The engine’s completely unique. No-one else makes an 849cc DOHC water-cooled vertical twin with five valves per cylinder, and a complex balancer system to absorb the raw vibration resultant from the 360 degree crankshaft throw. Halfway through its design someone had decided to cant it forward - well, that’s the way it looks to me - and the end result’s less than pleasing despite the butchness of the Deltabox frame. Amateur hour.
Such thoughts extend to the half fairing and the odd looking panels beneath it. These days, radiators can be made very small, certainly small enough to fit between the top of the engine and bottom of the frame. Once that’s done the whole ugly half fairing could be chucked, saving loads of mass and improving the appearance by a factor of ten.
The next area of complaint’s the exhaust system. A massive collector box, worthy of a V12 Jaguar, hides under the engine, perfectly sighted to pick up the worst of the road debris and rust through after the first English winter. The Yam cries out for a two into one. Dumping the exhaust and fairing would save fifty pounds, which would take the stock dry mass of 440lbs under the magic 400lbs mark.
God knows the 22000 mile example I borrowed for this treatise needed some help. I just couldn't believe that there were 75 horses trying to get out. The bike reminded me of the old Kawasaki 750 twin, an engine that spent most of its time overcoming the inertia of its balance shafts. In reality, the bike was moving fast, hitting the ton then 120mph just by using the throttle in fifth (top) gear.
The gearbox was interesting. Oh, was it interesting. It was as slack as the box in a sixties Honda and grumbled like a seventies BMW boxer. The total unpredictability of its action, the total lack of feel and feedback, and the destructive noises, meant the best bet was to hit fifth as soon as possible and slip the clutch when the going got slow.
That wasn’t the end of the matter. The transmission, even when one was lucky enough to engage gear, appeared to have a large amount of rubber winding up and then unravelling. The bike surged forward some moments after the throttle was hit, would occasionally speed off up the road all of its own accord, taking a few more moments to react to a dead throttle.
This weirdness went a long way to camouflaging the extravagant mix of torque and power, making the TDM seem much less than the sum of its parts. At least the riding position was initially reassuring. None of that race replica nonsense with wasted wrists, knackered neck and hunch-back spine. It was the kind of riding position that encouraged the killer instinct in town and the bike would blow away just about everything if left in second and used hard on the throttle.
That was OK, then, apart from doing awkward turns when the beast went top heavy and threatened to tumble down to base earth - it felt so heavy at times that I expected it to crash straight through mere tarmac. The bars and the mirrors were rather wide, needing some ducking and diving to avoid collision with other traffic. When used in desperation, the twin discs would shudder the whole front end but allowed me to escape death several times.
Skidding to a halt, letting off the brakes and then charging forward, pulling hard on the bars as I snaked around the obstacle and finally giving the bike enough throttle to get up on the back wheel, was fucking hard work! The front end, even at low speed, lacked accuracy. Quite seriously, a sixties Norton 650SS had much superior steering accuracy at all speeds, was easier to flick through bends but maintained a useful stability.
What it lacked, of course, was the comfort of long travel suspension. In the TDM’s case this was something of a joke. True, there was both adjustment for preload and rebound damping at both ends but some curious design quirk made it impossible to remove the first three inches of mush from the front forks. The TDM had an almost BMW-like need to waggle around on its suspension when what was really needed was the firmness of the units fitted to the FZR1000.
It's no good having suspension that can absorb foot deep craters, which the Yam couldn't manage anyway, if the first time you hit 80mph the whole plot goes into a weave redolent of some seventies behemoth. Whilst the undoubted strength of the Deltabox frame, aided by the forward weight bias of the engine, stopped such weaves going way out of line I never found the bike reassuring to ride long and hard, unlike, say, an FZR1000 or CBR600, or even an old Norton twin (though doubtless engine worries would intrude).
Even more unforgivable, with its lack of race replica nonsense, was that long distance work became very uncomfortable. I mean there’s no excuse for this, even if you know sod all about motorcycle ergonomics all you have to do is take a tape measure to a BMW! There was a fundamental mismatch between handlebar and footrest position, the key being to leave forearms and thighs parallel. With a correct riding position saddle shape takes on a secondary consideration, but when it’s wrong any minor imperfections in seat design become much magnified as too much mass is being fed down the rider’s spine into his backside. A few inches here and there in bar and peg position can literally lead to agony.
Thus after 200 miles on the Yam I felt like I'd been raped up the wotsit whilst some kind soul reshaped my spine with a large hammer. I sort of staggered off bent double, mumbling incoherently, frightening the shit out of a couple of cagers who were parked up in the lay-by enjoying afternoon tea on a picnic table. Once I'd straightened up and explained the horrors of modern Jap motorcycles I was invited to join them. Very quaint, but there you go!
From certain angles the TDM looks quite sexy but most of the time it’s as likely to inspire children to throw bricks as those silly little men who wear fluorescent helmets when riding bicycles at about 5mph. I think Happy Henry should be let loose on them with his tyre iron. Where was I? Yep, it’s easy to see that the TDM has loads of potential in there trying to get out. A few detail alterations, a bit more effort might free the beast. Or not!
My own idea is that any vertical twin with the pistons moving up and down together, at least over 250cc, is a pile of crap and destined to failure. This was the design concept that ruined the British motorcycle industry. Light weight, good torque, punchy power, cheap to manufacture, nice exhaust noise... an almost endless list why it should work well or even brilliantly. The fundamental flaw’s the raw primary vibes, just like having two bloody big singles side by side.
It just doesn't work, especially at 850cc. The TDM has some nasty vibes when pushed into red but there’s buzzing at most revs and lots of churning from the engine. Get into one of the smoother zones and it's not too bad. The only way to go with big twins is having the pistons going up and down alternatively. Perfect primary vibes but some torque reaction that can be dealt with by a single balancer. I've even read that 76 degree throw cranks are better, though the theory behind that lost me completely.
Once you compensate for the TDM's flaws it can be a fun bike to ride. Certainly, its owner laughed off all my moans and roared off up the street on one wheel. If you're considering one, test ride first and make up your own mind. To me, it’s one seriously flawed motorcycle. The engine design's basically wrong, the gearbox’s a waste of time, the riding position is out of the ark and the fun factor’s on a par with having root canal dental work... I've just found out the bike was crashed and clocked. Oh well!
Dick Lewis