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25 Things You Must Look For When Buying A Used Dirt Bike

When buying a used dirt bike, or any vehicle for that matter, you never truly know what you are getting. Just because the seller says it was rebuilt, doesn’t mean it won’t grenade on you an hour after you get home. You don’t know what exactly has been done to it, and they may not have rebuilt it correctly. Not everyone lies about what they have or what’s been worked on, but some people just don’t know. That’s why it’s YOUR job as a buyer to do as much research and scrutinizing of the bike as possible. The more you know about the model of bike you’re looking at, as well as the bike itself, the better you can judge its value.

If you’ve never gone to look at a used bike before, asking a friend to come along that is very experienced with wrenching on bikes is highly recommended because they generally know what to look for. However, you can use this list of things to look for to give yourself a jump-start on bike mechanics 101.

These guidelines relate to motocross bikes, trail bikes, 2-strokes, 4-strokes, air-cooled and liquid-cooled bikes for every make.

  1. “Just look at it” – Upon arrival, you can sometimes tell if a dirt bike is a cherry, or if it is a complete junkbox on wheels. Look at the plastic, frame, and over-all cleanliness of it. If it was put away wet often, there will be a lot of stains and dirt caked on the bottom of the engine/chassis.
  2. Look At Surroundings – This doesn’t pertain to the bike specifically, but while looking at it, take a look around. Where and how is the bike sitting? Is the garage/place clean? How does the seller’s other vehicles look? If everything is clean and looks well taken care of, there’s a good chance the bike was, too. This alone shouldn’t be the determining factor though.
  3. Frame Damage/Straightness – If the dirt bike has been in a major or numerous crashes, the frame or subframe usually shows it. Check for unusual bends/cracks at the welds or where two sections meet. If the subframe is bent, it’s usually easy to see by looking at the bike from the rear. The fender will usually lean more to one side. If it’s too far to bend back, a used subframe is anywhere from 50-200 bucks depending on the bike.
  4. Wheels – Take a close look at both wheels for bends or cracks, as well as missing spokes. If anything is damaged or missing then the bike was ridden hard or rode on rough terrain. Spin the wheels to see if they wobble at all. Used wheels in good shape can be expensive.
  5. Tires – Are the tires worn out or cracked from old age? If they don’t have any sharp edges then you’ll want some fresh rubber for a big increase in traction, which is not only safer, but it will put more power to the ground. A pair of tires can cost close to 200 bucks or more, depending on what kind of performance you’re looking to get.
  6. Suspension – You may need to get it re-valved for your weight, or it may just need to be serviced if the seller hasn’t done it in a while (or ever). This could be as little as new oil and a charge of nitrogen (rear shock).
  7. Bearings - There’s quite a few bearings on a dirt bike, and most of the time you can expect them to be needing new grease at the minimum. Move the wheels side-to-side to check their bearings. If there’s any slop they they need to be replaced. The steering stem has bearings and are usually under-greased from the factory. If it’s hard to turn the handlebars, they may need to be replaced.
  8. Swing-arm/Linkage - With the bike on a center stand, move the swing-arm up and down, as well as side-to-side. It should move freely without binding. If it’s rough or wobbles, it will need to be serviced and may you may need a new bushing kit.
  9. Air Filter – If the seller won’t let you take the seat/panel off to look at the filter, he/she is probably trying to hide something. If you’re looking for a good running and reliable bike, it’s probably best to walk away if they say “No”. If they comply, take a look at how clean the filter itself is, as well as the rest of the airbox. Someone who takes good care of their bike will keep these both clean.
  10. Engine/Transmission Oil – This is just as important as the air filter, if not more so! Most bikes will either have a dipstick or a sight glass so you can easily check the oil level. You should be able to see some oil at least at the minimum level. If you can’t see oil, there’s not enough to properly lubricate. If it hasn’t already, it will cause damage, and is one of the leading causes of blown engines. Many air-cooled trail bikes, such as the Honda XR lineup, is so reliable that some owners never change the oil. Eventually it will run low and will start smoking or seize. However, some dirt bikes require you to start and idle them for a minute in order to check the oil. Make sure you know how to check it before you go.
  11. Chain – Chains can last a long time if they are taken care of. On the flip side, if the chain is never or rarely cleaned and lubed, it can wear out faster than the top-end on a motocross bike. Check for kinks, as well as how far it is on the adjuster. If there’s no room left for adjustment, it’s because the chain is stretched out and is in need of replacement. If the chain has a lot of corrosion or skips at all, it’s toast.
  12. Sprockets – Sprockets usually wear with the chain. You can often get one rear sprocket, and two front sprockets out of the life of a chain if properly maintained. Look at the teeth for any chunks missing or odd shaped teeth from wear.
  13. Brakes – Look at the brake pads for wear. If they’re close to the limit marks or metal, they need to be replaced. Also take notice of the brake fluid in the master cylinder(s). If it’s low or dirty, it may need to be flushed out. Most of this is just maintenance, though, and isn’t too costly.
  14. Coolant – Pop the radiator cap off and check the coolant level. It should be at or near the top. If it’s low then the engine may have overheated and spit some coolant out the overflow tube.
  15. Radiators – After you look at the coolant, take a closer look at the radiators. Are they smashed or bent? How do the fins look? If it looks like it’s been poorly repaired or patched up, you can count on needing a new one, which can be expensive, depending on what you get (new/used/aftermarket).
  16. Handlebars – They can get bent easily if the bike was flipped or wrecked. You can usually tell just by looking at it, but by a simple test ride you should be able to feel if they are bent or not. Aftermarket handlebars often means that the stock ones got bent, along with the possibility of other parts in the process, so pay close attention if so.
  17. Levers – Brake and clutch levers are very easy to bend/break. They are fairly inexpensive, but if more than one needs replacing, the repair bill quickly adds up. The shift lever and rear brake pedal can get bent as well. Make sure the shifter is on tight. If it’s sloppy, the splines are probably worn and it’ll need a new one.
  18. Seat – Does it have any rips? If the cover was replaced, was it put on correctly? This has little to no mechanical function, but some of us like our dirt bikes looking nice.
  19. Fork Seals – Fork seals are cheap and fairly easy to replace with the right tools. However, it can be time consuming, and is quite spendy to have a shop replace them. If they are barely seeping, you might be able to get away with just cleaning them.
  20. Engine Noises – Start and let the engine idle for at least a minute. Listen for any rattling or ticking. If it’s a 4-stroke and it ticks with the RPM of the engine, it’s probably a worn timing chain or tensioner. Fairly simple fix on most bikes. If there’s a rattle that gets noticeably quieter when the engine is fully warmed up, it may be piston rattle, which will require a rebuild.
  21. Transmission – The best way to test the transmission is by riding the bike and shifting through all the gears. It should shift easily up and down through all the gears, with or without the clutch. If you hit a ‘false neutral’ in between gears, it may have a bent shift fork, which requires the cases to be split (a lot of labor).
  22. Clutch – You can test the clutch while you’re riding as well. How big is the ‘friction zone’ or how much movement does the clutch lever have from disengaged to engaged? Or does it even fully engage? A slipping clutch will rev out and the engine may feel really low on power.  You can try dumping the clutch while in gear to see if it slips or engages and stalls. If it stalls or quickly goes to the correct RPM then it probably won’t need to be replaced.
  23. Exhaust – Look at the head pipe for dents or bends. If there’s any major damage, you’ll want to get it repaired or replaced. A crushed pipe will be lacking power. Also listen to the exhaust note. You can usually tell when there is little to no muffler packing because it’s loud and raspy. A freshly packed silencer is relatively quiet (depending on the specific silencer), and will sound nice and crisp. Packing is pretty cheap, but it’s not very fun to replace.
  24. Carburetor – You’re probably not going to be able to internally inspect the carb, but you can get a good idea on how dirty it may be when trying to start it and riding it. If the bike is hard to start and/or has a bog down low, there’s a good chance it will need to be cleaned. This is often the case if the dirt bike has set for a number of months (or even weeks).
  25. Recalls – If you’re going to spend a lot of money on a dirt bike, you might as well get to know your stablemate beforehand. Fortunately, it’s easier than ever these days with the internet. Do some research on the specific make, model, and year of the dirt bike you are looking to buy. Every bike will have common problems after years of use, and while some may cost more to fix than others, you can save money in the long run by planning ahead if you know that your particular bike may need a special part or ‘fix’ in the future.

I know all of this may seem like a lot to take in right away if you’ve never looked at a used dirt bike, but it gets a lot easier the more you do it. Like I mentioned above, it’s a great idea to have a knowledgeable person with you to help. Also, do not be afraid to walk away from a bike. Everyone may say that they have the nicest and fastest bike, but if you want a clean and reliable dirt bike, it’s better to wait than wasting your hard earned cash dollars on a pile of junk that’s going to sit in the corner of the garage after blowing up on your first ride.

Ride safe!

-Tom Stark

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How To Replace Fork Seals On A Dirt Bike TTR125

Step by step tutorial on how to replace fork seals on a conventional damper rod dirt bike fork, specifically the TTR125L. Special tips including a homemade damper rod holding tool.

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5 Signs That Your Dirt Bike Needs A New Top-end – 2 Stroke

If you buy or put a lot of hours on a 2-stroke motocross bike, chances are it will need the top-end replaced. A top-end rebuild is pretty easy to do on a two stroke engine, and the only special tool you’ll need is a torque wrench for most dirt bikes. However, before tearing your engine apart, there’s several signs that can tell you it has a worn top-end. If you have most or all of the symptoms listed below, you can count on replacing at least the piston and ring, and possibly a cylinder and head. Although, if none of the symptoms relate to your bike, there’s a good chance it won’t need a rebuild yet…

It Takes 50 Kicks To Start My Bike…

This is a common symptom for both two and four stroke dirt bikes. Unless you are riding in extreme climate, your bike shouldn’t take more than a few kicks to get started. Certain bikes require more muscle and/or technique to get started, but a solid running engine will only take 1-3 kicks to start, hot or cold. On the flip side, just because your bike takes forever to start doesn’t always indicate a worn top-end. For more info on a ‘no-start’, read this article on Diagnosing A No-Start

My Bike Is Gutless

Does your dirt bike feel like it lost its power-band(sarcasm)? A worn piston/ring will make the engine feel weak and low on power even when WOT (wide open throttle). This often happens after a top-end has so many hours on it, and will get worse/less powerful over time. A 2-stroke piston can last over a hundred hours if the bike was casually ridden and properly maintained, but an aggressive motocross racer can wear out a top-end in less than 20 hours of ride time.

This Thing Eats Spark Plugs

Shattered CR80 Piston

Shattered CR80 Piston

How often are you replacing the spark plug? If you have to put a new one in every ride, stop and inspect before riding again. If the jetting is right, a fouled spark plug can also be caused by a bad top-end or blow-by from the worn piston/ring/cylinder. This definitely indicates a new top-end is required, as well as a new spark plug. I have personally seen a CR80 that fouled plugs because of a bad top-end. It turned out that the piston was cracked and it eventually just lost compression. The cylinder was used again because it was surprisingly still in good shape! Here’s some more causes of a fouled plug.

Look For Scratches

A scored piston or cylinder can be caused by multiple things. A lack of lubrication from not enough 2-stroke oil in the gas or lean jetting can damage the piston and cylinder, as well as the crank assembly and bearings. Scoring is caused by metal to metal contact, which is common on 2-strokes when they aren’t warmed up properly. It makes me cringe when people try to warm up their dirt bike too quickly, and I see it quite often. A lot of top-end damage is done if you start your bike and immediately ride it hard or rev it without giving it enough time to warm up.

A piston has a certain amount of clearance between it and the cylinder wall. This clearance is for “growth”, because it will get bigger as it heats up. The size difference isn’t much, but if the piston heats up too quickly, it will expand faster and get too big to properly fit in the cylinder bore, thus creating scoring, and possibly a “cold seizure”. Read the article in the link above to learn how to warm up your dirt bike without damaging anything. You should also note that forged pistons, as opposed to stock cast pistons, are slightly smaller in diameter and require more warm-up time to expand; so take extra precaution.

You may have to take the cylinder head off to get a good look at the cylinder walls to check for scoring, but there’s a quick and dirty way to give you an idea of its condition without touching the engine itself. Just unbolt and remove the pipe/expansion chamber so you can look in the exhaust port of the engine. Shine a light in there and see if there’s any noticeable scratches. You can look at the piston as well, but any scratches/scoring that looks like something you can feel with your finger nail is damage and will most likely need repair/replacement. If you can’t see the cross-hatching on the cylinder walls then it is worn and probably out of spec.

Top-end Rebuild

Top-end Rebuild

My Bike Is Super Easy To Kick Over

If you don’t know already, this isn’t a good thing. While most 2-strokes are easier to kick over than a four-stroke dirt bike, you shouldn’t be able to push the kick-start lever down with one finger. If it kicks over with next to no resistance, the top-end is probably down on compression. Low compression will usually go hand-in-hand with taking a lot of kicks to start, as well as a weak engine.

A new piston ring may be the only thing that needs replacing if the piston and cylinder are still in good shape. Rings only last so long and eventually go out of spec (refer to your manual). If you have the cylinder off, check the ring gap with gauges and compare to what the manual says. If the gap is too big, replace the ring with a new one. You can usually re-ring a piston once before needing a new piston as long as everything else checks out.

These tips are only guidelines. Nothing is set in stone, as every bike is different. Just because your bike is hard to start doesn’t mean it will always need a new top-end. It could be something completely different, such as a dirty carburetor because the bike hasn’t been started for months. I put this list together because these are the most common symptoms of a bad top-end when all of the simple problems have already been checked.

Have fun, and ride safe!

-Tom Stark

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