Honda GB-500 FAQ
Maintainer: Alan Fleming
(alanf@dorje.com)
Version: 1.15
Date: 11/21/98
Maintainer: Alan Fleming
(alanf@dorje.com)
Version: 1.15
Date: 11/21/98
1) What engine did Honda put in the GB500? Is it the same engine that was in the Ascot, XL and XRs?
Pete Plassmann:
Yes, pretty much.
Duke Robillard:
It's a 500cc version of the XR single (The Ascot was before my time, so I dunno what's in there). The guys at my Honda dealer say these engines are bullet-proof.
From Cycle magazine (March 1989)
BHP 33.36 @ 7000 (on dyno)
Torque 26.34 @ 6000 (on dyno)
0-60 5.1
1/4 14.13 @ 89.7
Weight 390.5, wet
front wheel 2.15 x 18
tyre 90/90-18
rear wheel 2.50 x 18
tyre 110/90-18Phillip Gray:
The GB is a sleeved down XL600 engine displacing 498cc.. This means that it has the same stroke as the XL600 i.e 75mm. Its also running 8.9:1 compression so kickstarts are easy. Here's some stats for you on bores/strokes:
Model bore stroke
XR600 98mm 80mm (long stroke motor)
GB500 92mm 75mm (short stroke engine)
XL600 100mm 75mm (NZ, Australian model)
XR650L (NX650) 100mm 82mm (longer stroke again) (NX650 also called Dominator)
GB400 84mm 72mm (Japan model, imported in NZ, shares very few parts with the GB500, engine wise anyway)The engine has a gear driven balance shaft that is positioned at the front of the engine. This certainly helps keep it tame all the way to its 7800 red line. The single overhead cam is driven by chain that is on the right hand side of the engine. The Honda RFVC (Radial Four Valve Cam?) valve gear is accessed through the four separate covers.
Ray Hixon:
It's the later RFVC motor. I'm not sure if it's sleeved or stroked or both down to 500cc. I'd assume the quickest and easiest hop-up is to put an XR/XL600 motor in it (who wants electric start anyway? *Real* men bump-start their Singles, or have rollers).
Doug Rinckes:
A 500 single, styled to look like a brit bike, wire wheels, single seat, round headlight and indicators. Dry sump engine, has kick as well as electric start. The engine is based on the XR/XL series, and a 600cc big bore kit is available. Consists of a new piston and a sleeve from the LA Sleeve Co.
Apparently it can have the 5-valve (?) head from the XR600 fitted to it, which gives it a good boost. Unfortunately XR600 parts are way rare here in Japan.
Will Connelly:
Gear ratios from the Honda GB-500 Service Manual:
Primary Driven 2.482 (72/29)
Final Reduction 2.466 (37/15)
Gear Ratio I 2.384 (31/13)
Gear Ratio II 1.555 (28/18)
Gear Ratio III 1.200 (24/20)
Gear Ratio IV 1.000 (23/23)
Gear Ration V .875 (21/24)Randall Zempel:
Not at all in regards to the Ascot. But, in respect to the XL/XR, both yes, and no. Within the RFVC family, there are two sub-families. One with electric start, the other without. The difference here is the left end of the crank. within sub-families, the crank is interchangeable, but not between them. (this is because the end is longer to accomodate the starter gear) Also, the pistons are different, so if you're changing the bore, you have to watch that. As the stroke "grew" from 75mm to 80mm, then to 82mm, Honda hid the extra throw in the wrist/gudgeon pin to deck height distance. The rods are all identical. Within the RFVC family of motors, there are a couple of transmissions with different shaft lengths and different gears. I haven't had enough of them apart to measure to make any really broad statements about them. But, the GB500 has a closer ratio gearbox than any of the 600 models. There are both left handed and right handed gear shift drums, so if the shift pattern is backwards from what you want, it is possible to change the drum instead of making a linkage. There are differences, also, in the output shaft lengths.
So, if you're swapping a different motor into your GB, careful measurement is a must for proper sprocket alignment. There are two head/rockerarm configurations within the RFVC motors. One has an automatic decompression release, the other is manual. The GB has the automatic release. In order to run an HRC cam, you need the manual release rockers and cover. The Megacycle cam, on the other hand, works with the automatic release cover. There are basically two heads available, a dual carb and a single carb. The dual head is so restricted I wouldn't fool with it. The single carb head is available with several different sized combustion domes (to match the bore of whatever engine it's for--there are no other differences). On my overbored motor, I use the GB500 (92mm bore) head because that gives me a 5mm squish band with my 102.4 bore.Just in case anyone else wants to know here is what I have for Honda RFVC CDI boxes: (The GB500 uses the MK6 CDI)
CDI part # idle advance full advance
MG3-003 6 BTDC below 1200 31 BTDC at 4000
MK6-671 8 BTDC below 1200 21 BTDC at 4000
MG2-871 11 BTDC below 1200 31 BTDC at 4000
MG2-891 11 BTDC below 1200 31 BTDC at 4000
MG2-892 11 BTDC below 1200 31 BTDC at 4000James Holland:
Gear ratios for XL600R/LM and earlier XR600s are:
1st 32or31/13 2.385
2nd 28/17 1.647
3rd 25/20 1.25
4th 23/23 1.0
5th 21/25 0.84
The XL has a slightly higher top gear than the XBR/GB but second and third are lower. The later XRs are advertised as having a close ratio box, does anyone have the ratios for these and the NX650.
Bruce Marshall:
When originally released in NZ, the GB's came in 3 basic models :-
1) GB400TT (dual seat, silver or deep blue, dual seat)
2) GB400TT, Mk2 (with half-fairing, silver, single seat with plastic cowling showing Mk 2 logo, & different footpeg outriggers to suit solo)
3) GB500TT (Metallic Brown, no fairing, dual seat, single with alt. pegs etc. as an option)
The obvious mix 'n match here is to convert a Mk 2 to 500, or 500 to Mk 2. While it may appear easier to just switch the fairing onto a 500, this actually entails quite a bit more work than swapping the engines. Mainly this is because the wiring harness isn't common - on the faired bike the wiring 'looms' in a special container below the instruments, whereas on the unfaired bike this happens inside the headlight shell.
Unfortunately the harness lengths aren't the same so are not simply interchangeable, & the consequences multiply 'something terrible'. Like, the harness swap entails having to exchange the ignition switches (which are sealed, so you can't just switch the wiring), to keep the single key the fuel caps have to be switched over & also the seat latch/helmet lock (which is mounted with break-off bolt heads, needing drilled out etc).
The brake lines also differ between the models so have to be switched too, re-bled etc, it goes on & on. The engine swap is a breeze by comparison.
2) Are other parts on the bike from other bikes? (forks, swing arm, instruments, etc?)
Pete Plassmann:
Not that I know of.
Phillip Gray:
Other than the engine, the parts are all unique to the GB as far as I can tell. There is not another Honda model that uses the same suspension parts.
In Japan and NZ the GB400 derivative is available. (In Japan the GB500 is not sold, according to my Honda dealer.) In Australia, and the UK the GB500 engine is housed in a different chassis and is called the XBR500. (It looks like shit.)Ray Hixon:
Common parts w/ other bikes: none that I know of.
Thomas Cohen:
The XBR500 is similar in concept, so it may have some of the same parts.
Just what people have mentioned to me - I know it uses the same rear shocks.
Philip Penhey:
I am the proud owner of a NZ new, 1985 GB400MK2. To my knowledge, these were the only GB fitted with a half fairing from the factory, and in my personal opinion, are the best looking of the bunch. As for the comment about the 400's sharing little of the 500's parts, the only actual difference is in the engine department. Otherwise they are identical - frame, wheels, brakes, tinware, etc.
Bruce Marshall:
There is one VERY useful thing which the GB series shares with the yuky XBR - the workshop manual, which to my knowledge wasn't produced in English for GB's. As far as the engine unit is concerned the content is for the same thing. XBR W/S Manual part # is C2008812F, published in 1985 All the GB's I have seen here in NZ have had only Japanese language labeling & no owners handbooks were available in English from the factory. However, the NZ Honda Importer (Blue Wing Honda) had some produced locally in English.
3) What are the most common modifcations for the street? Are there any fork, brake and/or wheels that are bolt on options? Are there any companies in the US or elsewhere that sell hop-ups, additions, etc?
Pete Plassmann:
I've seen major engine work by Muzzy and White Bros. Also hop-ups from Al BakerDuke Robillard:
White Bros has a bunch of stuff (carbs, exhaust, fork springs, shocks, big bore kits). One of the magazines had them build a super-GB-500 back in 1990, so now they sell all the parts. I haven't done much to mine, 'cause I don't much see the point in hopping up this kind of bike...Although I did get steel brake lines after a few years, and I may replace the exhaust next year, 'cause my stock one is all scraped up.
White Brothers also lists two Cams for the GB-500Core Lift Part #
All Around [2] .350" WB 1650
Track [3] .380" WB 1651[2] Requires Heavy Duty Valve Spring Kit [3] Requires Heavy Duty Valve Spring Kit and shortened valve guides
The also list the Valve Springs and guides:
18-133 (springs)
18-134 (springs & short guides)
18-135 (springs & short guides; titanium collars)Phillip Gray:
I did a bore to a 100mm piston in mine, most people down here have modded theirs in some way. What I used.
1 XL600 sleave (from LA sleave co LA)
1 XL600 wisco piston (from Wisco !)
1 XL600 top end gasket kit (from Honda)
If you want to do any engine work yourself buy a Kymer or Haynes manual for the XL/XR series engines and you'll be away. I did 99% of the work myself it is not that hard. This kind of modification is getting very common here in NZ, it is getting hard to find a GB500 that has not been worked a little. Some of them a getting a bit stupid, like going to reframe and such. If you buy a Wisco piston note the following:
Always check the piston ring end gap well before you attempt installation.
The Wisco kit I purchased had the wrong rings it, they over laped in the new bore by 2.5 mm!! I also plan on installing a Barnet kevlar XR600 clutch since its cheaper than Honda and fits straight in.
Ray Hixon:
Dave Fredricks used to race one in WERA, and (I think) Kurt Hall bought the bike for Pam to ride after that. From what I gleaned from Jack MacAllister, DF's mechanic, they laced the rear rim up front, and put in the widest rim they could in back -- it wasn't very wide; the swingarm limited the width.
They ended up with an RS600 engine in it. For Hop-ups: XR's Only, WB, Muzzy, etc. Motorcyclist had a hop-up article on the GB; it was a Muzzy 600 engine.
Bob Green:
I road race a 618cc version of this 75mm stoke motor in England. You should be careful if you overbore to 101mm (mine is 102.4mm) using a Wiseco piston. I have destroyed two cylinder barrels by overboring to 101mm. The problem is that the thinner liner weakens the overall integrity of the barrel and a crack develops at the front of the cam chain tunnel. I would recommend using a barrel from an XL600 - 83-87 (75mm stroke), I've had no failures with a 102.4mm Wiseco since I started using this barrel . I would also recommend talking to Omega pistons in England 0044? 0121-559-6778. Omega make a very light 100mm & 102mm piston for the XR motors - around 100gm lighter than the Wiseco. Its a proper forged slipper piston with a 22mm pin so you'll need to sleeve the small end. Its worth trying to get if you're into tuning it, as another major problem I've had is a snapped crankpin at 8500 RPM in top gear !!! using a Wiseco. In standard trim its as bullet proof as they come. I get 62BHP @ 8300 RPM at the back wheel on a Dynojet with a bit more to come. Its cost a bit to get. If anyone wants a wicked XBR/GB/XR talk to me. Mine drives out of corners harder than a CBR600.
Steve Wells:
I'm a New Zealander with a GB-400, and here's some info you may find useful. The Mark 1 GB-400 is identical in every way to the GB-500 except in engine size and the seat (the Mk.1 GB-4 has a double seat, the Mk.2 GB-4 and the GB-5 have single seats), all other bits are interchangable.
The Mk.2 GB-400 is identical other than it has a medium-fairing which sits on a frame mounted to the main frame and has the headlight bracket on it. The fairing bubble provides adequate wind protection for shorter (sub-5'10") people and is okay for taller folks if they duck down a bit. The ends of the fairing can be a nuisance for long-legged people as they hit you in the knees when stopping quickly or going down steep hills. Only two bolts need to be removed to switch the Mk.2 single seat footpegs to the double seat setup of the Mk.1. The Mk.2 single seat has a bubble at the back which the toolkit fits into just as on the Mark 1/GB-500. The GB-4 engine puts out about 27.5BHP at about 7200 rpm and about 21 torqe just about all across the revs (highest peak at ~5000). (Dyno tested).
Torque drop from 3000 to 4200rpm, and drops off after 7000rpm. Power curve is steady & linear with only a tiny drop at about 4000. YMMV.
I use a good quality "Ventura" magnetic tankbag which fits as though it were made for the GB. We get both GB-400 (both versions) and GB-500 here. GB400's are quite common bikes on the roads.
I have koni shocks on the rear, and progressive fork springs in the front with pressure caps on the top of the forks. I'm currently running Bridgestone Battleax tyres on front and rear.
A local firm (Dynotech) has a 600cc kit for the GB-400 (and 500) which almost doubles the torque and gets the BHP to just under 40. IIRC it involves using a Honda XR-600 crankshaft. I've seen a couple of Mark-1 GB-400s (and a GB-500) with an accessory bikini fairing which basically hooks around the headlight and provides a _bit_ of wind protection.
Philip Penhey:
I have had my 1985 GB400MK2 slightly worked by Dynotech in Wellington, NZ with a little porting, a huge K&N air filter as well as new rings etc (normal engine rebuild stuff) and it now dyno's the same as a stock 500.
Not bad for the runt of the pack. My long term intentions are to ditch the 400 motor in favour of an NX650 lump, with a little work I should see close to 60 horse. Yee haaaa. Additionally, the editor of Australian Performance Streetbike just did a performance upgrade to his GB400Mk2 and is including articles about this in the magazine. Other than a new paint job (the stock was pearl silver) the modifications were: an engine sourced from a NX650 Dominator. Suspension is Koni dial-a-ride's out back and Progressive Suspension fork springs at the front. The exhaust pipe is a locally made item. He also attended to the mundane stuff like brake pads, tyres etc. Not a radical hot-rodding by any-means, but he's certainly got himself a tidy bike for his troubles. He spent almost $7K (Australian) which to me seems to be a hell of a lot for what he ended up with, but considering he outsourced _all_ the work, I guess you get what you pay for.
Richard Moore:
I thought someone might be interested in what I've done to my 1985, Japanese-Spec GB500. With a *lot* of help from my friendly neighbourhood mechanic (OK, he did virtually everything), I have transplanted a 1990, UK-Spec NX650 Dominator motor into it(from a stolen/recovered bike from a bike breaker). Bolted straight in, though we had to swap the alternator, igniter and kickstart levers over. The 500's top end pull to the red line is gone, but in its place I have enormous gobs of stonking torque that peak at 5000 revs (power peaks at 6000). The gearing is a bit tall (15 and 36 tooth sprockets): 5000 at 70 mph - in fourth! 4000 in fifth; but once we've got the breathing sorted out and the fairing back on the bike I'd like to see how far it'll pull in top. (Dropping to a 14-tooth front sprocket at a later date gave much more usable gearing.) We need to attach a rearset linkage for the gear lever, as at the moment I have 1-up 4-down, which is not very satisfactory, as every now and again I forget... Thanks to Laf Young for going on before and providing lots of useful information.
Will Connelly:
Mine is basically stock with a SuperTrapp pipe, air pump removed, and bar end mirror replacing stockers. Planning on a set of shocks (Koni?), fork springs and new tires (Metzlers or Avons) for next year. I have several bikes and this is the one I usually jump on when the opportunity for an unplanned ride arises.
Mark Novak:
The simple use of a hacksaw to allow the fuel mixture screw to turn and richen the bottom end has given me a noticeable performance difference in the bottom end and a reduction if not complete omitance of backfiring.James Holland:
I used to road race an XBR500 in England, currently I use the bike on the road. The engine has been fitted with an XL barrel and 100mm Wiseco piston and Kent cam, carb is 40mm Dellorto. With a road legal Micron 2-1 exhaust and an extra base gasket (to give the starter motor an easier time) I get 48bhp on a dynojet dyno. Here are a few points which may be of interest.
The XBR500 has a 275mm front disc with a six point 165mm pcd mounting. The front discs from a VFR750FJ/K have the same fitting but are 296mm. A simple bracket can be made from ally plate to relocate the stock caliper. The XBR is fitted with comstar wheels, there is little room between the disc and the spokes so it is unlikely that a 4pot caliper could be used. I use Astralite wheels from an old TZ/E with a 320mm EXUP front disc and a GSXR 4pot caliper. The rear wheel has an XS650 caliper and disc fitted. Also I have a HRC cam (genuine), the timing info I have for this is: inlet opens 45 closes 50, exhaust opens 60 closes 35, using a dial gauge I get: inlet 55/60 exhaust 70/45. Can anyone confirm these figures are correct.
My 83 XL600R has inlet ports approx 31mm dia at the entry point, however a manifold I got from an 85 model tapers sharply to 28mm, this suggests that the later heads may be much more restrictive. As a side note two 28mm ports have, give or take, an area equivalent to a 40mm dia port, they just look small. XL parts are difficult to get hold of in England so as an experiment I have converted an XBR head to dual port. I hope to do some flow bench testing later in the year. Dual ports enable much greater carburettor areas to be achieved ie 2x 34mm carbs = 1x48mm. The later NX650s have a battery powered CDI, so the alternator rotor can be junked completely and the ignition run 'total loss'. I'm working on my own digital ignition which will be run total loss and will enable the advance curve to be programable.
One important thing to note if you do any major overhaul of one of these engines. The oil pump may well need to be primed, use a liberal amount of oil around the rocker gear and squirt some down the bore, loosen the oil pipe from the head and turn the engine over to check the oil supply. To get mine working I filled a plastic bottle with oil, disconnected the feed pipe from the oil tank and squeezed the bottle as hard as I could into the pipe to force oil into the pump while a friend turned over the motor.
Bruce Marshall:
Presently I have 2 GB's. One is a 3000km brown 500 which I've had from new, with the fairing swap & braided brake hose, otherwise a delicious 'minter'. The other is a very tidy silver Mk 2 with a lightly worked XR600 donk. Previously I ran it with a 500 motor with high comp piston, cam, light head work, 40mm flatslide, pipe etc; while it had a bit more puff, particularly from about 6000, it wasn't really worth all the bother, & $$$'s. I got a XR600 parts bike and put that effortlessly grunty donk in the GB. That motor now has a Wiseco 625, extra comp'n, head job, extra flywheel (see below), bigger headers & a slightly muffled mega. The XR carb is a bit of a bother to squeeze into the GB, & the flatslide wasn't very smooth for normal road use, but the thing runs beautifully with the original GB carb, airbox, choke etc. The XR also feeds the GB electric system OK. The XR motor fits in perfectly, & if you dont want to split the cases to fit an opp. hand shift drum to get 1Dn4Up it is quite simple to rig a 'rearset' type linkage. You can even re-commission the neutral switch easily if you want everything seeming original - the XR shift drum comes complete with the hole to accept the neutral switch pickup, just machine a suitably sized snap off button, install thru the switch hole in the case, drift it home & snap it off, fit the GB switch/pickup, & presto - green light! The XR oil pump doesn't seem to be able to self prime in the GB, perhaps due to tank height, head, etc. So, for a telltale crack the joint on the topend feed & give the oiltank some pressure from your air compressor - a rag jammed around the airgun nozzle in the tank opening will hold enough huff to move the oil thru.
4) What about touring on the bike?
Pete Plassmann:
Why not?Duke Robillard:
I did a 7 hour, one day trip last summer, and boy was I stiff. :-)
It's a little small for touring; you get blown around on the interstates, the pegs are pretty high, and there's no fairing.
I used put over-the-seat saddle bags and a tank bag, and that fit enough stuff for a weekender.
Phillip Gray:
I have been on holiday with mine and found it comfortable to ride for most of a day. The gearing is real low however and the engine is using about 80% of max RPM to do around 75mph. In fact, at 5200rpm the GB sits on 120kmph. Cop safe, but I the engine seemed a little strained.
From 4700-4800rpm the shakes increase, but smooth out at 4900. If anything the GB is under geared. It feels as though it will pull a sixth gear with ease but only has five. It will pull red line in 5th, thats 160kmph, just under the tonne (100mph). Comfort wise, the seat has nice fake seude ripples on it that cut into your butt real bad so for a long journey pad the seat with a towel for get the suede taken off.
You can get 220km+ to the tank, not bad I guess. 22km to the litre.
Thomas Cohen:
If you up the horsepower (by whatever route) and have mainly touring in mind, you could up the gearing. On the assumption that it's the same as my GB400 (39 teeth rear) you could use the rear sprocket from an XBR500 which has 36 teeth. Then again, if you up the power enough you could run this gearing as standard. If you're touring with no hurry, then there is no reason why a GB400/500 shouldn't do. My GB400TT has a fairing, so I don't have one of the above problems.
David "Cochid Whyny" Bower:
I use my GB as the BIG gun of the open road. I have logged numerous 900+ days with out problems. I have found that the buzz goes away just above 80mph and will cruise at that speed all day. The luggage I prefer is an Eclipse deluxe tank bag circa 1985. The modifications made to the bike have been a supertrapp pipe, Metzler tires, and removal of the unsightly air pump located on the left side of the cyclinder. With my 34" inseem I often desire more seat to peg distance. Nine days of the year are devoted to traveling the roads of the western U.S. aboard this more than capable tourer.
5) Any must-have accessories?
Pete Plassmann:
Pudding-bowl helmet (Davida), black leathers, and facetted goggles!Phillip Gray:
I've just fixed a set of progressive fork springs from progressive suspension. You need these, they help the front end in an enormous way.
The thing to do is, fit Marzochi or Koni shocks to the back. Rising the back end is not a bad idea here as the front is real light. I've pulled my forks about 10mm through the triple trees to help this, its worked, but some times, like when you are just off the throttle the front wobbles.
Pull the brakes on and this goes away. The single front disk, drum rear are evenly matched to the GBs power and weight. You can not do stoppies (getting the rear end off the ground on brakes), but you can lock the front wheel if you try. The rear brake seems to lack a bit of feel, it is useful for stopping at traffic lights, where it and the engine brake will easily bring you to a halt. I have yet to see a dual disk front end on a GB, but I don't think that is far off. I keep running out off brakes when I go out on the track, I need a new disk to, but the whole plot goes real mushy and comes into the bar, not good when your flat out going into a hairpin =8-}. I also fit a very sticky Dunlop K591SP front tire which, due to the light front end, has lasted 20000km! The GB uses an uncommon 530 size chain, and this makes replacement chains expensive. A 525 conversion kit is available from MCA Australia. Finally, the side stand is best removed, it always scrapes on left hand corners.
Thomas Cohen:
The rear shocks are typical standard Honda commuting stuff - absolutely appalling and limited in adjustment. By now they'll be long past their best if they're original. Get Koni shocks for the XBR500.
Frank Ball:
For tires, check out the Metzeler ME33 Lazer front tires. They are available in standard and Comp K (extra sticky) compound. They are available in the older skinny sizes. If you have 18" wheels front and rear, the Metzeler ME55 rear tire is also probably what you are looking for.
Doug Rinckes:
My flatmate has a Dunlop K591 on the front and a Bridgstone on the rear of his GB. Grips like heck.
Karen L. Black:
For saddlebags, I use the Chase Harper Aeropac bags. While they aren't leather, they are small enough to fit behind my legs and in front of the rear turn signals. They also have a plastic shell inside that holds the bag's shape, keeping your stuff off the tailpipe. I've been very pleased with Chase Harper; they recently repaired my tankbag and it is as good as new. When mounting your saddlebags, you may want to take off the fiberglass tail shell (or cover it with a cloth) as scratches can be a problem.
Depending on how much you carry to work, a tankbag may be an alternative.
I also use the Chase Harper Aeropac tankbag (the larger one with the map pouch). It has served me well for a "briefcase" and overnight bag.
Brad LaBroad:
My GB has a choice of three tankbag options out in the garage. All work to some degree.
[1] A Hondaline magnetic tankbag. Very thin but easy to flop on. Be sure rotate and scrunch it around a little to grind the dirt into your nice paint. This bag is available at your Honda dealer. I use it to carry a pair of shoes and a file or two on the rare occasion I ride to work. Too small for serious riding although fine for a day trip if you're eating in restaurants.
[2] Chase Harper 1100 bag. The quick clip mounting system avoids any mounting hardware left on your bike, although I have managed to attach and dress the alternative mounting system (Fastex buckles) so that they do not foul any cabling, the engine, the frame, etc. This bag is fine for an overnighter, etc. although it's a little squirrelly at speed and seems to always keel over to the left (must be that extra-large bottle of Advil I keep on that side). There are a whole slew of Chase Harper bags--well made--and readily available through Chapparal or Competition Accessories, etc.
[3] One day just for fun I took the three-storey skyscraper tankbag off my R100GS and tried in on the GB. Believe it or not it fits beautifully; the hold-down elastic clips stretch nicely and the front retaining clip fits neatly onto the tank. The only drawback is that bag sits to the rear of the tank (on the GS the tank is, er, large compared to the GB--but then, what isn't large compared to a GB?). This looks a little goofy, pose-wise, but I would not hesitate to use it from a practical standpoint and probably will obsolete my Chase Harper for that reason. This is the BMW Multivario tankbag and it is wonderful beyond words and just as expensive. Financing available on approved credit at your local BMW boutique.
6) What are the common problems/weaknesses with the GB?
Steve Wells:
Common problems with GB's:
1.) They _eat_ Camchains. I go through one about every 15,000 Km. The standard cam-chain tensioner is not very efficient and tends to wear out causing it to eat cam-chains even quicker.
2.) Starter Moters. The electronic starter motor also tends to die fairly commonly on GB's. Either the solenoid will pack up, the clutch will or it will just wear out. GB's with working starter motors are not all that common.
3.) Handlebar placement. If you drop the bike, you can be almost certain that the handlebar on the side you drop it on will be pushed back into the petrol tank and leave a fairly large dent. GB's without these dents aren't too common. Only thing to be done about it is lock the handles as far forward as possible and hope.
4.) Swingarm pivots. The sleeves used for these pivots are made of nylon, and wear out fairly quickly causing lots of rear-end movement. I've had mine replaced with metal rollers. If these pivots wear out and start chewing onto the swingarm axle, then it starts getting expensive.
Other than that, if treated well the engines last for ages. A couple of locals have had their GB-400 right around the clock, and they're still going. With a filter change, a complete oil fill uses just over 2 Litres. (2 litres fills it, then a bit more to top it up after you've done a few Km to mix it around). I do an oil change every 3000-5000Km depending on how long it takes to do that. I usually only do about 150-200Km/week.
Alan Deacon:
I don't know if this is the same on the GB but I recently had the following problem with my XBR 500 G: A tapping noise developed coming from the rocker box. It was most noticeable when the engine was warm, and at low revs. It sounded like loose tappets but a normal service failed to clear the noise. Performance was not noticeably affected.
An investigative foray revealed a totally knacked rocker and a badly scored camshaft. Only one rocker was damaged. The service engineer reckoned the likely cause was a stuck valve lifter. The bike has only done around 23,000 miles and has been regularly serviced. Is the automatic valve lifter failing a known problem? If so I'll re-route the cable and fit a manual lifter like on my Matchless G80. I think it would be worth people checking the lifter from time to time when they've got the tank off.
Randall Zempel:
The GB motor, like all the RFVC motors, suffers from marginal cam oiling. In low-stress street use, this isn't usually a problem. However, in high performance engines this will manifest itself with a worn third lobe and follower. Honda's racing division (HRC) solved this problem in its RS600 flattrack motor by using a high volume oil pump and larger diameter external oiling tube. Both of these parts are still available from HRC. Personally, I have not installed these pieces. I have used fully synthetic oil, changed it frequently, and not seen any wear on my cam or followers. On the other hand, my motors tend to explode at low mileage intervals while racing, so they don't get much time to wear, either.
Not strictly a GB problem, but: If you take-down, reassemble your motor frequently the head bolts will pull out of the cheesy aluminum the cylinder is made of. This is excerbated by boring the cylinder and installing a bigger bore sleeve--apparently heat is a culprit in this problem.Bruce Marshall:
In July '87 Blue Wing Honda issued a service bulletin to cover their response to the then frequently encountered problem where 'a few' GB's had 'an annoying habit of stopping whilst the machine was sitting idling'. The (warranty covered) response covered quite a variety of mods including -
Replace the cylinder head
Change the cam & bearings.
Change various jets (sizes given)
Increase valve openings
Required mods to 'ignition pulser rotor' - ie, weld one side, grind the other, to move the timing.
Use 'low -octane fuel'
They even get down to quoting all the part #'s to be offered as replacements for the dodgy bits which Honda Inc had got wrong!
Also, starter motor failure, while aggravated by infrequent oil changes, shows early with the development of slight highs & hollows on the two faces which the sprags lock against, probably due to poor surface hardening. Eventually a sprag will hit a highpoint once too often & break. By the time 3 or more have quit things are getting really graunchy in there, & there isn't enough grip produced to lock. Failure can be kept at bay by dismantling for inspection every 10 thousand or so, & having a machinist dress the faces lightly, even re-harden or chrome. This isn't as silly as it might seem if you price replacement parts at broken sprag time, as the hub & gear face items have to be renewed as well as the new sprag, otherwise the new sprag will quit in no time. However, there is enough range of rotation in the sprag rollers so that a new one will accommodate resurfaced hub & gear faces, if the budget is tight. While in this area, if you can live without the electric start an available bonus is to biff the electric starter gear altogether, including the sprag assy & hub, & use the space to add some flywheel. To my mind the idea of trying to squeeze a lot more power out of these motors is less rewarding than going for torque & flexibility, & an easy way of getting a good return is to add flywheel. Any good machinist will skim down the stiffening ribs inside the alternator cover to make room for an extra ring on the flywheel & a meaty backing plate The result is always there - increased smoothness & THUMP.
7) What magazine articles have been done on the bike?
Duke Robillard:
Recently, I sent away to Ian Smith Information to get reprints of old articles on it. (I saw Ian's ad in the back of one of the Big American Bike Mags (tm). For $17? he'll look up articles on any bike, Xerox them and mail them to you.
PO Box 22517; Santa Fe, NM 87502-2517; 505 820 7844)
There are articles in the following back issues:
- Cycle World, February 1990 (They had White Bros trick it out; bore out the engine, new carb, etc.)
- Rider, August 1989
- Cycle, April 1989 (2 articles)
- Cycle World, March 1989 (2 Articles. One compares it with a Norton International and Velocette Venom)
- Bike Journal, November 1991 (an article comparing it to a Matchless G80)Philip Penhey:
- Australian Performance Streetbike, Oct/Nov 1997, issue 48 - This is the first in a series of articles about modifying a GB400.
- Australian Performance Streetbike, Dec/Jan 1998, issue 49 - This is the second in the above mentioned series.
Bruce Marshall:
- Bike Australia, Nov/Dec 92 - an article entitled DIY JAP by Peter Thoeming when he was first bitten by the GBug.
8) What is the going price for a good condition GB500?
Alan Fleming:
This is an anti-answer. The value of bikes if so heavily relativistic that the price in one area of the country for a given bike has no bearing on the price for the same bike in another part of the country.
I regularly see GB500s listed in the $2500 range but other people tell me that $3500 is a deal in their area. Ultimately, you need to determine local value by checking the classified section of your local newspaper, check with local shop and ask around.
Randall Zempel:
The GB was not popular when new. Like other initially unpopular bikes, it has developed a near cult status. This is understandable given it's classic good looks, reasonable power, and excellent handling. Prices have remained stable for many years. Occasionally, I see beautiful examples selling at the $1000 level. As a rule, however, they seem to sell for around $3000. Prices are inching higher all the time, though.
Duke Robillard:
In late '97 I sold my '89 for $2700. It had about 10,000 miles and a number of scrapes and scratches.
CQUINNN@aol.com:
The list price on the GB was an outrageus $4,198 for 1989 and reduced to $3,598 for 1990. The 1990 model listed for only $100 less than the high tech CB1 (a water cooled four cyl bike with gear-driven cam shafts.)
9) What resources are available on the net?
Alan Fleming:
The THUMPER web page (http://www.thumperpage.com/index.html) is an excellant resource for meeting other Thumper owners. Likewise, the THUMPER mailing list (listproc@dorje.com) is home to many GB owners.
Also, anyone interested in roadracing their Thumper should subscribe to the roadracing mailing list (listproc@micapeak.com).
Contributors:
Pete Plassmann (rmo@dpals.kaiserslautern.army.mil)
Duke Robillard (duke@io.com)
Phillip Gray (pgray@tssc.wlg.nec.co.jp)
Ray Hixon (fshixon@muskie.lerc.nasa.gov)
Thomas Cohen (Thomas.Cohen@nms.otc.com.au)
Frank Ball (frankb@hpsad.sad.hp.com)
Karen L. Black (weitek!kblack@caeis1.amd.COM)
Doug Rinckes (drinckes@tssc.wlg.nec.co.jp)
Brad LaBroad (bradl@tekig5.pen.tek.com)
Alan Deacon (ccaaaxd@ucl.ac.uk)
Bob Green (BGREEN@msmail.london.micrognosis.com)
Will Connelly (Wilcon@aol.com)
Steve Wells (steve@actrix.gen.nz)
Randall Zempel (rzempel@ix.netcom.com)
Philip Penhey c/o (DWT@netlink.co.nz)
David "Cochid Whyny" Bower (cochid@southwind.net)
Richard Moore (Richard.Moore@mail.bl.uk)
Mark Novak (betty@jomax.net)
James Holland (J_Holland@classic.msn.com)
? (CQUINNN@aol.com)
Bruce Marshall (bruce@marshall.co.nz)
Alan Fleming (alanf@dorje.com)
Think Peace.
- Alan (alanf@dorje.com)
http://www.dorje.com:8080/~alanf
KotBBBB (1988 GSXR1100J) RaceBike (FT500)
DOD# 4210 PGP key available