WORKSHOP: OLD FORKS
Scoop looks at old style forks and shows us how to refurbish them.
Scoop tackles both his Yammy’s gammy legs.
Before Ceriani came up with the idea of placing springs inside fork tubes the shock absorbing element of the front suspension sat outside of the stanchions. Due to the questionable aesthetics of coiled steel and its propensity for rusting, the fork leg and spring were generally covered by some form of shroud, steel tubing or concertinaed rubber boot being the normal options. Post Second World War telescopic motorcycle forks began to feature genuine hydraulic damping which necessitated some form of seal. Almost without exception this seal was contained in a standalone, screw on, device that was known by the highly novel term ‘seal holder’. No one today makes bike suspension with seal holder forks and for good reason – see our boxout on p81. However, in our classic world seal holder forks turn up with annoying regularity and especially so if your chosen steeds are pre 1975. All the Japanese players ran this set up at one time or another and it took the manufacturers quite some time to obsolete their older machines and move on to what we’d see as more conventional forks. Up on the ‘Workbench of Opportunity’ this month; are the forks from our Yamaha CS3C street scrambler. All signs to date indicate the 200cc twin led a short but hard life and I’ve little doubt as to when the fork oil was last changed – probably never. Not wanting to entrust my latter years to someone else’s potential bodges I’m stripping the forks down to their basic elements and rebuilding them. The MO may be a little more convoluted than many might be used to with more modern
machines but the principles are still the same: check for wear/damage, replace worn parts, fit new seals and keep everything clean. With a hammer and some duct tape to hand, no seriously, we’re stripping down a pair of forks that haven’t been apart since the latter portions of 1969!
11/ The gaiters simply pull off the lower leg along with the spring to reveal the lower and upper portions of the fork leg. The oily rust tells us action is definitely needed.
76/ Once free, the lower fork leg is turned off the seal holder; it’s a long, fine, thread so will take some time to undo. Make notes and/or take pictures of how each component fits ready for the rebuild. 7/ This is the upper fork bush and officially a service item. It will need checking for wear and damage. Fortunately it’s something a decent machinist can knock up if you need a replacement and no one can supply one.
3Closer examination of the thinner tube (the fork stanchion) shows evidence of stone/grit/ sand damage by way of the long scar running up the chrome plating. Above this there are signs of some stunt monkey damage with a pipe wrench. The black plastic moulding is the lower spring seating bush. 3/ It might look mad but it works! Tapping the seal holder hard with a plastic mallet loosens up the threads inside. If there’s rust etc. heat and/or easing fluid may be needed before attempting the next stage.
5It’s not as barbarous as it looks, honestly! Four or five turns of good quality duct tape will protect the chrome perfectly well. A decent, bench mounted, vice makes what’s coming next so much easier. 5/ Inserting a suitable lever into the wheel spindle mount the lower fork leg can be unscrewed from the seal holder. Manuals may suggest using a chain wrench on the seal holder but I’ve found it’s not that effective: this way you can add some serious leverage if necessary.