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Moulton Front Fork Renovation

The chief difficulty in renovating front forks is taking them apart. Putting them back together again should be relatively straightforward. Provided that you are using all the same parts that came from the forks in the first place. Do not try to mix parts from Mk3 forks with those from earlier Moulton forks. The threads are different sizes and you will not be able to screw on the splined bearing cup, or use the other models headset parts. There is also a different number of splines on the lower bearing, 36 for Series 1 and 2 and 24 for Mk3.

There can be a significant variation in the size of the nylon bearings, particularly the top bearing. It is this wide tolerance that is responsible for play in many a Moulton's front suspension. Michael Woolf of Moulton Preservation will assist in matching a new bearing to your steerer tube. It may take a few attempts to get it right.

Start off by cleaning all your parts, inside and out. Paraffin is a good solvent that can be wiped dry. Jizer is excellent, but note that you will need to wash the parts in hot water and detergent afterwards, then dry fully. Ensure that there is no rust on the inside surfaces, particularly where the nylon bushes will rub. Clean inside the top of the steerer tube (only where the handlebar stem will fit into) with a small wire brush, wipe out and apply sparingly a film of copper grease.

For slightly firmer suspension, grind through the spring about ¼ to 1/3 of the way up and cut through the rubber with a sharp knife. The rubber springs do vary in stiffness and the rubber often goes soft at one end. Determine the soft end and remove this as shown.

Front Fork Rebuild

The replacement section of spring is made from ¾ inch diameter wooden dowel in this case. Alternative materials are Delrin, Nylon or aluminium. Take care if using a tube that you place a 5p coin between the tube and the spring or else the rubber will push down inside the tube.

Front Fork Rebuild

Use a toothbrush and C.V. (car constant velocity) grease or Molyslip grease to coat thoroughly all the surfaces of the inside of the steerer tube that you can reach. Note that this zone of the suspension does not contact the rubber. Molyslip grease does not appear to dry up and go sticky in service.

Front Fork Rebuild

It is very important at this stage to assemble on the splines the three parts that must be present after the forks are assembled. If you forget the bellows retaining ring for example, the forks will require dismantling. Put the ring on first, holes down, followed by the screw cup to hold the splined bearing. Next try the nylon splined bearing in several different orientations to find the snuggest fit. Push on in any orientation but with the narrower diameter stepped lugs downwards.

Note: In my experience, the lower bearing of Moulton suspensions rarely becomes seriously worn. The sizing on the splines is normally very accurate and the bearing is fastened tightly into the other tube. If you have play in your suspension it will almost certainly be in the top bearing.

Front Fork Rebuild

Fit a nylon top bearing by pushing it on the fork mounting and testing for play. It is very likely to have play due to manufacturing tolerance and this must be taken up by putting a shim of aluminium drinks can between the bearing and the fork tube. Cut a can up with scissors, and try a complete ring of shim. If this is insufficient to remove play, wrap a longer shim round 1.5 times. If a ring of shim is too much, try ¾ of a turn or ½ a turn of shim. Put the shim in place on the fork, grease, then push the bearing onto it. The forks shown did not require a shim which is highly unusual.

Front Fork Rebuild

Next, try pushing the fork carefully into the steerer tube to try it for size. (If it is stiff and feels like it might jam, do not push it in. Remove the bearing and contact Moulton Preservation for a different one. If the forks are too tight a fit, they simply will not work.) Engage the splined bearing in the steerer tube cutouts and try to shake the fork within the steerer tube to test for play in the stop bearing. If you can feel any rocking, this will be amplified when the bike is completely assembled. The bike will ride fine, but there may be clanking noises and play when braking. Try to have high standards about the fit and this will be rewarded. Contact Moulton Preservation for a new top bearing if yours is too loose.

To remove the circlip that secures the top bearing, push it over with a large screwdriver opposite the join, then wiggle a small screwdriver into the join in the ring. Twist the small screwdriver to push the end of the ring out of the groove, then lever around the ring as if you are opening a tin can, holding a finger over it to prevent loss.

Front Fork Rebuild

Grease the splines with Molyslip or CV grease above the splined nylon bearing.

Front Fork Rebuild

Grease the the top bearing, also with Molyslip or CV grease.

Front Fork Rebuild

Grease the inside of the steerer tube generously with Molyslip.

Front Fork Rebuild

Push the fork into the steerer tube, engage the splined bearing in the cutouts, and tap the bearing up with a small drift and hammer. Screw on the bearing retainer cup with the correct C spanner, taking great care that you do not cross-thread it. If there is any resistance, there is probably something wrong. Do not over-tighten. The fork is held in the vice with just sufficient force to allow the cup to be tightened.

Front Fork Rebuild

Stretch the bellows over the lower headset bearing and into place between this bearing and the retainer ring. Note that the bellows should go on with the short ‘neck’ uppermost as shown.

Front Fork Rebuild

Use a thin brush fastened to a piece of stiff wire to grease the upper sections of the inner fork, particularly within the annular section. Spend some time diong this, as this is where the rebound spring will locate. In used Moulton forks, it is the often rebound spring that is responsible for squeaks.

Front Fork Rebuild

Note that the small brush was on the end of a long spoke in this picture.

Front Fork Rebuild

Put the forks, inverted, into the vice, grease the rebound spring and drop it in. It is an advantage if it does not drop down quickly….

Front Fork Rebuild

…as the rebound stop may be placed on top of it and the pair pushed down the tube together. This prevents the rebound stop from flipping over.

Front Fork Rebuild

Use a flat-bladed screwdriver to rotate the rebound stop so that it’s lug fits into the small cutout on top of the stool within the fork. When it is in the correct place, the rebound stop will not rotate.

Front Fork Rebuild

Use a long-bladed No2 Phillips screwdriver with the cross-head screw. Holding the screwdriver vertically with the point upwards, balance the rebound screw on the end, perhaps with the aid of Blu-Tac. Holding the rebound stop in with the other long-bladed screwdriver, carefully raise the screw up within the vertical fork tube, feeling where the narrower hole to the stool begins. You can usually tell if the screw has fallen off the driver. Push up as far as possible and screw the screw into place.

Front Fork Rebuild

Note that this is the quickest method, but there are variations. You can put the rubber spring in, which holds the rebound stop in place, before putting the screw in. This allows you to turn the forks on their side or the right way up, and drop the rebound stop screw in from the top.

Use Molyslip or CV grease to lubricate the inside of the fork tube using a toothbrush, and also the coils of the rubber spring. The aim is to stop rust and squeaks on the spring. In my experience Molyslip does not affect the rubber, or deteriorate it. However, ordinary lithium grease may well swell and soften the rubber so do not use it. Never oil a front fork. Drop the rubber spring into the fork, followed by the wooden dowel.

Front Fork Rebuild

Have a four inch nail handy, or the front brake itself if you are ready to put it on. Press in the abutment with the open end downwards using your thumb and simultaneously pull up on the top of the fork crown with an action like squeezing a syringe. This compresses the rebound spring, making the job easier. Push the nail through the retainer ring holes, fork, abutment and out the other side, taking particular care not to bend the tang of the delicate retainer ring.

Front Fork Rebuild

The finished forks. The splines below the bearing can also be sparingly re-greased with Molyslip before putting the bellows over them.

Front Fork Rebuild

When you put the forks in the frame, do listen carefully for any scraping against the rivets of the badge before putting the locknut and handlebars on. If scraping is heard, file the rear of the rivets a little and re-test.

Last Updated on Sunday, 07 November 2010 22:55