|Cyril Bonnett||29/12/2020 16:35:18|
|243 forum posts|
The Honda 750F2 that replaced the commando which no one in Edinburgh or Glasgow wanted took me to West Berlin in the winter of 1975 travelling through East Germany, other UK personal were forced to use the train to take their bikes. West Berlin was an amazing 'bikers' world, big Germans on small 50cc Italian motorbikes were a sight to seen.
The Honda was driven all year round and went on to do 120,000 with only tyres, oil filters and plugs replaced, I must admit that one thing did go wrong, the gear indication switch that screwed into bottom of the gear box needed to be replaced, cost about £10 and one socket and no more neutrals at 100 down the autobahn. It ended up with a Rickman full fairing and a set of their panniers.
One night in Richmond we went through a rotten farm gate into a very boggy field, hit a pheasant at 70+mph and it still started first thing in the winter after standing outside all night.
Edgar Brothers sold me a 'topper' which took me thousands of happy miles the Honda was sold and I started long association with shaft drive Yamaha's, even their 650 Turbo that used to take us to the Alps from Scotland.
Age catches up and todays traffic could ruin a life long love of motorbike so I gave them up.
I once drove over Blackmount on my XS850 on a freezing January morning, coming towards me the police 4x4 waved so waved back, later I was asked why I didn't stop! would you stop on rutted Frozen snow.
5 Yamaha and the only fault with any of them was the bolt on the end of the gearbox main shaft, it sheared on the way to a 24 hour meeting in the South of France, I discovered that leaning the bike to the right the bolt head and washer moved out of the way of the gear selector, it took us back home over two Alpine passes and Yamaha UK gave me a new bolt a workshop manual and wished me the best of luck fixing it, the broke piece of the bolt screwed out by finger, new bolt installed and bike back on the road in less than two hours. Fault Japanese, No, fault NVT certainly, a name doesn't mean the goods are superior in anyway, 45 years on and with modern material the Norton Commando MK3 Interstate would be an amazing bike, the acceleration was amazing, it handled really well, it was nice to ride, but the taxi driver sitting along side me at the traffic lights on Lothian road couldn't stop laughing, pointing at the engine he waved his hand up and down. I got off the Honda and walked across to a motor cycle police rider to ask him about his Norton rotary, "what's the Norton like?" with a growl he told me to * off. Says it all.
|Ian Johnson 1||29/12/2020 17:41:22|
|334 forum posts|
Finally managed to upload a couple of photos of my MK3 Commando, Then realised the photos were over forty years apart!!! Time flies!
This is how I bought it around 1978-79ish. I put the air horns and dayglo stripe on the fairing, caught many a speeder with that haha!
And forty years later in 2020 having its third attempt at restoration. I'm determined to put a bit more effort into doing it up this time and actually getting it on the road. Need to spend at least a couple of thousand quid on it yet!
|Chris Evans 6||29/12/2020 19:01:52|
1862 forum posts
Big miles on Japanese bikes are not unusual, my Yamaha Diversion owned for 25+ years has 132,000 miles on it. It broke a starter gear at 12,000 miles which meant engine out and split the crankcases. All back together with silicone sealant as I could not afford a gasket set and not touched since. I commuted 200 miles a week plus a 90 mile round trip at the weekend to visit my Mother. I have never had an unreliable bike including all the old British stuff before the Yamaha, all were good.
|Jeff Austin 1||17/01/2021 08:55:14|
|11 forum posts|
I worked at A Honda dealers when the F2 was launched, forks were incredibly flimsy and would bend badly enough for seals to leak under heavy breaking (you could see the 'wiper' marks on rear of fork leg about 2" higher than on front)
Well forty years ish have passed since I told friends (probably while having a coffe and a pasty at Squires) that if you cornered reasonably hard (after changing the tyres for Pirelli phantoms) on my Suzuki GT750J that you could actually feel the forks flexing and even on the odd occasion see the flex and having them all sceptical I now have confirmation that the forks on those early jap bikes were so thin and flimsy and that I wasn't making it up !
Lots of coincidences here, I have had lots of bikes including some of the same ones, I now have a Honda CB550K3 with carb issues although hopefully I have addressed the issues this winter,
I have ridden trials myself on lots of different bikes, rode as a junior and then a roughly forty year gap before riding again, cannot remember who posted it but I have also ridden a fair number of Spen valley trials plus Bradford, Horsforth, West Leeds, Ripon, Wetherby, Richmond etc etc and one or two centre trials and the odd national including the Manx trial several times, still have a trials bike which is a genuine Majesty Yamaha 200 built form a new frame up and will hopefully be out riding again in 2021 once the current Covid situation has improved enough to resume normal activities,
Nice to now there are plenty of bikers here, they are the love of my life plus of course family and good friends.
|927 forum posts|
I now have confirmation that the forks on those early jap bikes were so thin and flimsy
And not just the early ones - I sold a late '90s Honda Transalp mainly because of fork flex.
The riding style I have developed over many years relies on pretty aggresive counter-steering to change direction. On the Transalp - with the combination of wide bars & long travel, skinny forks - I could feel the forks twisting with handlebar input during "spirited" back roads riding.The lack of front end grip from the equally skinny 90/90-21 front tyre was less than confidence inspiring as well.
Nice engine & comfortable, but the early (one of the first in the UK) Deauville that replaced it was a much better handling bike.
|Clive Foster||17/01/2021 12:41:48|
|2586 forum posts|
It always surprised me how tolerant the major motorcycle makers were of front fork flex. Especially on later designs.
Most of the earlier breeds had hefty front mudguards with equally hefty support brackets holding things straight but over the years things got slimmed down to the point of inadequacy. I guess riders of a "certain age", like myself, have distinct memories of the various machined alloy aftermarket fork braces sold in an attempt to alleviate the problems with large Japanese machines through the 1980's and on to the mid 1990's or so. Generally made to looks with no proper engineering input and, predictably, of little effect. It should have been obvious that clamping on the outside of where the top fork seal goes won't do much unless its so tight that the seal distorts and jams.
Design horrors like the Yamaha house style things fitted to the XJ900 et al with loose bottom bushes, tiny top bushes and serious clearance between the legs and slider didn't help. Those seem to have been designed on the assumption that twist was a good thing. I was somewhat surprised that the glass fibre front mudguard used with the Norton Commander fitment was considerably stiffer than the apparently quite solid metal brace used in Yamaha factory applications. Still twisted, but not as much. Tore up the "not sold as a separate part" bottom bushes quite effectively tho'.
The bushless, slider running directly on the leg, forks used by BSA/Triumph on the conical hub machines were probably the ultimate in optimism tho'. The mudguard being flexibly mounted on rubber bushes and thin wire stays specifically so as not to stiffen things in twist. Presumably to ensure things couldn't be assembled out of line causing the sliders to jam. Tolerances get pretty tight when you effectively have a sliding bush approaching two feet long. Substantial though they looked the four bolt end caps holding the spindle were never enough to stop the forks twisting sufficiently under breaking to earn the conical hub brakes a considerable reputation for inadequacy.
I had a one of the very rare Small Heath built five speed T150 Tridents with the full size exhaust port on the centre cylinder and, allegedly, certain other internal engine changes that never made it to the proper Meridian built production ones. Whatever it went "rather well" and definitely needed more stopping power up front. I obtained a double sided four leading shoe drum brake front wheel allegedly off an early TZ750 figuring that with suitably re-lined shoes it would be up to the job. As I needed to fit torque arm retainers I made a decent fork brace using a pair of old style Bonneville tubular top mudguard mounts cut and welded into a single unit picking up on the original mudguard bolts, One in front of the forks and one behind.
Test rides showed a great improvement in brake performance. I found that on a good dry surface it was possible to lock the front brake at about 110 mph. I figured that was good enough and sold the 4 LS unit at 200% profit.
Proving, I guess, that flex is a bad thing.
|927 forum posts|
Design horrors like the Yamaha house style things fitted to the XJ900
I don't recall anything particularly "horrific" about the XJ900 I had ?
I don't seem to have many pictures of it, though it only hung around for less than a year & did one European tour. This picture was taken at the finish point of the Stella Alpina Rally in '94 - I seemed to have had hair then (I'm wearing the BMW Club Tee shirt). Don't know who the Kawaski belonged to, it wasn't with us (Mrs B is behind the camera & seems to have parked her R65LS elsewhere).
Having previously had a BMW K100RT, I felt that the Yamaha was the better bike in pretty well all regards - certainly no handling issues that I recall. It was my last "four", as the penny finally dropped that it wasn't any particular "four" that I didn't get along with, it was the format. I have mainly stuck to twins since & been (largely) the happier for it ! The Yamaha was a pretty bike, though.
|duncan webster||17/01/2021 18:36:00|
3035 forum posts
Way back in the 1980s I went to a talk by a chap (who I think was called Rose) from Manchester University who had been working on motorcycle front fork problems brought about by some police riders having nasty experiences with big BMW flat twins. He advocated using leading link forks, and Gus Kuhn made some racing Beemers which did quite well. All this resulted in the BMW telelever, which is a sort of cross between teles and the old girder forks. Vincents stuck with Girder type until the end.
This is all based on 30+ year old memory, I suspect that a trawl through the IMechE archive might produce more information
|Clive Foster||17/01/2021 19:22:18|
|2586 forum posts|
My Norton Commanders would trash the XJ900 forks in about 50,000 miles. The inevitably loose fit of the split bush at the bottom of the leg letting things work around enough that the dry bearing coating was soon worn through leading to the metal backing wearing away the inside of the leg. I'm told by an inspector meticulous type that he found the slider bores weren't accurate enough as made to take a proper solid bush. He rebored them true and re-worked the end of the legs to take solid bronze bushes. Claimed a great improvement. But, after all that work, he would say that wouldn't he.
I suspect my habit swopping the standard twin piston brake callipers for XJ1200 four pot units didn't help prolong fork life. The extra front weight and non-existent engine braking of the big rotary decisively shifted the barely adequate in emergency performance on the XJ900 to scary inadequate when an "I'm sorry I didn't see you" moment looms. That was in brand new condition too before the seemingly endemic corrosion behind the seals issue rears its ugly head after a year or so. I've cleaned out the corrosion and fixed a fair few siezed and near sized ones over the years for folk. Who seemed more than happy with the results.
Unlike the morons who "fixed" the brakes on my official unofficial kid sisters XJ600 by discarding the rear seals leaving room for the corrosion to build up! Fortunately her brakes locked just at the end of my drive so retrieval was easy. Equally fortunately I had an ex Commander set properly refurbished before being put away with only 1,000 miles on them to swop in. But 10.30 pm on Sunday night is not a good time for major brake system work.
Your Stella Alpina picture reminds me that for my first run abroad included taking a K100RS up to the top and collecting a Tee shirt. Not an ideal venue, or bike, for first time off road.
Edited By Clive Foster on 17/01/2021 19:53:44
|Clive Foster||17/01/2021 19:51:20|
|2586 forum posts|
I suspect your talk would have been given by Dr(?) Gordon Roe. Probably related to this paper published in SAE Transactions of 1984 **LINK**.
As I recall it he subsequently attempted to patent his version of the leading link design claiming that any safe version had to have the same stiffness characteristics of his as derived by Finite Element Analyisis. Something that sound like nonsense. Certainly Tony Foale, who actually built a fair number of leading link systems for solo motorcyles, strongly disagreed. One day I'll track down a copy to verify the maths myself.
The issue with leading links has generally been the difficulty in affordably arranging an effective front brake without a relatively expensive to engineer parallelogram torque reaction system if its not to stand on tiptoe when braking. The pendulum effects of the asymmetric masses offset from the steering axis need to be considered too. Most noticeable with the full swinging arm Earls system, as anyone with experience of BMW or MZ so fitted knows, but less extreme variants suffer too. Allegedly the Ariel Leader /Arrow was given trailing links for this reason. The ent offset being much smaller. For production machines a tele fork was always said to be much cheaper than a well engineered leading link. Neater looking too.
|John Olsen||17/01/2021 20:28:50|
|1139 forum posts|
I think Clive has hit the nail on the head there, the tele fork is cheaper to make than alternatives and looks OK, while the alternatives are more expensive to make.
Back in the day, a friend had a Yamaha TX500, and turned up at my place complaining that the steering was pulling to one side when braking at high speeds. (By which he meant at around the ton.) Sounded a bit weird to me, so we started investigating. Turned out the brake had a piston on each side of the disk, and one was completely rusted solid in the caliper. So when he heaved on the brake, the working one would push on the disk, then the forks would distort until it had pushed the disk over against the other pad. No wonder it felt a bit funny!
|Chris Evans 6||17/01/2021 20:31:16|
1862 forum posts
I ran an R50S BMW with the Earls style forks. Smooth and reliable bike but I just did not gel with it. I went back to my preferred Norton's and bought an SS650, I still judge handling by the Norton standard.
|Mike Poole||17/01/2021 21:08:26|
2891 forum posts
The telescopic fork is still the fork of choice on most bikes including the upside down version. None of the alternatives have successfully displaced it other than on a few niche models. Much work has been done to help minimise the shortcomings of the telescopic fork like anti dive and complex spring rates and damping. Hub centre steering and the various link systems all suffer weight and wear problems so the humble tele has more or less prevailed. Twin discs must help to balance out the twist effect of a single sided setup. If you can brake hard enough to get the back wheel in the air without falling off then it’s probably working quite well.
|Bill Pudney||17/01/2021 22:45:45|
|500 forum posts|
I did a college final project in 1991 which ended up being called "Motorcycle Suspension". It required determining what loads are applicable to motorcycles on the road, it ended up demonstrating that braking loads are the major loads in normal use. It also demonstrated that compression of the front forks under braking reduces the stability of a motorcycle at exactly the time that maximum stability is required. To determine what order of magnitude these braking loads were a series of braking tests were performed from 30 up tp 100 kph. These tests established that...1/ The "old Wives tale" about the front brake doing 75% of the braking is about right. 2/ That extreme braking was indeed a tense affair because of reduced stability 3/ That under the right conditions "stoppies" (where the rear wheel comes off the road surface) are feasible on a single disc road bike.
I had felt for some twenty years prior that telescopic forks were somewhat limiting, and ended up proposing a system similar to the Hossack/Fior layout which ultimately was more or less copied by BMW with their Telelever .
The snag seems to be that motorcyclists are very fashion conscious and want something that looks like what the motogp riders use, and motogp manufacturers are hooked into suspension providers, who are mainly interested in selling stuff.
|duncan webster||18/01/2021 00:30:02|
3035 forum posts
Clive's right, it was Roe. I like the look of the Hossack setup referred to by Bill, but as SWMBO won't let me have a bike anymore I'll just have to dream
|Bill Pudney||18/01/2021 01:14:53|
|500 forum posts|
Like Duncan I don't have a bike anymore. Sadly after a lifetime of motor bicycling I was on my way to work one day, when I realised that I was just going through the motions and wasn't enjoying it any more....no more fun. It was like getting a bucketful of ice cold water over your head. I still fancy a 650SS, or a G80CS engine in a featherbed, or a Silk, but realistically those days are gone. Just, mainly happy memories!
|Peter Jones 20||18/01/2021 03:06:15|
54 forum posts
Interesting how far this has gone in only a few days..
I was working in Honda/Yamaha/Triumph/MZ/SILK dealers then moved across the street to Suzuki/BMW/Vespa (?) dealers. (later dropped BMW, didn't want to be a 'boutique' dealer before it was even invented) Did a bit of work on the K series, 750 was quite a nice bike and K100 would do crazy high miles (one customer did about 245,000 )
Switched back and forth every few years as general managers believed they didn't need me to run things after I got workshops running properly.
I have 'first hand' experience of majority of the bikes mentioned (nearest Kawasaki dealer was 20+ miles away so did quite a few of those as well.)
Suzuki GT750, wasn't just fork 'problem' the swing arm was incredibly flexible, it was just a bad design and would wallow around even when in good condition (probably the real reason it was called the water buffalo?)
Always found CB750 too wide and heavy the extra torque was Ok but dragging bits around in corners limited it's use for me, my 591cc CB550F1 was much better for all around use
Also had 550's F2 and K3 ( 550FourK ) at the same time (still have original 1977 F1 don't remember what happened to the others, my brother had the FourK for several years.
Really don't remember much about FJ900, 'we' sold a couple but the earlier XS 1100 and later FJ1100 were much 'nicer' bikes for hooligans (anyone remember the 'Martini Yamaha XS1100?) that was a lot of fun as you could drift it very easily in second gear and have it completely sideways at 50~60 mph.
Sold a lot ofYamaha 600 Diversion but GSX-R was mainstay at dealers
Early-mid 80's after the GSX-R 750 was launched was when things got worse rather than better. Apart from cost cutting, the 'weight savings' using less material became a selling point.
The 'Sport Tourer GSX-F (later Katana's) were a much better handling bike with the perimiter frame but were way too heavy (particularly the GSX600F) 750 top end was direct swap as bore spacing and crank main bearings were same on all model SACS motors (even 1100 and later 1200 Bandit)
(plus, I have a 750/600 motor 'in the shed)
Little bit of modification though and even 600 was Ok to about 135., 750 was good for around 155 (it was most powerful 750 on the market at the time - below 10,000 rpm) All the sport 750's were more powerful but had to be revved harder
That's all for now, been breaking stuff in workshop although welded parts are not quite as tough as if they were made from chill cast steel then 'repaired' by being built up with MIG (no after treatment or normalising) Surprised how hard even A36 gets though.
|colin wilkinson||18/01/2021 05:57:54|
|64 forum posts|
Mike, I agree most models have settled on telescopic forks but must take issue about the niche models bit. The most manufactured bike in the world, over 100 million, the humble Honda C90 and its derivatives had leading link forks.🙂 . My three Greeves race bikes, like most Greeves have leading link forks. Surprising how many have survived considering they closed in the early70s, although road bike production ceased earlier.
|Graham Stoppani||18/01/2021 06:33:47|
92 forum posts
as the old saying goes, "it's not what you know, it's who you know". An old friend of mine who's an ex-Cosworth employee was given the Triumph Hossack prototype as a gift by Keith Duckworth's widow.
He was allowed to pick any vehicle he wanted from a selection stored in a hanger. He wasn't allowed his first choice, a helicopter, and was told not to be silly!
|Mike Poole||18/01/2021 09:07:12|
2891 forum posts
It’s funny the thought went through my mind about the Honda as I wrote and nearly mentioned it. On its own it probably proves leading link is the most popular system in the world.
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