Wednesday, 6 November 2013

My Bike: Restoration, Suspension forks

Let’s assume you have the complete fork unit of the bike, if you are transporting the fork you will need to re-fit the bolts that held the fork to the upper crown as the top nuts have holes in them!

First I wanted to get the lower legs back in a presentable condition, rather than attack them with wet and dry (which is very aggressive and will end up with a highly polished finish) I decided to remove the corrosion with wire wool and Autoglym metal polish. I spent about half an hour on each lower leg to get them looking kind of how I wanted them – almost a brushed alloy finish, to get close to the original. I have to say I am fairly happy, but I am sure I will probably spend some more time on each leg to get them ware I want them.

before and after
Before and after...
Both stanchions were pitted so I have sourced two NOS genuine Honda stanchions (one from ebay, one from Honda M shop) plus a new pair of oil seals (pattern, wemoto). The dust seals are in good condition so I decided not to replace these.

Next was to pull the legs apart, just remove the top plug unit from the stanchion (this can be tight), remove the spring and drain the oil.

At the base of the leg is a 6mm hex socket, one of mine was rounded off so had to be drilled off. Once these are undone the stanchion will come out, keep a look out for the oil lock piece (often called a foot buffer) at the base of the damper rod.

a complete fork leg disassembled 
Remove the dust seal, oil seal cir-clip and price the oil seal out with a big flat bladed screw driver, now clean, degrease and inspect everything and note the ‘back up ring’ that sits under the oil seal.

To install the new oil seal I grease the internal and external part of the seal and seat  (don’t forget to fit the back-up ring) and drive the seal in with a large socket as close to the outside diameter of the oil seal as possible, re-install the cir-clip and re-fit the dust seal.

Drop the damper rod through the stanchion making sure the top out spring is retained on the rod, then add a dab of grease on the end of the damper rod and fit the oil lock piece – the grease just keeps it in place. Guide the stanchion through the oil seal making sure not to damage it.

Re-torque the bottom foot screw to torque to 20NM – this value is not clearly stated in the owner’s manual, but working of the thread size torque guide (8mm) of 18-25NM. As mentioned before I had to drill mine off, spares are easy to get, Honda part number 90116-383-721 so it might be worth replacing these as a matter of course? For speed I ordered form David Silver spares.

Re-fill with oil, the manual says 150cc of ATF fluid (automatic transmission fluid), however using this type oil is very old fashioned. ATF fluid has a very low viscosity so for a modern improvement I used SAE7.5w synthetic suspension fork oil.

Check your main spring to see if it is still within the manufacturing tolerance, it should measure a minimum of 482.5mm. Re-fit the spring with the tight coils to the top and refit the top plugs, these need to be torqued to 15-30NM.

For grease I used Morgan Blue Calcium grease, oil SilkolenePro RSF 7.5w.

fork exploded diagram

1 comment:

  1. Hi Dan ,
    Like the blog mate ...... I am into bike / scoots ect , I once owned a mb5 and a mbx 80lc , also Suzuki x1-50cc and many more!

    My blogspot was for scooter blogging , but after it got quite big I have needed to use it for my work!
    Kindest regards