HONDA CB400 FOUR
Ralph Ferrand sorts the forks in part two of this project.
Last month I cleaned and set up the carbs on a Honda CB400 Four that was running as rough as a Badger’s botty and I soon had it singing as smoothly as a Honda should. This month I turned my attention to the forks stanchions’ chrome that had more holes than a Swiss cheese. I explained to the customer that while his bike engine now ran like a (again) Swiss watch, it was unlikely to handle like one, given the amount of the suspension fluid that was outside the forks and I doubted that the MOT inspector would be especially impressed. While some would argue that getting original fork legs re-chromed can provide a better than new stanchion, I don’t have the luxury of having enough workshop space to keep a customer’s bike sans-front end for two months or more while the legs are re-plated and ground. For a time and financial saving, I can buy a set of brand new, quality Italian made legs from Wemoto’s trade counter and have them with me the next day – it’s a no-brainer: time to get busy with the spanners. As I knew I would be removing the brake caliper anyway, I sucked all the fluid out of the front brake system, through the caliper bleed nipple, using my giant air powered version of the Mityvac. I undid the brake line and took off the caliper. I popped the front wheel out and removed the mudguard, before slackening off the pinch bolts on the top and bottom yokes. I tend to only remove one fork leg at a time on a job like this; it keeps things simple. Over at the work bench, the first job was to drain out what oil was left in the leg. As this leg had a drain screw, I undid it and pumped the oil out through the drain hole into an old Swarfega tub. Given how much was left, an egg cup would have been sufficient! There was a bodge on these forks that I had not come across before. I can only conclude that when the legs were last stripped they leaked suspension fluid past the damper bolt, because the hole in the bottom of the leg was full of silicone. I had to cut it out with my trusty scalpel before I could get a hex driver on the bolt. As I did not know what damper rod securing tool would be required to hold the damper rod while removing the bolt (and Mr Honda wasn’t offering any) I took no chances and fitted the relevant size hex driver in my ‘takes no prisoners’ air impact wrench. It attacks with so much torque, so fast, the bolt is out before the damper rod has had time to consider turning. I’m afraid that the nearest a DIY-ER, without compressed air, is going to get to this, is a big breaker bar being helped by a trusting mate/wag, with the leg in the vice (with soft jaws of course), while you wallop the end of the bar very quickly with a seriously heavy plastic hammer. If you have a decent sized compressor (3hp is about the most you can hope for on a domestic ring main) you can get a cheap air impact wrench from the likes of Machine Mart for not very much money, but do use a heavy air line to feed it, because the small diameter lines, like the coloured curly
recoil ones, simply will not flow enough air for an impact wrench to bite properly. Once the bolt was out, it was only too obvious why the leg leaked last time the leg was reassembled; the copper washer had seen a lot of action. Copper sealing washers should always be replaced. The fork cap was next to be removed. It’s best to grip the stanchion in the vice, using soft jaws. I always ensure that both the stanchion and the soft jaws are grease free and grip the tube horizontally, thereby giving the most surface area for grip. The caps shouldn’t be tight, unless they have been previously replaced by a primate with more strength than intellect – it does happen. If you suspect that they have been previously been tightened by someone with the mechanical sympathy of Jeremy Clarkson, then you are best off cracking the cap loose when the tube is still being gripped by the yokes on the bike. Biker’s Toolbox supplies special plastic six point spanners for fork caps; in particular aluminium fork caps are very vulnerable to abuse. Many home mechanics think that because the head is relatively large, that the cap must be tightened up to a mega torque – this isn’t the case, but most classic fork caps I come across have been ruined by folk attacking them with DIY quality 12 point sockets and more muscle than understanding. I have even seen the unmistakable teeth marks of the ubiquitous mole grips! Once I had the cap out, I pulled the spring out, degreased it and found somewhere clean for it to await its return. I pulled the stanchion out of the lower leg together with the damper rod. The fork tube was inverted over the bench allowing the damper rod to slide out into my waiting gloved hand. I mention the gloved hand as the oils and greases used in motorcycle internals are not good for one’s skin. As I youngster I fervently believed that only wimps wore gloves. It took a while for me to connect this stupidity with the row of warts all along my knuckles. Oddly when I stopped being a soap dodger and protected my skin, they vanished; as if by magic! The stanchion then joined the ever growing stack of buggered fork tubes in the corner that I cannot bear to throw out but really have no use for! If I ever got burgled, I’d be spoilt for choice for a quality cosh! I then gently gripped the fork lower in the soft jaws of my vice. The dust seal was removed and skipped. Using a pick tool, I carefully removed the wire type clip that keeps the fork seal in place. Using my professional fork seal removal kit, I selected a suitable tool to extract the seal without damage to the aluminium leg. When I had the seal out, I discovered the previous ‘mechanic’ hadn’t bothered with such niceties as the right tool for the job. I had to get my engineer’s scrapers out and use a steady hand and all my years of skill to correct the damage. Previous bodges clock up my earning hours, but it frustrates me that I’m charging my customers for correcting damage that should never have happened.
As I had to remove metal, I had to give the insides of the slider a really thorough clean out, lest any slivers got stuck inside. I always clean all the parts anyway, but in a situation like this, one must be extra vigilant. Once the forks are stripped, it makes sense to give the sliders a quick polish on the buffing machine, while they are light and not attached to a motorcycle! Five minutes on the polishing machine equates to weeks with Autosol, a rag and a sore finger! I next unpacked the new fork leg and removed all the protective waxy grease with a cloth soaked in brake cleaner. I then dropped the damper rod into the stanchion. I dipped my gloved finger in a bottle of fork oil and smeared it around the bottom of the new stanchion and the mouth of the slider, before gently sliding the new fork tube in vertically so that the damper rod stays plumb and located in the bottom of the fork lower. I then carefully returned the spring and temporarily refitted the fork cap, to hold the damper rod while I tightened the securing bolt. The fork was carefully gripped in the soft jaws of the vice horizontally. The damper bolt was thoroughly degreased with brake cleaner and a new copper washer fitted to it. At this point I always apply a small amount of RTV silicone to both sides of the copper sealing washer for added security and a bit of 243 grade thread lock and seal to the threads of the bolt before screwing it in and torqueing it up to the specified setting from the workshop manual. I then removed the fork cap and spring so I could fit the seals and fill the fork with oil. I always lubricate the seal with fresh fork oil and cover the top of the stanchion
with light grade polythene, usually a bit of old parts bag, to protect the lips of the seal, before sliding it over the fork tube. I have seen all manner of damage to fork legs caused by folk too tight to buy the correct tool; a universal fork seal driver tool doesn’t cost a fortune, but saves on misery. You squeeze the bottom part of the tool over the seal and around the stanchion, while tapping it down with the knurled two-part slide hammer part. It’s good practice to keep moving the position of the tool to ensure that the seal is driven down evenly. If there’s any resistance investigate why. The seal is fully home when the top is level with the bottom of the clip groove. Once the seal clip is back in the dust seal can be replaced. As Honda chose not to supply an air height spec for filling the fork legs with oil (just a capacity) I did it by volume with a syringe. I pumped the stanchion up and down to get the oil where it should be, the spring was replaced, the fork cap fitted and fork leg refitted to the bike. cmm