jueves, octubre 09, 2014

Rebuilding Front Suspensions

There are a great number of Montesa motorcycles that use the Betor front suspension from about 1968 to the 1980’s.  This article will cover in detail the early units.  There are a number of tools used in this process.  I will indicate with an (*) the ones that are not needed for simple maintenance.  This process will involve a complete restoration of a poor working or seized unit.
  • Common screwdrivers: 1/8”, ¼”, 5/16”blade width
  • Internal and external snap ring pliers
  • Dead blow hammers: 1 lb. and 5 lb
  • Large wrench sockets.  Usually a 1” and 1 1/4” will be all that is necessary
  • Sharp cold chisel
  • Wire: 1/8” and ¼” about 18” to 24” length
  • Scribe/pick
  • Grease and grunge solvent
  • Substantial bench vise
  • Appropriate Allen wrenches.  Normally the choice would be a 6mm or an 8mm
  • *Tire iron
  • *WD-40
  • *Assorted files and abrasive paper
  •  Rubber gloves.  Keep the chemicals off your hands
  • *Wire wheel/buffer combination
  • *Gunk tank
  • *Two pound brass hammer
  • *Digital Camera.
  • *Compressor and air wrench
  • *Copy of the exploded illustration of the assembly found in the parts book
  • *An aluminum or steel tube or rod about 7/8” in diameter and 2 ½ feet long
  • *Taps and Dies



If the fork tubes are still in the triple clamps, loosen the fork cap.  Leaving it in clamps is the best way to hold the fork tube.  If the fork tube has been removed and the cap is stuck it will be necessary to either wrap the tube with a rag or install soft jaws in the vise to secure the tube well enough to remove the cap.  This will keep the fork tube from turning when you attempt to loosen the cap.  This should be enough to keep from damaging the chrome.  You may have to use quite a bit of pressure.

1. Remove the dust covers or rubber accordion (rubber) covers (gators).

2. Once the fork tube has been removed from the triple clamps it will be necessary to screw the cap back on about half the way in to preload the fork spring.

Note: Remember the dead blow hammers?  Use them to dislodge reluctant parts.  Never use ball pein or claw hammer for any of this repair work.

3.  If you have a compressor it is fairly easy to shock the Allen cap screw loose and remove it.  If you don’t have one it will be necessary to compress the fork spring by pressing toward the cap screw to increase friction.  The damper rod is connected to the cap screw and will turn if insufficient pressure is applied. 

HAVING TROUBLE?  If it won’t come loose and you temper has risen then find someone with an air compressor and air impact driver.


Go and find a tire iron that has a screwdriver like end opposite the bent socket end. 
With the cap and spring removed collapse the slide.

Insert the blade end of the tire iron into the tube and engage the slot located at the end of the damper rod. 

You can now remove the cap screw.

Use a snap ring pliers to remove the snap rings from the top of the fork seals and the retaining clip that holds the damper assembly to the fork tube.

Remove the slider from the damper rod/fork tube assembly.  Most assemblies will simply slide apart with little difficulty.

Note:  These can be extremely difficult to remove.  They can be driven out with the aid of the 7/8” rod or tube and a heavy hammer.  A tread release fluid may help with this process.

Now is the time to remove the fork seals from the slider. 

Note:  If you are dealing with a magnesium slider, stop now. You are working on Marzocchi forks.  You are supposed to be working on aluminum Betor forks; remember?  You will chip or crack the edge.  No one will want to weld this damage.  Chewing gum will not work.  You will have to seek a replacement and that is very expensive.

Fold a rag and place it on the edge of the tube.

Use a common screwdriver by inserting the blade under the top seal and levering against the rag.  The top seal will come out more easily then the bottom seal.

Now try removing the lower seal in the same fashion.  It may come out as easily as the top one but if not you will have to move on to another tactic.

If there is worrisome resistance, take your cold chisel and drive it down on the parameter of the seal to cause it to bow.

Now remove in the same manner as the top seal.  By bowing the seal it releases the holding power of the fit.

Place the damper rod on a clean light colored background.  Photograph it.  At least sketch the location of the parts on a paper so you can reassemble it later.  You will forget the way it comes apart if you don’t do this.  I guarantee it.

Clean All parts.  I use a long rod and a wad made from a piece of paper towel to clean the insides of the fork tube.  Various solvents and snake oils can help in removing the contaminates.  WD-40 works well.

Check the fork tubes for straightness.  Straighten or replace before reassembly.

Note:  Many of the forks have a washer that floats free at the bottom of the damper assembly in the slider.  If the internals are contaminated with grungy oil, it will fall out during cleaning.  The cones on the end of the damper rod need to be removed.  It may take a lot of coaxing.  It is a slide fit. 

FORK SEAL INSTALATION:  The Montesa forks take 2 single lip seals per leg.  They need to be installed with the lips pointed down with the open groove side down.

Clamp the fork leg between vise jaws.

Place one seal on the top of the seal channel.

Using the 1 pound dead blow lightly tap the seal flush with the top of the slider lip.

Select the 1 ¼” socket and place it over the seal.

Use the 5 pound dead-blow hammer and strike the socket to drive the seal to the bottom of the channel.

Place the second seal as the first and repeat steps 4 & 5.

Install the retaining clip.

  1. Reassemble the damper assembly following your photo or parts book diagram.
  2. Slide damper assembly into bottom of fork tube.
  3. Replace internal snap ring to retain damper assembly in fork tube.
  4. Insert the fork spring and screw the fork cap on a few threads to provide pressure to the damper rod.
  5. Put a little WD-40 on the seal lips.
  6. Place washer into slider.
  7. Slide fork tube-damper assembly into slider.
  8. Install cap screw through washer and into damper and tighten down.
  9. Fit dust cover/gator.
  10. Install drain screw and gasket.
Note:  Now I digress.  Most of the following steps I perform in a restoration.  If you don’t want to go to this trouble then replace the seals, reassemble, and pour in the required amount and weight of oil.  Reinstall on the motorcycle and go ride it.   I have found that some things I do with a buffer will ease the reassembly of the forks.


1.  Use white rouge on a buffing wheel and buff the chromed fork tubes.  When finished there will be a thin coating of wax on the surface.  This will help ease the fork boots down the tubes and it will make it easy to slide the tubes past the seals and into the slider.

You may have to file, sand, or wire wheel the sliders to remove surface corrosion before buffing.  Determine what will work best and apply sufficient effort to reach this goal.  If you use sandpaper you will need to reduce the grade to 400 or 600 grit before buffing.

2.  Clean all threads and threaded fasteners with appropriate taps and dies.

3.  Replace all broken, lost, or distorted pieces.

4.  Refer to your sketch as to how to reassemble and assemble the damper rod.

 5.  Lubricate the fork seals with oil.  A drop or two of the oil you are going to use will suffice.  I usually use a little WD-40 instead.

6.  Insert the fork tube/damper assembly into the slider.  You did put the spring back in and screwed the cap down a few threads didn’t you?

7.  Replace washer that was removed from the bottom of the fork slider.

8.  Align the damper with the hole in the washer and slider.

9.  Place the retaining Allen bolt into the hole.

10.  Compress the spring to gain pressure and tighten the cap screw.

11.  Reinsert the drain plug with its washer.

12.  Install the fork boot or dust cover.

13.  Remove the fork cap if the hole in the triple clamps is smaller than the cap.

Note:  When you are ready to assemble the fork tube into the triple clamps you should thoroughly clean the area to be clamped of wax residue where the clamps pinch the tube.  Windex is a safe cleaner for this task.  Otherwise you will never get the forks to quit twisting during your ride.  Control will suffer.  The motorcycle will not go where you want it.  Etc. etc. etc.

14.  Fill the forks with correct oil amount and weight.

15.  Replace for cap and tighten.

Back to Rocky Mountain Montesa

No hay comentarios:

Publicar un comentario

Como diría Juan Ramón Jiménez, mi troll es pequeño, peludo, suave; tan blando por fuera, que se diría todo de algodón, que no lleva huesos.

Probablemente no tiene huesos y por eso insulta bajo seudónimo. Pero además de cobarde es tan coñazo que he decidido que sólo me moleste a mi. De tal modo que a partir de ahora me quedo con la exclusiva de leer sus bobadas. Disculpadme el resto que os haga pasar por la "moderación" de vuestros comentarios.