Suspension - Forks, Shock and Swingarm

Maintained by mods and admins. but contains all the answers to all those questions that get asked over and over and over . .
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knackeredMk1
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Suspension - Forks, Shock and Swingarm

Post by knackeredMk1 » 31 Oct 2009, 12:38

The suspension on all CRMs is soggy and for many bikes the fact that they have been unserviced for many years makes this worse.

All Mks of shocks and forks can be serviced.

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Forks

Post by knackeredMk1 » 31 Oct 2009, 12:42

Forks will benefit from new seals if oil is leaking and you might as well replace the bushes at the same time. Give the forks a good clean, particularly the sediment that collects at the bottom of the tubes and refill to the correct level with a good quality correct specification oil. - This is generally a DIY job.

To the best of the forum's knowledge fork seals and bushes are generally common across CRM and CR ranges as long as fork stantion diameter is taken into account. E.G. CR250 forks that have 45mm stantions use the same seals and bushes as those of a Mk2/3/AR.

There are other changes that can be made:

1). The preload and general softness can be improved by getting a stiffer set of springs. If you make big changes here you probably need to make changes to the damping as well.

2). Increasing the oil level in the forks will increase air pressure / air spring assistance towards the end (last 1/3 aprox) of the stroke so make it harder to bottom out the forks. Do this in 10mm intervals and test all the time.

3). Increasing the viscosity of the oil (the weight) will increase both the compression and rebound damping. Standard is 5 or 10 wt this can be increased up to 20.

4). The forks can be changed. This has generally been done with fitting CR125 forks as these have the most combatible damping and springing characteristics. I have recently found that CR250 forks are only slightly firmer than CR125 so would be suitable though I believe CR500 to be too hard. Mk2s onwards (all those with USD forks) can be a straight swap CR - CRM (1991 CR forks fit but it appears that some others are not without some milling work :?: ) but Mk1s require the fork yokes to be milled out from 41mm to 43mm to fit conventional CR forks (Also need to change wheel bearings, spacers and axle to 17mm). If you want to change Mk1 forks to USDs then you have to get new yokes (and retain the original steering post) and mess around with the front wheel spindle, bearings and spacers.

Early ninties (USD) forks seem to be the easiest to fit on Mk2s and later as some are a direct swap. These tend to have only compression damping adjustment but are certainly better than standard CRMs. The later you go then the better forks you get but also the more things you need to change (a selection of - wheel bearings, spacers, spindle, brake bracket, milling yokes, new yokes, steering post.....)

41mm XR250R forks are a direct replacement (same external measurements in every dimension) for Mk1 forks and probably the best option with no work needed and well sprung and damped. They are 41mm but have adjustable cartridge damping and are a lot better. They also use the same 15mm axle. 1990s - 2004 will do but as always later is better. Do check fork diameters before you buy as early XR 250 forks are thinner.

XR400/650 conventional forks are good, and probably the best (compression and rebound adjustment), replacement for a Mk1, but they do require the yokes being milled out to 43mm and changes to the front wheel setup so as to use the 17mm spindle etc of the XRs.

If you want to change Mk1 forks for USD or any forks that need you to change the yokes you will have to change the steering stem. I.E. You will have to change the stem on the new yokes for the one on the original yokes. This is because the steering stem is slightly shorter than most other off road orientated bikes and might mean that the new 'adjusted' fork yokes don't fit the new forks anymore :?: (So check first :!: ).

You may also find that you need to do this for other Mk CRMs if you are using fitting more modern forks. The same is true for the spindle, bearings and spacers.

Remember that when you buy secondhand forks they may well need to be serviced and this could mean new bushes, new seals and oil. Beware of nicks or rust spots on the chrome slider as this can kill seals very quickly and is expensive to repair.

5). You can get the forks resprung and revalved by a professional suspension specialist.

6). If you raise either end of the bike by putting in say longer forks then you have to minimise the change in geometry. In this case by raising the forks in the yokes (but not so much the tyre hits the mud guard :shock: ) and if neccessary applying more preload to the shock.


Changing fork seals:

As written by Slider . Describes the procedure for USDs but the same principles apply to conventional forks -

Ahh cr*p . This is gonna take ages .

1: With the forks off the bike, undo the top cap. (It's easier to loosen the cap with the forks in the yokes before you disassemble).
2: You should be able to see the damper rod nut (the top cap should still be connected to the damper rod) using a spanner on the damper rod nut, remove the top cap from the damper rod.
3: Tip the forks upside down into a container and then go have a brew and a fag for 20 minutes. (Avoid going into the house as you'll probably get stiffed into doing the washing up/hoovering etc).
4: After avoiding hosehold chores, remove the dust seal from the bottom of the fork outer tube. Behind the dust seal you'll see the fork seal & its retaining clip, gently lever the clip out of its locating ring in the seal housing.
5: Look underneath the damper rod nut and you should see a bevelled washer that has a slot cut out of it. You should be able to pull this washer out without removing the damper rod nut.

6: With the washer out of the way, tip the forks upside down. The spring spacing tube, spring spacing cup and spring should slide out. May require a bit of a violent shaking.
7: When this is done your ready to seperate the inner & outer tubes. Using the inner like a slide hammer, yank it away from the outer. You'll probably have to do this a few times to dislodge the fork seal but they will seperate eventually. You should remove the dust seal and the retaining clip before you do the 'sliding hammer bit' as it is a lot easier.
8: With the two tubes seperated look at the inner and you should see the dust seal, retaining clip, forkseal, bottom bush washer, bottom bush and the top bush still in its recess on the inner fork tube.
9: Remove the top bush from the fork leg by inserting a screwdriver into the slot in the bush and twisting till the bush comes out of its recess and slides off.
10: Slide the bottom bush, washer and fork seal off as well.

11: Using a socket or similar of matching size tap the bottom bush back into the bottom of the fork outer tube.
12: Put your outer fork tube into a workmate or vice with the bottom of the seal housing (larger silver part at the bottom of the outer fork tube) facing upwards and butted up against the jaws of the vice/wormate. If your using a vice take steps to make sure the seal housing does not get damaged. The reason for using the workmate/vice is that when you tap the seal in place, the housing has a nasty habbit of sliding up the fork leg and if your like me and its the first time you've come across this type of setup on usd forks, it just might stop your world falling out of your a**e.
13: Put the bottom bush washer in place & using a socket or something of the same diameter (split plastic drain pipe will do) & tap the new fork seal back into place.
14: Reinstall the seal retaining clip.
15: With the dust seal in place on the inner fork tube and the top bush not fitted,slide the inner into the outer tube,taking great care not to damage the new seal.

16: Tap the dust seal into place then push the inner & outer together completely & remove from the workmate/vice and turn the assembly the right way up. Now take the outer bush and slide it over the top of the inner fork tube, using two small flat blade screwdrivers push the bush down til it slips into its recess on the inner fork tube.
17: With the fork vertical pour in your fork oil (600ml-mk2 or 650-mk3. These are not the actual required amounts as it is easier to fill the forks than remove oil to get the correct oil height!!). Remember the forks must be fully together i.e fork bottom in contact with the dust seal. Adjust the amount of fork oil 'till you reach the measurement from the top of the fork outer tube (mk2-108mm,mk3-90mm). Pump the damper rod up and down a dozen or so times and re check the oil height.
18: With the oil level set install the fork spring, spacer cup and spacer tube. Best doing this at a slight angle so the damper rod doesn't slide back into the fork leg. Reinstall the bevelled washer between the spring spacer and the damper rod nut & refit the fork top to the damper rod and lock into place.
19: Slide the outer tube up and tighten the fork top into it.
20: Job done. Have a fag and a brew, then repeat on the remaining fork .

This is how I did my seals it may, or may not be, the approved method so I don't want any earache about it. It worked for me and thats that.
I dont want aggro for encouraging smoking or avoiding chores either .


Fork Seal Video

http://www.youtube.com/watch?v=Y43k1qFV ... re=related

http://www.youtube.com/watch?v=C9ICr-DO ... re=related

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Shock

Post by knackeredMk1 » 31 Oct 2009, 12:54

Shocks can generally only be serviced professionally as they contain pressurised nitrogen at ~ 200 psi. All CRM shocks can be serviced for a basic cost of about £100 without any springing or damping changes.

Mk1 & 2 shocks are unique to those models but Mk3 and AR can be exchanged. Performance can be improved by increasing both spring rate and damping. Hagon make an aftermaket shock for the Mk2 - http://www.hagon-shocks.co.uk/catalog/p ... tno=M61021 (which is also their shock for an '89-'95 XR250R), and Mugen made one for the Mk2 and Mk3/AR.

You cannot replace a CRM shock with any other shock (other than '89-'95 XR250R for a Mk2), e.g. CR, to a CRM without a huge amount of work. They can be made to fit in place but they are always different in length and/or, damping, and/or springing, etc.... Just don't do it unless you really are an expert.

Suspension specialists:

K-Tech
Revs Racing
Brooks
...

Or any reputable company that deals with off road bikes.


XR250R shock '89-'95 fits straight on to a Mk2. This gives firmer springing and damping, also adjustable compression and rebound damping. It gives a big improvement in handling. The later version you can get the better as improvements were made over the period covered.

The 'R' is important in what model of XR250 the shock is for as there are several models, inc. XR250L ....... The 'R' is the full enduro spec.

The spring on the XR250R shock gives the correct bike and rider sag for a 13-14 stone rider rather than the 9-11 stone of the original CRM spring.

Hagon make a shock to fit the Mk2. This is exactly the same part no. as they supply for the XR250R shock of this period


Wilbers, I think a German company, make shocks for the AR. They make various specifications and do SM and 'Enduro' parts. These will fit a Mk3. Cost ~ £400-600.

http://wilberssuspension.co.uk/products.php

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Lowering Bikes

Post by knackeredMk1 » 23 Nov 2009, 20:46

The front can be lowered by rising the forks through the yokes but this can only be done a small amount due to the obvious effect. I.e. When the suspension is fully compressed the wheel must not touch the mudguard otherwise the wheel will come to an abrupt stop and so will the bike :!: . (Without the rider :shock: .)

The rear can be lowered by using longer 'dog bones' in the suspension linkage. How much longer is a matter of experimentation but it has been done by members of this forum. Unfortunately lengthening the 'dog bones' does change the characteristics of the suspension - generally making it softer, depending on the degree of extension.

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Suspension Servicing - Bearings, Seals & Bushes

Post by knackeredMk1 » 28 Nov 2009, 21:37

Suspension bearings, seals and bushes. Parts, partic. seals, can be removed and taken to a bearing/seal supplier and non-Honda alternatives found. (Part nos. and dimensions if non-Honda specific). Swing arm, dog bones and linkages are all the same for Mk2, 3 & AR. (The Mk1 swing arm is not interchangeable with any other CRM):

Mk2, 3 & AR:

Swing arm pivot -

4 x 91106-kf0-008 / 20x26x12 bearings (can be replaced with 20x26x18 with an internal seal at one end for better performance)
2 x 91254-ks6-003 / 20x26x4.5 seals
2 x 52144-kr8-005 seals
2 x 52141-kae-000 bushes

Swing arm connection to linkage -

1 x 91052-kz9-711 / 17x24x25 bearing
2 x 91262-mg7-005 / 17x27x5 seals

Linkage -

2 x 91052-kz9-711 / 17x24x25 bearings
1 x 91079-kn5-003 / 15x22x17 bearing (Difficult to get from bearing suppliers but Pivot Works have them under pn. H-FCBE-006 (Thanks to maciej_mi :) ))
4 x 91262-mg7-005 / 17x27x5 seals
2 x 91262-mb2-005 / 15x25x5 seals
2 x 52473-kz9-710 bushes
1 x 52464-kae-000 bush

Top eye of shock -

1 x 91077-gs2-702 / 16x22x12 bearing
2 x 91351-gs2-701 seal
1 x 52486-gs2-700 bush

Mk1:
.
Swing arm connection to linkage

1 x 91071-kv3-005 bearing
Seals as others.

Linkage -

1 x 91079-kn5-003 / 15x22x17 bearing (Difficult to get from bearing suppliers but Pivot Works have them under pn. H-FCBE-006 (Thanks to maciej_mi :) ))
4 x 91052-zv4-003 / 15x21x12 bearings
4 x 91262-gs2-701 seals
2 x 91262-mb2-005 seals / 15x25x5 seals
2 x 52463-kae-000 bushes
1 x 52464-kae-000 bush

Top eye of shock -

1 x 91077-gs2-702 / 16x22x12 bearing
2 x 91351-gs2-701 seals
1 x 52486-gs2-700 bush

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General Suspension Tuning

Post by knackeredMk1 » 30 Nov 2009, 09:15

Skimark put together this list.

viewtopic.php?f=6&t=3453 - note website in Gwyns post (7th down)

viewtopic.php?f=6&t=72

viewtopic.php?f=4&t=4527 - Experience of fitting CR shock to CRM.


Further - Auzzy specialist has AR and setup proceedure (Use the XR400 heights in the table) -

http://www.teknikracing.com/teknikal-li ... etup-guide


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