VFR Cartridge Fork Service
Author: Robyn Landers, firstname.lastname@example.org
Copyright (c) the author, 1996
Distribution: May be copied as long as this header is retained.
Improved versions will appear on my web page.
Being the maintenance keener I am¹, and having coincidentally come across an article in the May 1993 Motorcyclist magazine regarding the necessity of servicing cartridge style forks, and being confident that my '93 model bought used with 15,000 km on it had never had its fork oil changed, I decided I'd better remove the forks and disassemble them for cleaning and oil change, rather than simply draining and replacing the oil. One weekend in February 1996 I finally got started. Mileage at the time was 17,000 km. This series of four articles [all four parts have been reproduced together here--Ed.] started as just an off-the-cuff description I sent to a friend, but then I started thinking of it more for general distribution. So, although I've been over it a couple times for improvements, the writing style varies from informal narrative to step-by-step instructions, and it's not what I'd call well-written. Oh well.
2. Fork Removal
2.1 Support the Bike
I have installed the optional centrestand on my VFR. If you don't have a centrestand, this part is trickier. Thanks to previous experience I knew enough to ignore the manual when it says the first thing to do is jack up the bike. 'Fraid not! How about slightly loosening axle nut, pinch bolts, caliper bolts, fork cap bolts, and triple clamp bolts while the front end is still firmly planted on the ground so that sufficient force can be exerted without knocking the bike off the jacks. I used two hydraulic jacks, one beside the drain bolt on the RHS of the oil pan, and one near the left rear corner of the oil pan. Jack up each side a few mm at a time and be careful that the bike doesn't tip over or lift a centrestand leg too far off the ground. Not much height is needed to get the front wheel clear of the floor. You need remove no plastic other than the front fender to remove the forks, and you may need to remove the belly pan in order to jack the bike up.
2.2 Remove Handlebars, Fender, Calipers, Brake Line brackets
Following the shop manual procedures, removal of all the required bits went fairly smoothly and of course I was working very slowly and carefully seeing as this was the first time working on this bike for me and I want to keep it scratch-free. The only problem was another incident with those nice looking allen bolts with the dome shaped heads. I don't know what it is with those things but they sure seem to want to seize in place. A pair of these hold the front fender on and it was a real struggle trying to get one of them out. I was sure I was going to strip the head of the bolt out. Mercifully it broke free at last.
2.3 Remove Forks From Triple Clamps
Removal of the forks from the triple clamps was actually fairly easy. There was enough room (just enough) to get my socket wrench in there and loosen the bolts. The torque was low enough that I could crack the bolts loose with one hand in the close quarters. Then the forks easily slid down and out. Next I removed the drain bolt at the bottom of the fork leg and pumped out the fork oil. There was a fair bit of dark sediment in the formerly red fluid. Overall the jar of drained fluid looked quite dark with particles. What is this stuff? It is metal particles worn off the fork springs and other moving parts, as well as wear particles from the Teflon(R)² fork bushings.
3. Fork Disassembly (overview)
I took the fork legs to my friendly neighbourhood shop where they happily loosened the damper rod bolt for me at no charge. This step requires an air impact wrench according to the manual. The mechanic disassembled one fork for me, and pumped the remaining oil from the cartridge. He felt the oil didn't look so bad compared to what dirt bikes are subjected to, but when I showed him the jar of fluid he agreed it certainly needed replacing. Seeing how the cartridge is assembled and how much more oil got pumped out after disassembly that I couldn't get out before made me believe that in addition to say a yearly simple fluid drain and fill, disassembly for complete draining and cleaning is certainly warranted periodically. We inspected the cartridge components and his opinion was that things weren't dirty enough to have necessitated the full disassembly at this point. But hey, I've gone this far, and it certainly won't hurt. Without some point of reference I wouldn't know how often to do it. All set with a bottle of new fork oil I returned home to disassemble and clean everything. I did find a piece of metal flashing jammed between a couple of the "valves" in one cartridge, and got a fair bit more sediment out of the various internal components when flushing them with solvent. So my conclusion at this point is that I needn't have fully disassembled the fork at the current mileage, but I will do the fork oil yearly, and save the full disassemblies for perhaps every 24,000 km or so (which is about the valve adjustment interval if memory serves). Details of fork disassembly appear in the next section.
In Part One, I described removal of the forks as I embarked on the project of cleaning the cartridges and changing the oil. Recall that my bike had about 17,000 km and has almost certainly never had the oil changed. In Part Two I describe the procedure for disassembly of the fork and cleaning of the internals. Comments on the condition of my forks are interspersed.
4. Fork Disassembly and Cleaning
I had removed the forks after slightly loosening the cap bolts, drained the oil via the drain bolt at the bottom of the fork legs, and then took them to my friendly neighbourhood shop so they could remove the damper rod bolt from the bottom of the fork leg. This required the fork to be clamped in a vise and the bolt was extracted with an air impact wrench. Remaining disassembly was left to me. If you don't have a shop manual, make notes on the orientation and location of all internal parts, and the order in which you removed them. (I highly recommend buying a shop manual! How can you spend thousands on a new bike and not be willing to cough up another $50 for the manual?)
To disassemble the fork, finish unscrewing the cap bolt from the fork tube. (With the fork fully extended there is very little pressure from the spring so this is easy. You can make it even easier by reducing the preload setting on 92+ models.) The cap bolt remains attached to the internal damper rod. Use two wrenches, one on the locknut and one on the flat surfaces provided on the cap bolt, to unscrew the cap bolt from the damper rod. (If you backed off the preload, you'll have to turn it back in so as to expose enough of the bolt flats to get your wrench on it.) Both the cap bolt and the locknut are threaded normally. (Some bikes apparently use reverse (left-hand) threads.) Set aside the cap bolt, the notched spring seat, and the flat spring seat.
Now you can pull the damper rod assembly up out of the fork. Remove the oil lock piece (little aluminum cup) from the bottom of the damper rod assembly. This piece just slips off the end. The cartridge will still be full of fork oil even though you drained the fork via the drain bolts on the bottom of the fork legs. Pump the rod slowly with the bottom end in a jar until you get all the oil out. Careful or you'll squirt oil onto your pants and shoes. Have a look at the condition of this oil. On my bike, it was not disgustingly filthy but it was well-laced with fine metallic sediment from bushing and other parts wear. Inspect the Teflon(R) bushings on the forks to see if they still have a good layer of grey Teflon(R) on them. If they're chewed up or the Teflon(R) is worn down enough that you can see the underlying metal, get new bushings.
Next I submerged the cartridge in a jar of fresh Varsol and pumped it some more to clean out the remaining oil. The shop manual does not discuss removal or disassembly of the cartridge. To do this, use something like a dental scaler to carefully pick out the C-clip from just inside the lower end. Thread a bolt into the end of the valve assembly. Say, the damper rod bolt just happens to fit :-) Hold onto the bolt and carefully pull the valve assembly straight out. It will offer resistance because of an O-ring. Once you have it out, examine the O-ring for damage. This part is not sold separately by Honda, so if you damage it you'll have to find a replacement yourself. My local shop had an assortment on hand. This valve assembly is the compression damper. Clean it with Varsol and examine closely to look for trapped debris. I found a piece or two of metal flashing wedged between the washers in both of mine. Other than that they weren't too dirty. (If you were going to attempt to change the damping behaviour of the fork, you would need to proceed to disassemble the valve assembly and replace the washers. I didn't. This is where people such as Lindemann work their magic, in knowing what washers to select to produce the desired behaviour.)
With the compression valve out, the damper rod can be slid out of the housing after you remove the locknut from the upper end. There's another valve assembly on the lower end of the damper rod. This is the rebound stack. Clean and inspect it as you did the other one. Examine the housing itself. There are several sets of holes drilled through it. I found more metal flashings on these holes and scraped them off. This is probably the source of the bits that were stuck in the valve assemblies. I damaged the O-ring on one of the valve assemblies due to a nick in the groove where the C-clip sits. With some 400-gritsandpaper I smoothed off the nick to prevent damage to the new O-ring upon re-assembly. With a lint-free cloth, wipe off the fork spring thoroughly. Switching now to the fork, clean out residue of thread locking agent from the threads in the bottom of the fork leg. Remove this residue from the damper rod bolts as well. Clean out the fork tube and stanchion by reinstalling the fork drain bolt and plugging the bottom hole with your finger and then pouring some Varsol into the fork. Slosh it around and then let it drain. Wipe remaining Varsol off all parts and set aside to dry off while you go take a break. :-)
Now some editorializing. At 17,000 km, the fork oil in my bike was definitely dirty enough to warrant changing. The cartridges themselves weren't too bad, and if it weren't for the bits of metal flashing trapped in them they mightn't have needed this full procedure. But how is one to know until you get inside to look? The magazine article I used as a guide suggested that a new street bike should have its fork disassembled and cleaned like this after the first 40 hours or so of use. After that, change the oil yearly (simple drain and refill), and do the full disassembly as recommended by the manufacturer. Well, Honda does not specify a service interval for this. Judging by the filth in my oil, I'd agree with the full treatment early on for a new bike, and then perhaps again every valve adjustment interval (25,000 km). I would also recommend doing it right away if you buy a used bike. Then you can start off with the fork in top condition and you have a reliable basis for judging future performance, rather than basing your opinions on a fork with unknown amounts of crud and mis-adjustment. Next, re-assembly.
5. Fork Re-assembly
5.1 Choosing Fork Oil
Okay, now all the parts have been cleaned and you're ready for re-assembly. You'll need a quart of suspension fluid. You must use the proper type. Do not use ordinary fork oil. Use oil specifically made for cartridge forks. This is important for proper performance of the fork. Cartridge fork oils are much more specialized than regular damper-rod fork oils. The manual calls for Pro Honda SS-7. This does not mean 7 weight! In fact it works out to what is usually called about a 2.5 weight On the official rating scale for cartridge fork oils this works out to "85", according to my trusty local bike shop owner. The unit of measure for cartridge fork oil viscosity is Sabel Universal Seconds (SUS). The general idea is that it measures how long it takes for a certain amount of oil to pass through a hole of a certain diameter. A second scale takes into account the viscosity retention of the oil over a temperature range. The oil I used is Golden Spectro 85/150. The SUS rating is 85, while the 150 refers to the temperature rating. (No, this does not mean 150 degrees.) It says right on the bottle that 85/150 is for Showa cartridge forks, which is what Honda uses. (Honda owns Showa.) A different viscosity is used for Kayaba cartridge forks. Having said all this, someone else on the net phoned up Spectro to ask about cartridge versus non-cartridge oil. The person at Spectro said race applications are where it could show a difference, not street riding. Oh well.
Reassemble in order of disassembly:
This is the fourth and final installment in my report on VFR fork service. We left off with the forks cleaned and mostly re-assembled with just the fork cap bolt and related bits plus the fork spring waiting for reinstallation. Before doing that we need to install the fork oil and bleed the air out.
5.3 Fork Oil Filling
Measure into a clean container the specified quantity of fork oil: Oil Quantity Oil Level USA Model 1990-91: 383cc per leg 175mm 1992-93: 386cc 178mm 1994 on: 412cc 177mm Canada Model 1990-91: 394cc 187mm other years as per USA chart European Modelssorry I have no info. Compress the fork fully. Pour the oil in slowly. Avoid "glug-glug" soundsthis is air getting trapped. To bleed the air out, follow this two-part procedure.
5.4 Final Fork Re-assembly
Slide the clean fork spring over the damper rod and into the fork leg. The tightly coiled end goes down. Make sure the locknut is fully seated on the damper rod. Install the flat washer so it sits on the fork spring, and then the notched washer over it with the dish down. Note that the chamfered end of the locknut sits in the dish of the notched washer. (If the chamfered end of the locknut is facing up, you have it on upside down.) Thread the fork cap bolt onto the damper rod and snug it up against the locknut using two wrenches. Then back the preload adjuster out. Now extend the fork fully and thread the fork cap bolt back into the fork tube. Recall previous warnings about being careful not to cross-thread. You needn't get it fully tightened; just in as far as the O-ring is good enough for now.
6. Put the Forks Back on the Bike
Hey! You're almost done! Reinstall the forks on the bike. Refer to the notes you made prior to disassembly when positioning the fork in the clamp for proper height. The shop manual calls for1.5" between the top of the upper triple clamp and the edge of the fork tube (not counting fork cap bolt) on 1994+ models. For 1990-93 models it says to position the fork tube groove even with the upper edge of the triple clamp. But there is no groove on my 1993! I measured it at the same 1.5" as it turns out. Tighten the lower triple clamp bolts first, and then the fork cap bolts, and finally the upper triple clamp bolts. There's enough room to get your torque wrench in to the lower triple clamp from the top, but not really enough from below. You needn't worry about alignment of the fork lowers because they can rotate on the fork tubes. Rotate the fork lowers as needed and then slide the axle into place to ensure they are straight. Position the oil line brackets but do not insert the bolts yet as the manual says. This is clearly a mistake -- the bolts have to thread into nuts, which are permanently mounted inside the fender! Now put the front fender in place. You'll need to pinch it to prevent it from scraping on the fork legs. Line up the oil line bracket holes with the rear nuts in the fender, and line up the allen head bolts with the front nuts in the fender, then install the oil bracket bolts and the allen bolts.
7. Reinstall Remaining Components
From here on, it's straightforward reinstallation of front wheel, axle, fork pinch bolts, brake calipers, handlebars, switches, wiring restraints. As you slide the forks up into the triple clamp, make sure you have the brake/clutch hoses, switch wiring, and throttle/choke cables oriented properly! Congratulations, you're done! Now your forks shouldbe in good-as-new condition (assuming the seals and bushingswere okay to begin with). Enjoy. Refer to various other articles on how to adjust pre-load, measure and adjust sag, tune damping characteristics with fork oil viscosity, and so on.
This article was edited and condensed from the original four-part series by VSource.org
Footnotes by VSource.org:
¹ This must be Canadian-speak... Ed.
² DuPont's lawyers have warned that this footnote must be shown. "Teflon® is a registered trademark of DuPont for its fluoropolymer resins."
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