FRONT FORK SEALS – UP AND DOWN
Suspension on any motorcycle, be it an on- or off-road model, is very important as it determines the overall handling characteristics of the machine. In this article we look at the front forks and the replacement of the all-important front fork seals which retain the oil. Most front forks found on the twin-shock machines are very similar in how they operate and also how they are serviced, including the front fork seals which we are looking at here. In this article we visited the superb workshop facilities at AG Bikes, with their workshop mechanic Michael ‘Jacko’ Jackson carrying out the work. The front forks we used for the article are from a Bultaco Sherpa but the procedures are very much the same for most models
Article Copyright Words and Pictures: Classic Trial Magazine
1: First things first – and that means you should only ever carry out maintenance on clean components. General workshop knowledge is required to work on the front forks and to carry out the procedure to change the front fork seals. In this article we have rebuilt the front forks but as it’s such an essential part of the safety of the machine, if you are in any doubt of your capabilities we would suggest you do not undertake the work but take the machine to your nearest dealer, who will advise you on what is required to do the task and carry out the work if you require it. It’s always good to have a look at (and read!) the machine manual, or ask your local dealer what suitable replacement parts are available before starting work. If you are carrying out the work we suggest wearing the appropriate safety clothing and eye protection, and using a good set of quality tools.
2: Front forks get abused; it’s a fact. Positioned at the front of the machine they are subject to mud, dust and water, which finds its way into forks and contaminates the oil, which generally mess up the workings. It’s well worth putting your own service plan together for all the major components on your machine to keep it in tip top condition, and the front forks are no different. There are usually a few reasons for dismantling the forks. The first and most obvious is to replace worn leaking oil seals. The second is to drain the damping fluid and thoroughly clean the internals and third, if you are very unlucky, is to straighten bent stanchions or sliders. In this shot here you can see the stripped-down forks from the Bultaco with the internals removed ready to replace the seals. The procedure for rebuilding is the same as pulling them apart. All parts should be checked for wear or damage.
3: Using soft jaws in a vice, clamp the fork bottom in a suitable place giving easy access for the rebuild.
4: Inspect the slider tube for any damage before gently easing it into the fork bottom.
5: Make sure that this insert is located correctly into the spring before assembly into the slider.
6: Reposition the fork bottom in the vice to a horizontal position so the insert does not lose its positioning.
7: Once the spring and insert are located into the fork bottom slightly raise the position of the assembly.
8: Push the damper rod assembly retaining screw into the fork bottom and, making sure it has located the internal thread inside, gently start it by hand.
9: Once the retaining screw has started to locate safely you can use a ‘Tee Bar’ to take it all the way home.
10: Leaving the ‘Tee Bar’ in position you will then need to put a long-reach extension piece on a ratchet tool with a 3/8th flat screwdriver end inside the slider all the way to the bottom to hold the damper rod assembly to tighten up.
11: Make sure that now the slider is in place that it is fastened and secure.
12: Before fitting the first seal, place a little grease on the inside edge.
13: Wipe the slider down before you slide the new seal down.
14: Slide the seal down so it’s just above the housing.
15: Using a special fork-seal fitting tool gently use the slide’s hammer action to take the seal all the way home to its housing.
16: The Bultaco front forks have two seals but many other machines only have one. Carry out the same procedure with the second seal. Some types of front forks may have a circlip to retain the seals in position.
17: Check the dust cover for damage and splits before sliding it into position.
18: Find out from your machine user manual the correct grade and quantity of oil required for your model.
19: Take your time pouring the oil in to make sure you have no spillage!
20: Many types of front forks have a spacer in the top. Make sure it is located correctly in the spring.
21: The majority of fork tops are manufactured from aluminium, so please take your time to make sure that the thread is started correctly when you mate the top with the slider.
22: We suggest you push the rebuilt fork leg into the machine yokes and clamp the slider with the bottom yoke pinch bolts so that the top nut can be tightened securely.
23: Always make sure you use the correct size socket on the fork top.
24: With everything now back in place you start on the other leg!
If you encounter any other problems concerning this ‘front fork article’ procedure contact your local dealer for advice. Classic Trial Magazine would like you to note that they carry no responsibility for any problems with carrying out this procedure as it is all done at your own risk.
Classic Trial Magazine would like to thank the staff at AG Bikes for their kind cooperation in producing this article: www.agbikes.co.uk
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