


It would be useful to add the tools and service items (seals / bushes / oil) required as a primer at the top, if you have the time and inclination, just so someone starting out has a checklist to make sure they have everything they need.
« Last Edit: 22 May 2020, 04:18:32 pm by PieEater »

robbo

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Re: Fork overhaul procedure
« Reply #3 on: 22 May 2020, 06:43:21 pm »
Well done, very precise. Maybe you could add taking the preload off the springs whilst still on the bike, so then the caps will be under the least amount of pressure when you unscrew them. Just a thought.
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