Dirt
The
The lowdown on buying,selling and improving your classic
THIS MONTH: 90 Expert on: yamaha tz250/350
Richard Tracy of Rave Motorsport gives you the benefit of his knowledge on Yamaha’s over-the-counter racers
96
sorted:
mz trophy sport
He didn’t think much of them but Pete Ball has now changed his mind. Here’s why
100 buying: Velocette venom
Velocette’s sports single and its successors. Authoritative advice on which one to get
106 a-z directory: Find a specialist
Specialists are the backbone of classic bike fettling. Find one fast in this listing
112 for sale: your next bike
What do you fancy riding this summer? If you’re buying, remember that subscribers have a head start (see page 22 to find out how to be one)
90 april 2010 Classic Bike
Ex-Roberts TZ250 (middle) campaigned in 1974/5 season
Richard Tracy of Rave Motorsport tightening down the clutch springs on a TZ350A with Harris monoshock conversion
expert on...
Yamaha tz250 and 350
Richard Tracy is a leading light in the TZ Owners’ Club. The former drive-line engineer has also set up Rave Motorsport, specialising in parts, rebuilds and restorations for these definitive post-classic racers Interview and photography: Gerard Kane Yamaha’s twin cylinder TZs are probably the finest, and most competitive, over-thecounter racers to be built in the golden era of two-stroke GPs. The ‘classic’ era for TZ twins ends with the 1980 G models. Between 1973, when the TZ250 and 350 A models appeared, and 1980, a privateer could buy a bike and realistically hope to run with all but the top factory teams in a GP. The beauty of (pre-H model) TZs is that everything you need to keep them running is readily available – often through Yamaha themselves. Before you start trawling eBay, check that the part you want isn’t still listed by Yamaha – many, including 350 pistons for example, are. They cost £85 plus £13 for a ring. Pistons for 250s are no longer listed at the moment – which is why you’ll see more 350s being ridden – but there’s a good chance they will be available again. There are lots of TZ fans out there who keep coming up with new products.
Measuring the thickness of a clutch plate
Maintaining a TZ in good order is not really any more difficult than keeping an RD up to scratch. But everything needs doing more often on a TZ. The key to keeping on top of it is to stick to a strict maintenance schedule. Before the TZ range, Yamaha offered the 250cc TD1, TD2 and TD3 and the 350cc TR2 and TR3. Essentially, they’re just aircooled TZs. But all the true TZs are watercooled. The TZ timeline runs like this: 1973-75: TZ250A and TZ350A. There is a B model, but it is exactly the same as the A. All A and B models have double-sided tls front drum brakes and twinshock rear suspension. 1976: TZ250C and TZ350C. The first monoshock TZs and the first to have disc front brakes. 1977: TZ250D and TZ350D. Similar to the C model, but with silencers as standard and modified cylinder heads and porting. 1978: TZ250E and TZ350E. Much the same
as the D, but with removable alloy front engine plates. 1979: TZ250F and TZ350F. New ‘Lo-boy’ frame and revised forks. Box-section alloy swingarm, alloy brake calipers, magnesium clutch cover, adjustable forks and power-jet carburettors. 1980: TZ250G and TZ350G. The 250 is the same as the previous year’s model apart from larger inlet ports. This is the year the 350 class was dropped from GPs. It’s also the last year of eligibility for the post-classic racing class. There are a few 1981 H-model TZ350s around, but they are identical to the G. The 1981 TZ250H is an entirely different beast with a totally new power-valve engine. To keep a TZ at its best you need to keep a ‘tight’ engine. Check the crankcase faces regularly by using engineers’ blue on a surface plate or sheet of plate glass to identify any highspots. If there are any, you can have the cases machined or flat them on plate glass using grinding paste. Piston to barrel clearance should be no more than 1.5 thou. Keep a close eye on ring and bore wear – inspect after every race if you are competing. When the main bearings go, they can damage the crankcases. It’s possible to convert RD cases to suit TZs, though. TZ cases have four locating grooves for the main bearings and RD cases only have one. To convert RD cases, you have to machine extra main bearing grooves and bore the front engine mounts to accept the TZ rubber bushes. The transfer ports can be opened up to replicate TZ specification. You can use aircooled RD crankcases from the A-F model RD250s and 400s. The TZ’s water pump is outboard of the crankcases and can use the RD oil pump drive – though it does need the genuine TZ drive gear. Crank rebuilds are easy enough to get done. The crank seals are the same as on RDs, as
Classic Bike april 2010 91
Dirt
The
expert on... Yamaha TZ250/350 seasons out of them but, if you’re racing, reckon on changing pistons and rings every couple of meetings. With cranks and rods, two per season is about right for racing, but parading will extend that considerably – maybe to a couple of seasons. Check them regularly. Any movement on the crank and out it comes.
Dean Want (left), runs Part Restoration Services and collaborates on some TZ projects with Richard
The alloy brake calipers on G models are prone to expanding and locking up. Use the earlier cast-iron type or a Lockheed/Brembo caliper with a conversion plate from Spondon Engineering (01332 662157). Steel brake hoses are a good idea too – you can get them in black now, to look more like the originals. Spondon also do good pattern discs if original looks are not a concern. Exhaust pipes are critical on TZs. It’s not difficult to find used originals for the C-G models, but Swarbrick (01995 640291) and Gibson (01708 372122) do good systems too. CONTACT: 01252 702610 www.raveengineering.com
tools of my trade Richard tracy Installing Kevlar clutch plates (made by Rave). Left: detonation damage on a TZ350 head
are the inner mains. But TZ outer mains are needle rollers rather than the roller type used on the RD. A crank rebuild will cost about £300 and new rod kits are still available. TZ barrels were chromed originally, but Nikasil is the way to go. There is a guy in France who manufactures replica G barrels (and new cranks). You have to use different rings if you’re running a Nikasil bore. Dennis Trollope Racing can supply suitable rings. They are a good source of TZ parts. TZ thermostats can seize due to internal corrosion, then the engine overheats. They’re not hard to find though, they’re the same as RD/LC and Banshee quad thermostats. But most people I know run without a thermostat. Second and third gear tend to get a bit of hammer on TZs, but Greenham Racing (01234 356900) in Bedfordshire can supply all the gears and shafts. All European market TZ250s and 350s were fitted with Femsa electronic ignition, but the rest of the world got Hitachi units. The Hitachi is the one to have. It should be set at 2mm before TDC. Electrex World (01491 682369) do a good modern replacement. Up until the G model, TZ rear suspension only had preload and compression damping adjustment. And twinshock TZs only have
92 april 2010 Classic Bike
preload adjustment. Maxton (01928 740531) do good modern shocks for all TZs. Steel clutch plates are still available through Yamaha, but they are pressed and have very sharp edges that damage the clutch basket. And the standard friction plates are alloy-backed and can shatter under load. One solution is to use a bronze-backed plate (if you can find a good used one), but we manufacture new Kevlar plates that avoid the problem. We’re also working on betterfinished steel clutch plates. The steel plates have to be absolutely flat. Check them regularly on a surface plate or sheet of plate glass. Lay them flat and try to insert the thinnest feeler gauge you have under them. If you can slide it in, bin the plate. The rear engine mountings can break. Most riders take the top engine mounting plate off – if it fails, it can take out a chunk of the crankcase round the engine mount. The rear engine mount on the frame can crack too. Boring the frame mounting to take an isolastic-type bush usually solves the problem. Use good quality gearbox oil and twostroke oil. We fix the fuel at 33:1 and use a 50/50 mix of Avgas and Super Unleaded. Pistons and rings last pretty well – particularly in a well-plated barrel. For parading, it’s possible to get a couple of
Yamaha clutch holder
TZ clutches need regular maintenance and a good clutch holder is essential – especially if you’re working on your own. The clutch centre is torqued up to 40lb-ft, so you need something to hold it securely. Price: about £20. Contact: Dennis Trollope Racing. 01179 570821 (also has an eBay shop).
Dial gauge
If you haven’t got the ignition timing right on a TZ, forget it. This is essential kit. Mine is a genuine Yamaha tool. You can order one through any Yamaha dealer. Price: I paid about £50 three years ago. CMSNL (Holland) list a genuine Yamaha gauge at €382, but an engineering supplier should be able to sort you out for a fraction of that. Contact: Good engineering suppliers.
Metrinch ¼in-drive socket set
Handles metric and Imperial fasteners. The 10mm socket doubles as a 3/8in. The ¼in drive will fit into tight spaces. It’s small enough to throw in my race toolbox. Price: £86.19 for a 48-piece, ¼in drive kit. Contact: www.directsupplyukltd.co.uk