BUYING A USED GSPD
The BMW GS/PD is a great bike but buying the wrong one could be frustrating and expensive - if it's been used hard and in the dirt beware - these machines aren't designed as a serious dirt bike and can suffer expensive problems if abused.
Don't get me wrong, they are a great fun if used within their limitations. If you are planning a trip around Africa, India or South America, then my advice is - don't do it on a paralever GS. Unless you are prepared to sit around for a week or two waiting for a replacement drive shaft to be flown in. Don't think "it won't happen to me" 'because it will! The early GS (1981-86) would probably be a wiser choice for a trip such as this - lighter, better fuel economy and most important of all, no paralever shaft and a Bosch starter motor. Have you tried push starting a fully loaded GS with a dead starter?
OK, so you're standing there looking at a potential future pride and joy - the seller is watching your every move and thinking to himself, "will he spot those dodgy head races"? Don't be intimidated - not checking everything thoroughly couldd be costly. If you think you might forget to check some of the essentials, write out a check list.
Start with basics by checking that all the lights and the horn. A non working indicator may be nothing more than a blown bulb or it could indicate a major problem with the wiring harness.
Now is the time to get hands dirty. Hold the front wheel at the top and bottom and try to rock the wheel sideways, any play here is a sign that the bearings need replacing. These bearings do last but if used in the dirt and water they may be suffering. While you're on you're hands and knees, pry off the brake caliper cover and check that the pads are still serviceable. Then carefully check the brake disk for cracks - look for hair-line cracks running between the holes and look for a deep ridge around the outside circumference which will indicate a badly worn disc. If it's a late model GS, it may have a floating brake disc - there should be some movement of the disc but if it's very sloppy, it could be that the mounts are worn and need replacing.
Next, hold the bottom of the fork legs with the front wheel in the air and try pulling and pushing the forks horizontally, there should be no movement here (be careful not to confuse center stand movement with play in the forks). If there is play, then the odds are that the steering bearings will need replacement. Keeping the front wheel in the air, turn the handlebars slowly from side to side to feel for any stiffness or notches - if the bearings are notched you will feel an extra resistance as the bars pass the center position.
Now move to the rear wheel and push and pull from the top and bottom to check for movement - if there is a small amount of play, the bevel drive may need shimming but if there is a lot of play you may need a new bearing in the drive. This bearing is expensive! Hold the rear of the wheel with one hand and while pushing and pulling the wheel sideways feel for any play between the bevel drive and the swing arm - if there's play, then the pivot bearing in the swing arm is probably failing - check the tire hasn't been rubbing the swing arm as this is also a warning of bearing failure.
Spin the rear wheel, listen and feel for any rumbling as it spins. If you hear something, lay a hand on the bevel drive, the swing arm and the gearbox to try and determine where the noise is coming from. If there is a rumble which is loud enough to hear, then there are various possible causes. The bevel drive could need major work although this is fairly rare, and the likelihood is that this machine has either the well known failing drive shaft or transmission bearing failure problems. Both of these faults are common and expensive! Ignore these warning signs at your own risk! A new drive shaft will cost around $500 and a transmission rebuild is likely to cost around the same - so unless you are confident that you can repair these faults yourself, forget this bike unless it's very cheap and you're prepared to spend money.
Another relatively common fault on the late models is a bad starter motor. From around 1988/9 BMW stopped using the Bosch starter and began to supply a French made Valeo starter. These starters are unreliable, not repairable and cost around $500. The cheapest cure for this is to throw away the Valeo and replace with a used Bosch motor - from '76 on they are interchangeable.
Check for major oil leaks etc. which can be expensive to cure unless you can do the work yourself, Listen carefully to the engine - if it sounds OK it probably is as they are pretty sound - use common sense here - if you're not sure, either get a second opinion or forget it.
Still happy ? Then go for it - you'll have great fun on one of the best BMWs around.
Checking a used GS/PD
Look over the motorcycle for general condition and cleanliness. Check for oil leaks mainly at the pushrods and rear main seal.
Check compression. It should be 130-140 psi on both sides. Less than 120 psi generally reflects bad valves and/or rings which can be expensive ($300 upwards). Be sure you ground the spark plugs when checking compression! Condition of the valves can be checked by looking through the spark plug hole or removing the valve cover and inspecting area around stem. Exhaust gas blow-by from a badly burnt valve will cause a brownish discoloration.
Check charging system. This can be done at the alternator or battery. Normal range is 13.5-14.0 VDC. Less than 13.2 V can reflect a bad ground or faulty diode board (replacement cost $100). Charging amperage can range from about 10 amps for a discharged battery to 4 amps for a fully charged one.
Remove carburetor bowls and inspect for residue and/or water. The latter may reflect water in the fuel tank, which may have severe consequences especially on a metal GS tank.
Spin and rock front and rear wheels sideways to check bearings. Check steering head and final drive bearings by rocking forks back and forth and drive-shaft housing sideways. Listen for noises in the transmission.
Any binding or strange noises found noted when spinning the rear wheel may be cause by a bad drive shaft U-joint. If in doubt pull back rubber boot and visually inspect the joint. If still suspicious, you may consider removing the shaft drive and doing a thorough check. This is an expensive replacement item ($500 plus) which you do not want to miss.
Ride the bike. Make sure it tracks straight. If it doesn't the frame could be bent. This is very expensive to repair. Unevenly worn tires could be due to under inflation, but wheels out of alignment could cause that as well. Shift up and down making sure it does so smoothly.
A thorough inspection by a qualified BMW mechanic should take about 2 hours. Depending upon your local shop's labor rates this could come out to $100 or more. It is a good investment though that could keep you from spending thousands of dollars later on. It might also give you a good basis for bargaining with the seller if you still like the bike and are willing to put some money into it.
best of luck