Buying a Big - What to look for part 1

What to look for when buying, maintenance tips, etc.

Buying a Big - What to look for part 1

Postby BigBob » Fri Apr 01, 2011 2:35 pm

A brief history

The Dr Big is the mass production model of the DR-Z750, ridden by Gaston Rahier and others at the Paris-Dakar rally back in 1987. It competed up till 1992 without a great deal of success, though it proved to be very reliable. 60 bhp carrying 60 litres of fuel made it a very heavy beast to ride through sand.
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First introduced to the public back in 1988, with a displacement of 727cc (105 x 84), it produced a claimed 52 bhp, though about 45 bhp at the back wheel is more realistic. Single disc up front and drum rear brake. Available in white/blue or white/orange.
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1989 saw the Big get a rear disc instead of the drum and also revised switchgear.
Colours were now blue or red
1988_DR750-Big_blue_450.jpg
1988_DR750-Big_red_250.jpg


The DR800 replaced the DR750 in 1990. The engine got six mm longer stroke (the bore was unchanged at 105 mm), and the cylinder displacement increased from 727 cc to 779 cc. Otherwise it was still just about the same bike. Again available in blue or red.
1990_DR800_blue_250.jpg



The Dr Big saw a major update in 1991. The 29l twin tanks was downsized by five litres, now being a 24 litre single tank. The frame and bodywork was completely redesigned, as were the electrics. The exhaust now became a twin silencer affair. All this pushed up the weight from 179kg on the 750 to around 200kg on the 800. The 800 was sold in the UK till 1993, but in Germany till around 1997, though the German models are only 50 bhp to comply with insurance regs. The UK models are 53 bhp.
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Around 25,000 Bigs were produced altogether, most of them going to Germany, Italy, France and the UK, though none went to the USA. Many of the Bigs now running in the UK are Italian imports, with the only difference being km clocks and r/h headlight.

What to look for……..

The Big has an absolutely massive roller bearing crank that wouldn`t disgrace a tractor, and never ever gives any trouble, providing the oil supply is there. Due to it`s low revving nature and monster sized piston, the barrel and rings never seem to wear out, and there are many examples over 100k that have never been touched and still use minimal amounts of oil. The average Big will use about 0.5l per 3000 miles on average, depending on how hard it`s used. The head and cams usually don`t show signs of wear, though they are usually the first things to go if the oil level gets too low. Most Bigs clatter a lot, it`s just one of the things they do. If it sounds like a bag of nails, don`t be put off, as it will probably sound just the same in 60k miles from now. Mechanically, they are extremely robust if looked after. However, the same can`t always be said for the starter gear. Due to the peculiar nature of a monster single, if the ignition is turned off when the piston is coming up to tdc, it will sometimes recoil against the starter clutch, often resulting in a loud bang. The effect of this continuously happening is often to destroy the starter clutch and/or intermediate gears. The answer is to use the decompression lever to kill the engine first before switching off the ignition. The 1991 on 800 is less affected as it uses a torque limiter to prevent it happening.

The carbs are essentially the same as used on the early Gixxers, GSXF`s, Bandits and GS500`s and are pretty reliable. It`s not unknown for the plastic slides to wear eventually at high mileage which can make it run fluffy and the o rings in the needle jet can perish which makes it flood the engine. To connect the carbs, fuel pump and the two tanks together is a lot of plumbing. Unfortunately, Suzuki tend to use fuel lines that are different diameters either end, which makes it difficult to replace them with cheaper aftermarket items. It`s not unknown for them to split when they get old and brittle, though I only know of one bike that caught fire.

Original exhausts will almost certainly have rotted through by now as they were painted mild steel. They were pretty ugly by any standards but they ran best with the original can. Not a huge choice of silencers available, but Marving, Sebring, GPR and BSM are still being produced. Unfortunately Devil have stopped making them as they were probably the best. Holeshot still make a stainless downpipe. If the can is a home made affair, check that the junction with the downpipe is a good one. It sits behind the side panel, so it could hide some hideous attempt at welding.

Forks rarely leak or give trouble, as does the front wheel. The front brake can be very poor if neglected; a combination of 80`s design and seized brake pins due to winter salt can leave it feeling very wooden and desperately ineffective. The remedy is pretty easy. New seals and genuine pads usually sort it out. Adding a Bandit master cylinder, which can be bought dirt cheap on Ebay, gives it a lot more bite.

Drive chains take an absolute hammering on the Big due to the great gobs of torque yanking at the chain continuously. In fact, it`s probably the worst of all models. It`s also only a 520 chain. A dry, rusty chain with a tight spot will definitely snap some time soon, so it`s worth checking it carefully, as it will probably take out the casing when it goes. There is nowhere in the manual that says you can lube a chain too often, only the opposite. The 1988 drum brake model can be uprated to a 530 chain, which is highly recommended, as it is much smoother and will last much longer. The rear disc model 750/800 can be uprated to a 525 chain which is also recommended.

Rear suspension lasts a surprisingly long time, considering Suzuki used pretty poor quality shocks during the 80`s and 90`s, the Bandit being a case in point, as it was notorious for losing its damping completely in a short space of time. Most Bigs still have the original shock and are none the worse for it. Not a lot of choice of aftermarket shocks really. Hagon or Wilbers, both of which cost £££`s.

Discs last pretty well considering, and there`s a big range of pads available, though not in the HH range apart from Goldfren, though I was seriously unimpressed and binned them after a few hundred miles. Suzuki originals are by far the best, though will be a couple of quid more. How much is your life worth?

Most of the big brands make pretty good tyres for the Big, though they can range from road biased to very chunky knobblies. Favourites are Metzeler Tourance, Bridgestone Trailwings, Conti TKC, Pirelli Scorpions, Michelin Sirac etc, all of which are good. There are plenty of cheap and nasty tyres out there that come from China etc, all of which should be binned and replaced with something of appropriate quality. Again, how much is your life worth? Do not be tempted to put BT45 or other road based tyres on as they will screw up the handling and you will not feel safe. Tyre life is pretty good and you can expect about 10k from a set of tyres, though the handling will go as they square off. The Big is absolutely brilliant in the wet, even with knobblies, and far more stable than any sports bike, and is one of the most balanced bikes ever made.

Due to their age, not many Bigs will be that original now, so use common sense when evaluating modifications, though most mods are only upgrades like a decent exhaust, new shock and progressive springs. Avoid anything that has been supermoto`d. It transfers all the weight bias from the back to the front and totally screws up the handling. I`ve seen some very iffy examples in my time as well as some excellent examples of innovative engineering like this one.
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Electrics are generally not a problem, though ignition switches can give trouble due to corrosion/damp across the contacts causing it to cut out. Starter relays get a hard time and are known to fail, though as it`s the same one as the one used on early Gixxers and Teapots, there are plenty on Ebay cheap enough. Rectifiers don`t seem to fail,. unlike other Suzukis of this era, and alternators are pretty reliable. Switches don`t generally give trouble either, and it`s usually the starter switch that causes any problems.

To be continued....................
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