Click on these links for a "hot lap" of the TZ350 and 250 Website:
Picture: No, not a 350 but the TZ750 as raced by Kurt Lentz in the late seventies in the USA.
There can be few bikes which have enjoyed the sort of giant-killing reputation earned by the TZ350. From its undisputed dominance in the '70s up to the present day, its balance of power, handling and light weight has proved capable of embarrassing all sorts of megabuck machinery - even at national level.
So it should come as no surprise that many established riders are hanging on to their 'old' TZs and more than a few up-and-comings are realising that the 350 class offers close, competitive racing with the chance to shine in open class events. And for less than the price of a Ministock slug.
The difficulty for a new entrant to the class looking for a bargain racer is likely to be sorting the wheat from the plain bloody awful. None of these machines is basically any younger than ten years old, and a lot can happen in that time. Anything which has survived this long will have been rebuilt 50 to 100 times. Few (if any!) of the bits in the engine will be original, and it'll be little short of a miracle if the cycle parts haven't been subject to some form of butchery over the years. It can be a daunting prospect trying to find a bike that won't cost an arm and both legs to sort out. And do they really cost the earth to run? How do you make them go best? Unless you're lucky enough to have the help of an obliging TZ owner it wouldn't be hard to end up buying a dog and spending a lot of time and money trying to make it reliable and competitive.
Enter one obliging TZ owner. Actually, strictly speaking I'm a recently-ex TZ owner, but one thing you soon find is that fellow TZ boys either avoid telling you their 'secrets' or quite simply have the same knowledge gaps as yourself. When I bought my TZ I ended up with something that broke frames like it was going out of fashion and went like 347cc of pure snot. Well, nobody told me what to look for. What I needed then, and a buyer needs now, is an expert to guide the purchase and give hints and tips towards the best preparation and use of the bike. Well, tough. You've got me. I'm not an expert and I don't lay claim to knowing all the tricks of the trade. But I am someone who's gone through all the nausea of buying, preparing and using a TZ350 for four years, and in that time I've tried to sort out the truth from the old wives tales.
The earliest TZ350 you're likely to find in use is the E model. This is identifiable principally by the horizontal frame top tubes. Compared to the later models, the chassis and its handling are a touch heavy and the front wheel can tend to wash out if you're a bit enthusiastic in bends. The motor is characterised by stubby pipes, six-port barrels, upright plugs and wicked power delivery. It's unlikely that you'll find a full E engine in a bike nowadays as the G is easier to ride and the conversion is simple – all models of the TZ350 share a common bottom end (early A/B primary drives and clutch outer different – KW), y'see. This kind of E/G hybrid could be attractive to someone on a really tight budget but don't forget that it's a competitive class and people with the latest model will have an edge. The rarest TZ model is the 350F. Not because they made few, but rather because the frame, which was the first of the production 'lowboy' (sloping top tubes) types, was made of such crappy material that the headstocks used to detach themselves with great regularity and little warning. In its introductory year, the type was nearly banned from the TT on safety grounds. Most Fs have by now been re-framed or consigned to the spares bin.
The most common type is the TZ350G. It has a ‘lowboy' frame, 38mm power-jet Mikuni carbs, eight-port cylinders, sloping plugs and aluminium swinging arm. You may hear of H models being referred to, but these are actually Gs which were built from spare parts in Japan after the development on the range was stopped.
Most buyers opt for the 350G as it's generally accepted to be the best in the range. It's also worth mentioning the fairly small number of Formula 2 machines. These use tweaked LC engines of various specs in TZ chassis. The best of these are as quick as TZs, but by no means all of them are. The reed-valve induction tends to give them the advantage of being very quick starters.
Finally, a few 350s are starting to appear with trick rising-rate aluminium frames, the most popular being from Spondon. Users sing its praises but it's designed for the TZ250 and access to the larger 350 engine is very limited.
Before you go diving into the small ads, take the trouble to go to a few club meetings. The riders are always approachable and you can learn a lot just by looking over the TZs and talking to the owners. You may well find some up for sale - and what better opportunity to see how they go? If you don't see one you like at the races, though, the MCN small ads are probably the best place to look. After you've read the columns for a couple of months you'll get to know what features command what prices. There are no hard guidelines, but for an E/G hybrid you could pay as little as $A3,000 , a tidy G maybe about $A4000, but double that for the latest ally-framed one. In addition to the basic price, don't forget that you'll need running spares and it's cheaper to buy these with the bike than separately.
You'll need sprockets and jets at an absolute minimum, wheels with wets are well worth having and anything else will probably come in handy at some time. A spare engine is a definite asset if you do two-day meetings or The Island. All this doesn't come free, of course. Basic spoked wheels should cost about $A400 the pair and an engine anything from $A500 to $A1,000. The prices I've given assume that the bike will need a full engine rebuild (as most do!). A bike with a freshly rebuilt engine will cost more, but not if it's been used since the rebuild, so find out what 'ready to race' means.
There are some common departures from the factory spec. The crossover exhausts are usually replaced by Swarbrick or Tony Green pipes which give worthwhile improvements in top- and mid-range power; the Yam front disc tends to fade and other types are regularly fitted; the standard wheels are pretty good but lighter types can be had at a price; Hitachi ignition is the best for power as you can time cylinders individually, but it's pricey to replace if it breaks; and some people prefer to remove the thermostat on the grounds that it's one more thing that could go wrong.
Once you know what you can afford, arrange to go look at a few. Ideally you'd like to get a test ride, but don't be surprised if the owner declines the request. You must see it running, though. It should sound crisp, and the only rattles should come from the clutch. When warm, it should start within a few steps. While you're waiting for the engine to cool, take off the tank and fairing for a closer look. Cosmetic crash damage doesn't matter, bent frames, forks or yokes do. And watch out for frame cracking - the lowboy frames were all a bit fragile, despite the fitting of headstock conversions on most. Heavily notched clutch centres or baskets make slip or plate breakage likely and are expensive to replace.
Drain the water and take off the head. Is there any detonation? Nasty gouges or cracks in the cylinders? Wear ridges near the top are normal, but if it's worn through the plating you know to deduct the price of a recoating job (about $A600).
When you find the Right One the real work starts. Your new purchase now needs an engine rebuild. The first time may be better left to a specialist so you know you've got a good engine. A new crank, two sets of pistons and rings plus all the odds and sods will set you back to the order of $A800. Sure, that's a lot of drinking vouchers but it leaves you set up for the whole season with a good engine. This is important. If you try to cut corners you will end up with an engine that's uncompetitive, unreliable and likely to land you on your ear when you least need it - look on it as an investment.
Picture: Dutch TZ enthusiast Ludy Beumer on his immaculate TZ350F in Holland 2003. Ludy is the proud owner of a number of restored Yamahas and regularly parades his race bikes in and around The Netherlands.
If you prefer to do it yourself you'll find that the TZ engine is a very well thought-out unit - easy to work on, and the only special kit you're likely to need is the clutch locking tool. No Haynes manuals exist, so much of the spannering and checking comes down to common sense. Look carefully for cracks, damaged bearings or gears, wear on mating faces, spinning main bearings, loose clutch rivets, worn seals, chipped 0-rings or flaking cylinder plating. Crankshafts can be rebuilt with new rod kits and mains but this is definitely a specialist job as they must be trued exactly. Even expert attention doesn't guarantee perfection - after three trouble-free years I recently broke two (rebuilt) cranks within a month! Cylinders can be re-plated if worn through the plating, although for best performance this should ideally be done every year. Standard Yam barrels are hard chromed and this works well. Nikasil, which is nickel plate with embedded silicon particles, is successfully used by quite a few people although it is necessary to use chrome rings and oilier mixtures in order to avoid rapid piston and ring wear (rapid wear not seen with chrome rings and modern synthetic oils- KW). (Hope that's OK, Steve!) Chamfer the port edges on newly-replated cylinders to stop the rings snagging.
Pistons are available in sizes 96-98 and must be sized to your bores individually. Optimal skirt/wall clearance is 1.5 thou, but if in doubt take it to the dealer to have it sized. Piston clearance is absolutely critical in these engines. Use E pistons and gudgeon pins in all models, sawing off the two small 'ears' at the base of the skirt and snipping off most of the tang on the circlips. With a Swiss file, gently chamfer the abutting ends of the rings to stop them sticking in their grooves later. Any detonation problems can be tackled by a specialist by fitting bronze squish bands in the head and re-machining to a more suitable compression ratio.
Reassembly, as they say in the best manuals, is in the reverse order to strip. Points to note are to use a little Loctite to help stop the mains from spinning, adhere strictly to recommended torques, and torque the head in diagonal sequence. Put 1500cc of oil in the gearbox; any more than that just comes back out of the breather when you run. Set ignition timing to 1.6mm BTDC. Fit bronze clutch plates to the two inboard positions - these are virtually unbreakable, unlike the standard ones which tend to fly apart when the clutch gets a bit old and the fit becomes sloppy.
You're probably wondering where all the porting tips are. The secret is, there aren't any. Smarter people than me have tried to improve on the standard engine and failed. It is possible to extract more power from a TZ350 but the resulting animal is too peaky to ride and is grossly unreliable. The people who are winning today are doing it on well-prepared but essentially standard engines
The crank should be replaced every 600 miles - that may not sound like much but for most people it's a whole season's riding. Pistons in chrome bores last 300 miles barring disasters, and small end pins and bearings can be used twice if they're not damaged. Rings lose their seal and springiness quite quickly and should be changed every 150 miles. There's only one ring per piston and they're quite cheap, so don't panic. Although some folk do extend those mileages it's a bad idea as you lose a lot of power and starting ability with worn pistons or rings, and of course bottom end breakages can be very expensive.
Carburettors (which are prone to flood if the petrol is left on for long) are best fitted with Q4 needle jets and 6DH7 needles (second notch), and 75 pilot jets. Different bikes react to main and power jets differently so you'll have to work that out yourself. As a fairly safe starting point, try 300/80 on a cool day and ask around the paddock. Plugs to use normally are NGK B9EV, Champion N84 or equivalent. On a really balls-out circuit like The Island you'll need to go to B10EV/N82 and jet for caution. There are as many opinions about oils as a dog has fleas. I know people who go well on R30 at 16:1 and others (including myself) who swear by Pro2 at 35:1, so make up your own mind.
Out on the track discover the secret of the TZ's success. It is a beautifully balanced package. Power is between 8000 and ll,000 rpm, which is all you need with the six-speed gearbox. The only time you'll ever need the steering damper is when the front starts getting light. Spring preload adjustment is available front and rear, and the rear shock also has a damping adjuster. Best water temperature during running is 60-70° but don't worry unless it goes over 90. In the rain or without a thermostat, the temperature can drop off the gauge - again, not usually a cause for panic. Quickest starts are achieved with a coolish engine - 40-50° - and once fired up the best getaway method is to give it full wellie, controlling the revs with the clutch. I have found a cricket box to be a useful investment in this respect. Right. End of lecture. Go out and get one before you come to your senses.
Written by Des Senior sometime in the late Eighties, early Nineties.
Additional comments by Kerry Wilton marked "KW".
Price estimations quoted are very approximate and in Aussie dollars, these replace the original British currency figures in the original story which are now well and truly out-dated !!
Thanks to Kerry Wilton for supplying the article.
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03/23/08 06:37 AM +1000
This website © Greg Bennett 2002.